A miniature laser and optical imaging system

Abstract

The application provides an optical imaging system, comprising a micro laser, a filter, a second focusing mirror, a third focusing mirror, a reflecting mirror, an objective lens, an electric displacement platform, an acrylic box, an ultrasonic transducer, an amplification filter, an oscilloscope and a computer which are sequentially arranged; the micro laser comprises a programmable pulse power supply, a laser diode, a collimating mirror, a first focusing mirror and a laser resonant cavity which is composed of a laser crystal, a saturable absorber, a nonlinear crystal and an output coupling mirror and which are sequentially arranged; the programmable pulse power supply is connected with the laser diode; pulse pump light generated by the laser diode is incident into the laser resonant cavity after collimating and focusing by the collimating mirror; stable pulse laser output is realized by controlling the repetition frequency, the pulse width and the current size of the programmable pulse power supply; the output multi-wavelength nanosecond pulse laser is used as an excitation light source of an photoacoustic imaging system; and a modulation signal of the programmable pulse power supply is directly used as a trigger source of the photoacoustic imaging system.

Description

Technical Field

[0001] This invention relates to the fields of solid-state lasers and photoacoustic imaging technology, and more particularly to a miniature laser and optical imaging system. Background Technology

[0002] Photoacoustic imaging is a novel imaging technology that combines the high resolution of optical imaging with the deep penetration of ultrasound imaging, and it has broad application prospects in the biomedical field. Different biological tissues have high optical absorption coefficients for specific wavelengths of light. By utilizing optical nonlinear effects, the spectrum of the output laser can be expanded, which helps to improve the photoacoustic imaging effect.

[0003] Traditional photoacoustic imaging systems often use actively Q-switched solid-state lasers as excitation sources, such as acousto-optic Q-switching and electro-optic Q-switching. These active Q-switching methods are relatively large and costly; among them, electro-optic Q-switching requires a high driving voltage, making it difficult to implement and miniaturize.

[0004] However, existing passively Q-switched solid-state lasers still face some challenges in their application to photoacoustic imaging systems due to their large output pulse jitter amplitude and relatively low output stability. Therefore, it is of great significance to develop pulse-stable, portable, and low-cost passively Q-switched microchip lasers. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing passively Q-switched solid-state lasers due to large output pulse jitter amplitude, and to provide a miniature laser and optical imaging system. By using a programmable pulse power supply to adjust the energy, repetition rate, and pulse width of the pulse pump light, a stable pulsed laser output is achieved, and the repetition rate of the output laser is consistent with the repetition rate of the pump light modulation signal. The modulation signal output by the programmable pulse power supply can be directly used as the trigger for the photoacoustic imaging system, thereby realizing a low-cost, portable photoacoustic imaging system.

[0006] To address the aforementioned technical problems, the present invention provides a miniature laser, comprising a programmable pulse power supply, a laser diode, a collimating lens, a first focusing lens, a laser crystal, a saturable absorber, a nonlinear crystal, and an output coupling lens arranged sequentially; the laser crystal, the saturable absorber, the nonlinear crystal, and the output coupling lens are clamped and fixed together to form a laser resonant cavity, and the laser crystal is positioned facing the first focusing lens.

[0007] The programmable pulse power supply is connected to the laser diode. The output end face of the laser diode, the collimating lens, the first focusing lens, the laser crystal, the saturable absorber, the nonlinear crystal, and the output coupling mirror are arranged on the same horizontal line and are all placed vertically.

[0008] The programmable pulse power supply serves as the trigger source for the photoacoustic imaging system; the programmable pulse power supply provides pulse current, and the laser diode generates pulse pump light synchronized with the pulse current;

[0009] The collimating lens and the first focusing lens are used to collimate and focus the pulse pump light, respectively. The focal spot size of the focused pulse pump light is set on the order of tens to hundreds of micrometers. The pulse pump light is incident on the laser resonant cavity after passing through the collimating lens and the first focusing lens.

[0010] The laser crystal has a first antireflection coating and a first high-reflection coating on the side away from the saturable absorber, and a second antireflection coating on the side closer to the saturable absorber; both sides of the nonlinear crystal are coated with a third antireflection coating; a partial reflection coating is coated between the output coupling mirror and the nonlinear crystal, and the partial reflection coating serves as the output mirror of the laser resonant cavity.

[0011] In a preferred embodiment, the programmable pulse power supply is a constant current source, and the laser diode is a fiber-coupled laser diode;

[0012] The programmable pulse power supply has a maximum output current of 15A, an adjustable repetition rate from 0 to 20kHz, a minimum pulse width of 20μs, and can output an internally modulated signal.

[0013] The center wavelength of the output beam of the laser diode is 808nm; the core diameter of the coupling fiber is 200μm and the numerical aperture is 0.22.

[0014] In a preferred embodiment, the focal lengths of both the collimating lens and the first focusing lens are 11 mm.

[0015] In a preferred embodiment, the reflectivity of the first antireflection film, the second antireflection film, and the third antireflection film is greater than 99%; the reflectivity of the first high reflectivity film is less than 1%; and the reflectivity of the partial reflectivity film is 50%-98%.

[0016] In a preferred embodiment, the laser crystal is a rare-earth ion-doped laser crystal; the laser crystal is bonded to a saturable absorber to form a composite crystal.

[0017] In a preferred embodiment, the laser crystal is one of neodymium-doped yttrium aluminum garnet (Nd:YAG), neodymium-doped yttrium vanadate (Nd:YVO4), and ytterbium-doped yttrium aluminum garnet (Yb:YAG).

[0018] In a preferred embodiment, the saturable absorber is a chromium-doped yttrium aluminum garnet crystal (Cr). 4+ YAG) or two-dimensional nanomaterial saturable absorbers or semiconductor saturable absorbers (SESAM).

[0019] In a preferred embodiment, the nonlinear crystal is one of yttrium vanadate (YVO4), diamond, barium nitrate (BN), potassium gadolinium tungstate (KGW), potassium titanyl phosphate (KTP), barium β-borate (BBO), and lithium triborate (LBO).

[0020] In a preferred embodiment, the matrix of the output coupling mirror is made of fused silica or sapphire.

[0021] The present invention also provides an optical imaging system, including the aforementioned miniature laser. The imaging system comprises, in sequence, a filter, a second focusing lens, a third focusing lens, a reflecting mirror, an objective lens, an electric displacement platform, an acrylic cell, an ultrasonic transducer, an amplifying filter, an oscilloscope, and a computer on the rear side of the miniature laser; the filter is a long-pass filter.

[0022] The second and third focusing lenses constitute a beam expanding system, used to magnify the focal spot size of the pulse pump light after focusing;

[0023] The electric displacement platform has XY axis movement; the bottom of the acrylic box is sealed with a cover glass, on which a sample is placed and immersed in water;

[0024] The ultrasonic transducer uses a point-to-focus method.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0026] 1. This invention provides a triggerable, handheld, multi-wavelength, low-cost micro laser device suitable for photoacoustic imaging. Stable pulsed laser output is achieved by controlling the repetition frequency, pulse width, and current magnitude of a programmable pulse power supply. The output multi-wavelength nanosecond pulsed laser serves as the excitation source for the photoacoustic imaging system, while the modulation signal of the programmable pulse power supply directly serves as the trigger source for the photoacoustic imaging system.

[0027] 2. The laser of the present invention generates nanosecond-level pulsed laser through passive Q-switching technology, which is suitable as an excitation source for photoacoustic imaging systems; at the same time, the laser has a simple structure and low cost, which is conducive to the miniaturization and integration of photoacoustic imaging systems.

[0028] 3. This invention uses pulse pumping technology, which generates a stable pulsed laser sequence that is synchronized with the modulation signal of the pump light. The modulation signal output by the programmable pulse power supply can be directly used as the trigger for the photoacoustic imaging system, eliminating the need to use a photodetector to detect the output laser.

[0029] 4. The laser of the present invention, combined with a nonlinear crystal, can realize multi-wavelength lasers, which is beneficial for functional photoacoustic imaging. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the optical imaging system in a preferred embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the modulation signal of the pump in a preferred embodiment of the present invention;

[0032] Figure 3 This is a pump pulse sequence diagram obtained by a laser diode in a preferred embodiment of the present invention;

[0033] Figure 4 This is a diagram showing the output laser pulse sequence corresponding to the pulse pump light in a preferred embodiment of the present invention;

[0034] Figure 5 This is a pulse sequence diagram of the 20kHz output laser from the pulse power supply in a preferred embodiment of the present invention;

[0035] Figure 6 The intensity distribution diagram of 1000 20kHz output laser pulses in a preferred embodiment of the present invention is shown.

[0036] Figure 7 This is a distribution diagram of the beam spot and beam quality factor of the 20kHz output laser in a preferred embodiment of the present invention;

[0037] Figure 8 This is a schematic diagram of the pulse width when the output laser repetition rate is 20kHz in a preferred embodiment of the present invention;

[0038] Figure 9 This is a schematic diagram of the power of the output laser with a repetition rate of 20kHz in a preferred embodiment of the present invention;

[0039] Figure 10 The spectrum diagram of the output laser introduced into the photoacoustic imaging system obtained in a preferred embodiment of the present invention;

[0040] Figure 11 This is a lateral resolution diagram of the photoacoustic imaging system in a preferred embodiment of the present invention;

[0041] Figure 12 This is an axial resolution diagram of the photoacoustic imaging system in a preferred embodiment of the present invention;

[0042] Figure 13 The image shows the USAF 1951 resolution plate under lasers of different repetition frequencies, as presented by the photoacoustic imaging system in a preferred embodiment of the present invention.

[0043] Figure 14 This is a spectrum of the output laser in a preferred embodiment of the present invention;

[0044] Figure 15This is a photoacoustic image of a sample (beef tissue) obtained in a preferred embodiment of the present invention.

[0045] Explanation of reference numerals in the attached figures: 1. Programmable pulse power supply; 2. Laser diode; 3. Collimating lens; 4. First focusing lens; 5. Laser crystal; 6. Saturable absorber; 7. Nonlinear crystal; 8. Output coupling mirror; 9. Filter; 10. Second focusing lens; 11. Third focusing lens; 12. Reflecting mirror; 13. Objective lens; 14. Electric displacement platform; 15. Acrylic box; 16. Ultrasonic transducer; 17. Amplifying filter; 18. Oscilloscope; 19. Computer. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0047] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0049] refer to Figure 1This embodiment provides a miniature laser, specifically a passively Q-switched miniature laser device based on pulse pumping. The miniature laser includes, in sequence, a programmable pulse power supply 1, a laser diode 2, a collimating lens 3, a first focusing lens 4, a laser crystal 5, a saturable absorber 6, a nonlinear crystal 7, and an output coupling mirror 8. The laser crystal 5, saturable absorber 6, nonlinear crystal 7, and output coupling mirror 8 are clamped and fixed together to form a laser resonant cavity, with the laser crystal 5 facing the first focusing lens 4. Alternatively, the laser crystal 5 can be clamped and fixed together using a copper clamp to form a laser resonant cavity, with the laser crystal 5 facing the first focusing lens 4.

[0050] The programmable pulse power supply 1 has no explicit parameter limitations; the larger the output current and adjustable repetition frequency range, the better, and the narrower the pulse width, the better. The programmable pulse power supply 1 outputs a pulse modulation signal as the trigger source for the entire photoacoustic imaging system. The programmable pulse power supply 1 is a constant current source, with a maximum output current of 15A, an adjustable repetition frequency from 0 to 20kHz, a minimum pulse width of 20μs, and the ability to output an internal modulation signal.

[0051] The laser diode 2 is an optical fiber coupled laser diode 2; the input pulse current can realize pulse pump light output. The output power of the laser diode 2 is in the range of watts to tens of watts. The center wavelength of the output beam of the laser diode 2 is 808nm; the core diameter of the coupling optical fiber is 200μm, and the numerical aperture is 0.22.

[0052] The programmable pulse power supply 1 is connected to the laser diode 2. The programmable pulse power supply 1 provides pulse current to power the laser diode 2. The laser diode 2 generates pulse pump light synchronized with the pulse current. The pulse pump light generated by the laser diode 2 is incident into the laser resonant cavity after passing through the collimating lens 3 and the first focusing lens 4. The focal spot size of the pulse pump light after focusing is controlled in the range of tens to hundreds of micrometers.

[0053] The output face of the laser diode 2, along with the collimating lens 3, the first focusing lens 4, the laser crystal 5, the saturable absorber 6, the nonlinear crystal 7, and the output coupling mirror 8, are arranged on the same horizontal line and are all vertically placed. The collimating lens 3 and the first focusing lens 4 are used to collimate and focus the pulse pump light, respectively. The focal spot size of the focused beam can be changed by altering the focal length and position of the collimating lens 3 and the first focusing lens 4. In this embodiment, the focal length of both the collimating lens 3 and the first focusing lens 4 is 11 mm.

[0054] In this embodiment, the laser crystal 5 has a first antireflection film and a first high reflectivity film on the side away from the saturable absorber 6, and a second antireflection film on the side closer to the saturable absorber 6; both sides of the nonlinear crystal 7 are coated with a third antireflection film; a partial reflection film is coated between the output coupling mirror 8 and the nonlinear crystal 7, and the partial reflection film serves as the output mirror of the laser resonant cavity.

[0055] In actual experiments, part of the reflective film can be placed on the end face of the output coupling mirror 8 near the nonlinear crystal 7 or on the end face of the nonlinear crystal 7 away from the saturable absorber 6.

[0056] The first antireflection coating and the first high-reflection coating are disposed on the side closest to the pump light. The pump wavelength corresponds to the first antireflection coating, and the output laser wavelength corresponds to the first high-reflection coating, the second antireflection coating, the third antireflection coating, and the partial reflection coating. The reflectivity of each coating must be adapted to the parameters of other crystals in the resonant cavity. Specifically, the reflectivity of the first, second, and third antireflection coatings is greater than 99%; the reflectivity of the first high-reflection coating is less than 1%; and the reflectivity of the partial reflection coating is 50%-98%.

[0057] The laser crystal 5 is a rare-earth ion-doped laser crystal 5. The laser crystal 5 adopts one of the following crystal types, including but not limited to neodymium-doped yttrium aluminum garnet (Nd:YAG), neodymium-doped yttrium vanadate (Nd:YVO4), and ytterbium-doped yttrium aluminum garnet (Yb:YAG).

[0058] In this embodiment, the laser crystal 5 is selected as a neodymium-doped yttrium aluminum garnet crystal (Nd:YAG) with a doping concentration of 1 at.%, a thickness of 2.5 mm, and a diameter of 10 mm; the laser crystal 5 is coated with a first antireflection film with a wavelength of 808 nm and a first high reflectivity film with a wavelength of 1064 nm.

[0059] The saturable absorber 6 employs, but is not limited to, chromium-doped yttrium aluminum garnet crystals (Cr). 4+ YAG) or two-dimensional nanomaterial saturable absorber 6 or semiconductor saturable absorber 6 (SESAM).

[0060] In this embodiment, the saturable absorber 6 is selected from chromium-doped yttrium aluminum garnet crystals (Cr) with an initial transmittance of 80%, a thickness of 0.5 mm, and a diameter of 10 mm. 4+ (YAG); In this embodiment, the laser crystal 5 and the saturable absorber 6 are bonded together to form a composite crystal.

[0061] The nonlinear crystal 7 is made of one of the following crystals, including but not limited to yttrium vanadate (YVO4), diamond, barium nitrate (BN), potassium gadolinium tungstate (KGW), potassium titanyl phosphate (KTP), barium β-borate (BBO), and lithium triborate (LBO).

[0062] In this embodiment, the nonlinear crystal 7 is selected as a yttrium vanadate crystal (YVO4) with a thickness of 2 mm and a diameter of 10 mm and a tangential a-cut; in this embodiment, the wavelengths of the partial reflective film are 1064 nm and 1176 nm.

[0063] The matrix of the output coupling mirror 8 is made of, but is not limited to, high-quality fused silica or sapphire, and a film system with a suitable reflectivity is deposited on the surface of the output coupling mirror 8.

[0064] This embodiment also provides a low-cost portable optical imaging system, including the aforementioned miniature laser. The imaging system has a filter 9, a second focusing lens 10, a third focusing lens 11, a reflector 12, an objective lens 13, an electric displacement platform 14, an acrylic box 15, an ultrasonic transducer 16, an amplifying filter 17, an oscilloscope 18, and a computer 19 arranged sequentially on the rear side of the miniature laser.

[0065] The filter 9 is an 808nm long-pass filter to filter out the pump light; the second focusing lens 10 and the third focusing lens 11 have focal lengths of 75mm and 125mm respectively, forming a beam expanding system to amplify the spot size; the reflecting mirror 12 reflects the expanded beam into the back focal plane of the objective lens 13; the numerical aperture of the objective lens 13 is 0.1, and the focal length is 17.35mm; the motorized displacement platform 14 can move along the x and y axes, with a stroke range of 50mm and a maximum speed of 5mm / s; the bottom of the acrylic box 15 is sealed with a cover glass, on which is placed... A sample (using beef) is placed and immersed in water; the ultrasonic transducer 16 has a bandwidth of 4.7MHz, a focusing method of point-to-point focusing, and a focal length of 25mm; the amplification filter 17 can amplify the acquired photoacoustic signal by 46dB and filter it at a low frequency of 18MHz; the oscilloscope 18 uses the modulation signal of the programmable pulse power supply 1 as a trigger source to acquire the photoacoustic signal in real time and transmit it to the computer 19 for processing; the computer 19 processes the acquired photoacoustic signal in real time and performs image reconstruction, while controlling the electric displacement platform 14 to perform scanning.

[0066] By adjusting the energy, repetition rate, and pulse width of the pulsed pump light using a programmable pulse power supply 1, stable pulsed laser output is achieved. The repetition rate of the output laser matches the repetition rate of the pump light modulation signal, allowing the modulation signal output from the programmable pulse power supply 1 to be directly used as the trigger for the photoacoustic imaging system. The pump modulation signal is as follows: Figure 2 As shown, the pump pulse sequence acquired by laser diode 2 is as follows: Figure 3As shown, the output laser pulse sequence that excites the corresponding pulse pump light is as follows: Figure 4 As shown, the repetition rate of the output laser is adjustable.

[0067] The programmable pulse power supply 1 has an adjustable repetition rate from 0 to 20 kHz. Figure 5 A pulse sequence of 20kHz output laser was demonstrated; Figure 6 The intensity distribution of 1000 20kHz output laser pulses is shown; Figure 7 The beam spot and beam quality factor of a 20kHz output laser were demonstrated. Figure 8 This demonstrates that the pulse width is 2.8 ns when the output laser repetition rate is 20 kHz, making it suitable as a light source for photoacoustic imaging; such as Figure 9 As shown, the power stability RMS of the output laser with a repetition rate of 20kHz is less than 0.18%, indicating relatively stable performance; Figure 10 As shown, the output laser spectrum is centered at 20kHz, with a signal-to-noise ratio of 41dB. The obtained output laser is then introduced into the photoacoustic imaging system. Figure 11 and Figure 12 The lateral and axial resolutions of the photoacoustic imaging system were demonstrated to be 5.5m and 300m, respectively. Figure 13 The imaging results of the photoacoustic imaging system on the USAF 1951 resolution plate under excitation light with different repetition frequencies are shown, demonstrating the stability of the photoacoustic imaging effect. Raman laser output can be obtained through the Raman frequency shift in the nonlinear effect, and the spectrum of the output laser is as follows: Figure 14 As shown, the obtained Raman light wavelength is near the optical absorption peak of fat, and it can be used as the excitation source for a photoacoustic imaging system to perform functional photoacoustic imaging. Figure 15 The image shows a photoacoustic image of beef tissue, where the white areas represent fat within the tissue. Therefore, this invention enables the development of pulse-stabilized, triggerable, portable, multi-wavelength, nanosecond microlasers suitable for photoacoustic imaging.

[0068] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A micro-laser, characterized by: The programmable pulse power supply, the laser diode, the collimating mirror, the first focusing mirror, the laser crystal, the saturable absorber, the nonlinear crystal and the output coupling mirror are sequentially arranged; the laser crystal, the saturable absorber, the nonlinear crystal and the output coupling mirror are clamped together to form a laser resonant cavity, and the laser crystal is arranged towards the first focusing mirror; The programmable pulse power supply is connected with the laser diode, and the output end face of the laser diode is arranged on the same horizontal line as the collimating mirror, the first focusing mirror, the laser crystal, the saturable absorber, the nonlinear crystal and the output coupling mirror and is vertically placed; The programmable pulse power supply serves as a trigger source of the photoacoustic imaging system; the programmable pulse power supply provides a pulse current, and the laser diode generates pulse pumping light synchronized with the pulse current; The collimating mirror and the first focusing mirror are respectively used for collimating and focusing the pulse pumping light, and the size of the focal spot of the pulse pumping light after focusing is set to be in the order of tens to hundreds of microns; the pulse pumping light is incident into the laser resonant cavity after passing through the collimating mirror and the first focusing mirror; The laser crystal is coated with a first antireflection film and a first high-reflection film on the side away from the saturable absorber, and is coated with a second antireflection film on the side close to the saturable absorber; the nonlinear crystal is coated with a third antireflection film on both sides; and a partial reflection film is coated between the output coupling mirror and the nonlinear crystal, which serves as an output mirror of the laser resonant cavity.

2. A micro-laser according to claim 1, wherein: The programmable pulse power supply is a constant current source, and the laser diode is a fiber-coupled laser diode; The maximum output current of the programmable pulse power supply is 15 A, the repetition frequency is adjustable from 0 to 20 kHz, the minimum pulse width is 20 μs, and an internal modulation signal can be outputted; The central wavelength of the output light beam of the laser diode is 808 nm; the core diameter of the coupled optical fiber is 200 μm, and the numerical aperture is 0.

22.

3. The micro-laser of claim 1, wherein: The focal lengths of the collimating mirror and the first focusing mirror are both 11 mm.

4. The micro-laser of claim 1, wherein: The reflectivity of the first antireflection film, the second antireflection film and the third antireflection film is greater than 99%, the reflectivity of the first high-reflection film is less than 1%, and the reflectivity of the partial reflection film is 50%-98%.

5. The micro-laser of claim 1, wherein: The laser crystal is a rare earth ion-doped laser crystal; the laser crystal and the saturable absorber are bonded into a composite crystal.

6. A micro-laser according to claim 5, wherein: The laser crystal adopts one of a neodymium-doped yttrium aluminum garnet crystal (Nd:YAG), a neodymium-doped yttrium vanadate crystal (Nd:YVO4) and a ytterbium-doped yttrium aluminum garnet crystal (Yb:YAG).

7. A micro-laser according to claim 6, wherein: The saturable absorber employs a chromium-doped yttrium aluminum garnet crystal (Cr 4+ :YAG) or a two-dimensional nanomaterial saturable absorber or a semiconductor saturable absorber (SESAM).

8. The micro-laser of claim 1, wherein: The nonlinear crystal adopts one of a yttrium vanadate crystal (YVO4), a diamond crystal, a barium nitrate crystal (BN), a potassium gadolinium tungstate crystal (KGW), a potassium titanyl phosphate crystal (KTP), a beta-barium borate crystal (BBO) and a lithium triborate crystal (LBO).

9. The micro-laser of claim 1, wherein: The substrate of the output coupling mirror adopts fused quartz or sapphire.

10. An optical imaging system characterized by: The imaging system comprises the micro-laser according to any one of claims 1-9, and is sequentially provided with a filter, a second focusing lens, a third focusing lens, a reflecting mirror, an objective lens, a motorized displacement platform, a PMMA box, an ultrasonic transducer, an amplifier filter, an oscilloscope and a computer at the rear side of the micro-laser; the filter is a long-pass filter; The second focusing lens and the third focusing lens constitute an expansion system for amplifying the size of the focal spot of the focused pulsed pump light; The motorized displacement platform is provided with X-Y axis movement; the bottom of the PMMA box is packaged by a cover glass, and a sample is placed on the cover glass and immersed in water; The focusing mode of the ultrasonic transducer is point-to-focus.

Images