Patent Description:
In recent years, photoacoustic imaging that can image a sample of a living tissue, organ, cell or the like into a two-dimensional image or a three-dimensional image without using a dye, a label or the like has attracted attention. The photoacoustic imaging is a technique for imaging the sample based on an acoustic wave obtained from the sample when the sample is irradiated with a short pulse laser by using a photoacoustic effect (a phenomenon in which the acoustic wave is generated due to thermoelastic expansion caused by absorption of light energy by the sample). Here, since the acoustic wave generated in the sample is less attenuated in the sample, a deep part of the sample can also be imaged in the photoacoustic imaging.

Examples of conventional photoacoustic imaging apparatuses are disclosed in PATENT LITERATURES <NUM> to <NUM> and NON-PATENT LITERATURES <NUM> to <NUM> below. For example, the photoacoustic imaging apparatus disclosed in the following PATENT LITERATURE <NUM> uses a confocal photoacoustic microscope system, and includes a laser that generates a light pulse, and a focusing assembly that focuses the light pulse on a region inside an object, an ultrasonic transducer that receives sound waves emitted from the object, and an electronic system that processes the sound waves to generate an image of the region inside the object. Here, the focusing assembly includes a separating member (a member in which a silicon oil layer is provided between two prisms) disposed on the object side of an objective lens, and the light pulse and an acoustic signal are separated by the separating member.

By the way, since the photoacoustic imaging apparatus disclosed in PATENT LITERATURE <NUM> described above separates the light pulse and the acoustic signal by the separating member disposed on the object side of the objective lens, a distance between the objective lens and the sample inevitably increases. Further, in the photoacoustic imaging apparatus disclosed in PATENT LITERATURE <NUM> described above, the acoustic wave generated in the sample passes through various members (for example, a prism and an acoustic lens constituting the separating member) before being guided to a detector (an ultrasonic transducer).

Therefore, in the photoacoustic imaging apparatus disclosed in PATENT LITERATURE <NUM> described above, there is a possibility that the acoustic wave generated in the sample is attenuated before it is detected by the detector, and a signal intensity of the acoustic wave detected by the detector is reduced. Further, there is also a possibility that aberrations may occur in a configuration of the photoacoustic imaging apparatus disclosed in PATENT LITERATURE <NUM> described above. If there is such attenuation or aberration of the acoustic wave, for example, there is a possibility that the image of the sample is unclear.

In the photoacoustic imaging apparatus, in order to improve resolution, it is necessary to use, for example, the objective lens having a large numerical aperture (NA). However, since the objective lens having a large numerical aperture has a short working distance, it is difficult to use in a configuration in which the separating member is provided on the object side of the objective lens as in the photoacoustic imaging apparatus disclosed in PATENT LITERATURE <NUM> described above, and there is a problem that it is difficult to improve the resolution.

PATENT LITERATURE <NUM> describes a reflection-mode multispectral photoacoustic microscopy, PAM, system and related method, based on an optical-acoustic objective in communication with an ultrasonic transducer. It is said this provides little to no chromatic aberration when aligned and positioned in a predetermined manner, and with convenient confocal alignment of the optical excitation and acoustic detection.

NON-PATENT LITERATURE <NUM> describes a PAM system with an optical-acoustic objective that integrates a customized ultrasonic transducer and a commercial reflective microscope objective into one solid piece. This is said to be a technical innovation that provides zero chromatic aberration and convenient confocal alignment of the optical excitation and acoustic detection. The authors claim to have demonstrated multispectral PAM over an ultrabroad spectral range of <NUM>-<NUM> with wavelength-tunable optical-parametric-oscillator laser, and that a near-constant lateral resolution of ~<NUM> p. m is achieved experimentally.

<CIT> Al describes a reflection-mode photoacoustic endoscope that includes a light source configured to emit a light pulse, a signal detection or transmission unit configured to detect or emit an ultrasonic pulse, and a rotatable reflector. The rotatable reflector is configured to reflect at least one of the light pulse and the ultrasonic pulse into a target area of an object, and reflect a response signal to the signal detection unit. The response signal is one of a photoacoustic wave generated by the object responsive to the light pulse and an ultrasonic pulse echo generated by the object responsive to the ultrasonic pulse.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide the objective optical system and the photoacoustic imaging apparatus capable of obtaining a clearer image of the sample than before.

In order to solve the above problems, there is provided an objective optical system as set out in Claim <NUM>.

There is also provided a photoacoustic imaging apparatus as set out in Claim <NUM>.

According to the present invention, that is solely defined by the appended claims, by using the objective optical system including: a first mirror having a convex reflecting surface for reflecting light traveling toward a sample; a second mirror having a concave reflecting surface for reflecting the light reflected by the first mirror and irradiating the sample with the light; and a detector having at least one end portion provided on an object side of the first mirror, and detecting an acoustic wave obtained by irradiating the sample with the light, since the objective optical system can be disposed close to the sample, there is an effect that it is possible, when using the construction as defined by claim <NUM>, to obtain a clearer sample image (image based on the acoustic wave obtained from the sample) than before.

Described herein is an objective optical system (<NUM>, 23A to 23D, <NUM>, 53A) that includes: a first mirror (<NUM>) having a convex reflecting surface for reflecting light traveling toward a sample (SP); a second mirror (<NUM>) having a concave reflecting surface for reflecting the light reflected by the first mirror and irradiating the sample with the light; and a detector (<NUM>) having at least one end portion provided on an object side of the first mirror, and detecting an acoustic wave obtained by irradiating the sample with the light.

In an objective optical system described herein, a hole portion (H) through which the light traveling toward the sample passes is formed in a central portion of the second mirror, and the first mirror, the second mirror, and the detector are arranged in an order of the second mirror, the first mirror, and the one end portion of the detector on an optical axis (AX) of the light traveling toward the sample.

In an objective optical system described herein, the detector is rod-shaped, and a hole portion (h) through which the detector is to be inserted is formed in a central portion of the first mirror.

In an objective optical system described herein, the detector is disposed outside an optical path of the light irradiated to the sample so as not to block the light irradiated to the sample.

In an objective optical system described herein, the detector includes an acoustic lens (103A) for collecting the acoustic wave obtained by irradiating the sample with the light.

An objective optical system described herein includes a transparent cover member (<NUM>) that is provided on the object side of the first mirror and the second mirror, forms a boundary surface with liquid, and prevents the liquid from entering the first mirror and the second mirror.

In an objective optical system described herein, the detector is fixed to the object side of the cover member, and the first mirror is provided on an opposite side to the object side of the cover member.

In an objective optical system described herein, at least one of a light incident surface (105a) and a light exit surface (105b) of the cover member is formed in a substantially spherical surface, and a center of curvature of the spherical surface is substantially equal to a focal position (P) of a reflective optical system formed by the first mirror and the second mirror.

In an objective optical system described herein, an optical path in which the light reflected by the second mirror reaches the sample or a container (CT1) of the sample is filled with liquid.

An objective optical system described herein includes an optical member (<NUM>) having a first surface (200a) in which the first mirror is formed in a central portion thereof, and a transmissive portion (TS) is provided in a peripheral portion thereof, and a second surface (200b) in which the light traveling toward the sample is incident on a central portion thereof, and the second mirror is formed in a peripheral portion thereof, wherein the detector is fixed to a central portion on the object side of the optical member.

In an objective optical system described herein, the transmissive portion is formed in a substantially spherical surface, and a center of curvature of the spherical surface is substantially equal to a focal position (P) of a reflective optical system formed by the first mirror and the second mirror.

An objective optical system described herein includes: a lens barrel (<NUM>) for supporting at least the second mirror therein; and a tubular liquid holding member (<NUM>, <NUM>) that is provided so that one end portion thereof surrounds a periphery of the object side of the lens barrel and can hold liquid (WT, CF) therein.

An objective optical system described herein includes a liquid conduit (<NUM>, <NUM>, <NUM>) for introducing the liquid into the liquid holding member.

In an objective optical system described herein, a bottom portion of the container (CT1) of the sample is disposed close to the other end portion of the liquid holding member, and a space between the liquid holding member and the bottom portion of the container is filled with the liquid (WT) held inside the liquid holding member.

In an objective optical system described herein, the liquid holding member is a tubular member having a diameter reduced from the one end portion to the other end portion.

Described herein is a photoacoustic imaging apparatus (<NUM>, <NUM>) for generating an image of a sample based on an acoustic wave obtained by irradiating the sample with light, including an objective optical system (<NUM>, 23A to 23D, <NUM>, 53A) according to any one of the above, that irradiates the sample with light and detects the acoustic wave obtained by irradiating the sample with the light.

A photoacoustic imaging apparatus described herein includes a scanning optical unit (<NUM>) for scanning the light irradiated to the sample, wherein a pupil position of the objective optical system is optically conjugated with inside or vicinity of the scanning optical unit.

In a photoacoustic imaging apparatus described herein, the pupil position of the objective optical system is a position of the first mirror.

A photoacoustic imaging apparatus described herein includes an optical system (<NUM>) for converting light incident on the objective optical system into the light having a ring-shaped cross-section.

In a photoacoustic imaging apparatus described herein, the optical system is configured by using two axicon lenses (19a, 19b) arranged so that apex angles thereof are opposed to each other.

A photoacoustic imaging apparatus described herein further includes: a photodetector (<NUM>) for detecting fluorescence obtained by irradiating the sample with the light; and an image generator (<NUM>) for generating a photoacoustic image based on a detection result of the acoustic wave and generating a fluorescence image based on a detection result of the photodetector.

An objective optical system and a photoacoustic imaging apparatus according to embodiments of the present invention will be described in detail with reference to the drawings below. In the drawings referred to below, dimensions of members are appropriately changed as necessary for easy understanding. In the following, positional relationship between members will be described with reference to an XYZ orthogonal coordinate system set in the drawing as necessary. In the XYZ orthogonal coordinate system, an X axis and a Y axis are set in a horizontal plane, and a Z axis is set in a vertical direction. However, for convenience of explanation, origin of the XYZ orthogonal coordinate system shown in the drawings is not fixed, and its position is changed as appropriate for each of the drawings.

<FIG> is a diagram showing a main configuration of the photoacoustic imaging apparatus. As shown in <FIG>, a photoacoustic imaging apparatus <NUM> of the present embodiment includes a confocal unit <NUM>, an inverted microscope <NUM>, and a controller <NUM> (image generator), and generates an image of a sample SP based on an acoustic wave or fluorescence obtained by irradiating pulsed laser light (hereinafter referred to as pulsed light) on the sample SP stored in a sample container CT1. Hereinafter, the image based on the acoustic wave obtained from the sample SP is referred to as a "photoacoustic image", and the image based on the fluorescence obtained from the sample SP is referred to as a "fluorescence image".

The confocal unit <NUM> is a unit forming a main portion of a confocal microscope. The confocal microscope is realized by attaching the inverted microscope <NUM> to the confocal unit <NUM>. Note that not only the inverted microscope <NUM> can be attached to the confocal unit <NUM>, but other microscopes (for example, an upright microscope) can also be attached thereto. That is, an arbitrary microscope can be attached to the confocal unit <NUM> according to an application of the confocal microscope.

The confocal unit <NUM> includes a laser light source <NUM>, a dichroic mirror <NUM>, a scanning optical unit <NUM>, a pupil projection lens <NUM>, a fluorescence filter <NUM>, a lens <NUM>, a pinhole <NUM>, and a photodetector <NUM>. The laser light source <NUM> emits the pulsed light for irradiating the sample SP stored in the sample container CT1 under control of the controller <NUM>. A wavelength of the pulsed light emitted from the laser light source <NUM> can be set to an arbitrary wavelength depending on the sample SP. Further, the laser light source <NUM> may be capable of changing the wavelength continuously or discretely.

The dichroic mirror <NUM> is a mirror that reflects the light having the wavelength of the pulsed light emitted from the laser light source <NUM> and transmits the light having a wavelength of the fluorescence obtained from the sample SP. The dichroic mirror <NUM> is disposed on a -Z side of the laser light source <NUM>, and reflects the pulsed light emitted in a -Z direction from the laser light source <NUM> in a +X direction, to transmit the fluorescence emitted from the scanning optical unit <NUM> and traveling in a -X direction.

The scanning optical unit <NUM> is a unit for scanning the pulsed light irradiated to the sample SP in a plane orthogonal to an optical axis AX under the control of the controller <NUM>. Specifically, the scanning optical unit <NUM> includes a variable mirror 13a that reflects the pulsed light reflected in the +X direction by the dichroic mirror <NUM> in the -Z direction, and a variable mirror 13b that reflects the pulsed light reflected in the -Z direction by the variable mirror 13a in the +X direction. The variable mirrors 13a and 13b are configured to be rotatable about axes orthogonal to each other. For example, the variable mirror 13a is configured to be rotatable about an axis parallel to the Y axis, and the variable mirror 13b is configured to be rotatable around an axis, which is included in a ZX plane and along a reflecting surface of the variable mirror 13b. Rotations of the variable mirrors 13a and 13b are controlled by the controller <NUM>.

The pupil projection lens <NUM> is disposed on a +X side of the variable mirror 13b provided in the scanning optical unit <NUM>, collects the pulsed light reflected in the +X direction by the variable mirror 13b, and converts the fluorescence emitted in the -X direction from the inverted microscope <NUM> into parallel light. In an example shown in <FIG>, the pulsed light is collected in the confocal unit <NUM> by the pupil projection lens <NUM>, and the diverging pulsed light is emitted from the confocal unit <NUM>. Note that the pulsed light (diverging pulsed light) emitted from the confocal unit <NUM> is incident on the inverted microscope <NUM>.

The fluorescence filter <NUM> is disposed on the -X side of the dichroic mirror <NUM> and selectively transmits the fluorescence obtained from the sample SP. The lens <NUM> collects the fluorescence that has transmitted through the fluorescence filter <NUM>. The pinhole <NUM> is disposed at a focal position (focal position on the -X side) of the lens <NUM>. The photodetector <NUM> is disposed on the -X side of the pinhole <NUM> and detects the light that has passed through the pinhole <NUM>. A detection signal of the photodetector <NUM> is output to the controller <NUM>.

The inverted microscope <NUM> includes an imaging lens <NUM>, a mirror <NUM>, and an objective optical system <NUM>, and observes the sample SP stored in the sample container CT1 from a lower side (the -Z side). The imaging lens <NUM> is a lens that converts the pulsed light emitted from the confocal unit <NUM> and incident on the inverted microscope <NUM> into parallel light, and forms an image of the fluorescence reflected by the mirror <NUM> and traveling in the -X direction. The mirror <NUM> is disposed in the +X direction of the imaging lens <NUM>, reflects the pulsed light traveling in the +X direction through the imaging lens <NUM> in a +Z direction, and reflects the fluorescence traveling in the -Z direction through objective optical system <NUM> in the -X direction.

The objective optical system <NUM> is disposed on the +Z side of the mirror <NUM>, collects the pulsed light reflected in the +Z direction by the mirror <NUM> to irradiate the sample SP with the light, and converts the fluorescence obtained from the sample SP into parallel light. Further, the objective optical system <NUM> detects the acoustic wave obtained by irradiating the sample SP with pulsed light. A detection signal of the objective optical system <NUM> is output to the controller <NUM>. The objective optical system <NUM> is configured to be movable in the Z direction under the control of the controller <NUM>. Details of the objective optical system <NUM> will be described below.

The controller <NUM> controls operation of the photoacoustic imaging apparatus <NUM> in an integrated manner. For example, the laser light source <NUM> provided in the confocal unit <NUM> is controlled to emit or stop the pulsed light irradiated to the sample SP. Further, the scanning optical unit <NUM> provided in the confocal unit <NUM> and the objective optical system <NUM> provided in the inverted microscope <NUM> are controlled to scan the sample SP with the pulsed light (X-axis, Y-axis, and Z-axis scanning). Further, the controller <NUM> performs signal processing of the detection signal output from the photodetector <NUM> provided in the confocal unit <NUM> to generate a fluorescence image and display it on a display monitor <NUM>, and performs signal processing of the detection signal output from the objective optical system <NUM> to generate the photoacoustic image and display it on the display monitor <NUM>. The display monitor <NUM> is a monitor provided with, for example, a liquid crystal display device.

<FIG> is a cross-sectional view showing a main configuration of the objective optical system according to the first embodiment of the present disclosure. As shown in <FIG>, the objective optical system <NUM> of the present embodiment includes a lens barrel <NUM>, a convex mirror <NUM> (first mirror), a concave mirror <NUM> (second mirror), an ultrasonic detector <NUM> (detector), a mirror holding member <NUM>, a glass cover <NUM> (cover member), and a water receiving member <NUM> (liquid holding member). The lens barrel <NUM> is a circular annular member for holding the convex mirror <NUM> and the concave mirror <NUM> therein. Note that a shape of the lens barrel <NUM> is not limited to a circular annular shape, but may be another shape (for example, a square annular shape).

The convex mirror <NUM> is disposed on the optical axis AX of the pulsed light traveling toward the sample SP, and is a mirror having a convex reflecting surface for reflecting the pulsed light traveling toward the sample SP. Specifically, the convex mirror <NUM> is held by the mirror holding member <NUM> so that its central portion is disposed on the optical axis AX on one end side (the +Z side) of the lens barrel <NUM>. A position of the convex mirror <NUM> is a pupil position of the objective optical system <NUM>. The convex mirror <NUM> is optically conjugated with inside or vicinity of the scanning optical unit <NUM> by the imaging lens <NUM> provided in the inverted microscope <NUM>, the pupil projection lens <NUM> provided in the confocal unit <NUM>, and the like.

<FIG> is a bottom view showing the mirror holding member in the first embodiment of the present disclosure. As shown in <FIG>, the mirror holding member <NUM> has two circular annular portions 104a and 104b having different concentric diameters, and is configured such that the circular annular portions 104a and 104b are connected by a plurality of (four in an example shown in <FIG>) connecting members 104c extending radially. The circular annular portion 104a has an outer diameter substantially the same as an inner diameter of the lens barrel <NUM>, and is a portion that is fixed to an inner wall of the lens barrel <NUM>. The circular annular portion 104b has an inner diameter substantially the same as an outer diameter of the convex mirror <NUM>, and is a portion in which the convex mirror <NUM> is fixed. Since the circular annular portion 104a and the circular annular portion 104b are connected by the connecting members 104c, the convex mirror <NUM> is supported inside the lens barrel <NUM>. A space (excluding the connecting members 104c) between the circular annular portion 104a and the circular annular portion 104b is a passage portion PS through which the pulsed light (pulsed light reflected by the concave mirror <NUM>) passes.

The concave mirror <NUM> is a mirror having a concave reflecting surface for reflecting the pulsed light reflected by the convex mirror <NUM> and irradiating the sample SP with the light. The reflecting surface of the concave mirror <NUM> is designed so that the reflected pulsed light is focused on the sample SP. The concave mirror <NUM> has an outer diameter substantially the same as the inner diameter of the lens barrel <NUM>, and a hole portion H through which the pulsed light traveling toward the sample SP (the pulsed light reflected in the +Z direction by the mirror <NUM>) passes is formed in its central portion. The concave mirror <NUM> is held on the other end side (the -Z side) of the lens barrel <NUM> so that the hole portion H is disposed on the optical axis AX.

The ultrasonic detector <NUM> is provided on the +Z side (an object side) of the convex mirror <NUM> in a state where its one end portion provided with a detection surface faces the sample SP side (+Z side), and detects the acoustic wave obtained by irradiating the sample SP with the pulsed light. Specifically, the ultrasonic detector <NUM> is attached to a central portion of the glass cover <NUM> that is a glass disk-shaped member, and the glass cover <NUM> is attached to the lens barrel <NUM> so as to close the one end side (+Z side: object side end portion) of the lens barrel <NUM>, so that the ultrasonic detector <NUM> is disposed on the +Z side of the convex mirror <NUM>. Thus, the ultrasonic detector <NUM> is supported by the glass cover <NUM> on the +Z side of the convex mirror <NUM>, and is disposed outside an optical path of the pulsed light irradiated to the sample SP so as not to block the light irradiated to the sample SP.

<FIG> is a cross-sectional view schematically showing a main configuration of the ultrasonic detector according to the first embodiment of the present disclosure. As shown in <FIG>, the ultrasonic detector <NUM> includes an acoustic lens 103A, an acoustic matching layer 103B, a piezoelectric vibrator 103C, and a backing material 103D. The ultrasonic detector <NUM> is supported by the glass cover <NUM> by being coupled to the glass cover <NUM> in a state where the acoustic lens 103A is disposed on the object side (sample SP side).

The acoustic lens 103A collects the acoustic wave obtained by irradiating the sample SP with the pulsed light. Specifically, the acoustic lens 103A has a focal position that matches a focal position of the pulsed light, and selectively collects the acoustic wave generated at and near the focal position of the pulsed light. The acoustic matching layer 103B is a layer for matching acoustic impedance, and the acoustic lens 103A is bonded to one surface thereof, and the piezoelectric vibrator 103C is bonded to the other surface thereof.

The piezoelectric vibrator 103C is an element that detects the acoustic wave through the acoustic lens 103A and the acoustic matching layer 103B and outputs the detection signal. Electrodes (not shown) are provided on both surfaces of the piezoelectric vibrator 103C, and lines 103a are respectively electrically connected to the electrodes. The detection signal of the piezoelectric vibrator 103C is output from the lines 103a. The backing material 103D suppresses excessive vibration of the piezoelectric vibrator 103C and is bonded to a back surface (a surface opposite to a surface to which the acoustic matching layer 103B is bonded) of the piezoelectric vibrator 103C.

Here, as shown in <FIG>, the convex mirror <NUM>, the concave mirror <NUM>, and the ultrasonic detector <NUM> are arranged in an order of the concave mirror <NUM>, the convex mirror <NUM>, and the ultrasonic detector <NUM>, in the direction from the -Z side to the +Z side on the optical axis AX of the pulsed light traveling toward the sample SP. The detection signal of the ultrasonic detector <NUM> is output to the controller <NUM> through the lines 103a. The lines 103a of the ultrasonic detector <NUM> are drawn to the +Z side of the connecting members 104c forming the mirror holding member <NUM>, and extended from a side surface of the lens barrel <NUM> to the outside. This is done so as not to block the pulsed light passing through the passage portion PS shown in <FIG> as much as possible.

The water receiving member <NUM> is provided on the one end side (+Z side: object side end portion) of the lens barrel <NUM> so that its one end portion (-Z side end portion) surrounds a periphery of the glass cover <NUM>, and is a tubular member that can hold a liquid WT therein. As shown in <FIG>, a bottom portion of the sample container CT1 is disposed close to the other end portion (+Z side end portion) of the water receiving member <NUM>. A space between the glass cover <NUM> disposed at the one end portion of the water receiving member <NUM> and the bottom portion of the sample container CT1 disposed in the vicinity of the other end portion of the water receiving member <NUM> is filled with the liquid WT held in the water receiving member <NUM>.

This is in order that the acoustic wave obtained from the sample SP is detected by the ultrasonic detector <NUM> without being attenuated as much as possible. That is, since a path through which the acoustic wave is transmitted from the sample SP to the ultrasonic detector <NUM> is filled with the liquid (culture fluid CF in the sample container CT1 and liquid WT), it is possible to detect the acoustic wave obtained from the sample SP by the ultrasonic detector <NUM> without being attenuated as much as possible. As described above, since the objective optical system <NUM> is configured to be movable in the Z direction, a distance between the other end (+Z side end portion) of the water receiving member <NUM> and the bottom portion of the sample container CT1 may be changed. However, as schematically shown also in <FIG>, it is possible to maintain the above-described state (the state where the space between the glass cover <NUM> and the bottom portion of the sample container CT1 is filled with the liquid WT) by surface tension of the liquid WT.

When the operation of the photoacoustic imaging apparatus <NUM> is started, the laser light source <NUM> is first controlled by the controller <NUM>, and the pulsed light is emitted in the -Z direction from the laser light source <NUM>. The pulsed light emitted from the laser light source <NUM> is reflected in the +X direction by the dichroic mirror <NUM> and then incident on the inverted microscope <NUM> through the scanning optical unit <NUM> and the pupil projection lens <NUM> in this order. The pulsed light incident on the inverted microscope <NUM> passes through the imaging lens <NUM> and is then reflected in the +Z direction by the mirror <NUM> to be incident on the objective optical system <NUM>.

The pulsed light incident on the objective optical system <NUM> passes through the hole portion H formed in the concave mirror <NUM> and is incident on and reflected by the convex mirror <NUM>, and then incident on and reflected by the concave mirror <NUM> to be irradiated to the sample SP. At this time, the pulsed light is irradiated so as to be focused on the sample SP. When the pulsed light is irradiated to the sample SP, the fluorescence is emitted from fluorescent substance contained in the sample SP.

The fluorescence emitted from the sample SP travels in a reverse direction along the optical path of the pulsed light, and is guided to the dichroic mirror <NUM> through the objective optical system <NUM>, the mirror <NUM>, the imaging lens <NUM>, the pupil projection lens <NUM>, and the scanning optical unit <NUM> in this order. The fluorescence guided to the dichroic mirror <NUM> transmits through the dichroic mirror <NUM> and is then incident on the fluorescence filter <NUM>. Only a specific wavelength component transmits through the fluorescence filter <NUM> out of wavelength components included in the fluorescence. The wavelength component transmitted through the fluorescence filter <NUM> is incident on the pinhole <NUM> through the lens <NUM>, and only the light from a focal plane transmits through the pinhole <NUM> to be incident on and detected by the photodetector <NUM>.

The detection signal of the photodetector <NUM> is output to the controller <NUM> and converted into a digital signal, to be associated with a scanning position (scanning position in an XY plane by the scanning optical unit <NUM> and the scanning position in the Z direction by the objective optical system <NUM>). The above operation is performed while changing the scanning position in the XY plane by the scanning optical unit <NUM> (and further changing the scanning position in the Z direction by the objective optical system <NUM>).

Here, as described above, since the pupil position of the objective optical system <NUM> (the position of the convex mirror <NUM>) is optically conjugated with the inside of the scanning optical unit <NUM> provided in the confocal unit <NUM> or the vicinity thereof, even when the pulsed light to be irradiated to the sample SP is scanned by the scanning light unit <NUM>, almost all the pulsed light passes through the pupil position of the objective optical system <NUM>. That is, a state equivalent to scanning the pulsed light at the pupil position of the objective optical system <NUM> is obtained. Thus, loss of the pulsed light can be reduced. A two-dimensional or three-dimensional fluorescence image is generated by performing such an operation. The generated fluorescence image may be displayed on the display monitor <NUM> or stored in an internal memory (not shown).

When the operation of the photoacoustic imaging apparatus <NUM> is started, the pulsed light is emitted from the laser light source <NUM> and irradiated to the sample SP through the above-described optical path, as when generating the fluorescence image. Here, when there is a substance that absorbs the irradiated pulsed light inside the sample SP, the sample SP is locally heated and rapidly expands, so that a local acoustic wave is emitted from the sample SP. The acoustic wave passes through the sample container CT1 and then travels through the liquid WT held inside the water receiving member <NUM> to be detected by the ultrasonic detector <NUM>.

In consideration of transmission of the acoustic wave, the sample container CT1 is preferably formed of a material whose acoustic impedance density is close to the acoustic impedance density of the liquid WT. For example, when the sample container CT1 is formed of a resin such as polystyrene, the acoustic impedance is closer to the acoustic impedance of the liquid WT than when the sample container CT1 is formed of glass. This is preferable because loss of ultrasonic transmission is reduced.

At this time, in the ultrasonic detector <NUM>, the acoustic wave generated near a focal point of the pulsed light is selectively collected by the acoustic lens 103A shown in <FIG>, and the acoustic wave is efficiently transmitted to the piezoelectric vibrator 103C without being almost not reflected by the acoustic matching layer 103B and converted into an electric signal (the detection signal). Extra vibration of the piezoelectric vibrator 103C is suppressed by the backing material 103D bonded to the piezoelectric vibrator 103C. Therefore, the piezoelectric vibrator 103C outputs the detection signal having a high signal level and low noise.

The detection signal of the ultrasonic detector <NUM> is output to the controller <NUM> and converted into the digital signal, to be associated with the scanning position (the scanning position in the XY plane by the scanning optical unit <NUM> and the scanning position in the Z direction by the objective optical system <NUM>). The above operation is performed while changing the scanning position in the XY plane by the scanning optical unit <NUM> (and further changing the scanning position in the Z direction by the objective optical system <NUM>).

Here, since the pupil position of the objective optical system <NUM> (the position of the convex mirror <NUM>) is optically conjugated with the inside of the scanning optical unit <NUM> provided in the confocal unit <NUM> or the vicinity thereof, even when the pulsed light to be irradiated to the sample SP with the scanning optical unit <NUM> is scanned by the scanning light unit <NUM>, almost all the pulsed light passes through the pupil position of the objective optical system <NUM>. That is, the state equivalent to scanning the pulsed light at the pupil position of the objective optical system <NUM> is obtained. Thus, the loss of the pulsed light can be reduced even when generating the photoacoustic image. A two-dimensional or three-dimensional photoacoustic image is generated by performing such an operation. The generated photoacoustic image may be displayed on the display monitor <NUM> or stored in the internal memory (not shown).

As described above, the present embodiment uses the objective optical system <NUM> including the convex mirror <NUM> that reflects the pulsed light traveling toward the sample SP, the concave mirror <NUM> that reflects the pulsed light reflected by the convex mirror <NUM> and irradiates the sample SP with the light, and the ultrasonic detector <NUM> that is provided on the object side of the convex mirror <NUM> and detects the acoustic wave obtained by irradiating the sample SP with the light. Thus, unlike the related art, there is no need to arrange a separating member for separating the light pulse and the acoustic signal on the object side of the objective lens, and the objective optical system <NUM> can be disposed closer to the sample SP than before. Therefore, since it is possible to prevent attenuation and aberration of the acoustic wave, and to use the objective optical system <NUM> having a large numerical aperture (for example, the objective optical system <NUM> having a numerical aperture of about <NUM> to <NUM>), it is possible to obtain a clear image with higher resolution than before.

In the present embodiment, since the ultrasonic detector <NUM> is disposed on the object side of the convex mirror <NUM>, it is possible to reduce the pulsed light blocked by the ultrasonic detector <NUM> as much as possible out of the pulsed light that is reflected by the concave mirror <NUM> and irradiated to the sample SP. In addition, since the pulsed light irradiated to the ultrasonic detector <NUM> can be reduced as much as possible, it is possible to reduce noise due to thermal expansion generated when the pulsed light is irradiated to the ultrasonic detector <NUM>.

Since the objective optical system <NUM> is a reflective optical system including the convex mirror <NUM> and the concave mirror <NUM>, the aberration does not occur over a wide wavelength band from ultraviolet to infrared. Thus, it is possible to observe the sample SP using the pulsed light of various wavelengths. In addition, since the objective optical system <NUM>, which is the reflective optical system, has a small dispersion, a pulse width of short pulse light can be maintained. Further, since the optical path (route) from the sample SP to the ultrasonic detector <NUM> is filled with the liquid WT, it is possible to improve both transmittivity of the pulsed light and transmittivity of the acoustic wave.

In the present embodiment, the pupil position of the objective optical system <NUM> (the position of the convex mirror <NUM>) is optically conjugated with the inside of the scanning optical unit <NUM> provided in the confocal unit <NUM> or the vicinity thereof. Thus, even when the pulsed light to be irradiated to the sample SP is scanned by the scanning light unit <NUM>, almost all the pulsed light passes through the pupil position of the objective optical system <NUM>. Therefore, in the present embodiment, the loss of the pulsed light can be reduced and light utilization efficiency can be improved.

In the above-described embodiment, in order to facilitate understanding, the operation when generating the fluorescence image and the operation when generating the photoacoustic image have been described separately. However, when the sample SP is irradiated with the pulsed light emitted from the laser light source <NUM>, the fluorescence is emitted from the fluorescent substance contained in the sample SP, and at the same time, the local acoustic wave is emitted from the sample SP. Therefore, the controller <NUM> can also simultaneously generate the fluorescence image and the photoacoustic image based on a detection result of the ultrasonic detector <NUM> provided in the objective optical system <NUM> and a detection result of the photodetector <NUM> provided in the confocal unit <NUM>. Thus, it is possible to superimpose the fluorescence image and the photoacoustic image of the same observation place obtained by performing observation simultaneously. Further, in the present embodiment, since the sample SP is observed by immersion, the resolution can be improved as compared with the case of observing the sample SP without immersion.

An overall configuration of the photoacoustic imaging apparatus of the present embodiment is a configuration in which an optical system <NUM> shown in <FIG> is added to the photoacoustic imaging apparatus <NUM> shown in <FIG>, and the objective optical system <NUM> is replaced with an objective optical system 23A shown in <FIG>. <FIG> is a diagram showing a configuration of an optical system provided in the photoacoustic imaging apparatus according to a second embodiment of the present disclosure. As shown in <FIG>, the optical system <NUM> includes two axicon lenses 19a and 19b arranged so that their apex angles are opposed to each other, and is an optical system for converting a cross-sectional shape (shape in a plane perpendicular to the optical axis) of incident light. Specifically, the optical system <NUM> shown in <FIG> converts light having a circular cross-sectional shape that travels from the right side of the drawing to the left side of the drawing into light having a ring-shaped cross-section. On the contrary, the light having a ring-shaped cross-section that travels from the left side to the right side of the drawing is converted into the light having a circular cross-sectional shape.

Such an optical system <NUM> is desirably arranged, for example, on the optical path between the imaging lens <NUM> and the mirror <NUM> provided in the inverted microscope <NUM> shown in <FIG>, or on the optical path from the laser light source <NUM> to the scanning optical unit <NUM> provided in the confocal unit <NUM>. With this arrangement, the cross-sectional shape of the light incident on the objective optical system 23A (light incident on the convex mirror <NUM>) shown in <FIG> can be made ring-shaped.

Thus, the light incident on the central portion of the convex mirror <NUM> that does not contribute to measurement can be eliminated, so that the light utilization efficiency can be improved. In addition, since reflected light in the central portion of the convex mirror <NUM> can be eliminated, so that the noise can be reduced. The operation of the photoacoustic imaging apparatus of the present embodiment is the same as the operation of the photoacoustic imaging apparatus <NUM> shown in <FIG> except that the light (light having a ring-shaped cross-section) converted by the optical system <NUM> is incident on the objective optical system 23A. Therefore, detailed description of the operation of the photoacoustic imaging apparatus of the present embodiment will be omitted.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to the second embodiment of the present disclosure. In <FIG>, members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system <NUM> A of the present embodiment has a configuration in which a rod-shaped ultrasonic detector <NUM> is used, and a rear end cover <NUM> and a wiring protection tube <NUM> are added thereto accordingly.

The ultrasonic detector <NUM> is a rod-shaped device in which the acoustic lens 103A, the acoustic matching layer 103B, the piezoelectric vibrator 103C, and the backing material 103D illustrated in <FIG> are housed in, for example, a cylindrical metal casing. The ultrasonic detector <NUM> is disposed so that its longitudinal direction is in the Z direction, and is water-tightly bonded to the glass cover <NUM> with its one end portion being disposed closer to the object side (+Z side) from the glass cover <NUM>. Here, the ultrasonic detector <NUM> is attached to the glass cover <NUM> so that the focal position of the acoustic lens 103A provided therein coincides with the focal position of the objective optical system 23A (the focal position of the pulsed light). The convex mirror <NUM> is the same mirror as the convex mirror <NUM> shown in <FIG>, however, a hole portion h in which the ultrasonic detector <NUM> is to be inserted is formed in the central portion thereof.

The rear end cover <NUM> is, for example, a substantially bottomed circular annular member, and is attached to the other end side (-Z side) of the lens barrel <NUM>. A hole portion H1 through which the pulsed light traveling toward the sample SP (pulsed light reflected in the +Z direction by the mirror <NUM>) passes is formed in a central portion of the rear end cover <NUM>. Further, a bottom surface of the rear end cover <NUM> is provided with a projecting portion 107a that has the same inner diameter as the hole portion H1 and projects in the -Z direction with a threaded portion SR formed on its outer surface. The objective optical system 23A is fixed to the inverted microscope <NUM> by screwing the threaded portion SR of the projecting portion 107a to a support member (not shown). The inner diameter of the hole portion H1 formed in the rear end cover <NUM> is substantially the same as that of the hole portion H formed in the central portion of the concave mirror <NUM>. Note that the light incident on the objective optical system 23A is the light having a ring-shaped cross-section converted by the optical system <NUM> shown in <FIG>. Therefore, although the ultrasonic detector <NUM> is disposed on the optical axis AX, it is disposed outside the optical path (inside the ring) of the pulsed light irradiated to the sample SP so as not to block the light irradiated to the sample SP.

The wiring protection tube <NUM> is a pipe for protecting the line 103a extending from the other end portion of the ultrasonic detector <NUM>. For example, a hollow circular annular metal pipe can be used as the wiring protection tube <NUM>. The wiring protection tube <NUM> is provided in the rear end cover <NUM> so that one end thereof is disposed at the central portion of the hole portion H1 formed in the rear end cover <NUM> (the portion close to the optical axis AX not irradiated with light), and the other end thereof is disposed on one surface side of the rear end cover <NUM>. The line 103a extending from the other end portion of the ultrasonic detector <NUM> is inserted into the wiring protection tube <NUM> from one end of the wiring protection tube <NUM>, and drawn out from the other end of the wiring protection tube <NUM> to the outside of the wiring protection tube <NUM> (the outside of objective optical system 23A).

The objective optical system 23A having such a configuration uses the rod-shaped ultrasonic detector <NUM> that is more general than the ultrasonic detector used in the first embodiment, so that the same effects as in the first embodiment can be obtained. Further, in the objective optical system 23A having such a configuration, the light incident on the objective optical system 23A (light having a ring-shaped cross-section) is irradiated to the wiring protection tube <NUM>, however, since the light is not irradiated to the line 103a inserted into the wiring protection tube <NUM>, the wiring 103a can be protected.

<FIG> is a cross-sectional view showing a modification of the objective optical system according to the second embodiment of the present disclosure. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system 23B of the present embodiment has a configuration in which the rod-shaped ultrasonic detector <NUM> is used in the same manner as the objective optical system 23A shown in <FIG>, and a rear end cover 107A and a circular annular mirror <NUM> are added thereto accordingly. Further, the objective optical system 23B of the present embodiment is configured such that the light having a ring-shaped cross-section is incident from the side (from the -X side). Such an objective optical system 23B is used, for example, by omitting the mirror <NUM> shown in <FIG> and being placed at a position where the omitted mirror <NUM> was placed.

The ultrasonic detector <NUM> is the same as that shown in <FIG>, but a holding portion 103b is provided at the other end portion thereof. The holding portion 103b is a portion fixed to the rear end cover 107A, and has an outer diameter larger than that of a main body portion of the ultrasonic detector <NUM>. The ultrasonic detector <NUM> is disposed so that its longitudinal direction is in the Z direction, and is water-tightly bonded to the glass cover <NUM> with the one end portion being disposed closer to the object side (+Z side) from the glass cover <NUM>, in the same manner as that shown in <FIG>. The ultrasonic detector <NUM> is attached to the glass cover <NUM> so that the focal position of the acoustic lens 103A provided therein coincides with the focal position of the objective optical system 23B (the focal position of the pulsed light).

The rear end cover 107A is, for example, the substantially bottomed circular annular member, and is attached to the other end side (-Z side) of the lens barrel <NUM>. A hole portion H2 extending in the Z direction is formed in the central portion of the rear end cover 107A, and a hole portion H3 extending in the X direction is formed on one side surface of the rear end cover 107A. A holding portion 103b of the ultrasonic detector <NUM> is inserted into the hole portion H2, and the pulsed light having a ring-shaped cross-section (the pulsed light traveling in the +X direction through the imaging lens <NUM>) is incident on the hole portion H3. A bottom surface (surface on the +X side) of the hole portion H3 is a slope SL having an angle of <NUM>° with the XY plane.

Further, the bottom surface of the rear end cover 107A is provided with the projecting portion 107a that has the same inner diameter as the hole portion H2 and projects in the -Z direction with the threaded portion SR formed on the outer surface. The objective optical system 23B is fixed to the inverted microscope <NUM> by screwing the threaded portion SR of the projecting portion 107a to the support member (not shown). The inner diameter of the hole portion H2 formed in the rear end cover 107A is smaller than the hole portion H formed in the central portion of the concave mirror <NUM>, and is approximately equal to the outer diameter of the holding portion 103b of the ultrasonic detector <NUM>. The inner diameter of the hole portion H3 formed in the rear end cover 107A is, for example, approximately equal to the diameter of the hole portion H formed in the central portion of the concave mirror <NUM>.

The circular annular mirror <NUM> is a circular annular flat mirror, and is disposed on the slope SL formed on the rear end cover 107A. That is, the circular annular mirror <NUM> is disposed at an angle of <NUM>° with respect to the XY plane. The circular annular mirror <NUM> is provided to reflect the pulsed light incident on the hole portion H3 of the rear end cover 107A in the +Z direction. That is, the circular annular mirror <NUM> is provided to bend the optical axis AX of the pulsed light incident on the hole portion H3 of the rear end cover 107A by <NUM>°. As shown in <FIG>, the ultrasonic detector <NUM> is inserted into the circular annular mirror <NUM>. In the present embodiment, the line 103a is drawn to the outside (outside of the objective optical system 23B) through the hole portion H2 formed in the rear end cover 107A.

The objective optical system 23B having such a configuration can obtain the same effects as the first embodiment by using a general rod-shaped ultrasonic detector <NUM> in the same manner as the objective optical system 23A shown in <FIG>. In the objective optical system 23B having such a configuration, the ultrasonic detector <NUM> can be firmly supported by the glass cover <NUM> and the rear end cover <NUM>. Further, in the objective optical system 23B having such a configuration, a member (the wiring protection tube <NUM> shown in <FIG>) for protecting the line 103a can be omitted.

<FIG> is a diagram showing the main configuration of the photoacoustic imaging apparatus according to a third embodiment of the present disclosure. As shown in <FIG>, a photoacoustic imaging apparatus <NUM> of the present embodiment includes a confocal unit <NUM>, an upright microscope <NUM>, and a controller <NUM>, and generates the photoacoustic image of the sample SP based on the acoustic wave obtained by irradiating the sample SP stored in a sample container CT2 with the pulsed light. Although the photoacoustic imaging apparatus <NUM> of the first embodiment can generate the fluorescence image and the photoacoustic image, the photoacoustic imaging apparatus <NUM> of the present embodiment can generate only the photoacoustic image of the sample SP.

The confocal unit <NUM> is a unit forming a main portion of the confocal microscope, and the confocal microscope is realized by attaching the upright microscope <NUM> to the confocal unit <NUM>. Note that not only the upright microscope <NUM> can be attached to the confocal unit <NUM>, but other microscopes (for example, the inverted microscope) can also be attached thereto. That is, an arbitrary microscope can be attached to the confocal unit <NUM> according to the application of the confocal microscope in the same manner as the confocal unit <NUM> of the first embodiment.

The confocal unit <NUM> includes a laser light source <NUM> and a matching lens <NUM>. The laser light source <NUM> emits the pulsed light for irradiating the sample SP stored in the sample container CT2 under the control of the controller <NUM>. As in the first embodiment, the wavelength of the pulsed light emitted from the laser light source <NUM> can be any wavelength depending on the sample SP, and the laser light source <NUM> may be capable of changing the wavelength continuously or discretely. The matching lens <NUM> is disposed on the +X side of the laser light source <NUM> and is a lens for matching the pulsed light emitted from the laser light source <NUM> with the upright microscope <NUM>.

The upright microscope <NUM> includes an imaging lens <NUM>, a mirror <NUM>, an objective optical system <NUM>, and a moving stage <NUM>, and observes the sample SP stored in the sample container CT2 from the upper side (+Z side). The imaging lens <NUM> is a lens for converting the pulsed light emitted from the confocal unit <NUM> and incident on the upright microscope <NUM> into the parallel light. The mirror <NUM> is disposed in the +X direction of the imaging lens <NUM>, and reflects the pulsed light traveling in the +X direction in the -Z direction through the imaging lens <NUM>.

The objective optical system <NUM> is disposed on the -Z side of the mirror <NUM>, collects the pulsed light reflected in the -Z direction by the mirror <NUM> and irradiates the sample SP with the light, and detects the acoustic wave obtained by irradiating the sample SP with the pulsed light. The detection signal from the objective optical system <NUM> is output to the controller <NUM>. The objective optical system <NUM> is configured to be movable in the Z direction under the control of the controller <NUM> similarly to the objective optical system <NUM> shown in <FIG>. Details of the objective optical system <NUM> will be described below.

The moving stage <NUM> is a stage on which the sample container CT2 storing the sample SP is placed, and the placed sample container CT2 can be moved in the XY plane under the control of the controller <NUM>. As the moving stage <NUM>, for example, a linear XY stage can be used. Note that the sample container CT2 is filled with the culture fluid CF (see <FIG>), and the sample SP is immersed in the culture fluid CF.

The controller <NUM> controls the operation of the photoacoustic imaging apparatus <NUM> in an integrated manner. For example, the laser light source <NUM> provided in the confocal unit <NUM> is controlled to emit or stop the pulsed light irradiated to the sample SP. Further, the objective optical system <NUM> and the moving stage <NUM> provided in the upright microscope <NUM> are controlled to scan the sample SP with the pulsed light (X-axis, Y-axis, and Z-axis scanning). Further, the controller <NUM> performs signal processing of the detection signal output from the objective optical system <NUM> to generate the photoacoustic image and display it on a display monitor <NUM>. The display monitor <NUM> is a monitor provided with, for example, the liquid crystal display device similarly to the display monitor <NUM> shown in <FIG>.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to the third embodiment of the present disclosure. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system <NUM> of the present embodiment is different from the objective optical system <NUM> shown in <FIG> in that the water receiving member <NUM> is omitted, and the glass cover <NUM> is in contact with the culture fluid CF in which the sample SP is immersed, with the Z direction being arranged in the opposite direction.

That is, in the objective optical system <NUM> of the present embodiment, the convex mirror <NUM>, the concave mirror <NUM>, and the ultrasonic detector <NUM> are arranged in the order of the concave mirror <NUM>, the convex mirror <NUM>, and the ultrasonic detector <NUM>, in the direction from the +Z side to the -Z side on the optical axis AX of the pulsed light traveling toward the sample SP. Further, the objective optical system <NUM> of the present embodiment is designed to have a smaller numerical aperture (for example, about <NUM>) than the objective optical system <NUM> shown in <FIG>. This is to obtain a tomographic image (cross-sectional image in the Z direction) of the sample SP at a higher speed than in the first embodiment.

When the operation of the photoacoustic imaging apparatus <NUM> is started, the laser light source <NUM> is controlled by the controller <NUM>, and the pulsed light is emitted in the +X direction from the laser light source <NUM>. The pulsed light emitted from the laser light source <NUM> is incident on the upright microscope <NUM> through the matching lens <NUM>. The pulsed light incident on the upright microscope <NUM> is converted into the parallel light by the imaging lens <NUM>, and then reflected by the mirror <NUM> in the -Z direction to be incident on the objective optical system <NUM>.

The pulsed light incident on the objective optical system <NUM> passes through the hole portion H formed in the concave mirror <NUM> and is incident on and reflected by the convex mirror <NUM>, and then incident on and reflected by the concave mirror <NUM> in the same manner as in the first embodiment. Then, the pulsed light reflected by the concave mirror <NUM> passes through the passage portion PS of the mirror holding member <NUM>, and then sequentially transmits through the glass cover <NUM> and the culture fluid CF in the sample container CT2 to be irradiated to the sample SP. At this time, the pulsed light is irradiated so as to be focused on the sample SP.

<FIG> is an enlarged view of vicinity of a condensing point of the pulsed light in the third embodiment of the present disclosure. When the objective optical system <NUM> is designed to have a small numerical aperture (for example, about <NUM>) as in the present embodiment, a section in which the condensed diameter of the pulsed light is almost constant is generated as indicated as a depth of focus DOF in <FIG>. In the present embodiment, the position of the objective optical system <NUM> in the Z direction is adjusted by the control of the controller <NUM> so that the position (position in the Z direction) of a deep portion of the sample SP to be observed is within the depth of focus DOF.

When there is a substance that absorbs the irradiated pulsed light inside the sample SP, the sample SP is locally heated and rapidly expands, so that the local acoustic wave is emitted from the sample SP. The acoustic wave is transmitted through the culture fluid CF in the sample container CT2 to be detected by the ultrasonic detector <NUM>. The detection signal of the ultrasonic detector <NUM> is output to the controller <NUM>, and converted into the digital signal, to be associated with the scanning position (the scanning position in the XY plane by the moving stage <NUM>).

Here, since the controller <NUM> also controls the laser light source <NUM> provided in the confocal unit <NUM>, it grasps a time when the pulsed light is emitted from the laser light source <NUM>. The controller <NUM> can know a depth (position in the Z direction) of acoustic wave generation source by determining how much delayed the detection signal obtained from the ultrasonic detector <NUM> is obtained after the pulsed light is emitted from the laser light source <NUM>. Thus, it is possible to obtain information on a depth direction (Z-direction information) of the sample SP within the depth of focus DOF by observing the detection signal obtained from the ultrasonic detector <NUM> in time series after one pulsed light is emitted from the laser light source <NUM>.

The above operation is performed while changing the scanning position in the XY plane by the moving stage <NUM>. By performing such an operation, the photoacoustic image of the tomographic image of the sample SP is generated. Further, when the position of the objective optical system <NUM> in the Z direction is adjusted by the control of the controller <NUM>, and the same operation is performed while changing the scanning position in the XY plane by the moving stage <NUM>, the photoacoustic image of the tomographic image of the sample SP at a position different in the depth direction (Z direction) is generated. The generated photoacoustic image may be displayed on the display monitor <NUM> or stored in the internal memory (not shown).

As described above, the present embodiment uses the objective optical system <NUM> including the convex mirror <NUM> that reflects the pulsed light traveling toward the sample SP, the concave mirror <NUM> that reflects the pulsed light reflected by the convex mirror <NUM> and irradiates the sample SP with the light, and the ultrasonic detector <NUM> that is provided on the object side of the convex mirror <NUM> and detects the acoustic wave obtained by irradiating the sample SP with the light. Since the objective optical system <NUM> has the same configuration as the objective optical system <NUM> of the first embodiment, it is possible to prevent attenuation and aberration of the acoustic wave. Thus, it is possible to obtain a clearer image than before also in this embodiment.

In the present embodiment, as in the first embodiment, the pulsed light blocked by the ultrasonic detector <NUM> can be reduced as much as possible, and the noise due to thermal expansion caused when the pulsed light is irradiated to the ultrasonic detector <NUM> can also be reduced. Further, since the aberration does not occur over the wide wavelength band from ultraviolet to infrared, it is possible to observe the sample SP using the pulsed light of various wavelengths. Furthermore, since the dispersion is small, the pulse width of the short pulse light can be maintained.

In the present embodiment, since the numerical aperture of the objective optical system <NUM> is designed to be smaller than that of the objective optical system <NUM> of the first embodiment, the resolution is inferior to that of the first embodiment, however, it is possible to create the tomographic image at a higher speed than in the first embodiment. In the present embodiment, since the upright microscope <NUM> is used, observation in an upright type is possible, and it is also possible to be used for observation of animals and the like. In the above-described embodiment, although a case where the numerical aperture of the objective optical system <NUM> is reduced is described as an example, it is possible to increase the numerical aperture of the objective optical system <NUM> to increase the resolution. Further, in the present embodiment, since the sample SP is observed by immersion, the resolution can be improved as compared with the case of observing the sample SP without immersion.

The overall configuration and operation of the photoacoustic imaging apparatus of the present embodiment are the same as the overall configuration and operation of the photoacoustic imaging apparatus <NUM> shown in <FIG>. Therefore, the detailed description of the overall configuration and operation of the photoacoustic imaging apparatus of the present embodiment will be omitted.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to a fourth embodiment of the present disclosure. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system <NUM> of the present embodiment is different from the objective optical system <NUM> shown in <FIG> in that a water receiving member <NUM> is provided.

The water receiving member <NUM> is provided on the one end side (-Z side: object side end portion) of the lens barrel <NUM> so that one end portion 110a surrounds the periphery of the glass cover <NUM>, and is a tubular member having a diameter decreasing from the one end portion 110a to the other end portion 110b. At the one end portion 110a of the water receiving member <NUM>, for example, a suction tube <NUM> (liquid conduit) connected to a suction pump (not shown) is provided. Further, a diameter of tip of the other end portion 110b of the water receiving member <NUM> is made smaller than a diameter of the sample container CT3 in which the sample SP is stored.

Therefore, by operating the suction pump (not shown) while the other end portion 110b of the water receiving member <NUM> is immersed in the culture fluid CF in the sample container CT3, a state in which the culture fluid CF is held inside the water receiving member <NUM> (a state in which the inside of the water receiving member <NUM> is filled with the culture fluid CF) can be achieved. In the third embodiment described above, it is necessary to bring the glass cover <NUM> into contact with the culture fluid CF in the sample container CT2 using the sample container CT2 having a diameter larger than that of the glass cover <NUM> as shown in <FIG>, however, in the present embodiment, it is possible to use a sample container CT3 having a smaller diameter than the sample container CT2 used in the third embodiment.

As described above, although the present embodiment is different from the third embodiment in that the water receiving member <NUM> is provided, the objective optical system <NUM> having the same configuration as that of the third embodiment is used. Therefore, also in the present embodiment, it is possible to obtain a clearer image than before, and to create the tomographic image at a high speed. In the present embodiment, similarly to the third embodiment, it is possible to reduce the pulsed light blocked by the ultrasonic detector <NUM> as much as possible, and to reduce the noise due to the thermal expansion caused when the pulsed light is irradiated to the ultrasonic detector <NUM>. Further, it is possible to observe the sample SP using the pulsed light having various wavelengths, and to maintain the pulse width of the short pulse light since the dispersion is small.

The overall configuration of the photoacoustic imaging apparatus of the present embodiment is the same as the overall configuration of the photoacoustic imaging apparatus <NUM> shown in <FIG>. Therefore, the detailed description of the overall configuration of the photoacoustic imaging apparatus of the present embodiment will be omitted.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to an embodiment of the present invention. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, an objective optical system 23C of the present embodiment is different from the objective optical system <NUM> shown in <FIG> mainly in that the lens barrel <NUM>, the glass cover <NUM>, and the water receiving member <NUM> are changed, the mirror holding member <NUM> is omitted, and a supply tube <NUM> (liquid conduit) is added.

The lens barrel <NUM> is the substantially bottomed circular annular member, and holds the concave mirror <NUM> therein. A hole portion H4 through which the pulsed light traveling toward the sample SP (pulsed light reflected in the +Z direction by the mirror <NUM>) passes is formed in a central portion of a bottom surface of the lens barrel <NUM>. Further, the bottom surface of the lens barrel <NUM> is provided with a projecting portion 100a that has the same inner diameter as that of the hole portion H4 and projects in the -Z direction with the threaded portion SR formed on its outer surface. The objective optical system 23C is fixed to the inverted microscope <NUM> by screwing the threaded portion SR of the projecting portion 100a to the support member (not shown). The inner diameter of the hole portion H4 formed in the lens barrel <NUM> is substantially the same as that of the hole portion H formed in the central portion of the concave mirror <NUM>. Note that the shape of the lens barrel <NUM> is not limited to a bottomed circular annular shape, and may be another shape (for example, a bottomed square annular shape).

The glass cover <NUM> is a partially spherical shell-shaped member formed of, for example, glass, transparent resin or the like, and is attached to the water receiving member <NUM> so as to partition an internal space of the water receiving member <NUM> into an internal space Q1 and an internal space Q2. The glass cover <NUM> is firmly fixed (for example, bonded) to the water receiving member <NUM> so that the liquid WT held in the internal space Q1 of the water receiving member <NUM> does not enter the internal space Q2.

The glass cover <NUM> is disposed on the optical path of the pulsed light reflected by the concave mirror <NUM>, and has an incident surface 105a on which the pulsed light reflected by the concave mirror <NUM> is incident, and an exit surface 105b from which the pulsed light incident from the incident surface 105a is emitted. When the liquid WT is held in the internal space Q1 of the water receiving member <NUM>, the exit surface 105b is a liquid contact surface contacting the liquid WT. According to the invention, the incident surface 105a is formed so as to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM> except for the central portion. According to the invention, the exit surface 105b is also formed to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM>. The reason for forming in this way is to prevent chromatic aberration from occurring in the wide wavelength band by preventing (as much as possible) refraction at the incident surface 105a (an interface between the air and the glass cover <NUM>) and the exit surface 105b (an interface between the glass cover <NUM> and the liquid WT).

For example, the incident surface 105a of the glass cover <NUM> is formed into a spherical surface except for the central portion, and its center of curvature is set equal to a focal position P of a reflective objective mirror (Schwarzschild reflective objective mirror) formed by the convex mirror <NUM> and the concave mirror <NUM>. The exit surface 105b of the glass cover <NUM> is also formed into the spherical surface, and its center of curvature is set equal to the focal position P described above. Note that a portion of the glass cover <NUM> through which the pulsed light transmits is a transmissive portion TS.

In the present embodiment, since the mirror holding member <NUM> is omitted, the convex mirror <NUM> is fixed to a central portion of the incident surface 105a of the glass cover <NUM> so that the central portion thereof is disposed on the optical axis AX, on the object side (+Z side) of the concave mirror <NUM>. Therefore, the central portion of the incident surface 105a is made flat. The ultrasonic detector <NUM> is provided on the exit surface 105b of the glass cover <NUM> with the detection surface facing the sample SP side (+Z side). Specifically, the ultrasonic detector <NUM> is disposed in a concave portion 105c formed in the central portion of the exit surface 105b of the glass cover <NUM>, and is provided on the emission surface 105b of the glass cover <NUM> so as to overlap the convex mirror <NUM> when viewed from the Z direction. As described above, the convex mirror <NUM> is disposed in the central portion of the incident surface 105a of the glass cover <NUM>, and the ultrasonic detector <NUM> is disposed in the central portion of the exit surface 105b of the glass cover <NUM>.

The water receiving member <NUM> is a tubular member having a diameter decreasing from one end portion 106a to the other end portion 106b, and the one end portion 106a is attached to an end portion on the object side of the lens barrel <NUM>. The water receiving member <NUM> supports the glass cover <NUM> so that the internal space is partitioned into the internal space Q1 and the internal space Q2 by the glass cover <NUM>. The water receiving member <NUM> can hold the liquid WT in the internal space Q1 partitioned by the glass cover <NUM>. Further, since the diameter of the water receiving member <NUM> is reduced from the one end portion 106a to the other end portion 106b, even if the sample container CT1 is small, the liquid WT can be held between the sample container CT1 and the water receiving member <NUM>. Holes portions h1 and h2 that communicate with the internal space Q1 of the water receiving member <NUM> and the outside of the water receiving member <NUM> are formed on a side surface of the water receiving member <NUM>.

The supply tube <NUM> is a tube for supplying the liquid WT to the internal space Q1 of the water receiving member <NUM>. The supply tube <NUM> is formed of, for example, rubber or resin, and has one end inserted into the hole portion h1 formed in the side surface of the water receiving member <NUM>, and the other end portion connected to a liquid supply device (not shown). The liquid WT is supplied from the liquid supply device to the internal space Q1 of the water receiving member <NUM> through the supply tube <NUM>. The line 103a of the ultrasonic detector <NUM> is drawn out of the water receiving member <NUM> to be connected to the controller <NUM>, through the hole portion h2 formed in the water receiving member <NUM>. The detection signal of the ultrasonic detector <NUM> is output to the controller <NUM> through the line 103a.

The operation of the photoacoustic imaging apparatus of the present embodiment (the operation at the time of generating the fluorescence image and the operation at the time of generating the photoacoustic image) is the same as that in the first embodiment except for the operation in the inverted microscope <NUM>. Therefore, the operation in the inverted microscope <NUM> will be described below. Hereinafter, in order to avoid redundant description, the operation in the inverted microscope <NUM> at the time of generating the fluorescence image and the operation in the inverted microscope <NUM> at the time of generating the photoacoustic image will be described together.

When the pulsed light emitted from the confocal unit <NUM> is incident on the inverted microscope <NUM>, it is reflected in the +Z direction by the mirror <NUM> after passing through the imaging lens <NUM>, and is incident on the objective optical system 23C. The pulsed light incident on the objective optical system <NUM> C passes through the hole portion H4 formed in the lens barrel <NUM> and the hole H formed in the concave mirror <NUM>, and is incident on and reflected by the convex mirror <NUM>, and then incident on and reflected by the concave mirror <NUM>. As shown in <FIG>, the pulsed light reflected by the concave mirror <NUM> is incident on the incident surface 105a of the glass cover <NUM>, transmits through the glass cover <NUM>, then exits from the exit surface 105b, and passes through the liquid WT (including the liquid WT held between the water receiving member <NUM> and the sample container CT1) held in the internal space Q1 of the water receiving member <NUM>, to be irradiated to the sample SP.

Here, the incident surface 105a of the glass cover <NUM> is formed to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM> except for the central portion. Therefore, the pulsed light reflected by the concave mirror <NUM> is perpendicularly incident on a peripheral portion (portion excluding the central portion) of the incident surface 105a of the glass cover <NUM>. The exit surface 105b of the glass cover <NUM> is also formed to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM>. Therefore, the pulsed light transmitted through the glass cover <NUM> is emitted in a direction perpendicular to the exit surface 105b. Therefore, the pulsed light reflected by the concave mirror <NUM> travels straight without being refracted by the glass cover <NUM>.

The optical path of the pulsed light transmitted through the glass cover <NUM> has a refractive index close to the refractive index of the sample SP and the sample container CT1 by the liquid WT held in the internal space Q1 of the water receiving member <NUM> and the liquid WT held between the water receiving member <NUM> and the sample container CT1. Therefore, reflection of the pulsed light transmitted through the glass cover <NUM> (reflection at the bottom portion of the sample container CT1 and the surface of the sample SP) is extremely reduced, and a lot of pulsed light is incident on inside of the sample SP. Further, the refraction of the pulsed light transmitted through the glass cover <NUM> (refraction at the bottom portion of the sample container CT1 and the surface of the sample SP) is extremely reduced, and the pulsed light transmitted through the glass cover <NUM> travels almost straight to be condensed at the focal position P. As described above, in the objective optical system 23C of the present embodiment, since the refraction of the pulsed light hardly occurs, the pulsed light can be condensed at the original focal position P of the Schwarzschild reflective objective mirror formed by the convex mirror <NUM> and the concave mirror <NUM>.

When the space between the glass cover <NUM> and the bottom surface of the sample container CT1 is filled with the liquid WT, since the refractive indices of the sample container CT1 and the liquid WT are close to each other, the reflection of the pulsed light is less than that in the case where it is not filled with the liquid WT (the case where it is filled with the air). However, depending on the sample container CT1 used, it is conceivable that it is difficult to make the refractive indices of the liquid WT and the sample container CT1 close to each other so that the refraction caused between the liquid WT and the sample container CT1 can be ignored. Here, as thickness of the bottom portion of the sample container CT1 is thinner, variation of the optical path due to the refraction is less, and thus it is preferable to use the sample container CT1 having a thin thickness of the bottom portion. Further, it is also preferable to incorporate an optical system for correcting the variation of the optical path, which is caused on an upper surface and a lower surface of the bottom portion of the sample container CT1, into the objective optical system 23C. For example, since the bottom surface of the sample container CT1 is often made of glass having a thickness of <NUM>, the concave mirror <NUM> configured to correct the variation of the optical path when passing through the glass may be used.

When the sample SP is irradiated with the pulsed light, fluorescence is emitted from the fluorescent substance contained in the sample SP, or the local acoustic wave is emitted from the sample SP. The fluorescence emitted from the sample SP travels in the reverse direction along the optical path of the pulsed light. As shown in <FIG>, since the ultrasonic detector <NUM> is disposed on the optical axis AX, the cross-sectional shape of the fluorescence emitted from the objective optical system 23C (the shape in the plane perpendicular to the optical axis AX) is a ring shape. The local acoustic wave emitted from the sample SP passes through the sample container CT1, and then passes through the liquid WT held between the sample container CT1 and the water receiving member <NUM> and the liquid WT held in the internal space Q1 of the water receiving member <NUM>, to be detected by the ultrasonic detector <NUM>.

As described above, in the present embodiment, the objective optical system 23C is configured such that the glass cover <NUM> having the incident surface 105a and the exit surface 105b formed to be orthogonal to the optical path of the light reflected by the concave mirror <NUM> is attached to the water receiving member <NUM>, so that the liquid WT can be held in the internal space Q1 of the water receiving member <NUM>. Thus, since the refraction hardly occurs in the objective optical system 23C, the chromatic aberration hardly occurs. Therefore, it is possible to cope with the light in a wide wavelength range from ultraviolet light to near infrared light by one objective optical system 23C. Further, not only the chromatic aberration, but also various aberrations due to curvature can be reduced. Furthermore, in the present embodiment, since the sample SP is observed by immersion, the resolution can be improved as compared with the case of observing the sample SP without immersion.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to a sixth embodiment of the present disclosure. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system 53A of the present embodiment is mainly different from the objective optical system <NUM> shown in <FIG> in that the lens barrel <NUM> is changed, the mirror holding member <NUM> and the glass cover <NUM> are omitted, an optical member <NUM> is provided instead of the convex mirror <NUM> and the concave mirror <NUM>, and a suction tube <NUM> (liquid conduit) is added. The lens barrel <NUM> is the same as the lens barrel <NUM> shown in <FIG>, however, a hole portion h10 is formed in the side surface of the lens barrel <NUM> of the present embodiment.

The optical member <NUM> is a substantially columnar member that is formed of, for example, glass, transparent resin or the like, and has one surface 200a formed in a substantially concave shape and the other surface 200b formed in a substantially convex shape. The convex mirror <NUM> is formed in the central portion of the one surface 200a of the optical member <NUM>, and the transmissive portion TS is provided in a peripheral portion thereof. A central portion of the other surface 200b of the optical member <NUM> is formed flat, and the concave mirror <NUM> is formed in the peripheral portion thereof. A diameter of the central portion of the other surface 200b of the optical member <NUM> (a diameter of the portion formed flat) is made larger than the inner diameter of the hole portion H4 formed in the lens barrel <NUM>.

The optical member <NUM> has an outer diameter substantially the same as the inner diameter of the lens barrel <NUM>, and is held by the lens barrel <NUM> so that the other surface 200b is in contact with the bottom surface of the lens barrel <NUM> and the one surface 200a faces the object side. The optical member <NUM> is held such that the central portion of the other surface 200b closes the hole portion H4 formed in the lens barrel <NUM>. Therefore, the pulsed light traveling toward the sample SP (the pulsed light reflected in the -Z direction by the mirror <NUM>) is incident on the central portion of the other surface 200b of the optical member <NUM>.

The convex mirror <NUM> formed on the one surface 200a of the optical member <NUM> is disposed on the optical axis AX of the pulsed light traveling toward the sample SP, and reflects the pulsed light traveling toward the sample SP. The concave mirror <NUM> formed on the other surface 200b of the optical member <NUM> reflects the pulsed light reflected by the convex mirror <NUM> toward the sample SP. The concave mirror <NUM> is designed so that the reflected pulsed light is condensed at the sample SP. The convex mirror <NUM> and the concave mirror <NUM> form the Schwarzschild reflective objective mirror.

The convex mirror <NUM> is formed, for example, by depositing a metal film on the central portion of the one surface 200a of the optical member <NUM>, and the concave mirror <NUM> is formed, for example, by depositing the metal film on the peripheral portion of the other surface 200b of the optical member <NUM>. The metal deposited on the optical member <NUM> is desirably a metal such as gold or silver having a high reflectance with respect to the light in the wide wavelength range from ultraviolet light to near infrared light.

Here, a central portion CA of the convex mirror <NUM> is different in that its reflectance is set lower than that of other portions of the convex mirror <NUM>. When the light reflected by the central portion CA of the convex mirror <NUM> is incident on the confocal unit <NUM>, the noise is generated. Therefore, the reflectance of the central portion CA of the convex mirror <NUM> is set lower than that of other portions of the convex mirror <NUM>, so that the noise is reduced by reducing return light described above. A method of reducing the reflectance of the central portion CA of the convex mirror <NUM> includes, for example, a method of not depositing the metal on the central portion CA of the convex mirror <NUM>, or of removing the metal deposited on the central portion CA of the convex mirror <NUM>.

The transmissive portion TS provided on the one surface 200a of the optical member <NUM> is a portion through which the pulsed light reflected by the concave mirror <NUM> is transmitted. As shown in <FIG>, the transmissive portion TS is immersed in the culture fluid CF in the sample container CT3 and thus has a liquid contact surface in contact with the culture fluid CF. The transmissive portion TS is formed orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM>. For example, the transmissive portion TS is formed into a spherical surface, and a center of curvature thereof is set equal to the focal position P of the reflective objective mirror formed by the convex mirror <NUM> and the concave mirror <NUM>. This is to prevent chromatic aberration from occurring in the wide wavelength band by preventing (as much as possible) refraction at the transmissive portion TS (an interface between the optical member <NUM> and the culture fluid CF). Note that a communication path PS1 communicating with the transmissive portion TS from the side surface is formed inside the optical member <NUM>.

The ultrasonic detector <NUM> is provided at the central portion of the one surface 200a of the optical member <NUM> with the detection surface facing the sample SP side (-Z side). As shown in <FIG>, since the ultrasonic detector <NUM> is attached to the surface on the -Z side of the convex mirror <NUM>, the light transmitted through the central portion CA of the convex mirror <NUM> is not irradiated to the sample SP. In <FIG>, the line connected to the ultrasonic detector <NUM> (the line corresponding to the line 103a in <FIG>) and the hole portion formed in the water receiving member <NUM> (the hole portion corresponding to the hole portion h2 in <FIG>) are not shown.

The suction tube <NUM> is a tube for supplying the liquid WT to the internal space Q of the water receiving member <NUM>. The suction tube <NUM> is formed of, for example, rubber or resin, and has one end portion inserted in the hole portion h10 formed in the side surface of the lens barrel <NUM>, and the other end portion connected to the suction pump (not shown). As shown in <FIG>, the optical member <NUM> is disposed such that the communication path PS1 communicates with the hole portion h10 formed in the lens barrel <NUM>. Therefore, by operating the suction pump (not shown), the culture fluid CF in the sample container CT3 is introduced to the internal space Q of the water receiving member <NUM>, so that the state in which the culture fluid CF is held in the internal space Q of the water receiving member <NUM> (the state in which the internal space Q of the water receiving member <NUM> is filled with the culture fluid CF) can be achieved.

The operation of the photoacoustic imaging apparatus of the present embodiment is the same as that of the third embodiment except for the operation in the upright microscope <NUM>. Therefore, the operation in the upright microscope <NUM> will be described below. When the pulsed light emitted from the confocal unit <NUM> is incident on the upright microscope <NUM>, it passes through the imaging lens <NUM> and is then reflected in the -Z direction by the mirror <NUM>, to be incident on the objective optical system 53A.

The pulsed light incident on the objective optical system 53A passes through the hole portion H4 formed in the lens barrel <NUM> and is then incident on the optical member <NUM> from the central portion of the other surface 200b of the optical member <NUM>. The pulsed light incident on the optical member <NUM> is reflected by the convex mirror <NUM> and then incident on and reflected by the concave mirror <NUM>. The pulsed light reflected by the concave mirror <NUM> is emitted to the outside of the optical member <NUM> from the transmissive portion TS provided on the one surface 200a of the optical member <NUM>. The pulsed light emitted from the optical member <NUM> is irradiated to the sample SP after passing through the culture fluid CF in the sample container CT3.

Here, the transmissive portion TS of the optical member <NUM> is formed to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM>. Therefore, the pulsed light reflected by the concave mirror <NUM> is emitted in a direction perpendicular to the transmissive portion TS. Therefore, the pulsed light reflected by the concave mirror <NUM> travels straight without being refracted when being incident on the culture fluid CF from the optical member <NUM>.

The optical path of the pulsed light emitted from the optical member <NUM> is set to have the refractive index close to the refractive index of the sample SP by the culture fluid CF in the sample container CT3. Therefore, the reflection of the pulsed light emitted from the optical member <NUM> (the reflection on the surface of the sample SP) is extremely reduced, and a lot of pulsed light is incident on the inside of the sample SP. Further, the refraction of the pulsed light emitted from the optical member <NUM> (the refraction at the surface of the sample SP) is also extremely reduced, and the pulsed light emitted from the optical member <NUM> travels almost straight to be condensed at the focal position P. As described above, the objective optical system 53A of the present embodiment also hardly refracts the pulsed light, so that the pulsed light can be condensed at the original focal point P of the Schwarzschild reflective objective mirror formed by the convex mirror <NUM> and the concave mirror <NUM>.

When the pulsed light is irradiated to the sample SP, the local acoustic wave is emitted from the sample SP. The local acoustic wave emitted from the sample SP passes through the culture fluid CF and the liquid WT, held in the sample container CT3 and the internal space Q of the water receiving member <NUM>, to be detected by the ultrasonic detector <NUM>.

As described above, in the present embodiment, the convex mirror <NUM> is formed in the central portion of the one surface 200a, the concave mirror <NUM> is formed in the peripheral portion of the other surface 200b, and the objective optical system 53A is configured using the optical member <NUM> in which the transmissive portion TS formed to be orthogonal to the optical path of the light reflected by the concave mirror <NUM> is provided in the peripheral portion of the one surface 200a. The objective optical system 53A is used in a state where the one surface 200a of the optical member <NUM> is in contact with the culture fluid CF in the sample container CT3.

Therefore, since the refraction hardly occurs in the objective optical system 53A, the chromatic aberration hardly occurs. Thus, it is possible to cope with the light in the wide wavelength range from ultraviolet light to near infrared light by one objective optical system 53A. Further, not only the chromatic aberration, but also various aberrations due to the curvature can be reduced. Furthermore, in the present embodiment, since the sample SP is observed by immersion, the resolution can be improved as compared with the case of observing the sample SP without immersion.

In the present embodiment, the Schwarzschild reflective objective mirror is formed only by the optical member <NUM>. Therefore, since the number of parts can be reduced as compared with the third embodiment, the cost can be reduced and the number of assembling steps can be reduced. Further, since the Schwarzschild reflective objective mirror is formed by depositing metal on the optical member <NUM>, it is possible to reduce a relative positional shift between the convex mirror <NUM> and the concave mirror <NUM> due to vibration or the like compared with the first embodiment.

<FIG> is a cross-sectional view showing the main configuration of the objective optical system according to a seventh embodiment of the present disclosure. In <FIG>, the members corresponding to those shown in <FIG> are denoted by the same reference numerals. As shown in <FIG>, the objective optical system 23D of the present embodiment is different from the objective optical system <NUM> shown in <FIG> mainly in that an optical member <NUM> is provided instead of the concave mirror <NUM>, and the glass cover <NUM> is omitted.

The optical member <NUM> is a substantially columnar member that is formed of, for example, glass, transparent resin or the like, and has one surface 300a formed in a planar shape and the other surface 300b formed in a substantially concave shape. The concave mirror <NUM> is formed in the peripheral portion of the other surface 300b of the optical member <NUM>. The concave mirror <NUM> is formed, for example, by depositing the metal film on the peripheral portion of the other surface 300b of the optical member <NUM>. The metal deposited on the optical member <NUM> is desirably the metal such as gold or silver having a high reflectance with respect to the light in the wide wavelength range from ultraviolet light to near infrared light. The central portion of the other surface 300b of the optical member <NUM> may be a concave surface, or may be formed, for example, flat.

The optical member <NUM> has an outer diameter approximately equal to the inner diameter of the lens barrel <NUM>, and is held by the lens barrel <NUM> so that the other surface 300b faces the object side at the other end side (-Z side) of the lens barrel <NUM>. Therefore, the pulsed light traveling toward the sample SP (the pulsed light reflected in the +Z direction by the mirror <NUM> in <FIG>) is incident on the central portion of the one surface 300a of the optical member <NUM>. The pulsed light incident on the central portion of the one surface 300a of the optical member <NUM> passes through the optical member <NUM>, and is emitted toward the +Z direction from the central portion of the other surface 300b of the optical member <NUM>.

The concave mirror <NUM> formed on the other surface 300b of the optical member <NUM> reflects the pulsed light reflected by the convex mirror <NUM> toward the sample SP. The concave mirror <NUM> is designed so that the reflected pulsed light is condensed on the sample SP. The convex mirror <NUM> and the concave mirror <NUM> formed on the optical member <NUM> form the Schwarzschild reflective objective mirror.

Here, the glass cover <NUM> is omitted in the present embodiment. Therefore, the ultrasonic detector <NUM> is attached and fixed to the +Z side (object side) of the convex mirror <NUM> with the one end portion provided with the detection surface facing the sample SP side (+Z side). Note that, as in the first embodiment, the ultrasonic detector <NUM> is disposed outside the optical path of the pulsed light irradiated to the sample SP so as not to block the light irradiated to the sample SP on the +Z side of the convex mirror <NUM>.

In the objective optical system 23D of the present embodiment, since the glass cover <NUM> provided in the objective optical system <NUM> shown in <FIG> is omitted, the liquid WT is held in not only the internal space of the water receiving member <NUM> but also the internal space of the lens barrel <NUM>. Thus, the object side of the optical member <NUM> is filled with the liquid WT, and the convex mirror <NUM> and the concave mirror <NUM> are immersed in the liquid WT. In this state, since the refraction does not occur in the optical path in which the pulsed light emitted from the central portion of the other surface 300b of the optical member <NUM> toward the +Z direction reaches the sample container CT1, the chromatic aberration hardly occurs. Thus, it is possible to cope with the light in the wide wavelength range from ultraviolet light to near infrared light by one objective optical system 23A. Further, not only the chromatic aberration, but also various aberrations due to curvature can be reduced. Furthermore, in the present embodiment, since the sample SP is observed by immersion, the resolution can be improved as compared with the case of observing the sample SP without immersion.

The objective optical system and the photoacoustic imaging apparatus according to the embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments but can be freely changed within the scope of the present invention. For example, both the fluorescence image and the photoacoustic image can be generated in the first, second, fifth, and seventh embodiments, and in the third, fourth, and sixth embodiments, the photoacoustic imaging apparatus capable of generating only the photoacoustic image has been described as the example. However, any of the photoacoustic imaging apparatuses of the first to seventh embodiments can be designed to generate both the fluorescence image and the photoacoustic image, or can be designed to generate only the photoacoustic image. Further, the optical system <NUM> (see <FIG>) in the second embodiment can also be used in the third to seventh embodiments.

In the fifth embodiment described above, the incident surface 105a (excluding the central portion) and the exit surface 105b of the glass cover <NUM> are formed to be orthogonal to the optical path of the laser light reflected by the concave mirror <NUM>. In the sixth embodiment, the example in which the one surface 200a (the transmissive portion TS excluding the central portion) of the optical member <NUM> is formed to be orthogonal to the optical path of the pulsed light reflected by the concave mirror <NUM> has been described.

However, the shapes of the incident surface 105a, the exit surface 105b, and the transmissive portion TS can be changed if the refraction at the interface with the liquid WT or the like is slight and the resolution is not greatly reduced. For example, taking the glass cover <NUM> as an example, it is possible to change the shape of the incident surface 105a (excluding the central portion) or the exit surface 105b so that a radius of curvature r of an arbitrary point on the incident surface 105a (excluding the central portion) or the exit surface 105b satisfies a relational expression of <NUM> ≤ r ≤ <NUM>, where a distance from the point to the focal position P is S. Further, the incident surface 105a (excluding the central portion) and the exit surface 105b are not limited to spherical surfaces, but may be aspherical surfaces.

Claim 1:
An objective optical system (<NUM>, <NUM>), comprising:
a first mirror (<NUM>) having a convex reflecting surface configured to reflect pulsed light traveling toward a sample (SP);
a second mirror (<NUM>) having a concave reflecting surface configured to reflect the light reflected by the first mirror and irradiate the sample (SP) with the light;
a detector (<NUM>) having at least one end portion provided on an object side of the first mirror, and configured to detect an acoustic wave obtained by irradiating the sample (SP) with the light;
and
a transparent cover member (<NUM>) that is provided on the object side of the first mirror and the second mirror, configured to form a boundary surface with liquid, and configured to prevent the liquid from entering the first mirror and the second mirror, characterized in that the light incident surface (105a) of the cover member is formed so as to be orthogonal to the optical path of light reflected by the second mirror, except for a central portion of the light incident surface, and the light exit surface (105b) of the cover member is formed so as to be orthogonal to the optical path of light reflected by the second mirror.