Scanning probe microscope

A scanning probe microscope includes: a pump light output unit that emits pump light having a first specified phase to a specimen and performs emission of the pump light a plurality of number of times to excite the specimen; a probe light output unit that emits probe light having a second specified phase to the specimen once while the specimen is excited by one-time emission of the pump light; and a scanning probe that detects, from the specimen, a probe signal corresponding to each one-time emission of the probe light, wherein the pump light output unit or the probe light output unit includes a delay time adjustment unit that adjusts delay time from a start of the emission of the pump light until a start of the emission of the probe light.

TECHNICAL FIELD

The present invention relates to a scanning probe microscope.

BACKGROUND ART

Conventionally, there has been provided an Optical Pump-Probe Scanning Tunneling Microscopy (OPP-STM) as an apparatus for acquiring time-resolved information of a specimen through atomic- and molecular-level spatial resolutions. With the OPP-STM, a tunneling current flowing between a probe and the specimen is read as a probe signal while emitting a pulse pair immediately below the probe. Consequently, a surface phenomenon of the specimen can be analyzed in a femtosecond region. For example, PTL 1 discloses a pump probe measuring apparatus including: an ultrashort light pulse laser generation unit that generates a first ultrashort light pulse train which becomes pump light, a second ultrashort light pulse train which has first delay time with respect to the pump light and becomes probe light, and a third ultrashort light pulse train which has second delay time with respect to the pump light and becomes probe light; a light shutter unit into which the second and third ultrashort light pulse trains enter; a light shutter control unit that controls the light shutter unit; an irradiation optical system that emits the pump light and the probe light to a specimen; and a detection unit including a sensor for detecting a probe signal from the specimen, and a phase-sensitive detection means coupled to the sensor, wherein the second ultrashort light pulse train and the third ultrashort light pulse train are alternately emitted as the probe light to the specimen by the light shutter control unit by cyclically modulating the delay time of the probe light with respect to the pump light, and the probe signal is synchronized with the cyclic modulation of the delay time and then detected by the phase-sensitive detection means.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The inventors have found a new challenge that it is necessary to precisely evaluate quantum dynamics of a photoinduced carrier, including charge transfer, transition, and conduction, in order to further promote the advancement of nanoscale science technology and develop new functions. However, the invention described in PTL 1 cannot observe the dynamics while it's controlling.

Means to Solve the Problems

A scanning probe microscope according to a first aspect of the present invention includes: a pump light output unit that emits pump light having a first specified phase to a specimen and performs emission of the pump light a plurality of number of times to excite the specimen; a probe light output unit that emits probe light having a second specified phase to the specimen once while the specimen is excited by one-time emission of the pump light; and a scanning probe that detects, from the specimen, a probe signal corresponding to each one-time emission of the probe light, wherein the pump light output unit or the probe light output unit includes a delay time adjustment unit that adjusts delay time from a start of the emission of the pump light until a start of the emission of the probe light. A scanning probe microscope according to a second aspect of the present invention includes: a pump light output unit that emits pump light having a first specified phase to a specimen and performs emission of the pump light once or more to excite the specimen; a probe light output unit that emits probe light having a second specified phase to the specimen once or more while the specimen is excited by one-time emission of the pump light; and a scanning probe that detects, from the specimen, a probe signal corresponding to each one-time emission of the probe light.

Advantageous Effects of the Invention

The quantum dynamics can be controlled and observed according to the present invention.

DESCRIPTION OF EMBODIMENTS

First Embodiment

A first embodiment of an electron microscope which is a scanning probe microscope according to the present invention will be explained below with reference toFIG. 1toFIG. 4.

FIG. 1is a diagram illustrating a schematic configuration of an electron microscope1. The electron microscope1includes a pump light output unit2, a probe light output unit3, and a scanning probe5. The pump light output unit2and the probe light output unit3operate in synchronization with each other as described later. The probe light output unit3includes a delay time adjustment unit3A that adjusts delay-time.

FIG. 2is an enlarged view of an area around the tip of a scanning probe5. A specimen900is an observation object of the electron microscope1and is placed around the tip of the scanning probe5. The scanning probe5includes a probe51. When a voltage is applied between the probe51and the specimen900, a tunneling current flows between a probe tip51a,which is the tip of the probe51, and a surface of the specimen900. An electric field is enhanced by tip-enhancement at this probe tip51aand its enhancement width varies widely; and, for example, the electric field may be sometimes enhanced to 10 to the 5thto 6thpower.

The pump light output unit2emits pump light21to the specimen900and the probe light output unit3emits probe light31to the specimen900. When the specimen900is irradiated with the pump light21, it is excited; and the probe light31is emitted to the specimen900while the specimen900is excited as described later. As the probe light31causes a voltage to be applied between the probe51and the specimen900, the tunneling current flowing between the probe tip51aand the surface of the specimen900is acquired as a probe signal. The scanning probe5includes a storage unit, which is not illustrated in the drawing, and records the acquired probe signal.

The delay time adjustment unit3A adjusts time delay from the start of emission of the pump light21to the specimen900until the start of emission of the probe light31to the specimen900. Since the pump light output unit2and the probe light output unit3operate in synchronization with each other as mentioned earlier, the electron microscope1can set the delay time arbitrarily by means of the delay time adjustment unit3A. In the first embodiment, measurement is performed by changing the delay time in a plurality of manners by using the delay time adjustment unit3A.

The pump light output unit2is only required to have a specified phase and be capable of outputting the light with intensity suited for the emission to a tunnel junction generated between the probe tip51aand the surface of the specimen900, so that there is no particular limitation on its configuration. The pump light output unit2includes, for example, a laser light source and a nonlinear optical crystal; and the nonlinear optical crystal is irradiated with laser pulses generated by the laser light source, thereby generating terahertz waves. These terahertz waves have the same phase every time. A Ti-sapphire laser can be used as the laser light source. Crystal of lithium niobate (LiNbO3) can be used as the nonlinear optical crystal. Incidentally, the pump light output unit2may be configured by further including a plurality of optical systems.

FIG. 3(a)is a diagram illustrating a time waveform of the pump light21obtained by using a Ti-sapphire laser with iterative frequency of 1 MHz, pulse duration of 130 fs, and a center wavelength of 800 nm as a light source and causing this Ti-sapphire laser to transmit through the LiNbO3crystal.FIG. 3(b)is a diagram illustrating a frequency spectrum ofFIG. 3(a).FIG. 3(a)andFIG. 3(b)illustrate the time waveform and the frequency spectrum of the pump light21corresponding to one pulse which is output by the laser light source, and this is called the “pump light21which is output in one-time emission” in this embodiment. Since this the laser light source has the iterative frequency of 1 MHz, the pump light output unit2outputs the pump light21with the same phase as illustrated inFIG. 3every 1 μs.

The pump light output unit2does not include a mechanism for adjusting phases; however, as its physical property, the phases of the pump light21which is output become the same. In other words, the pump light output unit2outputs the pump light21having a first specified phase.

Time variation of the electric field intensity illustrated inFIG. 3(a)are as follows. Specifically speaking, the electric field intensity is 0 kV/cm at 0 ps at the left end of the drawing, swings significantly on the minus side at around 4 ps, and inverts at around 5 ps and rapidly increases and reaches to 10 kV/cm. Subsequently, the electric field intensity decreases to approximately −6 kV/cm and then repeats minutely increasing and decreasing at around 0 kV/cm. The details of the time variation of the electric field intensity are as described above; however, if an attention is focused on sine waves in a cycle of approximately 2 ps with an amplitude of 10 kV/cm with regard to the pump light21which is output in one-time emission as illustrated inFIG. 3(a), only a half cycle is included. Furthermore, considering that the size of the electric field intensity impacts a bias voltage, that is, the tunneling current between the probe51and the specimen900, the size of the electric field intensity will be determined based on a region (part) of the waves where the amplitude is relatively large.

Therefore, it can be considered that the pump light21which is output in one-time emission is composed of only a half cycle of the sine waves having a relatively large amplitude among these waves. In other words, the pump light21which is output in one-time emission is composed of only a half cycle of the waves with dominant intensity. Furthermore, a minus value which is −6 kV/cm exists around 6 ps inFIG. 3(a); and it can be considered that the pump light21which is output in one-time emission is composed of one cycle of the electric field with a certain large amplitude.

Since the pump light21contains a wide range of frequency components as illustrated inFIG. 3(b), various reactions can be caused by the pump light21.

The probe light output unit3like the pump light output unit2includes, for example, a laser light source and nonlinear optical crystal and generates light by irradiating the nonlinear optical crystal with laser pulses generated by the laser light source. However, the probe light31needs to have a shorter cycle than that of the pump light21, so that at least one of the laser light source and the nonlinear optical crystal to be used is different from that of the pump light output unit2. The probe light output unit3can use a Ti-sapphire laser with pulse duration of 10 fs as the laser light source. Gallium selenide (GaSe) can be used as the nonlinear optical crystal. Incidentally, the probe light output unit3may be configured by further including a plurality of optical systems. A waveform of the probe light31is substantially the same as that illustrated inFIG. 3(a). However, the probe light31has a shorter cycle than that of the pump light21and one cycle of the probe light31is approximately 30 fs (30×10{circumflex over ( )}-15 seconds).

Furthermore, the probe light output unit3, like the pump light output unit2, does not have a mechanism for adjusting phases; however, as its physical property, phases of the probe light31which is output become the same. In other words, the probe light output unit3outputs the probe light31having a second specified phase. The relationship between the phase of the pump light21and the phase of the probe light31is arbitrary and both the phases do not have to be the same. In this embodiment, it is important that the phases of the pump light21and the probe light31do not change.

The pump light output unit2and the probe light output unit3synchronize their outputs. Regarding a means for synchronization, their respective laser light sources may be operated in synchronization or the outputs from their respective laser light sources may be made to pass through the same slit or slits which operate in conjunction with each other.

The probe51is formed of, for example, a platina-iridium (80/20%) wire with a diameter of 0.3 mm and the probe tip51ahas a diameter of 40 nm.

FIG. 4is a schematic diagram illustrating time variation of the pump light21and the probe light31according to the first embodiment. An upper part ofFIG. 4is a diagram illustrating time variation of intensity of the pump light21emitted to the specimen900and a lower part ofFIG. 4is a diagram illustrating time variation of intensity of the probe light31emitted to the specimen900. However, in the lower part ofFIG. 4, emission time of the probe light31is indicated as longer than actual emission time in order to enhance visibility. Furthermore, for the convenience of drafting the diagram inFIG. 4, the intensity of the pump light21and the probe light31is expressed as rectangular waves; however, the intensity is actually as indicated inFIG. 3. Furthermore,FIG. 4shows that the phase of the pump light21is constant and the phase of the probe light31is constant.

In an example illustrated inFIG. 4, the delay time is set in five patterns. Specifically, there are: a first pattern indicated as time t1to t2; a second pattern indicated as time t3to t4; a third pattern indicated as time t5to t6; a fourth pattern indicated as time t7to t8; and a fifth pattern indicated as time t9to t10. However, t1to t10may be a continuous time series or may not be continuous. For example, the measurement may be conducted with the first pattern indicated as t1to t2one million times, and then the measurement may be conducted with the second pattern one million times, and further subsequently the measurement may be conducted with the third pattern one million times, and so on.

In any of the patterns, the emission time of the pump light21is 2 ps in common and the emission time of the probe light31is 30 fs in common. In any of the patterns, the probe light31is emitted once while the pump light21is emitted once. Regarding the first pattern, the pump light21and the probe light31are emitted to the specimen900without any delay, so that the delay time is zero. Regarding the second to fifth patterns, the delay time is T22, T33, T44, and T55, respectively. They have a relationship of T22<T33<T44<T55.

Then, a fall of PN5and a fall of Pb5, that is, the end of emission of the pump light21and the end of emission of the probe light31in the fifth pattern are simultaneous.

The following operational advantages can be obtained according to the above-described first embodiment.

(1) The electron microscope1includes: the pump light output unit2that emits the pump light21to the specimen900and performs emission of the pump light a plurality of number of times to excite the specimen900; the probe light output unit3that emits the probe light31to the specimen900once while the specimen900is excited by the one-time emission of the pump light; and the scanning probe5that detects the probe signal, which corresponds to each one-time emission of the probe light31, from the specimen900. The probe light output unit3includes the delay time adjustment unit3A that adjusts the delay time from the start of emission of the pump light until the start of emission of the probe light. Therefore, as the pump light21is emitted to the specimen900to excite the state of the specimen and the probe signal is obtained by emitting the probe light31during the excitation, the state of excitation, that is, quantum dynamics can be controlled and observed. Furthermore, the probe signal indicates the state immediately below the probe51, that is, the state of a very narrow area of nano-scale to atomic scale, the quantum dynamics of the local area can be controlled and observed by using the electron microscope1.

(2) The pump light21which is output by the pump light output unit2in one-time emission includes less than one cycle of waves with the dominant intensity. Furthermore, the phase of the electric field in each emission of the pump light21is constant and that phase can be controlled. Accordingly, changes of the specimen900caused by the emitted pump light21can be controlled precisely. If the phase of the pump light21which is emitted in one-time emission were not constant, reproducibility of the pump light21would become poor; and particularly because changes with time from the start of emission of the pump light21would not be constant, the probe signal would not be reproduced. Specifically speaking, for example, the probe signal obtained when conducting the measurement as indicated at the time t1to t2inFIG. 4would be different every time. As a matter of course, not all the properties of the specimen900would fail to be obtained; however, only a measured value which is, so to speak, averaged and ambiguous could be obtained. Therefore, how changes are being made under control of the pump light21could not be observed and we would end up measuring a relaxation process after the excitation by the pump light21. On the other hand, in this embodiment, the pump light21includes less than one cycle of the waves with the dominant intensity and its phase is constant and is controlled and, therefore, the probe signal in a constant state can be obtained by a plurality of number of trials under the same conditions. Therefore, a clear measured value under sort of the specified conditions can be obtained.

(3) The probe light31which is output by the probe light output unit3in one-time emission includes less than one cycle of the waves with the dominant intensity and can control the constant phase. Therefore, an impact caused by the probe light31on the probe signal can be calculated with high precision and the obtained probe signal can be analyzed with excellent precision.

The present invention may be applied to a Frequency Modulation-Atomic Force Microscope (FM-AFM) which is one type of an atomic force microscope. However, this FM-AFM is operated in a noncontact mode in which it is operated only in an attraction area. In this variation, the scanning probe5is configured so that the probe51is provided at the tip of a cantilever. Then, this probe51is caused by external force to vibrate and the cantilever is irradiated with light, and the impact of changes of the specimen900is read from the amplitude and the number of vibrations. Specifically, in this variation, the quantum dynamics of the local area is controlled and observed without using the probe light31and by having the pump light21excite the specimen900and then reading changes of the vibrations of the cantilever after certain delay time.

In this variation, it is necessary to precisely set the distance between the probe51and the specimen900as described below. Since the interatomic force acts at an interaction distance or less which is generally said to be 1 nm or less, the state of the specimen900can be measured at appropriate timing by setting the distance between the cantilever and the specimen900and the amplitude of the cantilever.

FIG. 5(a)is a diagram illustrating appropriate distance setting in Variation 1 andFIG. 5(b)andFIG. 5(c)are diagrams illustrating inappropriate distance settings. In each ofFIG. 5(a)toFIG. 5(c), the horizontal axis represents time and the vertical axis represents the distance between the specimen900and the tip of the cantilever. Under this circumstance, the interaction distance is set as 1 nm. Since the cantilever vibrates, the distance between the specimen900and the cantilever tip changes cyclically.

If the position of the cantilever and the amplitude were set as illustrated inFIG. 5(b), the tip position of the cantilever would be always farther than the interaction distance and it would be impossible to measure the state of the specimen900. Also, if the position of the cantilever and the amplitude were set as illustrated inFIG. 5(c), the tip position of the cantilever would be always closer than the interaction distance and would be always impacted by the specimen900. The state illustrated inFIG. 5(c)corresponds to a state where the probe light31is always emitting in the first embodiment.

If the position of the cantilever and the amplitude are set as illustrated inFIG. 5(a), the tip position of the cantilever is at the interaction distance or less only during the time from ts to te in vibration cycles of the cantilever and the cantilever is impacted by the specimen900. Specifically, the time from ts to te inFIG. 5(a)corresponds to the emission time of the probe light31in the first embodiment, for example, the time with the width of Pb1inFIG. 4. Therefore, operational advantages similar to those of the first embodiment can be obtained by using the FM-AFM by emitting the pump light21for a longer period of time than the time from ts to te as with the relationship between PN1and Pb1inFIG. 4. Furthermore, a non-conductive material can be also used as the specimen900according to this variation.

Incidentally, the frequency to vibrate the cantilever should preferably be a resonance frequency of the cantilever; and the resonance frequency of the cantilever is determined based on materials and shape of the cantilever. Furthermore, when the time during which the force of interaction acts is to be shortened, the impact on the cantilever will be minute, so that it is necessary to detect a sensitive signal, in other words, to devise some creative solution to reduce noise.

In the aforementioned first embodiment, the start of emission of the pump light21and the start of emission of the probe light31are simultaneous in the first pattern and the end of emission of the pump light21and the end of emission of the probe light31are simultaneous in the fifth pattern. However, in the first pattern, the start of emission of the pump light21and the start of emission of the probe light31do not have to coincide with each other; and in the fifth pattern, the end of emission of the pump light21and the end of emission of the probe light31do not have to coincide with each other. Furthermore, the delay time adjusted by the delay time adjustment unit3A does not have to be in five patterns and there may be at least one pattern of such delay time. Furthermore, the probe light output unit3may further emit the probe light31while the pump light output unit2is not emitting the pump light21.

In the aforementioned first embodiment, the probe light output unit3includes the delay time adjustment unit3A. However, the pump light output unit2may include a configuration similar to the delay time adjustment unit3A. In other words, in the first embodiment, the timing to output the pump light21is constant in any one of the first pattern to the fifth pattern and the timing to output the probe light31is changed; however, the timing to output the probe light31may be constant and the timing to output the pump light21may be changed. The relative relationship between the pump light21and the probe light31, that is, the length of the delay time is important and which should be the reference is merely a matter of designing.

In the aforementioned first embodiment, the probe light output unit3includes the laser light source and the nonlinear optical crystal. However, if the output of the laser light source can be used directly as the probe light, the probe light output unit3does not have to include the nonlinear optical crystal. For example, in a mid-infrared region where the wavelength is approximately 800 nm, if the pulse width output from the laser light source is shorter than 5 fs, that laser beam may be used as the probe light without being emitted to the nonlinear optical crystal.

In the aforementioned first embodiment, the pump light21which is output in one-time emission includes less than one cycle of the waves with the dominant intensity. However, the pump light21which is output in one-time emission may include a plurality of cycles of the waves having the same intensity.

FIG. 6is a schematic diagram illustrating time variation of the pump light21and the probe light31in Variation 5. In an example illustrated inFIG. 6, the pump light21which is output in one-time emission includes 3.5 cycles of waves with a certain constant amplitude unlike the first embodiment. On the other hand, the probe light31which is output in one-time emission includes less than one cycle of the waves with the dominant intensity just like the first embodiment. Specifically, for example, the measurement is conducted with a first pattern indicated at time t1to t2one million times, and then the measurement is conducted with a second pattern indicated at time t3to t4one million times, and further subsequently the measurement is conducted with a third pattern indicated at time t5to t6one million times. Under this circumstance, the timing to start emitting the probe light31is the same as the emission of the first cycle of the probe light PN1-1in the first pattern. In the second pattern, there is a delay of first specified time from the start of emission of the same first cycle of the probe light PN2-1. In the third pattern, there is a further delay, that is, a delay of second specified time from the start of emission of the same first cycle of the probe light PN3-1.

Accordingly, when the pump light21which is output in one-time emission includes a plurality of cycles of the waves with specified intensity, operational advantages similar to those of the first embodiment can be obtained by setting the timing to emit the probe light31to coincide with a specified cycle of the pump light21. Specifically, in this variation, the timing to emit the probe light31is set to coincide with the first cycle of the pump light21; however, the timing to emit the probe light31may be set to coincide with the second cycle or the third cycle.

In the aforementioned first embodiment, the probe light31includes less than one cycle of the waves with the dominant intensity. However, the probe light31may have an additional condition that positive and negative polarities of the electric field are asymmetric, or an additional condition that the probe light31includes less than a half cycle of only one polarity. The condition that the positive and negative polarities are asymmetric may be added because in a case of the positive and negative polarities which are symmetric, integration with respect to the electric field intensity results in zero, which is not desirable. Furthermore, only either the positive polarity or the negative polarity may be used and less than a half cycle may be included in order to prevent offsetting of the positive and negative polarities when integrated.

Second Embodiment

A second embodiment of an electron microscope which is the scanning probe microscope according to the present invention will be explained with reference toFIG. 7toFIG. 8. In the following explanation, the same reference numerals are assigned to the same constituent elements as those in the first embodiment and the differences between the embodiments will be mainly explained. Points which are not particularly explained are the same as the first embodiment. In this embodiment, the main difference from the first embodiment is that modulation of the probe light is performed.

FIG. 7is a diagram illustrating a schematic configuration of an electron microscope1A according to the second embodiment. The probe light output unit3according to this embodiment includes, in addition to the configuration of the first embodiment, a modulation unit3B that performs on-off keying or phase modulation. The scanning probe5includes a lock-in amplifier5A in addition to the configuration of the first embodiment. The lock-in amplifier5A is coupled to the modulation unit3B via a signal line5B. The modulation unit3B outputs a reference signal to the lock-in amplifier5A via the signal line5B. The lock-in amplifier5A extracts a component synchronized with the probe light31from the probe signal by using the reference signal which is input from the modulation unit3B.

The modulation unit3B can implement the on-off keying by using, for example, a slit. Particularly, the cyclic probe light31can be easily blocked by rotating a slit plate110described later which has an opening in a circumferential direction.

FIG. 8is a diagram illustrating the configuration of the modulation unit3B when performing the on-off keying. The modulation unit3B can implement the on-off keying by using the slit plate110. The slit plate110includes a notch113. The reference numeral OP indicated with hatching represents an optical path of the probe light31. Referring toFIG. 8, the position of the optical path OP is constant; and when the slit plate110rotates and the notch113reaches the position of the optical path OP, the probe light31is emitted to the specimen900.

The modulation unit3B can control the phase, that is, carrier-envelope phase (CEP) by using, for example, two lenses described below indicated with the reference numeral121and the reference numeral122.

FIG. 9is a diagram illustrating the configuration of the modulation unit3B when performing phase modulation. Referring toFIG. 9, the reference numeral OP indicated with hatching represents an optical path of the probe light31. A first lens121and a second lens122are placed opposite each other relative to the optical path OP as illustrated inFIG. 9. The probe light31can be controlled to a desired CEP by making the probe light31transmit through the first lens121and the second lens122.

Materials for the first lens121and the second lens122may be any materials that have transparency for the probe light31; and any materials with higher transparency are more preferable. The shapes of the first lens121and the second lens122should preferably be the same and spherical lenses or cylindrical lenses can be selected according to an aspect of the desired CEP. When the spherical lenses are placed as the first and second lenses in the modulation unit3B, the probe light31of a cosine type (φcep=0) can be converted to an inverse cosine type (φcep=π). On the other hand, when the cylindrical lenses are placed as the first and second lenses, the probe light31of the cosine type can be converted to a sine type (φcep=π/2). The direction of the electric field can be controlled by controlling the phase of the probe light31.

Then, the phase of the probe light31can be switched depending on whether or not the probe light31is made to transmit through the first lens121and the second lens122. For example, switching is made between whether the probe light31of the cosine type (φcep=0) should be made to output directly, or to transmit through one set of the lenses and output as the inverse cosine type (φcep=π), or to output as φcep=π/2.

Each of the first lens121and the second lens122has at least one incidence plane and one emission plane. An emission plane121bof the first lens121and an incidence plane122aof the second lens122are placed opposite each other. InFIG. 9which illustrates a specific example of an aspect to place the spherical lenses, the first lens121and the second lens122are placed so that: the emission plane121bof the first lens121and the incidence plane122aof the second lens122are placed opposite each other; and THz waves transmit from the incidence plane121aof the first lens121to the emission plane121b,and then transmit from the incidence plane122aof the second lens122to the emission plane122b.In a case where the cylindrical lenses are used, they should preferably be placed in the same manner.

The following operational advantage can be obtained according to the above-described second embodiment.

(4) The probe light output unit3includes the modulation unit3B that modulates the probe light. The electron microscope1A includes the lock-in amplifier5A that extracts the component synchronized with the probe light, which is modulated by the modulation unit3B, from the probe signal. Therefore, a desired signal can be obtained even if the probe signal contains noise. Incidentally, if an energy amount of the probe light31is relatively small, the on-off keying which is easily implemented can be used. However, if the energy amount of the probe light31is relatively large and the on-off keying is performed, the probe51expands and contracts in conjunction with on and off of the probe light31and is impacted significantly, that is, becomes a new noise source. In such a case, the phase modulation is used.

The modulation unit3B may perform modulation other than the on-off keying and the phase modulation. For example, the modulation unit3B may perform delay time modulation.

In the aforementioned second embodiment, the probe light output unit3includes the modulation unit3B. However, the pump light output unit2may include a modulation unit. This variation can also obtain the advantageous effect of being capable of obtaining a desired signal even if the probe signal contains noise.

Third Embodiment

A third embodiment of an electron microscope which is the scanning probe microscope according to the present invention will be explained with reference toFIG. 10. In the following explanation, the same reference numerals are assigned to the same constituent elements as those in the first embodiment and the differences between the embodiments will be mainly explained. Points which are not particularly explained are the same as the first embodiment. In this embodiment, the main difference from the first embodiment is that the probe light is emitted a plurality of number of times while the pump light is emitted once.

The configuration of the electron microscope1according to the third embodiment is similar to that of the first embodiment. However, a time interval of the probe light31which is output from the probe light output unit3is shorter than that of the first embodiment. Furthermore, the scanning probe5performs measurement every time the probe light31is emitted once. Specifically, in this embodiment, the time interval of emission of the probe light31is shorter than that of the first embodiment, so that response time measured and recorded by the scanning probe5is required to be shorter than that of the first embodiment.

FIG. 10is a schematic diagram illustrating time variation of the pump light21and the probe light31.FIG. 10corresponds toFIG. 4in the first embodiment. The emission time of the pump light21is, for example, 2 ps which is the same as the first embodiment; and the emission time of the probe light31is, for example, 30 fs which is the same as the first embodiment. In this embodiment, the probe light31is emitted a plurality of number of times, for example, a total of five times as indicated as Pb1to Pb5inFIG. 10while the pump light21is emitted. The scanning probe5measures and records the probe signal corresponding to each emission of the probe light31.

The following operational advantage can be obtained according to the above-described third embodiment.

(5) The electron microscope1includes: the pump light output unit2that emits the pump light21to the specimen900and performs emission of the plump light once or more to excite the specimen; the probe light output unit3that emits the probe light31to the specimen900twice or more while the specimen900is excited by the one-time emission of the pump light; and the scanning probe5that detects the probe signal corresponding to each one-time emission of the probe light31. Therefore, advantageous effects similar to those of the first embodiment can be obtained in a short amount of time. In other words, the electron microscope1according to the third embodiment can control and observe the quantum dynamics in a short amount of time.

In the above-described third embodiment, the start of emission of the pump light21and the start of the first emission of the probe light31are simultaneous and the end of emission of the pump light21and the end of the fifth emission of the probe light31are simultaneous. However, the start of emission of the pump light21and the start of the first emission of the probe light31do not have to coincide with each other and the end of emission of the pump light21and the end of the fifth emission of the probe light31do not have to coincide with each other. Furthermore, the number of times the probe light31is emitted while the pump light21is emitted once does not have to be five times and may be twice or more. Specifically, it is only required that the probe light31is emitted at least twice during the emission of the pump light21and the timing difference between the start of emission of the pump light21and the start of the emission of the probe light31is clear. Furthermore, the probe light31may be further emitted while the pump light21is not emitted.

In the above-described third embodiment, the pump light21which is output in one-time emission includes less than one cycle of the waves with the dominant intensity. However, the pump light21which is output in one-time emission may include a plurality of cycles of waves having the same intensity. In this case, the probe light31is output as many times as the number of cycles included in one-time emission of the pump light21.

FIG. 11is a schematic diagram illustrating time variation of the pump light21and the probe light31according to Variation 6. In an example illustrated inFIG. 11, the pump light21which is output in one-time emission includes three cycles of waves having a certain constant amplitude unlike the first embodiment. Broken lines inFIG. 11represent a starting point and an ending point of one cycle included in the pump light21. In a first pattern indicated at time t1to t4, the probe light31is output at the same time as the output of each cycle of the pump light21is started. In a second pattern indicated at and after time of day t5, the probe light31is output after specified delay time following the start of output of each cycle of the pump light21. However, only part of the second pattern is illustrated for the convenience of drafting the diagram.

The second pattern may be started after the first pattern is repeated many times, for example, 100,000 times; or the second pattern may be started after the first pattern is conducted only once.

According to this variation, the output of the pump light21and the probe light31as indicated at t1to t2inFIG. 4in the first embodiment is repeated a plurality of number of times, so that this variation has the advantage of enhancing the obtained probe signal more than the first embodiment.

The above-described embodiments and variations may be combined with each other. In the above explanation, the various embodiments and variations have been described; however, the present invention is not limited to the content of these embodiments and variations. Other aspects which could be thought of within the scope of the technical idea of the present invention may be included within the scope of the present invention.

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