Macroenergy single-frequency optical parametric oscillator

Abstract

The invention discloses a large-energy single-frequency optical parametric oscillator which comprises a pumping source, a resonant cavity, a first optical coupling system arranged between the pumping source and an input mirror of the resonant cavity, a seed source, a second optical coupling system arranged between the seed source and an output mirror of the resonant cavity, and a locking control system. The first optical coupling system comprises a variable-focus beam expander system and is used for adjusting the spot size of the pumping laser entering the resonant cavity. According to the invention, the size of the light spot of the pumping laser entering the resonant cavity is adjusted through the variable-focus beam expander system, and the generation of a continuous spectrum in the optical parameter generation process of the nonlinear optical crystal is inhibited, so that the continuous spectrum in the output signal light of the optical parametric oscillator is greatly reduced and even disappears. And on the basis, the spectrum of the output signal light of the optical parametric oscillator is pulled by the frequency of the seed light by virtue of a locking control system, so that the spectrum width of the output signal is narrowed.

Description

Technical Field

[0001] The present application relates to the technical field of optical elements, and more specifically, to a large-energy single-frequency optical parametric oscillator. Background Art

[0002] High-energy single-frequency pulsed laser light sources have the advantages of high coherence, narrow spectral width, high beam quality, high energy stability and large pulse energy. In addition, due to the good absorption and penetration ability of high-energy single-frequency lasers for various substances such as biological tissues, atmosphere and chemical elements, they are widely used in precision measurement, lidar, laser communication, laser spectroscopy, biological detection, laser guidance and industrial manufacturing and other fields, especially remote chemical analysis based on laser induced breakdown spectroscopy. The signal-to-noise ratio of laser induced breakdown spectroscopy can be improved by increasing the energy of a single laser pulse and narrowing its spectral width.

[0003] Up to now, the laser wavelength output by mature gain media can no longer meet the diverse needs of current scientific research and industrial production. At the same time, in the process of continuously improving the laser output energy, it is also faced with problems such as poor laser beam directivity and deterioration of light spot. In contrast, optical parametric oscillators pumped by mature near-infrared lasers (such as Nd:YVO4 lasers, Nd:YAG lasers) and their doubled and tripled frequency light have become important devices for obtaining lasers in other bands due to their high conversion efficiency and lack of thermal effect. However, due to the large acceptance bandwidth of nonlinear optical crystals in the optical parametric process, when the pulse pump gain is large, the spectral width of its output signal light can reach the nanometer level.

[0004] Usually, by inserting mode-selective elements such as etalons and gratings into the resonant cavity, the spectral width can be narrowed to the order of hundreds of megahertz, but this is still a certain distance from the spectral width of the Fourier transform limit. In addition, since there is no mode competition mechanism in the optical parametric process, the gain of the secondary mode will not be transferred to the main mode, so the output energy and conversion efficiency of the optical parametric oscillator using this solution will be limited to a low level.

[0005] Another method to narrow the spectral width is seed injection locking technology. This method uses a low-power continuous or pulsed single-frequency laser as the seed light. By increasing the gain of the mode corresponding to the seed light frequency in the optical parametric oscillator, the signal light in the resonant cavity is locked to the frequency of the seed light. This makes the spectral width of the output signal light of the optical parametric oscillator close to the spectral width of the seed light, ultimately achieving the narrowing of the signal spectrum width.

[0006] When the pulse energy of the signal light is continuously increased by increasing the pulse energy of the pump laser, the optical parametric oscillator will output the signal light simultaneously with the optical parameter generation process. In this case, whether the mode selection element or the seed injection locking technology is used, there will be a continuous spectrum generated by the optical parameter generation process, resulting in the continuous spectrum always existing in the output signal light of the optical parametric oscillator, resulting in the spectrum of the output signal light being unable to be pulled by the seed light frequency, and the purpose of narrowing the output signal spectrum width cannot be achieved. Summary of the invention

[0007] The present application provides a high-energy single-frequency optical parametric oscillator, which adjusts the spot size of a pump laser entering a resonant cavity through a variable-focus beam expander system, suppresses the generation of a continuous spectrum in the optical parameter generation process of a nonlinear optical crystal, and greatly reduces or even eliminates the continuous spectrum in the output signal light of the optical parametric oscillator. On this basis, with the help of a locking control system, the spectrum of the output signal light of the optical parametric oscillator is pulled by the frequency of the seed light, thereby achieving the narrowing of the output signal spectrum width, and finally achieving high-energy, single-frequency signal light output.

[0008] The present application provides a large energy single-frequency optical parametric oscillator, comprising a pump source, a resonant cavity, a first optical coupling system arranged between the pump source and an input mirror of the resonant cavity, a seed source, a second optical coupling system between the seed source and an output mirror of the resonant cavity, and a locking control system;

[0009] The first optical coupling system includes a variable focus beam expander system for adjusting the spot size of the pump laser entering the resonant cavity.

[0010] Preferably, two adjacent cavity mirrors are provided in the resonant cavity, and the two cavity mirrors form an equivalent confocal cavity structure.

[0011] Preferably, the resonant cavity comprises a first cavity mirror, a second cavity mirror and a third cavity mirror, the first cavity mirror is an input mirror, and a nonlinear optical crystal is arranged between the first cavity mirror and the second cavity mirror.

[0012] Preferably, the resonant cavity is an L-shaped folded cavity, and the second cavity mirror is placed at an angle of 45°; in the optical path, the first cavity mirror and the third cavity mirror are respectively located upstream and downstream of the second cavity mirror.

[0013] Preferably, the resonant cavity is an L-shaped folded cavity, and the first cavity mirror is placed at an angle of 45°; in the optical path, the second cavity mirror and the third cavity mirror are respectively located upstream and downstream of the first cavity mirror.

[0014] Preferably, the first cavity mirror is both an input mirror and an output mirror of the resonant cavity.

[0015] Preferably, the signal input end and the output end of the locking control system are respectively connected to the piezoelectric ceramics on the rear end surface of the detection cavity mirror in the resonant cavity and the feedback cavity mirror in the resonant cavity, and the detection cavity mirror is used to output the signal required by the locking control system;

[0016] The locking control system also includes an electro-optic modulator disposed between the seed source and the second optical coupling system.

[0017] Preferably, the second optical coupling system comprises a beam shaping system for adjusting the spot size of the seed light.

[0018] Preferably, the resonant cavity is a linear cavity structure, the second cavity mirror is an output mirror, and the third cavity mirror is a detection cavity mirror and a feedback cavity mirror.

[0019] Preferably, the third cavity mirror is an output mirror and a feedback cavity mirror, and the second cavity mirror is a detection cavity mirror.

[0020] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0022] Figure 1 A structural diagram of a first embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application;

[0023] Figure 2 A structural diagram of a second embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application;

[0024] Figure 3 A structural diagram of a third embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application;

[0025] Figure 4 A structural diagram of a fourth embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application;

[0026] Figure 5 A structural diagram of a fifth embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application;

[0027] Figure 6 A structural diagram of a sixth embodiment of a high-energy single-frequency optical parametric oscillator provided by the present application; DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0029] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0030] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0031] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0032] The present application provides a high-energy single-frequency optical parametric oscillator, which adjusts the spot size of the pump laser entering the resonant cavity through a variable focus beam expander system, suppresses the generation of a continuous spectrum in the optical parameter generation process of the nonlinear optical crystal, and greatly reduces or even eliminates the continuous spectrum in the output signal light of the optical parametric oscillator. On this basis, with the help of a locking control system, the spectrum of the output signal light of the optical parametric oscillator is pulled by the frequency of the seed light, thereby achieving the narrowing of the output signal spectrum width and outputting a single-frequency signal light. On the basis of the above, an equivalent confocal resonant cavity is set, and the mode matching of the cavity mode at the nonlinear optical crystal and the pump laser is achieved by adjusting the distance between the two cavity mirrors of the equivalent confocal cavity structure or changing the curvature radius of the two, so that the conversion efficiency of the optical parametric oscillator is maximized, and a high-energy signal light output is achieved. In addition, the mode matching of the seed light and the resonant cavity is achieved through a second optical coupling system, and the injection locking of the resonant cavity is achieved through a locking control system based on the PDH locking method, so as to achieve a high-energy, single-frequency signal light output.

[0033] The high-energy single-frequency optical parametric oscillator provided in the present application includes a pump source, a resonant cavity, a first optical coupling system arranged between the pump source and the input mirror of the resonant cavity, a seed source, a second optical coupling system between the seed source and the output mirror of the resonant cavity, and a locking control system.

[0034] The pump source is a high-energy pulsed laser light source, which is used to output the pump laser. The pump laser enters the resonant cavity after passing through the first optical coupling system and is injected into the nonlinear optical crystal in the resonant cavity. The nonlinear optical crystal has a specific cutting angle design. The nonlinear optical crystal that meets the phase matching condition converts the pump laser into signal light and idler light through the optical parametric oscillation process. The seed source uses a continuous wave single-frequency laser, a pulsed single-frequency laser, a continuous wave single-frequency optical parametric oscillator or a pulsed single-frequency optical parametric oscillator. The seed light emitted by the seed source enters the resonant cavity after passing through the second optical coupling system. The second optical coupling system is used for mode matching between the seed light and the resonant cavity, and then the seed injection locking is realized through the locking control system.

[0035] Among them, the first optical coupling system includes a variable focus beam expander system, which is used to adjust the spot size of the pump laser entering the resonant cavity to suppress the continuous spectrum generated by the nonlinear optical crystal through the optical parameter generation process, so that the continuous spectrum in the output signal light is greatly reduced or even disappears, so that with the help of the locking control system, the spectrum of the output signal light of the optical parametric oscillator is pulled by the frequency of the seed light, thereby achieving the narrowing of the output signal spectrum width and outputting single-frequency signal light.

[0036] The second optical coupling system includes a beam shaping system for adjusting the spot size of the seed light to achieve mode matching between the seed light and the resonant cavity.

[0037] The signal input and output of the locking control system are respectively connected to the detection cavity mirror in the resonant cavity and the piezoelectric ceramics on the rear end face of the feedback cavity mirror in the resonant cavity, and the detection cavity mirror is used to output the signal required by the locking control system. The locking control system also includes an electro-optical modulator, which is arranged between the seed source and the second optical coupling system.

[0038] On the basis of the above, preferably, two adjacent cavity mirrors are provided in the resonant cavity, and the two cavity mirrors form an equivalent confocal cavity structure, and the two cavity mirrors can be spherical mirrors or ball lenses. By adjusting the distance between the two cavity mirrors of the confocal cavity or changing the curvature radius of the two, the mode matching of the cavity mode at the nonlinear optical crystal and the pump laser is achieved, so that the conversion efficiency of the optical parametric oscillator is maximized, and a large energy signal light output is achieved.

[0039] Specifically, the resonant cavity at least includes a first cavity mirror, a second cavity mirror and a third cavity mirror, wherein the first cavity mirror is an input mirror, and a nonlinear optical crystal is arranged between the first cavity mirror and the second cavity mirror.

[0040] Figure 1-6 The structural diagrams of different embodiments of the high-energy single-frequency optical parametric oscillator provided in this application are described in detail as follows.

[0041] Example 1

[0042] like Figure 1 As shown, the high-energy single-frequency optical parametric oscillator includes a pump source 1, a seed source 2, a first spectroscope 3, a nonlinear optical crystal 4, a resonant cavity 5, a locking control system 6, a first optical coupling system 7 between the pump source 1 and the resonant cavity 5, and a second optical coupling system 8 between the resonant cavity 5 and the seed source 2.

[0043] The first optical coupling system 7 includes a first polarization optical system 71 and a variable focus beam expander system 72. The first polarization optical system 71 includes a first optical isolator 711 and a first half-wave plate 712. The first optical isolator 711 is used to prevent the reflected pump laser from entering the pump source 1 and causing damage. The first half-wave plate 712 is used to calibrate the polarization state of the pump laser entering the resonant cavity 5. The variable focus beam expander system 72 includes at least three lenses. Figure 1 Shown are the fourth lens 721, the fifth lens 722 and the sixth lens 723, which are used to flexibly adjust the spot size of the pump laser entering the resonant cavity 5, on the one hand to prevent the nonlinear optical crystal 4 from being damaged, and on the other hand to suppress the optical parameter generation process of the nonlinear optical crystal 4.

[0044] The pump laser output by the first optical coupling system 7 enters the resonant cavity 5 through the first beam splitter 3 , and the first beam splitter 3 is used to reflect the pump laser into the resonant cavity 5 .

[0045] like Figure 1 As shown, the resonant cavity 5 is an L-shaped folded cavity, which includes a first cavity mirror 51, a second cavity mirror 52, a first lens 53 and a third cavity mirror 54 in sequence. In the optical path, the first cavity mirror 51 and the third cavity mirror 54 are respectively located upstream and downstream of the second cavity mirror 52. The first cavity mirror 51 and the second cavity mirror 52 are both plane mirrors. The first cavity mirror 51 is used as the input mirror of the optical parametric oscillator and is coated with a dielectric film with high transmittance to the wavelength of the pump laser and the idler light and high reflection to the wavelength of the signal light. The second cavity mirror 52 is placed at an angle of 45° in the resonant cavity 5 and is coated with a dielectric film with high transmittance to the wavelength of the pump laser and the idler light and high reflection to the wavelength of the signal light. The third cavity mirror 54 is used as the output mirror of the optical parametric oscillator and is coated with a certain transmittance to the wavelength of the signal light. The first lens 53 is coated with a dielectric film that reduces the reflection to the wavelength of the signal light. At the same time, the third cavity mirror 54 is a plano-concave mirror (for example, the radius of curvature is 50 mm). The third cavity mirror 54 and the first lens 53 form an equivalent confocal cavity structure in the resonant cavity 5. By adjusting the distance between the first lens 53 and the third cavity mirror 54 and changing the curvature radius of the two, the cavity mode size between the first cavity mirror 51 and the second cavity mirror 52 is changed to achieve mode matching between the cavity mode at the nonlinear optical crystal and the pump laser.

[0046] The seed source 2 uses a continuous wave single-frequency laser. The seed light emitted by the seed source 2 enters the resonant cavity 5 through the electro-optic modulator 65 and the second optical coupling system 8 in sequence. Among them, the second optical coupling system 8 includes a second polarization optical system 81 and a beam shaping system 82. The second polarization optical system 81 includes a second optical isolator 811 and a second half-wave plate 812. The second optical isolator 811 is used to prevent the signal light and the reflected seed light from entering the seed source 2 and causing damage. The second half-wave plate 812 is used to calibrate the polarization state of the seed light entering the resonant cavity 5. The beam shaping system 82 includes an eighth lens 821 and a seventh lens 822, which are used to adjust the spot size of the seed light to achieve mode matching between the seed light and the resonant cavity 5. The signal light transmitted by the output mirror (i.e., the third cavity mirror 54) passes through the second optical coupling system 8, and the signal light is output from the backward escape window of the second optical isolator 811 as the output light source of the large energy single-frequency optical parametric oscillator.

[0047] The locking control system 6 uses the PDH locking method for injection locking. Specifically, the locking control system 6 includes a second beam splitter 61, a photodetector 62, a servo control system 63, a piezoelectric ceramic 64 bonded to the rear end face of the third cavity mirror 54 (as a feedback cavity mirror) of the resonant cavity 5, and an electro-optic modulator 65 placed between the seed source 2 and the resonant cavity 5. The locking principle is that the seed light is modulated by the electro-optic modulator 65 and injected from the output mirror (i.e., the third cavity mirror 54) of the resonant cavity 5 through the second polarization optical system 81 and the beam shaping system 82. When the cavity length of the resonant cavity 5 is equal to an integer multiple of the seed light frequency, the seed light resonates in the resonant cavity 5, which will help to narrow the signal spectrum generated by the optical parametric oscillation process. Since the coating of the optical lens cannot achieve 100% reflectivity, the small amount of signal light and its seed light that leak out can be filtered through the second cavity mirror 52 (serving as a detection cavity mirror) through the second beam splitter 61 coated with high reflectivity for the signal light wavelength and high transmittance for the pump light and idle light wavelengths, and the photodetector 62 can simultaneously perform saturation filtering on the pulse signal light portion, and finally output only the detection signal of the continuous light portion, and then the detection signal is mixed and filtered with the modulation signal through the servo control system 63, and then the feedback signal is obtained through proportional-integral-amplification operation and high-voltage amplification processing, and finally loaded onto the piezoelectric ceramic 64 to achieve the locking of the resonant cavity 5.

[0048] Example 2

[0049] like Figure 2As shown, the high energy single frequency optical parametric oscillator includes a pump source 1, a seed source 2, a first beam splitter 3, a nonlinear optical crystal 4, a resonant cavity 5, a locking control system 6, a first optical coupling system 7 and a second optical coupling system 8, and the respective structures and optical paths are the same as those in Example 1. On this basis, the high energy single frequency optical parametric oscillator of this embodiment also includes a third beam splitter 9, which is arranged on the optical path between the detection cavity mirror (the second cavity mirror 52) and the signal input end (the second beam splitter 61) of the locking control system 6. The surface of the third beam splitter 9 is coated with a dielectric film with high reflection to the wavelength of the pump light and high transparency to the wavelengths of the signal light and the idler light, and is used to re-inject the remaining pump laser in the optical parametric oscillation process into the nonlinear optical crystal 4, so as to improve the conversion efficiency of the optical parametric oscillation process. Meanwhile, the first optical isolator 711 of the first optical coupling system 7 is provided with a backward escape window, and the pump laser that returns to the resonant cavity through the third beam splitter 9 and passes through the input mirror (first cavity mirror 51) enters the first optical coupling system 7 after being reflected by the first beam splitter 3, and is emitted from the backward escape window of the first optical isolator 711 of the first optical coupling system 7. The first beam splitter 3 is used to reflect the pump laser to enter the resonant cavity 5, and transmit the signal light and idler light generated by the optical parametric process emitted by the first cavity mirror 51.

[0050] Example 3

[0051] like Figure 3As shown, the high energy single frequency optical parametric oscillator includes a pump source 1, a seed source 2, a first beam splitter 3, a nonlinear optical crystal 4, a locking control system 6, a first optical coupling system 7 and a second optical coupling system 8, and the structures of each are the same as those in Example 1. On this basis, in the high energy single frequency optical parametric oscillator of this embodiment, the resonant cavity 5 is an L-shaped folded cavity, including a first cavity mirror 51, a second cavity mirror 52, a first lens 53 and a third cavity mirror 54, and the first cavity mirror 51 is placed at a 45° angle; in the optical path, the second cavity mirror 52 and the third cavity mirror 54 are respectively located upstream and downstream of the first cavity mirror 51. The first cavity mirror 51 and the second cavity mirror 52 are both plane mirrors. The first cavity mirror 51 is used as the input mirror of the optical parametric oscillator and is coated with a dielectric film with high transmittance to the wavelengths of the pump laser and the idler light and high reflection to the wavelength of the signal light. The second cavity mirror 52 is placed at an angle of 0° in the resonant cavity 5 and is coated with a dielectric film with high transmittance to the wavelengths of the pump laser and the idler light and high reflection to the wavelength of the signal light. The third cavity mirror 54 is used as the output mirror of the optical parametric oscillator, and is coated with a certain transmittance for the signal light wavelength, and the first lens 53 is coated with a dielectric film for anti-reflection for the signal light wavelength. At the same time, the third cavity mirror 54 is a plano-concave mirror (for example, the radius of curvature is 50 mm). The third cavity mirror 54 and the first lens 53 form an equivalent confocal cavity structure in the resonant cavity 5. By adjusting the distance between the first lens 53 and the third cavity mirror 54 and changing the radius of curvature of the two, the cavity mode size between the first cavity mirror 51 and the second cavity mirror 52 is changed, so as to achieve mode matching between the cavity mode at the nonlinear optical crystal and the pump laser.

[0052] Example 4

[0053] like Figure 4 As shown, in the high energy single frequency optical parametric oscillator, the pump source 1, the seed source 2, the first beam splitter 3, the nonlinear optical crystal 4, the resonant cavity 5, the locking control system 6, the first optical coupling system 7 and the second optical coupling system 8, each of which has the same structure as in Example 1, but the optical path setting is different: in the resonant cavity 5, the first cavity mirror 51 is both the input mirror and the output mirror of the resonant cavity, and is coated with a dielectric film with high transmittance to the pump light and the idler light and a certain transmittance of the signal light wavelength. Therefore, the seed light emitted by the seed source 2 enters the resonant cavity 5 from the first cavity mirror 51 of the resonant cavity 5 through the electro-optical modulator 65, the second optical coupling system 8 and the first beam splitter 3 in sequence. The signal light output by the first cavity mirror 51 of the resonant cavity 5 enters the second optical coupling system 8 after being transmitted by the first beam splitter 3, and is output from the backward escape window of the second optical isolator 811.

[0054] Example 5

[0055] like Figure 5As shown, the high energy single frequency optical parametric oscillator includes a pump source 1, a seed source 2, a first beam splitter 3, a nonlinear optical crystal 4, a locking control system 6, a first optical coupling system 7 and a second optical coupling system 8, and the respective structures and optical paths are the same as those in Example 1. On this basis, in the high energy single frequency optical parametric oscillator of this embodiment, the resonant cavity 5 is a linear cavity structure, including a first cavity mirror 51, a second cavity mirror 52, a first lens 53 and a third cavity mirror 54 arranged linearly in sequence. The first cavity mirror 51 and the second cavity mirror 52 are both plane mirrors. The first cavity mirror 51 is an input mirror, which is coated with a dielectric film with high transmittance to the wavelengths of pump laser and idler light and high reflection to the wavelength of signal light. The second cavity mirror 52 is placed at an angle of 45° and is an output mirror, which is coated with a dielectric film with high reflection to the wavelengths of pump laser and idler light and a certain transmittance to the wavelength of signal light. The seed light emitted by the seed source 2 passes through the electro-optic modulator 65 and the second optical coupling system 8 in sequence, and then enters the resonant cavity 5 through the second cavity mirror 52. The resonant cavity 5 outputs the signal light through the second cavity mirror 52 , enters the second optical coupling system 8 , and is output from the rear escape window of the second optical isolator 811 .

[0056] At the same time, the second beam splitter 61 and the photodetector 62 are placed in the outer optical path of the third cavity mirror 54. The third cavity mirror 54 is a detection cavity mirror and a feedback cavity mirror. A piezoelectric ceramic 64 is provided on the rear end face of the third cavity mirror 54. A small amount of signal light and seed light are transmitted from the third cavity mirror 54 and injected into the photodetector 62 through the second beam splitter 61. The feedback signal obtained by the servo control system 63 is loaded on the piezoelectric ceramic 64 to realize the seed injection locking of the optical parametric oscillator.

[0057] In addition, the third cavity mirror 54 is coated with a dielectric film with high reflection to the wavelength of the signal light, and the first lens 53 is coated with a dielectric film with anti-reflection to the wavelength of the signal light. The third cavity mirror 54 is a plano-concave mirror, and the third cavity mirror 54 and the first lens 53 form an equivalent confocal cavity structure in the resonant cavity 5. By adjusting the distance between the first lens 53 and the third cavity mirror 54 and changing the curvature radius of the two, the cavity mode size between the first cavity mirror 51 and the second cavity mirror 52 is changed, so as to achieve mode matching between the cavity mode at the nonlinear optical crystal and the pump laser.

[0058] Example 6

[0059] like Figure 6As shown, the high energy single frequency optical parametric oscillator includes a pump source 1, a seed source 2, a first beam splitter 3, a nonlinear optical crystal 4, a locking control system 6, a first optical coupling system 7 and a second optical coupling system 8, and the respective structures and optical paths are the same as those in Example 1. On this basis, in the high energy single frequency optical parametric oscillator of this embodiment, the resonant cavity 5 includes a first cavity mirror 51, a second cavity mirror 52, a second lens 56, a third lens 57, a third cavity mirror 54 and a fourth cavity mirror 55, and the first cavity mirror 51, the second cavity mirror 52, the third cavity mirror 54 and the fourth cavity mirror 55 form a ring cavity, and are all plane mirrors placed at an angle of 45°. The first cavity mirror 51 and the second cavity mirror 52 are coated with a dielectric film with high transmittance to the wavelength of the pump laser and the idler light and high reflection to the signal light, and the first cavity mirror 51 serves as the input mirror of the resonant cavity 5. The third cavity mirror 54, as the output mirror of the optical parametric oscillator, is coated with a dielectric film with a certain transmittance to the wavelength of the signal light. The fourth cavity mirror 55 is coated with a dielectric film with high reflection to the wavelength of the signal light.

[0060] At the same time, the second lens 56 and the third lens 57 are coated with a dielectric film that reduces the reflection of the signal light wavelength, and the second lens 56 and the third lens 57 are arranged between the third cavity mirror 54 and the fourth cavity mirror 55, and the second lens 56 and the third lens 57 form an equivalent confocal cavity structure. By adjusting the distance between the second lens 56 and the third lens 57 and changing the focal length of the two, the cavity mode size between the first cavity mirror 51 and the second cavity mirror 52 is changed, and the mode matching of the cavity mode at the nonlinear optical crystal and the pump laser is achieved.

[0061] In addition, a piezoelectric ceramic 64 is provided on the rear end face of the third cavity mirror 54. The pump light and idler light transmitted from the second cavity mirror 52 enter the second spectroscope 61. The servo control system 63 obtains a feedback signal and loads it onto the piezoelectric ceramic 64 to achieve seed injection locking of the optical parametric oscillator.

[0062] The working principle of the high-energy single-frequency optical parametric oscillator provided in this application is as follows:

[0063] The high-energy pulse pump laser emitted by the pump source 1 is first calibrated for polarization state and spot size shaping by the first optical coupling system 7. Among them, the first optical isolator 711 in the first polarization optical system 7 is used to prevent the pump light reflected by the resonant cavity 5 from entering the pump source 1 and causing damage, and the first half-wave plate 712 is used to calibrate the polarization state of the pump light entering the resonant cavity 5. The variable focus beam expander system 72 is used to continuously adjust the spot size of the pump laser to ensure that the optical parametric oscillator cannot reach the threshold of optical parameter generation under different pump energies, so as to suppress the generation of continuous spectrum in the optical parameter generation process of the nonlinear optical crystal, so that the continuous spectrum in the output signal light of the optical parametric oscillator is greatly reduced or even disappears. At the same time, the variable focus beam expander system 72 adjusts the spot size of the pump laser to achieve the maximum conversion efficiency of the optical parametric oscillator. The pump laser is injected into the resonant cavity 5, and the signal light and idler light are simultaneously generated through the optical parametric oscillation process. In order to prevent the reverse conversion of the optical parametric process, the idler light generated is promptly guided out of the resonant cavity 5 through the detection cavity mirror. In order to achieve mode matching between the cavity mode at the nonlinear optical crystal 4 and the pump laser, the cavity mode size between the first cavity mirror 51 and the second cavity mirror 52 is finely adjusted by adjusting the distance between the two cavity mirrors in the equivalent confocal cavity structure or changing their curvature radius. The signal light transmitted by the output mirror passes through the second optical coupling system 8, and the signal light is output from the backward escape window of the second optical isolator 811 as the output light source of the large energy single-frequency optical parametric oscillator. At the same time, the seed source 2 emits a continuous wave single-frequency seed light, which is injected into the resonant cavity 5 through the second optical coupling system 8. Among them, the seed light emitted by the seed source 2 is transmitted forward along the second optical isolator 811 after passing through the electro-optical modulator 65, and at the same time, its polarization state is calibrated by the second half-wave plate 812 and its beam is shaped by the beam shaping system 82 to achieve mode matching between the seed light and the resonant cavity 5. Then, the optical parametric oscillator is injection locked with the help of the locking control system 6 based on the PDH locking method, and finally a large energy, single-frequency pulse signal light is obtained. The servo control system 63 generates a modulation signal and outputs it to the electro-optic modulator, so that it modulates the frequency of the seed light. At the same time, the servo control system 63 obtains a feedback signal after analyzing the detection signal generated by the photodetector 62, and loads it to the piezoelectric ceramic 64, and finally realizes the seed injection locking of the optical parametric oscillator. After injection locking, the cavity length of the resonant cavity 5 is equal to an integer multiple of the seed light frequency, and the seed light resonates in the resonant cavity 5, which will help to narrow the signal spectrum generated by the optical parametric oscillation process.

[0064] The high-energy single-frequency optical parametric oscillator of the present application shapes the pump laser through a variable-focus beam expander system to suppress the optical parameter generation process in the optical parametric oscillator, and at the same time uses low-power continuous or pulsed single-frequency seed light to perform seed injection locking on the optical parametric oscillator to achieve spectral width narrowing of the output signal light, and further achieves mode matching between the pump laser and the resonant cavity mode through a resonant cavity with an equivalent confocal cavity structure, so that the optical parametric oscillator achieves high conversion efficiency while narrowing the spectral width, and realizes high-energy single-frequency signal light output.

[0065] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A high energy single frequency optical parametric oscillator, characterized in that: It comprises a pump source, a resonant cavity, a first optical coupling system arranged between the pump source and an input mirror of the resonant cavity, a seed source, a second optical coupling system between the seed source and an output mirror of the resonant cavity, and a locking control system; The first optical coupling system comprises a variable focus beam expander system for adjusting the spot size of the pump laser entering the resonant cavity.

2. The high energy single-frequency optical parametric oscillator according to claim 1, characterized in that: Two adjacent cavity mirrors are arranged in the resonant cavity, and the two form an equivalent confocal cavity structure.

3. The high energy single-frequency optical parametric oscillator according to claim 2, characterized in that: The resonant cavity comprises a first cavity mirror, a second cavity mirror and a third cavity mirror, wherein the first cavity mirror is an input mirror, and a nonlinear optical crystal is arranged between the first cavity mirror and the second cavity mirror.

4. The high energy single-frequency optical parametric oscillator according to claim 3, characterized in that: The resonant cavity is an L-shaped folded cavity, and the second cavity mirror is placed at an angle of 45°; on the optical path, the first cavity mirror and the third cavity mirror are respectively located upstream and downstream of the second cavity mirror.

5. The high energy single-frequency optical parametric oscillator according to claim 3, characterized in that: The resonant cavity is an L-shaped folded cavity, and the first cavity mirror is placed at an angle of 45°; on the optical path, the second cavity mirror and the third cavity mirror are respectively located upstream and downstream of the first cavity mirror.

6. The high energy single-frequency optical parametric oscillator according to claim 3, characterized in that: The first cavity mirror is both an input mirror and an output mirror of the resonant cavity.

7. The high energy single-frequency optical parametric oscillator according to claim 3, characterized in that: The signal input end and the output end of the locking control system are respectively connected to the detection cavity mirror in the resonant cavity and the piezoelectric ceramics on the rear end surface of the feedback cavity mirror in the resonant cavity, and the detection cavity mirror is used to output the signal required by the locking control system; The locking control system further includes an electro-optic modulator disposed between the seed source and the second optical coupling system.

8. The high energy single-frequency optical parametric oscillator according to claim 7, characterized in that: The second optical coupling system includes a beam shaping system for adjusting the spot size of the seed light.

9. The high energy single-frequency optical parametric oscillator according to claim 7, characterized in that: The resonant cavity is a linear cavity structure, the second cavity mirror is the output mirror, and the third cavity mirror is the detection cavity mirror and the feedback cavity mirror.

10. The high energy single-frequency optical parametric oscillator according to claim 7, characterized in that: The third cavity mirror is the output mirror and the feedback cavity mirror, and the second cavity mirror is the detection cavity mirror.

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