Microscope apparatus

A microscope apparatus includes a microscope, and a time-resolved spectroscopy unit, a first light-guiding unit for guiding light from the speetroscopy unit into the microscope, a second light-guiding unit for guiding the light from the microscope into the spectroscopy unit. The microscope includes an illuminating optical system and an observing optical system. The time-resolved spectroscopy unit includes an ultrashort optical pulse source, a beam splitter for splitting the ultrashort optical pulse into a reference beam and another beam, an optical system for generating a pump beam and a probe beam from the beam other than the reference beam, and an imaging device for time-resolved spectroscopy for capturing an interference pattern formed by the light guided by the second light-guiding unit and the reference beam. A two-dimensional lightwave conversion optical system is interposed between the second light-guiding unit and the imaging device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microscope apparatus capable of carrying out time-resolved spectroscopy in a minute region under microscope observation.

This application is based on patent application Nos. 2004-182923, 2004-214699, 2004-217543, and 2004-218950 filed in Japan, the content of which is incorporated herein by reference.

2. Description of Related Art

An example of a known technology for carrying out time-resolved spectroscopy using a microscope is described below.

According to such a known technology, pulsed laser beams are focused on a subject and fluorescence emission produced at a minute area in the vicinity of the focal point is detected. Then, the energy transfer is measured based on the characteristics of how the fluorescence emission changes over time.

According to this technology, the environment of a fluorescent molecule included in a specimen can be analyzed based on the fact that the fluorescence lifetime of the molecule changes depending on the distance between the fluorescent molecule and other fluorescent molecules.

Recently, in the technical fields of optical communication and physical measurement, optical signals that change within an extremely short period of time on the order of picoseconds (1 ps=10−12s) to femtoseconds (1 fs=10−15s) are often used. The change of an optical signal within such an extremely short time period can be observed by a measuring device with excellent time resolution, for example, a time-resolved spectroscopy apparatus such as a time/2D-space conversion optical system.

The time/2D-space conversion optical system includes a diffraction grating, a one-dimensional Fourier transformation optical system, a time-to-frequency conversion filter, and a one-dimensional inverse Fourier transformation optical system.

Observation of an optical signal using such a time/2D-space conversion optical system is carried out as described below.

First, a signal beam having a plane wavefront is incident at an angle on the diffraction grating to obtain a diffracted beam whose propagation direction and spatial phase distribution intersect at an angle equal to the incident angle of the signal beam to the diffraction grating.

Next, Fourier transformation is performed on the horizontal component of the diffracted beam by the one-dimensional Fourier transformation optical system to obtain the spectral distribution of the signal beam as a spatial distribution.

The spectral distribution obtained in such a manner is filtered using the time-to-frequency conversion filter, which is disposed at a position where the spectral distribution is projected, so that the frequency of the extracted frequency components increases sequentially in the vertical direction.

Inverse Fourier transformation is performed on the horizontal components of the filtered lightwave by the one-dimensional inverse Fourier transformation optical system to obtain a lightwave distribution representing time delay in the horizontal direction and the distribution of the extracted spectral components in the vertical direction. A quasi-two-dimensional spectrogram is formed on the plane intersecting with the horizontal direction representing different degrees of time delay in the lightwave distribution.

By emitting a reference transform-limited (TL) pulse wavefront on the plane intersecting with the horizontal direction representing different degrees of time delay in the lightwave distribution so that the plane matches the wave surface of the emitted plane wavefront, an interference pattern caused by the lightwave distribution and the reference TL pulse wavefront is generated on the plane.

The interference pattern generated in such a manner corresponds to the change in intensity of the lightwave distribution over time. Therefore, by analyzing this interference pattern, information on the amplitude and phase of the signal beam to be measured can be obtained.

BRIEF SUMMARY OF THE INVENTION

A microscope apparatus according to an embodiment of the present invention includes an optical microscope, a time-resolved spectroscopy unit, a first light-guiding unit interposed between the time-resolved spectroscopy unit and the optical microscope, and a second light-guiding unit interposed between the time-resolved spectroscopy unit and the optical microscope at a position difference from the position of the first light-guiding unit. The time-resolved spectroscopy unit includes a light source for generating an ultrashort optical pulse, an imaging device, a light-splitting member interposed between the light source and the first light-guiding unit, a light-combining member interposed between the second light-guiding unit and the imaging device, and a two-dimensional lightwave conversion optical system interposed between the second light-guiding unit and the light-combining member.

It is preferable that the microscope apparatus having the above-described structure further include a relay optical system, and the two-dimensional lightwave conversion optical system of the microscope apparatus having the above-described structure include a beam expander, a first diffraction grating, a first lens having a positive refractive power, an optical filter, a second lens having a positive refractive power, and a second diffraction grating, wherein the first diffraction grating is disposed at a front focal point of the first lens, wherein the optical filter is disposed at a rear focal point of the first lens and a front focal point of the second lens, and wherein the second diffraction grating is disposed at a rear focal point of the second lens. The relay optical system is interposed between the second diffraction grating and the imaging device.

It is preferable that the relay optical system be a unit-magnification optical system.

It is preferable that the imaging device in the above-described microscope apparatus be disposed so that an image plane of the imaging device is orthogonal to an optical axis of the relay optical system.

It is preferable that the relay optical system included in the above-described microscope apparatus be a reducing optical system.

In the above-described microscope apparatus including a relay optical system, it is preferable that an imaging device be disposed so that an image plane of the imaging device disposed at an angle with respect to an optical axis of the relay optical system.

In the structure described in the first paragraph of this section, the two-dimensional lightwave conversion optical system includes in the above-described microscope apparatus may include a beam expander, a half mirror, a first diffraction grating, a lens having a positive refractive power, a reflective optical filter, and a relay optical system. The half mirror is disposed on the light-emission side of the beam expander. The first diffraction grating, the lens having a positive refractive power, and the optical filter are disposed on the light-reflection side of the beam expander. The first grating is disposed at a front focal point of the lens having a positive refractive power. The optical filter is disposed at a rear focal point of the lens having a positive refractive power. The relay optical system is interposed between the half mirror and the imaging device.

In the structure described in the first paragraph of this section, the two-dimensional lightwave conversion optical system includes in the above-described microscope apparatus includes a beam expander, a diffraction grating, a first lens having a positive refractive power, an optical filter, a second lens having a positive refractive power, and a relay optical system. The diffraction grating is disposed at a front focal point of the first lens. The optical filter is disposed at a rear focal point of the first lens and a front focal point of the second lens. The imaging device is disposed at a rear focal point of the second lens.

DETAILED DESCRIPTION OF THE INVENTION

There is a measuring technology employing the high-level time resolution of ultrashort pulses. By using this technology, various high-speed phenomena in the picosecond to femtosecond region can be observed, such as chemical reactions.

In view of this time-resolved measurement technique the microscope apparatus according to an embodiment of the present invention is configured.

The time-resolved measurement technique is described with reference toFIG. 13.

FIG. 13is a perspective view illustrating the overall structure of a two-dimensional space conversion optical system (two-dimensional lightwave conversion optical system) according to a technique for measuring the waveform of an ultrashort pulse.

The two-dimensional space conversion optical system includes a beam expander300, a diffraction grating500, a first cylindrical lens600, an optical filter700, and a second cylindrical lens800. The diffraction grating500is a transmissive diffractive optical element. The diffraction grating500is disposed at the front focal plane (front focal position) of the first cylindrical lens600. The optical filter700is disposed at the rear focal plane (rear focal position) of the first cylindrical lens600. The position of the optical filter700matches the rear focal plane of the second cylindrical lens800. The rear focal plane of the second cylindrical lens800and the front focal plane of the first cylindrical lens600are conjugate to each other.

Now, the time-resolved measurement method using the structure illustrated inFIG. 13will be described.

An incident light flux is expanded at the beam expander300and is transmitted to the diffraction grating500at an angle. The traveling path of each ray of the light flux will be described below. In this case, the individual light rays entering the diffraction grating500at an angle do not reach the incident plane of the diffraction grating500simultaneously. More specifically, when the diffraction grating500is viewed from the X direction, one end of the diffraction grating500will be disposed closer to the beam expander300and the other end will be disposed away from the beam expander300. Therefore, there will be a time difference between a light ray reaching one end of the diffraction grating500and another light ray reaching the other end of the diffraction grating500. In other words, light rays reach predetermined positions on the diffraction grating500in the X direction at different moments. With this in mind, the time-resolved spectrum of the light rays that reach the line P-Q in the drawing will be described below.

The diffraction grating500has a grating that diffracts incident light in the X direction according to each wavelength. Each wavelength component included in the light that reaches line P-Q is diffracted in the X direction at a different angle and is then focused at the rear focal plane of the first cylindrical lens600. Since, at this time, light is focused only in the X direction, streaks of light extending in the Y direction will be aligned in sequence in accordance with the wavelength along the X direction.

As illustrated inFIG. 14, the optical filter700includes a light-blocking region and a light-transmitting region. Here, the light-transmitting region is an opening. When viewed with respect to the X and Y axes of the optical filter700, the opening is formed on the optical filter700so that, as the opening extends in the X direction, it also extends in the Y direction. The area other than the opening of the optical filter700is a light-blocking region configured to block light.

Therefore, different wavelength components of the light transmitted through the optical filter700will be distributed along the Y direction with a time difference.

The wavelength distribution in the Y direction maintained at the rear focal plane of the second cylindrical lens800. Since the rear focal plane of the second cylindrical lens800is conjugate to the front focal plane of the first cylindrical lens600, the position of the line P-Q is conjugate with respect to the position of the line P′-Q′. As a result, light rays having different wavelengths are aligned along the line P′-Q′, as illustrated inFIG. 15.

The light rays reach the diffraction grating500at different moments depending on the position on the diffraction grating500. At the rear focal plane of the second cylindrical lens800, as illustrated inFIG. 15, the different wavelength components are distributed in the Y direction, and time changes in the X direction as indicated by an arrow (leftward in the drawing). In this way, an expanded spectrogram is generated. Hereinafter, this spectrogram is defined as a two-dimensional lightwave.

Since temporal changes in time of light are extremely high speed, a usual imaging device is not capable of capturing these temporal changes.

Accordingly, a reference beam referred to as a ‘gate pulse’ is simultaneously emitted at the rear focal plane of the second cylindrical lens800. In this way, the spectrogram can be obtained as an interference pattern.

The above-described two-dimensional space conversion optical system is capable of performing time-resolved spectroscopy of light modulated in some way due to a specimen and, more specifically, of ultrashort pulses.

The above-mentioned two-dimensional space conversion optical system has mainly been used in the fields of optical communication and physical measurement.

The applicant, however, has focused on the fact that the above-mentioned two-dimensional space conversion optical system can be effectively used in observing and measuring minute regions and has conceived the idea of using the above-mentioned two-dimensional space conversion optical system in a microscope apparatus. By using the microscope apparatus according to embodiments of the present invention, observation and time-resolved spectroscopy of an extremely small region can be carried out simultaneously.

FIG. 1illustrates a structure common to microscope apparatuses according to embodiments of the present invention.FIG. 2is an overview of a microscope included in the microscope apparatus illustrated inFIG. 1.

As illustrated inFIG. 1, the microscope apparatus according to embodiments of the present invention includes a microscope70, a time-resolved spectroscopy unit80, a first light-guiding unit91, and a second light-guiding unit92. The first light-guiding unit91guides light from the time-resolved spectroscopy unit80to inside the microscope70. The second light-guiding unit92guides light from the microscope70to the time-resolved spectroscopy unit80. The microscope apparatus is configured so that a specimen can be observed with the microscope70at the same time time-resolved spectroscopy is carried out on the specimen being observed by the time-resolved spectroscopy unit80.

The time-resolved spectroscopy unit80includes an ultrashort optical pulse source5, a splitter61, a two-dimensional lightwave conversion optical system1, a relay lens2, a multiplexer3, and a time-resolved-spectroscopy imaging device4(hereinafter, referred to as an ‘imaging device4’).

The ultrashort optical pulse source5is configured to generate ultrashort optical pulses.

The splitter61is configured to split an ultrashort optical pulse into a probe beam and a reference beam.

The first light-guiding unit91includes, for example, a mirror. The angle of the mirror can be adjusted to reflect the light emitted from the time-resolved spectroscopy unit80into the microscope70.

The second light-guiding unit92also includes, for example, a mirror. The angle of the mirror can be adjusted to reflect the light emitted from the microscope70to the time-resolved spectroscopy unit80.

The first and second light-guiding units91and92may be disposed in either the microscope70or the time-resolved spectroscopy unit80or may be disposed independently from the microscope70and the time-resolved spectroscopy unit80. The positions of the first and second light-guiding units91and92are not limited.

The two-dimensional lightwave conversion optical system1converts the light guided by the second light-guiding unit92into a two-dimensional lightwave.

The relay lens2forms an image of the two-dimensional lightwave on the image plane of the imaging device4through the multiplexer3.

The multiplexer3reflects the reference beam onto the image plane of the imaging device4. As a result, an interference pattern is formed on the image plane of the imaging device4.

Now, the microscope70will be described. The microscope70may be any type of optical microscope capable of observing a specimen. More specifically, the microscope70may be capable of bright-field microscopy, fluorescence microscopy, or differential interference microscopy.

According to the structure illustrated inFIG. 2, the microscope70includes a transmission-illumination light source71, a transmission-illumination optical system72, an optical system for observation73, an imaging device for observation74, a stage75, a fluorescence-illumination light source76, a fluorescence-illumination optical system77, a filter unit772, a beam splitter723, and a dichroic mirror78.

The transmission-illumination optical system72includes a collector lens721, an objective lens722, and a beam splitter723. The transmission-illumination optical system72radiates light generated at the transmission-illumination light source71onto a specimen S. Since the transmission-illumination optical system72includes the beam splitter723, a pump beam and a probe beam can be radiated onto a specimen via the beam splitter723. According to the structure illustrated inFIG. 2, the transmission-illumination optical system72also includes a polarizer724and a first differential interference contrast (DIC) filter725.

The optical system for observation73includes an objective lens731, a second DIC filter732, an analyzer733, and an imaging lens734.

The dichroic mirror78and the filter unit772are interposed between the analyzer733and the imaging lens734.

The filter unit772includes an excitation filter7721, a dichroic mirror7722, and an absorption filter7723. The excitation filter7721is used to select the excitation light to be emitted to the specimen S. The dichroic mirror7722reflects the excitation light towards the specimen S and transmits fluorescence emitted from the specimen S. The absorption filter7723blocks the excitation light reflected at the specimen S and transmits generated fluorescence.

The stage75includes an XY stage752. In this way, the position of the specimen S relative to the objective lenses722and731can be adjusted freely.

With the microscope apparatus according to an embodiment of the present invention, an extremely small region can be observed and, at the same time, time-resolved spectroscopy can be carried out on a probe beam modulated on the order of picoseconds to femtoseconds.

The main structures of embodiments of the present invention will be described below.

First Embodiment

FIG. 3illustrates a microscope apparatus according to a first embodiment and, more specifically, illustrates the detailed structure of a time-resolved spectroscopy unit80. The basic structure of the microscope apparatus according to the first embodiment is the same as the structure illustrated inFIGS. 1 and 2.

A two-dimensional lightwave conversion optical system1of the time-resolved spectroscopy unit80according to the first embodiment includes a beam expander10, a first diffraction grating12, a first cylindrical lens131having a positive refractive power, an optical filter141, a second cylindrical lens132having a positive refractive power, and a second diffraction grating array15.

A first light-guiding unit91includes a beam splitter723disposed to the side of the microscope70. A pair of mirrors may be disposed on the side of the time-resolved spectroscopy unit80so that the light flux emitted from the time-resolved spectroscopy unit80enters the beam splitter723. In such a case, one of the mirrors is held so that the X axis is the rotational axis and the other mirror is held so that the Z axis is the rotational axis. In this way, the emission angle of the light flux can be adjusted. The height of the light flux can be adjusted by changing the distance (in the Y direction) between the two mirrors.

A second light-guiding unit92includes a dichroic mirror78disposed to the side of the microscope70. According to this embodiment, a mirror68is disposed in the two-dimensional lightwave conversion optical system1. However, the microscope70and the time-resolved spectroscopy unit80may be disposed, without the mirror68, in a manner such that a probe beam from the second light-guiding unit92is directly guided to the two-dimensional lightwave conversion optical system1. Instead of providing the mirror68, a pair of mirrors may be disposed to the side of the time-resolved spectroscopy unit80, in the same manner as the first light-guiding unit91.

The splitter61is a beam splitter including a half mirror. An ultrashort optical pulse generated by the ultrashort optical pulse source5is split into two beams at the splitter61. The beam reflected at the splitter61is the reference beam. The beam that passes through the splitter61enters a delaying optical system6, where a probe beam and a pump beam are generated. The delaying optical system6includes a beam splitter62, mirrors63,64, and66, and a movable stage65.

The beam that passes through the splitter61is reflected at the mirror66. The reflected beam is split at the beam splitter62. The beam reflected at the beam splitter62is reflected at the mirror63and passes through the beam splitter62. The beam that passes through the beam splitter62is reflected at the mirror64and is then reflected at the beam splitter62. At this time, the stage65moves along the incident direction of the light. Consequently, a difference occurs in the length of the optical paths of the beam reflected at the mirror63and the beam reflected at the mirror64. By changing the optical path lengths of these reflected beams, one of the beams will have a time delay relative to the other beam. According to this embodiment, the beam not having a time delay is used as a pump beam and the beam having a time delay is used as a beam of probe light. The two types of beams are guided to the microscope70through the first light-guiding unit91.

In the propagating direction of the reference beam, a beam expander33, a mirror30, and the multiplexer3are disposed. The multiplexer3includes a beam splitter31and a lens32. Since the lens32functions as a beam expander when combined with the lens22, the reference beam that is split at the splitter61is emitted to the imaging device4as a collimated beam. The beam splitter31reflects the reference beam that has passed through the lens32and, at the same time, transmits the two-dimensional lightwave converted at the two-dimensional lightwave conversion optical system1. As a result, the two beams are combined in the direction of the imaging device4.

The structure for guiding the reference beam split at the splitter61to the multiplexer3may be a structure other than that described above.

The process of carrying out time-resolved spectroscopy using a microscope structured as described above will now be described.

The specimen S is observed through the microscope70. Different observation methods include bright-field microscopy, fluorescence microscopy, and differential interference microscopy. A minute region of the specimen S is moved to the center of the observation field of view for observation using a predetermined method. The specimen S is moved using an XY stage752of a stage75. The minute region is the region where time-resolved spectroscopy is carried out.

Next, the process of carrying out time-resolved spectroscopy on a minute region in the specimen S will be described.

The ultrashort optical pulse generated at the ultrashort optical pulse source5is split into a pump beam, a probe beam, and a reference beam at the splitter61and the delaying optical system6. The pump beam and the probe beam are delayed with respect to each other.

The pump beam and the probe beam are guided to the microscope70through the first light-guiding unit91. More specifically, the pump beam and the probe beam are guided to the beam splitter723disposed in the optical path of the transmission-illumination optical system72. Then, the pump beam and the probe beam are radiated onto the minute region in the specimen S through the beam splitter723. First, the minute region in the specimen S is excited by the pump beam. Then, the probe beam is radiated onto the same minute region with a time delay.

At this time, the probe beam is modulated by the minute region in the specimen S excited by the pump beam. The modulated probe beam (hereinafter referred to as “modulated probe beam”) is guided to the outside of the microscope70through an objective lens731and the dichroic mirror (second light-guiding unit)78. The probe beam enters the two-dimensional lightwave conversion optical system1of the time-resolved spectroscopy unit80.

The beam expander10expands the diameter of the modulated probe beam and emits this modulated probe beam to the first diffraction grating12at an angle. The first diffraction grating12is a transmissive diffraction grating. However, the first diffraction grating12may be a reflective diffraction grating. The first diffraction grating12is disposed at a predetermined angle θ so that it intersects with (i.e. so that it is not parallel to) a front focal plane F1of the first cylindrical lens131. According to this embodiment, the surface of the first diffraction grating12is disposed at an angle θ with respect to the X axis (a horizontal axis orthogonal to the optical axis (Z axis)). The first diffraction grating12is disposed in a manner such that the center of the surface of the first diffraction grating12is positioned at the front focal plane F1(front focal position) or in the vicinity of the front focal plane F1.

The first diffraction grating12diffracts in the X direction the sequentially radiated wavelength components of the modulated probe beam. The first cylindrical lens131distributes each of the wavelength components of the diffracted modulated probe beam on a rear focal plane F2. The resulting distribution is illustrated inFIG. 4.

The optical filter141is disposed in the vicinity of the rear focal plane F2of the first cylindrical lens131. The optical filter141has a slit, as illustrated inFIG. 5. This slit is formed from the lower left corner to the upper right corner of the optical filter141. By emitting a modulated probe beam to the first diffraction grating12at an angle, a modulated probe beam emitted with a delay depending on the incident positions along the X direction is obtained. Such a modulated probe beam is composed of a plurality of wavelength components. By using the optical filter141, each wavelength component is extracted in accordance with the position relative to the Y axis (vertical axis orthogonal to the optical axis (Z axis)). As a result, as illustrated inFIG. 6, the modulated probe beam is filtered so that different wavelengths are distributed along the Y axis. The modulated probe beam that has passed through the slit of the optical filter141enters the second cylindrical lens132. At this time, the wavelength components of the modulated probe beam are parallel to the X-Z plane and are aligned in the Y direction.

The beams of each wavelength (i.e., modulated probe beams) that have entered the second cylindrical lens132form an image on a plane F3ain the vicinity of the rear focal plane F3of the second cylindrical lens132. The position of the rear focal plane F3is conjugate to the position of the first diffraction grating12. As a result, as illustrated inFIG. 7, the different wavelength components are converted in a manner such that time is represented by the X axis and the wavelength is represented by the Y axis. More specifically, the modulated probe beam satisfies the following conditions: 1) the beams aligned along the X axis are sequentially delayed; and 2) the beams aligned along the Y axis are the wavelength components of the modulated probe beam that has been resolved. A two-dimensional lightwave is a modulated probe beam satisfying the conditions 1) and 2).

The second diffraction grating array15is disposed on the plane F3a. As illustrated inFIG. 8, diffraction gratings15A to15K having different grating constants (period) for each wavelength are aligned in the Y direction. As illustrated inFIG. 7, the different wavelength components of the two-dimensional lightwaves on the plane F3aare spatially separated along the Y direction. Therefore, the direction of diffraction of the wavelength components of the modulated probe beam can be matched by using the second diffraction grating array15. According to this embodiment, the propagating directions of the beams having different wavelengths each have an angular distribution (i.e., the directions vary) in the X direction. The second diffraction grating array15can reduce the angular distribution in the X direction. In this embodiment, the angular distribution of the beam emitted from the plane F3ais reduced to substantially zero by the second diffraction grating array15.

The relay lens2forms a two-dimensional lightwave image S4on an image plane F4of the imaging device4.

At the same time, the reference beam is emitted on the image plane F4through the multiplexer3. Accordingly, interference between the two-dimensional lightwave image S4and the reference beam occurs on the image plane F4. Consequently, a spectrogram of the modulated probe beam is generated as an interference pattern. This interference pattern enables the change of the wavelength components included in the modulated probe beam over time to be measured.

Second Embodiment

Now, a microscope apparatus according to a second embodiment will be described.

FIG. 9illustrates a microscope apparatus according to a second embodiment and, more specifically, illustrates the detailed structure of a time-resolved spectroscopy unit80.

The structure of the microscope apparatus according to the second embodiment is the same as that of the microscope apparatus according to the first embodiment except that the two-dimensional lightwave conversion optical system1included in the time-resolved spectroscopy unit80differs.

The two-dimensional lightwave conversion optical system1according to the second embodiment includes a cylindrical beam expander11, a first diffraction grating12, a first lens133having a positive refractive power, a first diffraction grating array142, a second lens134having a positive refractive power, and a second diffraction grating array15.

The cylindrical beam expander11expands the diameter of the modulated probe beam and emits this modulated probe beam to the first diffraction grating12at an angle. In this embodiment also, the first diffraction grating12is a transmissive diffraction grating. However, the first diffraction grating12may instead be a reflective diffraction grating. The first diffraction grating12is disposed at a predetermined angle θ with respect to the X axis so that it intersects with (i.e., so that it is not parallel to) a front focal plane F1of the first lens133. The center of the first diffraction grating12is disposed so as to be disposed at the front focal plane F1(i.e., front focal point) or in the vicinity of the front focal plane F1.

The first diffraction grating12diffracts the sequentially radiated wavelength components of the modulated probe beam in the X direction. The first lens133distributes the diffracted wavelength components of the modulated probe beam on a rear focal plane F2of the first lens133. The distribution is illustrated inFIG. 10.

The first diffraction grating array142is an optical filter disposed in the vicinity of the rear focal plane F2of the first lens133. As illustrated inFIG. 11, diffraction gratings142ato142khaving different grating constants (periods) are aligned along the X axis. As illustrated inFIG. 12, the different wavelength components of the modulated probe beam are diffracted at different angles along the Y axis at the diffraction gratings142ato142k. The wavelength components diffracted at the first diffraction grating array142are incident on the second lens134.

The wavelength components incident on the second lens134form an image on a plane F3ain the vicinity of a rear focal plane F3of the second lens134. The position of the rear focal plane F3and the position of the first diffraction grating12are conjugate to each other. As a result, as illustrated inFIG. 7, the wavelength components are converted into two-dimensional lightwaves, wherein time changes in the X direction and the wavelength components are distributed in the Y direction.

The subsequent steps are the same as those according to the first embodiment. In other words, a pump beam and a probe beam are radiated onto a minute region of a specimen S under microscope observation. The probe beam modulated at the minute region excited by the pump beam is converted into a spectrogram representing time and wavelength. In this way, time-resolved spectroscopy can be carried out at the minute region.

FIRST EXAMPLE

Now, detailed examples of the second embodiment will be described.

A microscope apparatus according to a first example more specifically exemplifies a structure of the microscope apparatus according to the first embodiment.

The drawings to be referred to are the same as those referred to in the first embodiment.

In the same manner as the microscope apparatus according to the first embodiment, the microscope apparatus according to the first example is constructed so that a specimen S is observed through a microscope70and time-resolved spectroscopy is carried out at a minute region of the specimen S by a time-resolved spectroscopy unit80. Only those parts that are specified more concretely than those of the microscope apparatus according to the first embodiment will be described below. Other structures and effects are the same as those of the first embodiment.

The beam used for carrying out time-resolved spectroscopy is an ultrashort optical pulse having a central wavelength of 800 nm, a linewidth of ±5 nm, and a pulse width of about 100 femtoseconds. This ultrashort optical pulse is used as a probe beam and is modulated. Time-resolved spectroscopy is carried out by obtaining a spectrogram of the modulated probe beam.

An ultrashort optical pulse source5generates an ultrashort optical pulse having a central wavelength of 800 nm, a linewidth of ±5 nm, and a pulse width of 100 femtoseconds.

A two-dimensional lightwave conversion optical system1includes a beam expander10, a first Bragg diffraction grating12, a first cylindrical lens131, an optical filter141, a second cylindrical lens132, and a second diffraction grating array15. The beam expander10includes a lens101having a focal length of 10 mm and a lens102having a focal length of 100 mm. The first cylindrical lens131has a focal length f=100 mm and a positive refractive power, and the second cylindrical lens132has a focal length f=100 mm and a positive refractive power.

The first Bragg diffraction grating12is a transmissive diffraction grating. The first Bragg diffraction grating12is disposed at a 45° angle with respect to the X axis so that it intersects with (i.e., so that it is not parallel to) a front focal plane F1of the first cylindrical lens131. The first Bragg diffraction grating12is disposed in a manner such that its surface is aligned with a plane F1ain the vicinity of the front focal plane F1(i.e., is aligned with the plane obtained by rotating the front focal plane F1of the first cylindrical lens131by substantially 45°). Accordingly, the angle between the normal of the first Bragg diffraction grating12and an optical axis AX is substantially 45°. With respect to the first and second cylindrical lenses131and132, the plane F1ais conjugate with the plane F3a. The plane F3ais obtained by rotating a rear focal plane F3of the second cylindrical lens132by 45°. Accordingly, the conjugate plane F3awill also be disposed at substantially 45° to the optical axis AX. The grating constant of the first Bragg diffraction grating12is set to 1,767 lines per millimeter so that the diffraction direction of the central wavelength component of the probe beam emitted at an incident angle of 45° substantially aligns with the optical axis AX.

In the first example, the modulated probe beam is expanded substantially ten times at the beam expander10. The size of the first Bragg diffraction grating12is about 14.14×10 mm. The modulated probe beam is incident on this first Bragg diffraction grating12at an angle. At this time, the modulated probe beam has a wavelength range of 800±5 nm. Consequently, as illustrated inFIG. 4, the wavelength components included in the modulated probe beam are distributed along the X axis on the rear focal plane F2of the first cylindrical lens131. For example, the wavelength components, 805 nm, 800 nm, and 795 nm are distributed at positions −1.26 mm, 0 mm, +1.24 mm, respectively, from the optical axis AX.

The structure of the optical filter141is the same as that of the optical filter141according to the first embodiment. A two-dimensional lightwave S3is generated on the plane F3athrough the optical filter141. In this example, the size of the two-dimensional lightwave S3is 14.14×10 mm.

The second diffraction grating array15corrects the angular distribution of each wavelength component in the two-dimensional lightwave S3incident on the plane F3a. The specification of the second diffraction grating array15is shown in Table 1 below. In Table 1, ‘Incident Angle’ is the angle between a wavelength component incident on the plane F3aand the normal of the second diffraction grating array15. If diffraction gratings15A to15K included in the second diffraction grating array15have periodic structures, as shown in Table 1, the diffraction angle for each wavelength component will be 45°. As a result, the angular distribution of the wavelength components emitted from the plane F3ais substantially zero.

The relay lens2distributes the two-dimensional lightwave image S4on the image plane F4. The relay lens2includes lenses21and22both having a focal length f21=100 mm.

The multiplexer3includes the lens32having a focal length of 100 mm and a beam splitter31.

By emitting a reference beam through the multiplexer3at the same time as the two-dimensional lightwave image S4is distributed on the image plane4, the two-dimensional lightwave image S4can be recorded as an interference pattern.

A charge-coupled device (CCD) is used as the imaging device4to obtain the interference pattern of the two-dimensional lightwave image S4.

The microscope apparatus according to the first example is capable of simultaneously carrying out microscopy of an extremely small region and time-resolved spectroscopy of a modulated probe beam on the order of picoseconds to femtoseconds.

SECOND EXAMPLE

A microscope apparatus according to a second example more specifically exemplifies a structure of the microscope apparatus according to the second embodiment. The second example differs from the first example only in the two-dimensional lightwave conversion optical system1.

The microscope apparatus according to the second example will be described with reference to the same drawings referred to in the description of the microscope apparatus according to the second embodiment. The two-dimensional lightwave conversion optical system1according to the second example will be described below. The structure and effects of the other components are the same as those according to the first example.

The two-dimensional lightwave conversion optical system1includes a cylindrical beam expander11, a first Bragg diffraction grating12, a first lens133having focal length f=40 mm and positive refractive power, a first diffraction grating array142, a second lens134having a focal length f=40 mm and positive refractive power, and a second diffraction grating array15. The cylindrical beam expander11includes a lens111having a focal length of 100 mm, a lens112having a focal length of 50 mm, and cylindrical lenses113and114having ten times (10×) magnification.

The first Bragg diffraction grating12is a transmissive diffraction grating. The first Bragg diffraction grating12is disposed at a 45° angle with respect to the X axis so that it intersects with (i.e., so that it is not parallel to) a front focal plane f1of the first lens133. The first Bragg diffraction grating12is disposed in a manner such that its surface is aligned with a plane F1ain the vicinity of the front focal plane F1(i.e., is aligned with the plane obtained by rotating the front focal plane F1of the first cylindrical lens133by substantially 45°). Accordingly, the angle between the normal of the first Bragg diffraction grating12and an optical axis AX is substantially 45°. With respect to the first and second cylindrical lenses133and134, the plane F1ais conjugate with the plane F3a. The conjugate plane F3ais obtained by rotating a rear focal plane F3of the second cylindrical lens134by 45°. Accordingly, the conjugate plane F3awill also be disposed at substantially 45° to the optical axis AX. The grating constant of the first Bragg diffraction grating12is 1,767 lines per millimeter so that the diffraction direction of the central wavelength component of the probe beam emitted at an incident angle of 45° substantially aligns with the optical axis AX.

In the second example, the modulated probe beam is expanded substantially ten times at the beam expander11. The size of the first Bragg diffraction grating12is about 14.14×1 mm. The modulated probe beam is incident on the first Bragg diffraction grating12at an angle. At this time, the modulated probe beam has a wavelength range of 800±5 nm. Consequently, as illustrated inFIG. 10, the wavelength components included in the modulated probe beam are distributed along the X axis on the rear focal plane F2of the first cylindrical lens133. For example, the wavelength components, 805 nm, 800 nm, and 795 nm are distributed at positions −0.5 mm, 0 mm, and +0.5 mm, respectively, from the optical axis AX.

The first diffraction grating array142functions as an optical filter. The structure of the first diffraction grating array142is the same as that according to the second embodiment. The specification of the first diffraction grating array142is shown in Table 2 below. In Table 2, the grating constant is positive when a beam is diffracted in the positive direction along the Y axis on the plane F2and is negative when a beam is diffracted in the negative direction along the Y axis on the plane F2. The Y coordinate represents the height of each wavelength component in the Y direction emitted from the second lens134.

TABLE 2Specification of First Diffraction Grating Array 142CentralGratingWavelengthConstantDiffractionY Coordinate(nm)(lines/mm)Angle (°)(mm)a805−154.1−7.1−5b804−123.8−5.7−4c803−93.1−4.3−3d802−62.3−2.9−2e801−31.2−1.4−1f80000.00g799+31.3+1.4+1h798+62.6+2.9+2i797+93.8+4.3+3j796+125.0+5.7+4k795+156.0+7.1+5

The wavelength components diffracted at the first diffraction grating array142pass through the second lens134and are incident on the conjugate plane F3aas a beam parallel to the XZ plane. At this time, the wavelength components of the probe beam are distributed along the Y axis on the conjugate plane F3a. As probe beams are sequentially radiated onto the first Bragg diffraction grating12at the plane F1a, the wavelength distribution moves along the X axis on the conjugate plane F3a. As a result, a two-dimensional lightwave S3is generated, as illustrated inFIG. 7, where time is represented by the X axis and the wavelength is represented by the Y axis. The size of the two-dimensional lightwave S3at the conjugate plane F3ais 14.14×10 mm.

The second diffraction grating array15corrects the angular distribution of each wavelength component of the two-dimensional lightwave S3incident on the conjugate plane F3a. The specification of the second diffraction grating array15is shown in Table 3 below. In Table 3, ‘Incident Angle’ is the angle of the wavelength component to the normal of the second diffraction grating array15when the beam is incident on the conjugate plane F3a. If the diffraction gratings15A to15K constituting the second diffraction grating array15have a periodic structure as shown in Table 3, the diffraction angle for each wavelength component will be 45°. As a result, the angular distribution of each wavelength component emitted from the conjugate plane F3ais substantially zero.

The microscope apparatus according to the second example is capable of simultaneously carrying out microscopy of an extremely small region and time-resolved spectroscopy of a probe beam modulated on the order of picoseconds to femtoseconds.

Third Embodiment

Now, a microscope apparatus according to a third embodiment will be described below with reference toFIGS. 16 to 22.

In a microscope apparatus according to the third embodiment, a time-resolved spectroscopy unit (time-resolved spectroscopy device)80ais used. The components that are the same as those included in the microscope apparatuses according to the above-described embodiments are represented by the same reference numerals and their descriptions are omitted.

The time-resolved spectroscopy unit80ais capable of observing the behavior of a specimen within an ultrashort time period on the order of picoseconds to femtoseconds by analyzing a light signal (probe beam) that has been modulated by the specimen.

A reducing optical system is used as a relay optical system according to this embodiment. This relay optical system will be described below.

To carry out satisfactory time-resolved spectroscopy, the diffraction efficiency of a diffraction grating must be increased. Therefore, when actually operating a two-dimensional lightwave conversion optical system, the diffraction grating is disposed at an angle so that the normal of the diffraction grating is about 45° to the optical axis of the two-dimensional lightwave conversion optical system.

By disposing the diffraction grating at an angle with respect to the optical axis of the two-dimensional lightwave conversion optical system, a surface of an optical system constituted of a first cylindrical lens, which is a one-dimensional Fourier transformation optical system, and a second cylindrical lens, which is a one-dimensional Fourier inverse-transformation optical system, that is conjugate with the diffraction grating will also be tilted with respect to the optical axis of the two-dimensional lightwave conversion optical system. Therefore, the image plane where an interference pattern is captured must also be disposed at an angle so that the image plane will be conjugate with the surface conjugate with the diffraction grating.

However, a usual imaging device, such as a CCD camera, is often not capable of handling beams incident on the image plane at an angle because shading occurs due to the structure of the imaging device. When the image plane is disposed at an angle with respect to the optical axis, the accuracy of the interference pattern captured by the imaging device is low. Therefore, it is difficult to carry out highly accurate time-resolved spectroscopy.

This is why a reducing optical system is used as the relay optical system according to this embodiment.

According to this configuration, a quasi-two-dimensional spectrogram formed by the two-dimensional lightwave conversion optical system on the surface conjugate with the diffraction grating is projected on the image plane of the imaging device through the relay optical system.

To project the quasi-two-dimensional spectrogram on the surface conjugate with the diffraction grating, the relay optical system and the image plane are positioned as described below.

A condenser lens included in the relay optical system is disposed so that its front focal point is disposed at the surface conjugate with the diffraction grating. A collimating lens included in the relay optical system is disposed so that its front focal point is aligned with the rear focal point of the condenser lens and is disposed at the image plane.

Since, in this configuration, too, the diffraction grating is disposed at an angle with respect to the optical axis, the surface conjugate with the diffraction grating is also disposed at an angle with respect to the optical axis. As a result, the image plane is disposed at a position where the line of intersection of an imaginary plane including the image plane and an imaginary plane including the surface conjugate with the diffraction grating is disposed on a reference plane orthogonal to the optical axis and passing through the rear focal point of the condenser lens. In other words, the image plane is disposed at an imaginary plane that: passes through the line of intersection of the imaginary plane including the surface conjugate with the diffraction grating and the reference plane; and passes through the imaginary plane passing through the rear focal point of the collimating lens.

Based on this, the angle of the normal of the image plane with respect to the optical axis depends not only on the angle of the diffraction grating but also on the position of the rear focal point of the collimating lens. The closer the rear focal point of the collimating lens is to the rear focal point of the condenser lens, the smaller the angle of the normal of the image plane to the optical axis will be.

In other words, the shorter the focal length of the collimating lens is, the smaller the angle of the normal of the image plane to the optical axis will be.

In the above-described relay optical system having a reducing power, the ratio of the focal length of the collimating lens to the focal length of the condenser lens is small compared to a unit-magnification relay optical system. In other words, in the time-resolved spectroscopy unit according to this embodiment, the length from the rear focal point of the condenser lens to the rear focal point of the relay optical system is shorter and the image plane is closer to the rear focal point of the condenser lens compared to the unit-magnification relay optical system.

In this way, with the above-described structure, the angle of the normal of the image plane to the optical axis can be reduced without reducing the angle of inclination of the diffraction grating. Accordingly, a light flux passing through the relay optical system can be radiated onto the image plane at a small incident angle with respect to the normal of the image plane without reducing the diffraction efficiency of the diffraction grating.

More specifically, as illustrated inFIGS. 16 and 17, a time-resolved spectroscopy unit80aincludes an ultrashort optical pulse source5, an irradiating optical system IR, and a beam expander (first beam-shaping optical system)10. The ultrashort optical pulse source5generates an ultrashort optical pulse having a pulse width on the order of picoseconds to femtoseconds. The irradiating optical system IR guides the ultrashort optical pulse generated by the ultrashort optical pulse source5to an XY stage752used for holding a specimen. The beam expander (first beam-shaping optical system)10shapes the ultrashort optical pulse (probe beam) that is emitted from the irradiating optical system IR, radiated onto the specimen on the XY stage752, and modulated by the specimen.

After the beam expander10, a first diffraction grating12, a two-dimensional lightwave conversion optical system34, and an imaging device4are disposed. The first diffraction grating12diffracts the probe beam collimated by the beam expander10. The two-dimensional lightwave conversion optical system34converts these first-order diffracted beams diffracted by the first diffraction grating12so as to generate a spectral distribution in a direction intersecting with the direction in which the spectral distribution was originally generated to form a quasi-two-dimensional spectrogram of the probe beam on a conjugate plane FC conjugate with the first diffraction grating12. The imaging device4is disposed so that an image plane F4and the conjugate plane FC are conjugate with each other.

A relay optical system40having an optical axis aligned with the optical axis of the two-dimensional lightwave conversion optical system34is interposed between the two-dimensional lightwave conversion optical system34and the imaging device4. In this way, the quasi-two-dimensional spectrogram formed on the conjugate plane FC is projected on the image plane F4.

A beam splitter53for splitting the ultrashort optical pulse generated at the ultrashort optical pulse source5so as to obtain a reference beam is interposed between the ultrashort optical pulse source5and the irradiating optical system IR.

After the beam splitter53, a beam expander35for shaping the reference beam is disposed. After the beam expander35, a multiplexer3afor combining the shaped reference beam and the probe beam emitted from the two-dimensional lightwave conversion optical system34is disposed.

Detailed structures of these components are described below.

For example, an ultrashort optical pulse laser oscillator is used as the ultrashort optical pulse source5. In this embodiment, the signal beam generated by the ultrashort optical pulse source5is an ultrashort optical pulse having a central wavelength of 800 nm, a linewidth of ±5 nm, and a pulse width of 100 femtoseconds.

The irradiating optical system IR includes a beam splitter54and a delaying optical system (delay generating unit)6a. The beam splitter54splits the ultrashort optical pulse from the ultrashort optical pulse source5into a pump beam and a probe beam. The delaying optical system6adelays the probe beam for a predetermined amount of time relative to the pump beam between the beam splitter54and the XY stage752. The beam splitter54may be a half mirror.

Since the delaying optical system6ain the irradiating optical system IR delays the probe beam relative to the pump beam, the probe beam is radiated onto the specimen after the pump beam is radiated onto the specimen, causing the specimen to be excited. As a result, the probe beam is modulated by the excited specimen.

In this embodiment, the delaying optical system6aincludes a mirror55for reflecting the probe beam and a stage (mirror-driving unit)56for moving the mirror55. The amount of time the probe beam is delayed relative to the pump beam can be adjusted by changing the length of the optical path of the probe beam by moving the mirror55using the stage56.

The irradiating optical system IR includes mirrors57,58,59, and60. The mirrors57,58, and59guide the ultrashort optical pulse, the pump beam, and the probe beam with predetermined optical paths corresponding to the positions of various components included in the irradiating optical system IR. The mirror60relays the pump beam and probe beam from the irradiating optical system IR to the beam expander10.

The beam expander10is, for example, constituted of lenses101and102. In this embodiment, the lens101has a focal length of 10 mm and the lens102has a focal length of 100 mm. In other words, the beam expander10magnifies ten times and collimates and emits the magnified probe beam.

The first diffraction grating12is a flat transmissive Bragg diffraction grating. The first diffraction grating12is disposed so that the angle between its normal L1and an optical axis AX2is θ1on a plane parallel to an optical axis AX1of the irradiating optical system IR and an optical axis AX2of the two-dimensional lightwave conversion optical system34. In second diffraction grating12, the grating grooves, which are orthogonal to the inclination direction, are formed with a uniform spacing therebetween in a direction parallel to the inclination direction.

In this embodiment, the optical axis AX1of the irradiating optical system IR and the optical axis AX2of the two-dimensional lightwave conversion optical system34are orthogonal to each other. In the description below, an imaginary plane F1is defined as a plane that includes the intersecting point of the optical axes AX1and AX2and that is orthogonal to the optical axis AX2. The X axis of the imaginary plane F1extends in a direction parallel to the optical axis AX1, the Y axis extends in a direction orthogonal to the X axis, and the Z axis extends in a direction parallel to the optical axis AX2. The intersecting point of the optical axes AX1and AX2is set as the origin, and the propagating directions of the probe beam along the X and Z axes are defined as the positive X and Z directions.

In this embodiment, the first diffraction grating12is disposed on an imaginary plane F1a, which is obtained by rotating the imaginary plane F1around the Y axis by 45°. In other words, the above-mentioned angle θ1is 45°. The length of the first diffraction grating12in the X direction along the imaginary plane F1ais about 14.14 mm and the length in the Y direction is about 10 mm. The grating constant is set to 1,767 lines per millimeter so that the diffraction direction of the central wavelength component of the probe beam emitted to the normal L1from the irradiating optical system IR at an incident angle of 45° substantially aligns with the optical axis AX2. In this way, a probe beam from the beam expander10is incident on the first diffraction grating12at a 45° angle and is diffracted highly efficiently toward the two-dimensional lightwave conversion optical system34(i.e., in the positive Z direction) on a plane parallel to the ZX plane.

The probe beam (signal beam) is converted into a group of first-order diffracted beams. The first-order diffracted beams, depending on their incident positions on the first diffraction grating12, are incident at different positions in the direction of spectral distribution (in the X direction) and are delayed by different amounts of time. In other words, the probe beam is converted into diffracted beams in which the propagation directions of the lightwave components and the spatial phase distribution intersect at an angle.

The two-dimensional lightwave conversion optical system34includes a first cylindrical lens (Fourier transformation optical system)131having a positive power in the X direction and having a front focal plane at the imaginary plane F1, an optical filter (time/frequency conversion filter)135disposed at the rear focal plane F2of the first cylindrical lens131, and a second cylindrical lens (Fourier inverse-transformation optical system)132having a positive power in the X direction and having a front focal plane at the optical filter135.

In this embodiment, the first and second cylindrical lenses131and132each have a focal length of f=100 mm.

The first cylindrical lens131collimates the first-order diffracted beams, which are diffracted by the first diffraction grating12onto a plane parallel to the X axis, onto a plane parallel to the ZX plane and emits the first-order diffracted beams onto the optical filter135at the rear focal plane F2. In this embodiment, the first cylindrical lens131emits wavelength components in the wavelength bands of, for example, 805 nm, 800 nm, and 795 nm included in the first-order diffracted beams so that the wavelength components are incident at positions on the rear focal plane F2where X equals −1.25 mm, 0 mm, and +1.24 mm, respectively, as illustrated inFIG. 18.

As illustrated inFIG. 19, the optical filter135includes a slit135aextending diagonally with respect to the X and Y axes. The slit135acuts out light flux from the first-order diffracted beams in a strip-shaped region extending in a diagonal direction with respect to the X and Y axes. This light flux includes wavelength components sequentially distributed along the Y axis.

The second cylindrical lens132focuses the light flux cut out by the optical filter135in the X direction so that the light flux is converted into a beam having a linear cross-section extending in the Y direction and projects this beam onto the conjugate plane FC conjugate with the imaginary plane F1ain the two-dimensional lightwave conversion optical system34.

As illustrated inFIG. 17, the conjugate plane FC is obtained by rotating the rear focal plane F3of the second cylindrical lens132around the Y axis by an angle θ1in a direction opposite to the rotational direction of the imaginary plane F1awith respect to the imaginary plane F1. In this embodiment, the rotational angle θ1of the conjugate plane FC is 45°.

Since first-order diffracted beams are emitted from the first diffraction grating12with time delays in accordance with their incident positions along the X axis, each first-order diffracted beam is incident on the conjugate plane FC at a different position along the X axis at a different instant. In this way, as illustrated inFIG. 20, a quasi-two-dimensional spectrogram Sp wherein time is distributed in the X direction and wavelength is distributed in the Y direction is formed on the conjugate plane FC.

The relay optical system40is a reduction optical system including a condenser lens41having a front focal point at the rear focal plane F3and a collimating lens42having a front focal point at the same point as the rear focal point R1of the condenser lens41.

In this embodiment, the condenser lens41is a spherical lens having a focal length of f41=100 mm and the collimating lens42is a spherical lens having a focal length of f42=40 mm. The magnifying power M of the relay optical system40is 0.4.

The imaging device4, for example, is a CCD camera including a matrix of photoreceptors arranged on a plane and having the image plane F4. The imaging device4is disposed so that the image plane F4is disposed at an imaginary plane F5aconjugate with the conjugate plane FC. Here, the imaginary plane F5ais obtained by rotating the imaginary plane F5, which is orthogonal to the optical axis AX2, around the Y axis by an angle φ in a direction opposite to the direction in which the conjugate plane FC is rotated with respect to the optical axis AX2. In other words, the angle φ is equal to the angle of the normal L2of the imaginary plane F5ato the optical axis AX2on the ZX plane.

The beam splitter53is constituted of, for example, a half mirror.

The beam expander35, for example, is constituted of lenses46and47. The beam splitter53also includes a mirror48for relaying a reference beam emitted from the lens47to the multiplexer3a.

In this embodiment, the focal lengths of the lenses46and47are 10 mm and 100 mm, respectively. In other words, the beam expander35, similar to the beam expander10, magnifies the incident probe beam about ten times and then collimates and emits the magnified probe beam.

The multiplexer3aincludes a half mirror51interposed between the two-dimensional lightwave conversion optical system34and the imaging device4. The half mirror51is disposed in the optical path of the probe beam at an angle relative to the optical path.

The reference beam from the beam expander35is incident on the half mirror51at an angle with respect to the optical path of the probe beam. More specifically, the half mirror51allows the probe beam to pass through and reflects the reference beam in a direction parallel to the probe beam, i.e., in the positive direction along Z axis at the imaging device4.

In this embodiment, the half mirror51is interposed between the condenser lens41and the collimating lens42of relay optical system40. A collimating lens52constituting the reducing optical system together with the collimating lens42is interposed between the half mirror51and the beam expander35. The reference beam is reduced by the same amount as the probe beam and is incident on the imaginary plane F4.

In this way, the quasi-two-dimensional spectrogram Sp is projected at the imaginary plane F4and, as a result, an interference pattern P1of the quasi-two-dimensional spectrogram Sp and the reference beam is generated on the imaginary plane F4(refer toFIG. 21). Accordingly, time-resolved spectroscopy of the probe beam can be carried out based on the region where the stripes constituting the interference pattern P1are present and the period of these bands (i.e., the distance between the bands).

In the time-resolved spectroscopy unit80a, the relay optical system40and the image plane F4are disposed as described below so as to project the quasi-two-dimensional spectrogram Sp formed at the conjugate plane FC at the image plane F4.

As illustrated inFIG. 22, the condenser lens41is disposed so that its front focal point is located at the conjugate plane FC, and the collimating lens42is disposed so that its front focal point is at the same point as the rear focal point R1of the condenser lens41and its rear focal point is located at the image plane F4.

Also in the time-resolved spectroscopy unit80a, the first diffraction grating12and the conjugate plane FC are disposed at an angle with respect to the optical axis AX2. Therefore, the image plane F4, which is in an image-forming relationship with the conjugate plane FC, is disposed so that the line of intersection U of the imaginary plane F5aincluding the image plane F4and the imaging plane F3aincluding the conjugate plane FC is disposed on a reference plane FS. The reference plane FS is a plane that is orthogonal to the optical axis AX2and passes through the rear focal point R1of the condenser lens41. In other words, the image plane F4is disposed at the imaginary plane F5athat passes through the line of intersection U of the imaginary plane F3aincluding the conjugate plane FC and the reference plane FS and that also passes through the rear focal point R2of the collimating lens42.

Consequently, the angle φ of the normal L2of the image plane F4to the optical axis AX2depends not only on the angle θ1of the first diffraction grating12but also on the position of the rear focal point R2of the collimating lens42. The closer the rear focal point R2of the collimating lens42is to the rear focal point R1of the condenser lens41, the smaller the angle φ of the normal L2of the image plane F4to the optical axis AX2will be.

In other words, the smaller the magnifying power of the relay optical system40is, the smaller the angle φ of the normal L2of the image plane F4to the optical axis AX2will be.

Next, the relationship between the angle φ of the normal L2of the image plane F4to the optical axis AX2and the magnifying power of the relay optical system40is described mathematically.

Since the conjugate plane FC and the image plane F4are in an image-forming relationship with respect to the relay optical system40, the line of intersection U of the imaginary plane F3aincluding the conjugate plane FC and the imaginary plane F5aincluding the image plane F4is disposed on the ZX plane on a half line UR1connecting the reference plane FS and the rear focal point R1of the condenser lens41.

Accordingly, a relationship represented by the following Formula (1) is established:
2f41tan(π/2−θ1)=2f42tan(π/2−φ)  (1)

In Formula (1), f41represents the focal length of the condenser lens41, and f42represents the focal length of the collimating lens42.

From Formula (1), the following Formula (2) is derived:
tan φ=f42/f41tan θ1  (2)

Formula (2) can be transformed into the following Formula (3) based on the definition of the relay optical system40having a magnifying power M (M=f42/f41)
tan φ=M tan θ1  (3)

Formula (3) indicates that the relationship between the magnitudes of the angle θ1of the conjugate plane FC and the angle φ of the image plane F4are determined based on the magnifying power M of the relay optical system40. More specifically, when M is greater than one (M>1), φ is greater than θ1(φ>θ1), and when M is smaller than one (M<1), φ is smaller than θ1(φ<θ1).

Accordingly, when the relay optical system40has a reducing power, the angle φ of the image plane F4is small compared to the angle θ1of the conjugate plane FC.

In this embodiment, the magnifying power of the relay optical system40is 0.4 and the angle θ of the first diffraction grating12is 45°. Thus, the angle φ of the image plane F4is 21.8°.

Now, the magnifying power between the conjugate plane FC of the relay optical system40and the image plane F4will be described. As illustrated inFIG. 22, the coordinate axis XFC is defined as an axis on the conjugate plane FC parallel to the ZX plane. The coordinate axis Xiis defined as an axis on the image plane F4parallel to the ZX plane.

The magnifying power of the relay optical system40in the Y direction is equal to the magnifying power M of the relay optical system40whereas the magnifying power between the XFCaxis and the Xiaxis is defined as M cos θ1/cos φ. Consequently, the length α in the XFC direction and the length in the Y direction (not shown in the drawing) of the quasi-two-dimensional spectrogram Sp formed on the conjugate plane FC are 14.14 mm and 10 mm, respectively. The length β in the Xidirection and the length in the Y direction (not shown in the drawing) of the quasi-two-dimensional spectrogram Sp projected on the image plane F4of the imaging device4are 4.31 mm and 4.0 mm, respectively.

As described above, in the time-resolved spectroscopy unit80a, the angle φ of the image plane F4may be set smaller than the angle θ1of the conjugate plane FC. More specifically, the time-resolved spectroscopy unit80acan maintain high diffraction efficiency without decreasing the angle of the first diffraction grating12to the optical axis AX2and is capable of emitting the light flux that has passed through the relay optical system40at the image plane F4at a small angle with respect to the normal L2of the image plane F4by reducing the angle φ of the normal L2of the image plane F4to the optical axis AX2.

When using a standard CCD camera, degradations, such as shading, can be sufficiently prevented by maintaining the incident angle of a beam at 25° or less. In this embodiment, as described above, although the angle θ1of the first diffraction grating12is 45°, the angle φ of the image plane F4is 21.8°, which is smaller than 25°. Hence, degradation, such as shading, of the imaging device4can be sufficiently prevented.

As described above, the time-resolved spectroscopy unit80acan satisfactorily capture the interference pattern using the imaging device4and can carry out highly accurate time-resolved spectroscopy.

Fourth Embodiment

A microscope apparatus according to a fourth embodiment of the present invention will be described below with reference toFIGS. 23 and 24.

As illustrated inFIG. 23, the structure of a time-resolved spectroscopy unit80bis the same as that of the time-resolved spectroscopy unit80aaccording to the third embodiment except that a beam expander11according to the second embodiment and a two-dimensional lightwave conversion optical system34aare provided instead of the beam expander10and the two-dimensional lightwave conversion optical system34. The components that are the same as those included in the microscope apparatuses according to the second and third embodiments are represented by the same reference numerals and their descriptions are omitted.

The cylindrical beam expander11shapes a probe beam emitted from an irradiating optical system IR into a beam having a linear cross-section extending along the inclination direction (Z direction) of a first diffraction grating12.

In this embodiment, the cylindrical beam expander11includes a reducing optical system having a magnifying power of 0.5. The reducing optical system includes a lens111(spherical lens) having a focal length of 100 mm and a lens112(spherical lens) having a focal length of 50 mm. A cylindrical lens113having a positive power in the Z direction and a cylindrical lens114having its front focal plane disposed at the rear focal plane of the cylindrical lens113are interposed between the reducing optical system and the first diffraction grating12. The cylindrical lenses113and114constitute a magnifying optical system having a ten-fold magnification and magnify the width (length in the Z direction) of a probe beam ten times in the Y direction.

More specifically, the cylindrical beam expander11magnifies the probe beam, which has been reduced by the lenses111and112, in only the direction of inclination of the first diffraction grating12(i.e., the Z direction) by the cylindrical lenses113and114. Therefore, the length of the probe beam in the Z direction is magnified to be longer than that when the probe beam entered cylindrical beam expander11and the length of the probe beam in the Y direction is reduced to be smaller than that when the probe beam entered the cylindrical beam expander11.

In this way, the probe beam shaped into a beam having a linear cross-section extending in the direction of inclination of the first diffraction grating12is diffracted by the first diffraction grating12. The group of first-order diffracted beams forms a beam having a linear cross-section extending in the direction the spectral distribution (i.e., the X direction).

The two-dimensional lightwave conversion optical system34ais the same as the two-dimensional lightwave conversion optical system34according to the third embodiment except that a spherical lens139is included instead of the first cylindrical lens131, a first diffraction grating array137is included instead of the optical filter135, and a spherical lens140is included instead of the second cylindrical lens132.

The spherical lens139collimates the first-order diffracted beams diffracted by the first diffraction grating12on a plane parallel to the X axis and emits these collimated beams to the first diffraction grating array137at a rear focal plane F2.

The first diffraction grating array137diffracts each lightwave component included in each first-order diffracted beam in a different direction on the YZ plane depending on the wavelength.

More specifically, as illustrated inFIG. 24, the first diffraction grating array137includes a plurality of diffraction gratings137a,137b,137c, . . . having a plurality of grating grooves formed along the Y direction and having different grating constants. The diffraction gratings137a,137b,137c, . . . are disposed in the order of the magnitude of the grating constants along the X direction. In this way, each first-order diffracted beam that has been spectrally distributed along the X axis by the first diffraction grating12is incident on one of the diffraction gratings having different grating constants based on wavelength and is diffracted on the YZ plane in a direction different from the diffraction direction of the other first-order diffracted beams.

For example, a first-order diffracted beam having a central wavelength of 805 nm is diffracted on the YZ plane at an angle of −7.1° in the Z direction. The smaller the wavelength is, the further away the diffraction angle is set in the positive direction on YZ plane. The first-order diffracted beam having a central wavelength of 800 nm is diffracted at an angle of 0° (i.e., propagates straight through) on the YZ plane. The first-order diffracted beam having a central wavelength of 795 nm is diffracted at an angle of +7.1° in the Z direction on the YZ plane.

The wavelength resolving power of the first diffraction grating array137can be improved by increasing the number of diffraction gratings. Since, in this embodiment, the wavelength range of the first-order diffracted beams is from 795 to 805 nm, the first diffraction grating array137includes ten diffraction gratings each corresponding to different wavelength bands at 1-nm intervals.

The spherical lens140focuses the beam diffracted by the first diffraction grating array137while maintaining it cross-sectional shape and projects this beam on a conjugate plane FC conjugate with an imaginary plane F1ain the two-dimensional lightwave conversion optical system34a. In this way, a quasi-two-dimensional spectrogram Sp of the probe beam is formed on the conjugate plane FC.

In this embodiment, the spherical lenses139and79each have a focal length of f=40 mm. The length of the quasi-two-dimensional spectrogram Sp formed on the conjugate plane FC in the Y direction is 14.14 mm and the length in the direction parallel to the ZX plane is 10 mm.

Since the time-resolved spectroscopy unit80bhaving the above-described structure does not eliminate any portion of the probe beam with a filter, it is capable of forming a quasi-two-dimensional spectrogram Sp using the entire probe beam without eliminating any portion of the probe beams with a filter. Hence, the probe beam is used efficiently and a clear interference pattern can be obtained even when the probe beam is weak.

In the relay optical system40according to this embodiment, the focal length f41of the condenser lens41is 100 mm and the focal length f42of the collimating lens42is 25 mm. In other words, the magnifying power of the relay optical system40is 0.25. Therefore, even when the angle θ1of the first diffraction grating12is 45°, the angle φ of the image plane F4of the imaging device4will be 14.0° based on the above-described Formula (3). Accordingly, the angle φ of the normal L2of the image plane F4to the optical axis AX2can be decreased while maintaining high diffraction efficiency without decreasing the angle of inclination θ1of the first diffraction grating12, and the beam that has passed through the relay optical system40can be emitted on the image plane F4at a small angle with respect to the normal of the image plane F4.

In this embodiment, the length of the quasi-two-dimensional spectrogram Sp projected on the image plane F4of the imaging device4in the XFCdirection and the Y direction are 2.58 mm and 2.5 mm, respectively.

Fifth Embodiment

Now, a microscope apparatus according to a fifth embodiment of the present invention will be described with reference toFIGS. 25 to 28.

As illustrated inFIG. 25, the structure of a time-resolved spectroscopy unit81according to this embodiment is the same as that of the time-resolved spectroscopy unit80aaccording to the third embodiment except that a second diffraction grating array82is provided on a conjugate plane FC conjugate with a first diffraction grating12. The components that are the same as those included in the time-resolved spectroscopy unit80aaccording to the third embodiment are represented by the same reference numerals and their descriptions are omitted.

The second diffraction grating array82is large enough to entirely cover a conjugate plane FC conjugate with a first diffraction grating12and diffracts wavelength components included in a probe beam (first-order diffracted beams) incident on the conjugate plane FC so that the difference in the incident angles on the image plane F4of the wavelength components is decreased.

More specifically, as illustrated inFIG. 26, the second diffraction grating array82includes a plurality of diffraction gratings82a,82b,82c, . . . having a plurality of grating grooves formed along the X direction and having different grating constants. The diffraction gratings82a,82b,82c, . . . are disposed in the order of the magnitude of the grating constants along the Y direction. In this way, the wavelength components of the first-order diffracted beams emitted from the two-dimensional lightwave conversion optical system34at the second diffraction grating array82on the conjugate plane FC are converted into collimated beams substantially parallel to the Z axis. Then, the wavelength components are incident on the image plane F4at substantially the same angles.

Now, the behavior of the probe beam in the time-resolved spectroscopy unit81will be described in detail below.

As illustrated inFIG. 25, the probe beam incident on the first diffraction grating12is diffracted at a predetermined range of angles with respect to the Z axis on the ZX plane by the first diffraction grating12, wherein a central wavelength component is diffracted in a central angle of the predetermined range of angles. InFIG. 25, a wavelength component λ1having the shortest wavelength in the probe beam is represented by a dotted line, and the central wavelength component λ2is represented by a solid line, and a wavelength component λ3having the longest wavelength is represented by a chain line.

In this embodiment, the wavelengths of the wavelength components λ1, λ2, and λ3are 795 nm, 800 nm, and 805 nm, respectively. The wavelength components λ1and λ3are emitted at a 0.7° angle with respect to the wavelength component λ2.

The wavelength components λ1and λ3are incident on the conjugate plane FC at the same position as the wavelength component λ2. However, the angle formed between the wavelength components λ1and the wavelength component λ2and the angle formed between the wavelength components λ3and the wavelength component λ2are both 0.7°, which is the same angle as that when the wavelength components are emitted from the first diffraction grating12.

In the above-described time-resolved spectroscopy unit80aaccording to the third embodiment, as illustrated inFIG. 27, after the wavelength components λ1, λ2and λ3obtained by diffracting the probe beam at the first diffraction grating12are incident on the conjugate plane FC, they are directly projected onto the image plane F4of the imaging device4by the relay optical system40.

Since the lateral magnification of the relay optical system40is 0.4, the angular magnification between the conjugate plane FC and the image plane F4is 2.5. Accordingly, the angular distribution of the wavelength components of the probe beam on the image plane F4is about ±2°, which is wider than the angular distribution of the when the wavelength components are diffracted by the first diffraction grating12or when the wavelength components are incident on the conjugate plane FC. The angular distribution increases even more as the magnifying power of the relay optical system40is set smaller.

As described above, since the wavelength components of the probe beam are incident on the image plane F4at different angles in the time-resolved spectroscopy unit80a, the wave components in an interference pattern P1of the probe beam and a reference beam, as illustrated inFIG. 21, will have different patterns having different periods.

On the contrary, in the time-resolved spectroscopy unit81according to this embodiment illustrated inFIG. 25, the wavelength components λ1, λ2and λ3incident on the conjugate plane FC are diffracted in a direction substantially parallel to the Z axis by the second diffraction grating array82disposed at the conjugate plane FC.

In this way, in the time-resolved spectroscopy unit81, the first-order diffracted beams emitted from the two-dimensional lightwave conversion optical system34at the conjugate plane FC are converted into collimated beams substantially parallel to the Z axis. Then, the wavelength components are incident on the image plane F4at substantially the same angles. Therefore, as illustrated inFIG. 28, the wave components in an interference pattern P2will have a pattern with similar periods.

Consequently, by using the time-resolved spectroscopy unit81according to this embodiment, analysis of an interference pattern is simplified, and highly accurate time-resolved spectroscopy can be carried out.

In the above-described embodiments, the relay optical system40is a reducing optical system. The structure, however, is not limited, and, instead, the cylindrical lenses131and132constituting the two-dimensional lightwave conversion optical system34may be configured as a reducing optical system to achieve the same effects as the above-described embodiment.

Sixth Embodiment

Now, a microscope apparatus according to a sixth embodiment will be described below with reference toFIGS. 29 to 31.

The structure of the microscope apparatus according to this embodiment is the same as that of the microscope apparatus according to the third embodiment except that a time-resolved spectroscopy unit83is provided instead of the time-resolved spectroscopy unit80a. The components that are the same as those included in the microscope apparatus according to the third embodiment are represented by the same reference numerals and their descriptions are omitted.

In this embodiment, an image plane is disposed at an angle with respect to the optical axis of a relay optical system. This configuration will be described below.

In a two-dimensional lightwave conversion optical system, the differences in the diffraction angles of wavelength components of each first-order diffracted beam incident on a second diffraction grating are canceled out by being diffracted at the first diffraction grating. Then, the wavelength components are converted into collimated beams propagating substantially parallel to each other.

Since the first diffraction grating is disposed at an angle with respect to the optical axis, a plane conjugate with the first diffraction grating is also disposed at an angle with respect to the optical axis. More specifically, since the second diffraction grating disposed at the plane conjugate with the first diffraction grating is disposed at an angle opposite to the first diffraction grating with respect to the optical axis, the first-order diffracted beams incident on the second diffraction grating are delayed in accordance with the incident positions on the second diffraction grating.

As described above, since the second diffraction grating is disposed on the optical axis at an angle opposite to the angle of the first diffraction grating with respect to the optical axis, the delays generated in the first-order diffracted beams are canceled out by being diffracted at the first diffraction grating.

The group of collimated beams that are not delayed with respect to each other form a quasi-two-dimensional spectrogram on a cross-sectional plane (hereinafter referred to as a ‘reference cross-sectional plane’) disposed at an angle the same as or opposite to the angle of the second diffraction grating.

Consequently, in order to capture the quasi-two-dimensional spectrogram with an imaging device, each of the collimated beams must have a different optical path between the second diffraction grating and the image plane of the imaging device. In other words, the imaging device must be disposed so that the image plane is conjugate with the reference cross-sectional plane.

Since in the above-described configuration, the image plane of the imaging device is disposed at an angle to the optical axis of the relay optical system, the image plane is disposed at an angle to the optical axis of the group of collimated beams. Consequently, the collimated beams have different optical paths (i.e., the image plane is conjugate with the reference cross-sectional plane) and a quasi-two-dimensional spectrogram is projected on the image plane.

According to this configuration, the propagation direction of part of the probe beam emitted from a beam expander is changed by being reflected at a half mirror. This reflected probe beam is incident on the first diffraction grating.

The probe beam that is incident on the first diffraction grating is converted into first-order diffracted beams by the first diffraction grating and is incident on a reflective optical filter after being shaped by a lens.

The first-order diffracted beams incident on the reflective optical filter are converted by the reflective optical filter so that a spectral distribution is generated in a direction intersecting with the direction in which a spectral distribution is generated on an imaginary plane intersecting with the optical axis of the lens. Then, the reflective optical filter reflects the first-order diffracted beams towards the lens, where the first-order diffracted beams are re-shaped by the lens.

The first-order diffracted beams re-shaped by the lens are diffracted again at the first diffraction grating and then are emitted to the half mirror. The first-order diffracted beams that pass through the half mirror and reach the relay optical system form a quasi-two-dimensional spectrogram.

According to the above-described configuration, the two-dimensional lightwave conversion optical system uses a reflective filter to diffract the first-order diffracted beam. Therefore, the number of lenses required is half of that required when a transmissive two-dimensional conversion device is used. Consequently, the production costs are reduced.

Furthermore, since the optical path of the first-order diffracted beam is reversed within the two-dimensional lightwave conversion optical system, the length of the optical path is about half the length when a transmissive two-dimensional conversion device is used. Consequently, the overall length of the two-dimensional lightwave conversion optical system can be reduced, and thus, the size of the time-resolved spectroscope including the two-dimensional lightwave conversion optical system can be reduced.

Since the first diffraction grating also functions as the second diffraction grating, the production costs are low compared to when the first diffraction grating and the second diffraction grating are provided separately.

As illustrated inFIGS. 29 and 30, the time-resolved spectroscopy unit83includes an ultrashort optical pulse source5, an irradiating optical system IR, and a beam expander10.

After the beam expander10, a first diffraction grating12, a two-dimensional lightwave conversion optical system34, and an imaging device4for capturing a quasi-two-dimensional spectrogram formed on a conjugate plane FC conjugate with the first diffraction grating12are disposed.

A second diffraction grating8having the same grating constant as the first diffraction grating12is disposed at the conjugate plane FC. More specifically, the second diffraction grating8is disposed at an angle with respect to the two-dimensional lightwave conversion optical system34so that first-order diffracted beams are diffracted in a direction intersecting with the optical axis of the two-dimensional lightwave conversion optical system34.

The imaging device4is disposed so that its image plane F4is disposed at an angle in the same direction as or opposite to the angle of the second diffraction grating8with respect to the optical axis of the first-order diffracted beams diffracted by the second diffraction grating8. In this embodiment, the image plane F4of the imaging device4is disposed so that it is disposed at an angle opposite to the angle of the second diffraction grating8.

A relay optical system40is interposed between the second diffraction grating8and the imaging device4so that its optical axis is aligned with the optical axis of the first-order diffracted beams diffracted by the second diffraction grating8.

A beam splitter53for splitting the ultrashort optical pulse generated by the ultrashort optical pulse source5so as to obtain a reference beam is interposed between the ultrashort optical pulse source5and the irradiating optical system IR.

After the beam splitter53, a beam expander35afor shaping the reference beam is disposed. After the beam expander35a, a multiplexer3afor combining the shaped reference beam and a probe beam emitted from the two-dimensional lightwave conversion optical system34is provided.

The second diffraction grating8is a flat transmissive Bragg diffraction grating having the same grating constant as the first diffraction grating12and is disposed at the conjugate plane FC. More specifically, in the same manner as the conjugate plane FC, the normal L3of the second diffraction grating8is rotated by an angle θ1around the Y axis with respect to the optical axis AX2of the two-dimensional lightwave conversion optical system34, but is rotated in an opposite direction to the first diffraction grating12. In second diffraction grating8, the grating grooves, which are orthogonal to the inclination direction, are formed with a uniform spacing therebetween in a direction parallel to the inclination direction.

In this embodiment, since the angle θ1of the second diffraction grating8is 45°, the first-order diffracted beams emitted from the two-dimensional lightwave conversion optical system34are incident on the second diffraction grating8at a 45° angle. The first-order diffracted beams are diffracted in a direction orthogonal to the optical axis AX2(i.e., the negative direction along the X axis) on a plane parallel to the ZX plane.

Since the second diffraction grating8has the same grating constant as the first diffraction grating12, the differences in the diffraction angles of wavelength components of each first-order diffracted beam incident on the second diffraction grating8are canceled out by being diffracted at the first diffraction grating12. Then, the wavelength components are converted into collimated beams propagating substantially parallel to each other. Hereinafter, the optical axis of the collimated beams is referred to as the optical axis AX3. In this embodiment, as described above, the optical axis AX2of the two-dimensional lightwave conversion optical system34and the optical axis AX3of the collimated beams are orthogonal to each other.

Since the first diffraction grating12is disposed at an angle with respect to the optical axis AX2, the conjugate plane FC is also disposed at an angle with respect to the optical axis AX2. More specifically, the second diffraction grating8disposed at the conjugate plane FC is disposed at an angle opposite to the first diffraction grating12with respect to the optical axis AX2. Therefore, the first-order diffracted beams incident on the second diffraction grating8are delayed in accordance with the incident positions on the second diffraction grating8.

As described above, since the second diffraction grating8is disposed on the optical axis at an angle opposite to the angle of the first diffraction grating12with respect to the optical axis AX2, the delays generated in the first-order diffracted beams are canceled out by being diffracted at the first diffraction grating12.

The group of collimated beams that are not delayed with respect to each other form a quasi-two-dimensional spectrogram Sp on a cross-sectional plane (hereinafter referred to as a ‘reference cross-sectional plane FR’) disposed at an angle in the same direction as or opposite to the angle of the second diffraction grating8. In this embodiment, the reference cross-sectional plane FR is a cross-sectional plane at the conjugate plane FC. More specifically, when the angle of the normal of the reference cross-sectional plane FR (which is identical to the normal L3of the second diffraction grating8) to the optical axis AX3is represented as γ, the angle γ is defined as (π/2−θ1), which is the same as the angle of the conjugate plane FC.

A relay optical system40is a reducing optical system including a condenser lens41and a collimating lens42. The condenser lens41is disposed so that its optical axis is aligned with the optical axis AX3of the collimated beams and has its front focal point at an imaginary plane F3c. The collimating lens42has its front focal point at the same point as a rear focal point R1of the condenser lens41.

As described above, the group of collimated beams emitted from the second diffraction grating8forms the quasi-two-dimensional spectrogram Sp on the reference cross-sectional plane FR disposed at an angle to the optical axis AX3. Consequently, the image plane F4of the imaging device4is disposed at an angle to the optical axis AX3so that the quasi-two-dimensional spectrogram Sp is formed on the image plane F4by generating a difference in the optical path of each collimated beam between the second diffraction grating8and the image plane F4. In other words, the image plane F4of the imaging device4is disposed at the imaginary plane F5aconjugate with the reference cross-sectional plane FR. In this embodiment, since the reference cross-sectional plane FR is a cross-sectional plane at the conjugate plane FC, the imaginary plane F5ais obtained by rotating the conjugate plane FC around the Y axis by an angle φ in a direction opposite to the conjugate plane FC with respect to the imaginary plane F5, which is orthogonal to the optical axis AX3. In other words, the angle of the normal L4of the imaginary plane F5ato the optical axis AX2on the ZX plane is φ.

The beam expander35a, for example, is constituted of lenses46and47. The beam expander35aincludes mirrors48and49for relaying the reference beam emitted from the lens47to a multiplexer3a.

In this embodiment, the focal lengths of the lenses46and47are 10 mm and 100 mm, respectively. In other words, the beam expander35a, similar to the beam expander10, magnifies the incident probe beam about ten times and then collimates and emits the magnified probe beam.

The multiplexer3aincludes a half mirror51interposed between the two-dimensional lightwave conversion optical system34and the imaging device4. The half mirror51is disposed in the optical path of the probe beam at an angle relative to the optical path.

The reference beam from the beam expander35ais incident on the half mirror51at an angle with respect to the optical path of the probe beam. More specifically, the half mirror51allows the probe beam to pass through and reflects the reference beam in a direction parallel to the probe beam, i.e., in the positive direction along Z axis at the imaging device4.

In this embodiment, the half mirror51is interposed between the condenser lens41and the collimating lens42of the relay optical system40. A collimating lens52constituting the reducing optical system together with the collimating lens42is interposed between the half mirror51and the beam expander35a. The reference beam is reduced by the same reduction power as the probe beam and is incident on the imaginary plane F4.

In this way, the quasi-two-dimensional spectrogram Sp is projected at the imaginary plane F4and, as a result, an interference pattern P3of the quasi-two-dimensional spectrogram Sp and the reference beam is generated on the imaginary plane F4(refer toFIG. 28). Accordingly, time-resolved spectroscopy of the probe beam can be carried out based on the region where the stripes constituting the interference pattern P3are present and the period of these bands (i.e., the distance between the bands).

In the time-resolved spectroscopy unit83, the relay optical system40and the image plane F4are disposed as described below so as to project the quasi-two-dimensional spectrogram Sp formed at the reference cross-sectional plane FR at the image plane F4.

As illustrated inFIG. 31, the condenser lens41is disposed so that its front focal point is located at the imaginary plane F3c, and the collimating lens42is disposed so that its front focal point is at the same point as the rear focal point R1of the condenser lens41and its rear focal point is located at the imaginary plane F5.

Also in the time-resolved spectroscopy unit83, the reference cross-sectional plane FR is disposed at an angle with respect to the optical axis AX3. Therefore, the image plane F4, which is in an image-forming relationship with the reference cross-sectional plane FR, is disposed so that the line of intersection U of the imaginary plane F5aincluding the image plane F4and the imaginary plane F3cincluding the reference cross-sectional plane FR is disposed on a reference plane FS. The reference plane FS is a plane that is orthogonal to the optical axis AX3and passes through the rear focal point R1of the condenser lens41. In other words, the image plane F4is disposed at the imaginary plane F5athat passes through the line of intersection U of the imaginary plane F3cincluding the conjugate plane FC and the reference plane FS and that also passes through a rear focal point R2of the collimating lens42.

Consequently, the angle φ of the normal L4of the image plane F4to the optical axis AX3depends not only on the angle γ of reference cross-sectional plane FR but also on the position of the rear focal point R2of the collimating lens42. The closer the rear focal point R2of the collimating lens42is to the rear focal point R1of the condenser lens41, the smaller the angle φ of the normal L4of the image plane F4to the optical axis AX3will be.

In other words, the smaller the magnifying power of the relay optical system40is, the smaller the angle φ of the normal L4of the image plane F4to the optical axis AX3will be.

Next, the relationship between the angle φ of the normal L4of the image plane F4to the optical axis AX3and the magnifying power of the relay optical system40is described mathematically.

Since the reference cross-sectional plane FR and the image plane F4are in an image-forming relationship with respect to the relay optical system40, the line of intersection U of the imaginary plane F3cincluding the reference cross-sectional plane FR and the imaginary plane F5aincluding the image plane F4is disposed on the ZX plane on a half line UR1connecting the reference plane FS and the rear focal point R1of the condenser lens41.

Accordingly, a relationship represented by the following Formula (4) is established:
2f41tan(π/2−γ)=2f42tan(π/2−φ)  (4)

In Formula (4), f41represents the focal length of the condenser lens41, and f42represents the focal length of the collimating lens42.

From Formula (4), the following Formula (5) is derived:
tan φ=f42/f41tan γ  (5)

Formula (5) can be transformed into the following Formula (6) based on the definition of the relay optical system40having a magnifying power M (M=f42/f41)
tan φ=M tan γ  (6)

Formula (6) indicates that the relationship between the magnitudes of the angle γ of the reference cross-sectional plane FR and the angle φ of the image plane F4are determined based on the magnifying power M of the relay optical system40. More specifically, when M is greater than one (M>1), φ is greater than γ (φ>γ), and when M is smaller than one (M<1), φ is smaller than γ (φ<γ).

Accordingly, when the relay optical system40has a reducing power, the angle φ of the image plane F4is small compared to the angle γ of the reference cross-sectional plane FR.

In this embodiment, the magnifying power of the relay optical system40is 0.4 and the angle γ of reference cross-sectional plane FR is 45°. Thus, the angle φ of the image plane F4is 21.8°.

Now, the magnifying power between the reference cross-sectional plane FR of the relay optical system40and the image plane F4will be described. As illustrated inFIG. 31, the coordinate axis XFRis defined as an axis on the reference cross-sectional plane FR parallel to the ZX plane. The coordinate axis Xiis defined as an axis on the image plane F4parallel to the ZX plane.

The magnifying power of the relay optical system40in the Y direction is equal to the magnifying power M of the relay optical system40, whereas the magnifying power between the XFRaxis and the Xiaxis is defined as M cos γ/cos φ. Consequently, the length α in the XFRdirection and the length in the Y direction (not shown in the drawing) of the quasi-two-dimensional spectrogram Sp formed on the reference cross-sectional plane FR are 14.14 mm and 10 mm, respectively. The length β in the Xidirection and the length in the Y direction (not shown in the drawing) of the quasi-two-dimensional spectrogram Sp projected on the image plane F4of the imaging device4are 4.31 mm and 4.0 mm, respectively.

As described above, in the time-resolved spectroscopy unit83, the angle φ of the image plane F4may be set smaller than the angle γ of the reference cross-sectional plane FR. More specifically, the time-resolved spectroscopy unit83can maintain high diffraction efficiency without decreasing the angle of the first diffraction grating12to the optical axis AX2and is capable of emitting the light flux that has passed through the relay optical system40at the image plane F4at a small angle with respect to the normal L4of the image plane F4by reducing the angle φ of the normal L4of the image plane F4to the optical axis AX2.

When using a standard CCD camera, degradations, such as shading, can be sufficiently prevented by maintaining the incident angle of a beam at 25° or less. In this embodiment, as described above, although the angle of inclination θ1of the first diffraction grating12and the angle γ of the reference cross-sectional plane FR are both 45°, the angle φ of the image plane F4is 21.8°, which is smaller than 25°. Hence, degradation, such as shading, of the imaging device4can be sufficiently prevented.

As described above, the time-resolved spectroscopy unit83can satisfactorily capture the interference pattern using the imaging device4and can carry out highly accurate time-resolved spectroscopy.

In the time-resolved spectroscopy unit83according to this embodiment, the first-order diffracted beams are converted into collimated beams in which the wavelength components are made to propagate substantially parallel to each other by the second diffraction grating8disposed at the conjugate plane FC, as described above. Therefore, the difference in the incident angles of the wavelength components on the imaging device4is decreased and the wave components in an interference pattern P3will have a pattern with similar periods. Consequently, by using the time-resolved spectroscopy unit83according to this embodiment, analysis of an interference pattern is simplified and highly accurate time-resolved spectroscopy can be carried out.

Seventh Embodiment

Now, a microscope apparatus according to a seventh embodiment of the present invention will be described below with reference toFIGS. 32 and 24.

As illustrated inFIG. 32, the structure of a time-resolved spectroscopy unit84is the same as that of the time-resolved spectroscopy unit83according the sixth embodiment except that a beam expander11and a two-dimensional lightwave conversion optical system34aare provided instead of the beam expander10and the two-dimensional lightwave conversion optical system34. The components that are the same as those included in the time-resolved spectroscopy unit83according to the sixth embodiment are represented by the same reference numerals and their descriptions are omitted.

The beam expander11shapes a probe beam emitted from an irradiating optical system IR into a beam having a linear cross-section extending along the inclination direction (Z direction) of a first diffraction grating12.

In this way, the probe beam shaped into a beam having a linear cross-section extending in the direction of inclination of the first diffraction grating12is diffracted by the first diffraction grating12. The group of first-order diffracted beams forms a beam having a linear cross-section extending in the direction of the spectral distribution (i.e., the X direction).

The two-dimensional lightwave conversion optical system34ais the same as the two-dimensional lightwave conversion optical system34according to the sixth embodiment except that a spherical lens139is included instead of the first cylindrical lens131, an optical filter135is provided instead of the filter37, and a spherical lens140is included instead of the second cylindrical lens38.

The spherical lens139collimates the first-order diffracted beams diffracted by the first diffraction grating12on a plane parallel to the X axis and emits these collimated beams to the optical filter135at a rear focal plane F2.

The optical filter135diffracts the wavelength components of the first-order diffracted beams in different direction on the YZ plane in accordance with the wavelengths.

The spherical lens140focuses the first-order diffracted beams by the optical filter135while maintaining the cross-sectional shape and projects the converged beams on a conjugate plane FC conjugate with an imaginary plane F1ain the two-dimensional lightwave conversion optical system34a. In this way, a quasi-two-dimensional spectrogram Sp of the probe beam is formed on the conjugate plane FC.

Since the time-resolved spectroscopy unit84having the above-described structure does not eliminate any portion of the probe beam with a filter, it is capable of forming a quasi-two-dimensional spectrogram Sp using the entire probe beam. Hence, the probe beam is used efficiently and a clear interference pattern can be obtained even when the probe beam is weak.

In the relay optical system40according to this embodiment, the focal length f41of the condenser lens41is 100 mm and the focal length f42of the collimating lens42is 25 mm. In other words, the magnifying power of the relay optical system40is 0.25. Therefore, even when the angle θ1of the first diffraction grating12and the angle γ of a reference cross-sectional plane are both 45°, the angle φ of the image plane F4of the imaging device4will be 14.0° based on the above-described Formula (6). Accordingly, the angle φ of the normal L4of the image plane F4to the optical axis AX2can be decreased while maintaining high diffraction efficiency without decreasing the angle of inclination θ1of the first diffraction grating12, and the beam that has passed through the relay optical system40can be emitted on the image plane F4at a small angle with respect to the normal of the image plane F4.

In this embodiment, the length of the quasi-two-dimensional spectrogram Sp projected on the image plane F4of the imaging device4in the XFCdirection and the Y direction are 2.58 mm and 2.5 mm, respectively.

Eighth Embodiment

Now, a microscope apparatus according to an eighth embodiment of the present invention will be described below with reference toFIGS. 33 and 34.

As illustrated inFIG. 33, the structure of a time-resolved spectroscopy unit85is the same as that of the time-resolved spectroscopy unit83according the sixth embodiment except that a beam expander10aand a two-dimensional lightwave conversion optical system86are provided instead of the beam expander10and the two-dimensional lightwave conversion optical system34. The components that are the same as those included in the time-resolved spectroscopy unit83according to the sixth embodiment are represented by the same reference numerals and their descriptions are omitted.

The beam expander10ahas the same structure as the beam expander10except that lenses103and104are disposed after lenses101and102. In this embodiment, the beam expander10amagnifies the probe beam ten times and collimates it before emitting the probe beam. Furthermore, in this embodiment, a mirror105is interposed between the lenses102and103so as to tilt the optical axis of the lenses103and104at an angle with respect to the optical axis of the lens102.

In this embodiment, the optical axis of the lenses103and104is defined as an optical axis AX1. The X axis extends along the optical axis AX1. The propagation direction of the probe beam is the positive direction of the X axis.

A half mirror106is disposed on the optical axis AX1at an angle with respect to the optical axis AX1. The half mirror106reflects the probe beam emitted from the beam expander10ain a direction that deviates from the optical axis AX1.

In this embodiment, the Z axis extends along the optical axis of the probe beam reflected by the half mirror106(hereinafter, this axis is referred to as an optical axis AX3). The direction opposite to the propagating direction of the reflected probe beam is the positive direction of the Z axis. The X and Z axes are orthogonal to each other. The Y axis is orthogonal to both the X and Z axes.

The first diffraction grating12is disposed on the optical axis AX3of the probe beam reflected by the half mirror106at an angle θ1with respect to the optical axis AX3. The first diffraction grating12diffracts the probe beam and emits the diffracted probe beam to the two-dimensional lightwave conversion optical system86.

In this embodiment, the optical axis AX2of the two-dimensional lightwave conversion optical system86is disposed at an angle with respect to the optical axis AX3. In this embodiment, a plane that includes the intersecting point of the optical axis AX2and the optical axis AX3and that is orthogonal to the optical axis AX2is defined as an imaginary plane F6. In this embodiment, the first diffraction grating12is disposed at an imaginary plane F6aobtained by rotating the imaginary plane F6by 45° around the Y axis. In other words, the angle θ1is 45°.

The two-dimensional lightwave conversion optical system86includes a cylindrical lens96having a positive power in the Z direction and having a rear focal plane at the imaginary plane F6and a reflective optical filter97(reflective two-dimensional lightwave conversion element) disposed at the rear focal plane F7of the cylindrical lens96.

The cylindrical lens96constitutes a Fourier transformation optical system for collimating first-order diffracted beams incident on the two-dimensional lightwave conversion optical system86on a plane parallel to the ZX plane and emitting the collimated probe beams to the reflective optical filter97. In this embodiment, the focal length of the cylindrical lens96is f=100 mm.

The reflective optical filter97includes a reflective region97aextending diagonally with respect to both the Y and Z axes. The reflective optical filter97cuts out a light flux from the first-order diffracted beams in a diagonal direction with respect to the X and Y axes. This light flux includes wavelength components sequentially distributed along the Y axis.

The cylindrical lens96constitutes an inverse Fourier transformation optical system for focusing the first-order diffracted beams reflected at the reflective optical filter97and emitted at the cylindrical lens96for a second time in the Z direction, converting the incident first-order diffracted beams into a light flux having a linear cross-section extending along the Y axis, and projecting the converted first-order diffracted beams on a conjugate plane FC conjugate with the imaginary plane F6aof the two-dimensional lightwave conversion optical system86.

As illustrated inFIG. 33, the conjugate plane FC is formed on the imaginary plane F6a.

The first diffraction grating12also functions as a second diffraction grating for diffracting the first-order diffracted beams from the cylindrical lens96and emitting the first-order diffracted beams at the half mirror106. More specifically, the first diffraction grating12collimates the wavelength components of the first-order diffracted beams and emits the collimated beams along the optical axis AX3(in the positive Z direction).

A relay optical system40, which is a reducing optical system, and an imaging device4are disposed on the optical axis AX3at the same positions as those according to the sixth embodiment. An interference pattern P3of a quasi-two-dimensional spectrogram Sp and a reference beam is captured in the same manner as the sixth embodiment. In this embodiment, the angle γ of the normal of a reference cross-sectional plane FR to the optical axis AX3is the same as the angle θ1of the conjugate plane FC.

In the time-resolved spectroscopy unit85, the two-dimensional lightwave conversion optical system86uses a reflective optical filter97to diffract the first-order diffracted beams. Therefore, the number of cylindrical lenses required is half of that required when a transmissive two-dimensional conversion device is used. Consequently, the production cost is reduced.

Furthermore, since the optical path of the first-order diffracted beam is reversed within the two-dimensional lightwave conversion optical system86, the length of the optical path is about half the length of when a transmissive two-dimensional conversion device is used. Consequently, the overall length of the two-dimensional lightwave conversion optical system86can be reduced, and thus, the size of the time-resolved spectroscope unit85can be reduced.

Since the first diffraction grating12also functions as the second diffraction grating, production cost is low compared to when the first diffraction grating12and the second diffraction grating are provided separately.

The time-resolved spectroscopy unit85according to this embodiment is constituted by applying the above-described features to the time-resolved spectroscopy unit83according to the sixth embodiment. However, the time-resolved spectroscopy unit85according to this embodiment is not limited and may be constituted by applying the above-described features to, for example, the time-resolved spectroscopy unit66according to the seventh embodiment.

Now, a time-resolved spectroscopy unit87constituted by applying the above-described technological ideas to the time-resolved spectroscopy unit66will be described with reference toFIGS. 35 and 36.

The structure of the time-resolved spectroscopy unit87is the same as that of the time-resolved spectroscopy unit85except that a first beam shaping optical system104and a two-dimensional lightwave conversion optical system86aare used instead of the beam expander10aand the two-dimensional lightwave conversion optical system86, respectively.

A first beam shaping optical system104is constituted by replacing the lenses103and104of the beam expander10aby the lenses111and112according to the seventh embodiment and cylindrical lenses113and114. The lenses111and112and the cylindrical lenses113and114are disposed in this order along the propagating direction of a probe beam.

The two-dimensional lightwave conversion optical system86ais constituted by replacing the cylindrical lens96and the reflective optical filter97by the spherical lens139according to the sixth embodiment and a reflective diffraction grating array (reflective two-dimensional lightwave conversion device)107of the two-dimensional lightwave conversion optical system86.

The reflective diffraction grating array107is the same as the optical filter135according to the seventh embodiment except that it is a reflective diffraction grating array.

The time-resolved spectroscopy unit87, similar to the time-resolved spectroscopy unit84according to the seventh embodiment, is capable of forming a quasi-two-dimensional spectrogram Sp using the entire probe beam without eliminating any portion of the probe beam with a filter. Hence, the probe beam is used efficiently and a clear interference pattern can be obtained even when the probe beam is weak.

Ninth Embodiment

Now the microscope apparatus according to a ninth embodiment will be described below with reference toFIG. 37.

As illustrated inFIG. 37, a two-dimensional lightwave conversion optical system88according to this embodiment has the same structure as the time-resolved spectroscopy unit87according to the eighth embodiment except that first-order diffracted beams are incident on a spherical lens139of a two-dimensional lightwave conversion optical system86aat a position decentered by a distance D from the optical axis AX2along the direction in which diffraction is exhibited by a reflective diffraction grating array107(i.e., the Y direction) This configuration is obtained, for example, by adjusting the incident position of the probe beams on a first diffraction grating12.

In the two-dimensional lightwave conversion optical system88having the structure described above, first-order diffracted beams are incident on the reflective diffraction grating array107at an angle. In other words, the first-order diffracted beams are incident on the reflective diffraction grating array107at a predetermined angle A.

In this way, among the first-order diffracted beams incident on the reflective diffraction grating array107, the beams that are simply reflected by the reflective diffraction grating array107at a reflection angle A that is the same as the incident angle A reach an area on the first diffraction grating12that is displaced from the optical axis AX2by a distance D.

The wavelength components (for example, λ1, λ2, and λ3illustrated inFIG. 37) of the first-order diffracted beams that are diffracted by the reflective diffraction grating array107are diffracted at different diffraction angles that are not equal to the incident angle A. Then, the wavelength components are incident on the first diffraction grating12in areas different from the areas where the reflected beams are incident. Subsequently, the wavelength components are diffracted at the first diffraction grating12and are incident on an imaging plane F4of an imaging device4through a relay optical system40.

In other words, with the two-dimensional lightwave conversion optical system88, the reflected beams and the diffracted beams reflected and diffracted, respectively, by the reflective diffraction grating array107are incident on the spherical lens139at different angles. The difference in the incident angles is caused not only by the angular difference due to the diffraction efficiency of the reflective diffraction grating array107but also by the difference in the diffraction angle and reflection angle.

Consequently, even if the diffraction efficiency of the reflective diffraction grating array107is low, the contrast of the obtained interference pattern P3becomes high by separating the reflected beams and diffracted beams, and the analysis of the interference pattern P3is simplified.

The time-resolved spectroscopy unit88according to this embodiment is constituted by applying the above-described features to the time-resolved spectroscopy unit87according to the eighth embodiment. However, the time-resolved spectroscopy unit88according to this embodiment is not limited and may be constituted by applying the above-described features to, for example, the time-resolved spectroscopy unit85having the reflective diffraction grating array107instead of the reflective optical filter97.

Tenth Embodiment

Now, a microscope apparatus according to a tenth embodiment will be described with reference toFIGS. 38 to 40.

The components that are the same as those included in the above-described embodiments are represented by the same reference numerals and their descriptions are omitted.

The structure of the microscope apparatus according to this embodiment is the same as that of the microscope apparatus according to the third embodiment except that a time-resolved spectroscopy unit89is used instead of the time-resolved spectroscopy unit80a. The components that are the same as those included in the third embodiment are represented by the same reference numerals and their descriptions are omitted.

As illustrated inFIGS. 38 and 39, the time-resolved spectroscopy unit89includes an ultrashort optical pulse source5, an irradiating optical system IR, and a beam expander10.

After the beam expander10, a first diffraction grating12, a two-dimensional lightwave conversion optical system34b, and an imaging device4are provided. The two-dimensional lightwave conversion optical system34bis capable of forming a quasi-two-dimensional spectrogram of a probe beam on a conjugate plane FC that is conjugate with the first diffraction grating12by converting first-order diffracted beams from the first diffraction grating12so that a spectral distribution is generated in a direction orthogonal to the original direction of the spectral distribution. The imaging device4has an imaging plane F4adisposed at the conjugate plane FC conjugate to the first diffraction grating12. These components enable the imaging device4to capture the quasi-two-dimensional spectrogram formed on the conjugate plane FC.

A beam splitter53for splitting the ultrashort optical pulse generated at the ultrashort optical pulse source5so as to obtain a reference beam is interposed between the ultrashort optical pulse source5and the irradiating optical system IR.

After the beam splitter53, a beam expander35for shaping the reference beam is disposed. After the beam expander35, a multiplexer3bfor combining the shaped reference beam and the probe beam emitted from the two-dimensional lightwave conversion optical system34bis disposed.

The first diffraction grating12is a flat transmissive Bragg diffraction grating. The first diffraction grating12is disposed so that the angle between its normal L1and an optical axis AX2is θ1on a plane parallel to an optical axis AX1of the irradiating optical system IR and an optical axis AX2of the two-dimensional lightwave conversion optical system34b. The first diffraction grating12has a plurality of grating grooves formed orthogonal to and aligned along the direction of inclination of the first diffraction grating12.

In this embodiment, the optical axis AX1of the irradiating optical system IR and the optical axis AX2of the two-dimensional lightwave conversion optical system34bare orthogonal to each other. In the description below, an imaginary plane F1is defined as a plane that includes the intersecting point of the optical axes AX1and AX2and that is orthogonal to the optical axis AX2. The X axis of the imaginary plane F1extends in a direction parallel to the optical axis AX1, the Y axis extends in a direction orthogonal to the X axis, and the Z axis extends in a direction parallel to the optical axis AX2. The intersecting point of the optical axes AX1and AX2is set as the origin, and the propagating directions of the probe beam along the X and Z axes are defined as the positive X and Z directions.

In this embodiment, the first diffraction grating12is disposed on an imaginary plane F1a, which is obtained by rotating the imaginary plane F1around the Y axis by 45°. In other words, the above-mentioned angle θ1is 45°. The length of the first diffraction grating12in the X direction along the imaginary plane F1ais about 14.14 mm and the length in the Y direction is about 10 mm. The grating constant is set to 1,767 lines per millimeter so that the diffraction direction of the central wavelength component of the probe beam emitted to the normal L1from the irradiating optical system IR at an incident angle of 45° substantially aligns with the optical axis AX2. In this way, a probe beam from the beam expander10is incident on the first diffraction grating12at a 45° angle and is diffracted highly efficiently toward the two-dimensional lightwave conversion optical system34b(i.e., in the positive Z direction) on a plane parallel to the ZX plane.

The two-dimensional lightwave conversion optical system34bincludes a first cylindrical lens136having a positive power in the X direction and having a front focal plane at the imaginary plane F1, a filter37disposed at the rear focal plane F2of the first cylindrical lens136, and a second cylindrical lens138having a positive power in the X direction and having a front focal plane at the filter37.

The first and second cylindrical lenses136and138constitute a reducing optical system. In this embodiment, the focal lengths of the first and second cylindrical lenses136and138are f136=100 mm and f138=40 mm, respectively. In other words, the magnifying power of the two-dimensional lightwave conversion optical system34bis 0.4.

The first cylindrical lens136collimates the first-order diffracted beams, which are diffracted by the first diffraction grating12onto a plane parallel to the X axis, onto a plane parallel to the ZX plane and emits the first-order diffracted beams onto the filter37at the rear focal plane F2. In this embodiment, the first cylindrical lens136emits wavelength components in the wavelength bands of, for example, 805 nm, 800 nm, and 795 nm included in the first-order diffracted beams so that the wavelength components incident onto positions on the rear focal plane F2wherein X equals −1.25 mm, 0 mm, and +1.24 mm, respectively, as illustrated inFIG. 40.

The second cylindrical lens138focuses the light flux cut out by the filter37in the X direction so that the light flux is converted into a beam having a linear cross-section extending in the Y direction and projects this beam onto the conjugate plane FC conjugate with the imaginary plane F1ain the two-dimensional lightwave conversion optical system34b.

As illustrated inFIG. 39, the conjugate plane FC is obtained by rotating the rear focal plane F3of the second cylindrical lens138around the Y axis by an angle φ in a direction opposite to the rotational direction of the imaginary plane F1awith respect to the imaginary plane F1. In other words, the normal L2of the conjugate plane FC intersects with the optical axis AX2at an angle φ on the ZX plane.

Since first-order diffracted beams are emitted from the first diffraction grating12with time delays in accordance with their incident positions along the X axis, each first-order diffracted beam is incident on the conjugate plane FC at different positions along the X axis at different instant. In this way, as illustrated inFIG. 20, a quasi-two-dimensional spectrogram Sp in which time is distributed in the X direction and wavelength is distributed in the Y direction is formed on the conjugate plane FC.

The imaging device4, for example, is a CCD camera including a matrix of photoreceptors arranged on a plane and having the image plane F4a. The imaging device4is disposed so that the image plane F4ais disposed at an imaginary plane F5aconjugate with the conjugate plane FC.

The multiplexer3bincludes a half mirror51ainterposed between the two-dimensional lightwave conversion optical system34band the imaging device4. The half mirror51ais disposed in the optical path of the probe beam at an angle relative to the optical path.

The reference beam from the beam expander35is incident on the half mirror51aat an angle with respect to the optical path of the probe beam. More specifically, the half mirror51aallows the probe beam to pass through and reflects the reference beam in a direction parallel to the probe beam, i.e., in the positive direction along Z axis at the imaging device4.

In this embodiment, the mirror51ais interposed between the first cylindrical lens136and the second cylindrical lens138of the two-dimensional lightwave conversion optical system34b. A reference beam reflected at the mirror51ais incident on the imaging plane F4athrough the second cylindrical lens138. A cylindrical condenser lens52athat constitutes a reducing optical system with the second cylindrical lens138is interposed between the mirror51aand a beam expander35. The reference beam is reduced by the same amount as the probe beam and is incident on the imaging plane F4a. The cylindrical condenser lens52ahas a positive power in the Z direction and reduces the reference beam in the Z direction.

In this way, the quasi-two-dimensional spectrogram Sp is projected at the imaginary plane F4aand, as a result, an interference pattern of the quasi-two-dimensional spectrogram Sp and the reference beam is generated on the imaginary plane F4a. Accordingly, time-resolved spectroscopy of the probe beam can be carried out based on the region where the stripes constituting the interference pattern P1are present and the period of these bands (i.e., the distance between the bands).

In the time-resolved spectroscopy unit89, the two-dimensional lightwave conversion optical system34band the image plane F4aare disposed as described below so as to project the quasi-two-dimensional spectrogram Sp on the image plane F4a.

As illustrated inFIG. 40, the first cylindrical lens136is disposed so that its front focal point is disposed at the first diffraction grating12. The second cylindrical lens138is disposed so that its front focal point is disposed at the same point as the rear focal point R1of the first cylindrical lens136and its rear focal point is disposed at the imaging plane F4a(conjugate plane FC).

Since, also in the time-resolved spectroscopy unit89, the first diffraction grating12intersects with the optical axis AX2at an angle, the conjugate plane FC of the first diffraction grating12is disposed so that the line of intersection U of the imaginary plane F1aincluding the first diffraction grating12and the conjugate plane FC is orthogonal to the optical axis AX2and is disposed at a reference plane FS (rear focal plane F2) passing through the rear focal point R1of the first cylindrical lens136. In other words, the conjugate plane FC passes through the line of intersection U of the imaginary plane F1aincluding the first diffraction grating12and the reference plane FS and passes through the rear focal point R2of the second cylindrical lens138.

Consequently, the angle φ of the normal L2of the image plane F4ato the optical axis AX2depends not only on the angle θ1of the first diffraction grating12but also on the position of the rear focal point R2of the second cylindrical lens138. The closer the rear focal point R2of the second cylindrical lens138is to the rear focal point R1of the first cylindrical lens136, the smaller the angle φ of the normal L2of the image plane F4ato the optical axis AX2will be.

In other words, the smaller the magnifying power of the two-dimensional lightwave conversion optical system34bis, the smaller the angle φ of the normal L2of the image plane F4ato the optical axis AX2will be.

Next, the relationship between the angle φ of the normal L2of the image plane F4ato the optical axis AX2and the magnifying power of the two-dimensional lightwave conversion optical system34bis described mathematically.

The line of intersection U of the imaginary plane F1aincluding the first diffraction grating12and the conjugate plane FC is disposed on the ZX plane on a half line UR1connecting the reference plane FS and the rear focal point R1of the first cylindrical lens136.

Accordingly, a relationship represented by the following Formula (7) is established:
2f136tan(π/2−θ1)=2f138tan(π/2−φ)  (7)

In Formula (7), f136represents the focal length of the first cylindrical lens136and f138represents the focal length of the second cylindrical lens138.

From Formula (7), the following Formula (8) is derived:
tan φ=f138/f136tan θ1  (8)

Formula (8) can be transformed into the following Formula (9) based on the definition of the two-dimensional lightwave conversion optical system34bhaving a magnifying power M (M=f138/f136):
tan φ=M tan θ1  (9)

Formula (9) indicates that the relationship between the magnitudes of the angle θ1of the first diffraction grating12and the angle φ of the image plane F4ais determined based on the magnifying power M of the two-dimensional lightwave conversion optical system34b. More specifically, when M is greater than one (M>1), φ is greater than θ1(φ>θ1), and when M is smaller than one (M<1), φ is smaller than θ1(φ<θ1).

Accordingly, when the two-dimensional lightwave conversion optical system34bhas a reducing power, the angle φ of the image plane F4ais small compared to the angle θ1of the first diffraction grating12.

In this embodiment, the magnifying power of the two-dimensional lightwave conversion optical system34bis 0.4 and the angle θ1of the first diffraction grating12is 45°. Thus, the angle φ of the image plane F4ais 21.8°.

Now, the magnifying power between the first diffraction grating12of the two-dimensional lightwave conversion optical system34band the image plane F4awill be described. As illustrated inFIG. 40, the coordinate axis X12is defined as a coordinate axis parallel to the ZX plane on the first diffraction grating12. The coordinate axis Xiis defined as a coordinate axis parallel to the ZX plane on the image plane F4a.

In the two-dimensional lightwave conversion optical system34b, the magnifying power between the X12axis and the Xiaxis is defined as M cos θ1/cos φ (magnifying power in the Y direction is 1). Consequently, the length α of the light flux formed on the first diffraction grating12in the X12direction is 14.14 mm. The length β of the quasi-two-dimensional spectrogram Sp formed on the image plane F4aof the imaging device4in the Xidirection is 4.31 mm.

As described above, in the time-resolved spectroscopy unit89, the angle φ of the image plane F4amay be set smaller than the angle θ1of the first diffraction grating12. More specifically, the time-resolved spectroscopy unit89can maintain high diffraction efficiency without decreasing the angle of the first diffraction grating12with respect to the optical axis AX2and is capable of emitting the light flux that has passed through the beam expander11at the image plane F4aat a small angle with respect to the normal L2of the image plane F4aby reducing the angle φ of the normal L2of the image plane F4ato the optical axis AX2.

When using a standard CCD camera, degradations, such as shading, can be sufficiently prevented by maintaining the incident angle of a beam at 25° or less. In this embodiment, as described above, although the angle θ1of the first diffraction grating12is 45°, the angle φ of the image plane F4ais 21.8°, which is smaller than 25°. Hence, degradation, such as shading, of the imaging device4can be sufficiently prevented.

As described above, the time-resolved spectroscopy unit89can satisfactorily capture the interference pattern using the imaging device4and can carry out highly accurate time-resolved spectroscopy.

Eleventh Embodiment

Now, a microscope apparatus according to an eleventh embodiment will be described with reference toFIG. 41.

As illustrated inFIG. 41, the structure of a time-resolved spectroscopy unit90of the microscope apparatus according to this embodiment is the same as the time-resolved spectroscopy unit89of the microscope apparatus according to the tenth embodiment except that a beam expander11and a two-dimensional lightwave conversion optical system34care used instead of the beam expander10and the two-dimensional lightwave conversion optical system34b. The components that are the same as those included in the tenth embodiment are represented by the same reference numerals and their descriptions are omitted.

More specifically, the beam expander11magnifies a probe beam that has been reduced by spherical lenses111and112by cylindrical lenses113and114only in the direction of inclination (Z direction) of a first diffraction grating12. Accordingly, the probe beam will be magnified in the Z direction and have a smaller length in the Y direction compared to the length before entering the beam expander11.

The probe beam shaped into a light flux having a cross-section extending in the inclination direction of the first diffraction grating12is diffracted by the first diffraction grating12. The group of first-order diffracted beams has a linear cross-section extending in the direction in which a spectral distribution is formed (i.e., the X direction).

The structure of the two-dimensional lightwave conversion optical system34cis the same as that of the two-dimensional lightwave conversion optical system34baccording to the tenth embodiment except that a spherical lens139having a focal length f139, a diffraction grating array (two-dimensional conversion device)137, and a spherical lens140having a focal length f140are provided instead of the first cylindrical lens136, the filter37, and the second cylindrical lens138, respectively. The magnification of the two-dimensional lightwave conversion optical system34bis M=f140/f139<1.

In this embodiment, a multiplexer3chas the same structure as that of the multiplexer3bexcept that a converging spherical lens52bis provided instead of the converging cylindrical lens52a.

The spherical lens139collimates first-order diffracted beams diffracted by the first diffraction grating12on a plane parallel to the X axis and emits these first-order diffracted beams at the diffraction grating array137on a rear focal plane F2.

The spherical lens140focuses the light flux diffracted by the diffraction grating array137while maintaining the shape of the cross-section and projects the light flux onto a conjugate plane FC conjugate with an imaginary plane F1ain the two-dimensional lightwave conversion optical system34b. In this way, a quasi-two-dimensional spectrogram Sp is formed on the conjugate plane FC.

In this embodiment, the spherical lenses139and140both have a focal length of f=40 mm. The length in the Y direction of the quasi-two-dimensional spectrogram Sp formed on the conjugate plane FC is 14.14 mm and the length in a direction parallel to the ZX plane is 10 mm.

Since the time-resolved spectroscopy unit90having the above-described structure does not eliminate any portion of the probe beams with a filter, it is capable of forming a quasi-two-dimensional spectrogram Sp using the entire probe beam. Hence, the probe beam is used efficiently and a clear interference pattern can be obtained even when the probe beam is weak.