A mid-infrared laser

Abstract

The application provides a mid-infrared laser, and relates to the technical field of lasers.The mid-infrared laser comprises a first pump source, a second pump source, a first crystal, a second crystal, an optical rotator, a first quarter-wave plate, a first high-reflection mirror, a polarization beam splitter prism, an electro-optical switch, a first saturable absorber, a second high-reflection mirror and a third high-reflection mirror; the first crystal and the second crystal are excited by initial light beams emitted by the first pump source and the second pump source to generate a first light beam and a second light beam; the optical rotator couples the first light beam and the second light beam to generate an initial state light beam; the first quarter-wave plate changes the phase of the initial state light beam to generate a first linearly polarized light beam in cooperation with the first high-reflection mirror; and the polarization beam splitter prism reflects the first linearly polarized light beam to enable the first linearly polarized light beam to continuously oscillate in a resonant cavity.When the electro-optical switch is started, the first linearly polarized light beam is converted into a second linearly polarized light beam which is output by the polarization beam splitter prism to output laser with high efficiency.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of laser technology, and particularly relate to a mid-infrared laser. BACKGROUND

[0002] The mid-infrared laser has a "molecular fingerprint" spectral characteristic, and is widely used in the fields of environmental monitoring (such as greenhouse gas detection), biomedical diagnosis (such as non-invasive blood sugar analysis), industrial process control (such as trace gas sensing), and national defense and security (such as explosive detection). The components of the mid-infrared laser include a gain medium, a pump source, a resonant cavity, a wavelength tuning device, and the like. Since the absorption peaks of most molecules in the mid-infrared region are widely and densely distributed, the laser is required to have a wide wavelength tuning capability to cover multiple target spectral lines; and, in order to realize the output of linearly polarized light, an anisotropic crystal is used as the gain medium, but the anisotropic crystal is prone to thermal effects due to the limitations of thermal and mechanical parameters, thereby reducing the efficiency of the laser resonant cavity and the output efficiency of the laser.

[0003] In order to improve the wavelength tuning capability of the laser, an optical parametric oscillator (OPO) can be used as a wavelength tuning device. The OPO is based on frequency conversion of a nonlinear crystal (such as PPLN), and a wide range of wavelength tuning is achieved by adjusting the pump wavelength or the crystal temperature. In order to increase the laser output efficiency, an isotropic crystal with high thermal and mechanical parameters can be used as the gain medium.

[0004] However, the OPO needs a large temperature range to tune the wavelength according to the change of the temperature, and the implementation is complex; the use of the isotropic crystal as the gain medium is difficult to produce linearly polarized light, and the thermal birefringence phenomenon will also occur, thereby reducing the output efficiency of the laser. SUMMARY

[0005] To solve the above problems, the present application provides a mid-infrared laser, which can solve the technical problems of difficulty in tuning the wavelength of the laser and low laser output efficiency.

[0006] To achieve the above object, the application provides a mid-infrared laser, comprising: a pumping module, the pumping module comprising a first pumping source and a second pumping source; the first pumping source is configured to emit a first initial light beam, and the second pumping source is configured to emit a second initial light beam; the first initial light beam and the second initial light beam propagate along a first optical axis, and the propagation directions of the first initial light beam and the second initial light beam are opposite; a resonant cavity, the resonant cavity comprising a first crystal, a second crystal, an optical rotator, a first quarter-wave plate, a first high-reflection mirror, a polarization beam splitter prism, an electro-optic switch, a first saturable absorption mirror, a second high-reflection mirror and a third high-reflection mirror; the first crystal and the second crystal are the same and are isotropic gain media; the first crystal and the second crystal are arranged on the first optical axis; the first crystal is configured to be excited by the first initial light beam emitted by the first pumping source to generate a first light beam; the second crystal is configured to be excited by the second initial light beam emitted by the second pumping source to generate a second light beam; the optical rotator is arranged between the first crystal and the second crystal along the first optical axis and is configured to couple the first light beam and the second light beam to generate an initial state light beam; the first quarter-wave plate is arranged perpendicularly to a second optical axis and is configured to change the phase of the initial state light beam; the second optical axis is perpendicular to the first optical axis; the first high-reflection mirror is arranged on the second optical axis and is configured to cooperate with the optical rotator to generate a first linearly polarized light beam; the polarization beam splitter prism is arranged perpendicularly to a third optical axis and is configured to reflect the first linearly polarized light beam; the third optical axis is perpendicular to the first optical axis; the second high-reflection mirror and the third high-reflection mirror are arranged on the first optical axis at a preset angle; the second high-reflection mirror is configured to reflect the first linearly polarized light beam to the polarization beam splitter prism; the third high-reflection mirror is configured to reflect the initial state light beam to the first quarter-wave plate; the electro-optic switch is arranged on the third optical axis and is configured to change the polarization direction of the first linearly polarized light beam to generate a second linearly polarized light beam; the polarization beam splitter prism is also configured to transmit the second linearly polarized light beam; and the first saturable absorption mirror is arranged on the third optical axis and is configured to reflect the first linearly polarized light beam or the second linearly polarized light beam.

[0007] The mid-infrared laser provided by the application emits two initial light beams through two pumping sources, irradiates the first initial light beam and the second initial light beam to the first crystal and the second crystal respectively to generate first light beams and second light beams of fixed wavelengths, couples the first light beams and the second light beams through the optical rotator to offset the thermal-induced birefringence of the first crystal and the second crystal, adjusts the phase difference of the coupled light beams through the quarter-wave plate, and forms the first linearly polarized light beam after reflection by the first high-reflection mirror; at this time, the polarization beam splitter prism reflects the first linearly polarized light beam, and the first saturable absorption mirror, the second high-reflection mirror and the third high-reflection mirror cooperate to enable the first linearly polarized light beam to continuously oscillate in the resonant cavity; when the electro-optic switch is started, the first linearly polarized light beam is converted into the second linearly polarized light beam, which is output in one time through the polarization beam splitter prism, so that the mid-infrared laser can output the mid-infrared laser with high efficiency.

[0008] In a possible implementation, the mid-infrared laser further includes a parametric oscillator; the parametric oscillator includes a multi-period crystal; the multi-period crystal is movably arranged on one side of the polarization beam splitter prism along a third optical axis and is configured to tune the wavelength of the second linearly polarized light beam.

[0009] In the above mid-infrared laser, the periods of the crystals have a corresponding relationship with the laser wavelength, and by arranging multiple crystals with different periods on the parametric oscillator, the parametric oscillator can output laser beams with different wavelengths, thereby improving the wavelength tuning capability of the mid-infrared laser.

[0010] In a possible implementation, the parametric oscillator further includes a driving motor; the driving motor is in transmission connection with the multi-period crystal and is configured to drive the multi-period crystal to move in a direction perpendicular to the second linearly polarized light beam.

[0011] In the above mid-infrared laser, by controlling the parametric oscillator to move in a direction perpendicular to the second linearly polarized light beam through the driving motor, the second linearly polarized light beam can be selectively emitted to the crystal with different periods, thereby realizing wavelength tuning.

[0012] In a possible implementation, the parametric oscillator further includes a fourth high-reflectivity mirror and an output coupling mirror; the fourth high-reflectivity mirror is arranged on the third optical axis and is configured to receive the second linearly polarized light beam and reflect idler light and signal light; the output coupling mirror is arranged on the third optical axis and is configured to output the idler light and reflect the signal light; wherein the idler light is the second linearly polarized light beam with a target wavelength, and the signal light is the second linearly polarized light beam with a non-target wavelength.

[0013] In a possible implementation, the fourth high-reflectivity mirror and the output coupling mirror are arranged on two sides of the multi-period crystal, respectively.

[0014] In the above mid-infrared laser, the combination of the high-reflectivity mirror and the output coupling mirror is adopted, and by using specific coating parameters for the high-reflectivity mirror and the output coupling mirror, the parametric oscillator can output only the mid-infrared laser with a specific wavelength required.

[0015] In a possible implementation, the resonant cavity further includes a second quarter-wave plate; the second quarter-wave plate is arranged perpendicularly on the third optical axis and is configured to perform fine adjustment on the polarization direction of the second linearly polarized light beam.

[0016] In the above mid-infrared laser, by arranging the second quarter-wave plate, fine adjustment can be performed on the polarization state change amount when there is a deviation in the polarization state change amount generated by the on-voltage of the electro-optical switch, thereby ensuring the accuracy of the polarization state change amount of the electro-optical switch and improving the efficiency and real-time performance of the output laser of the mid-infrared laser.

[0017] In a possible implementation, the first saturable absorption mirror is further configured to generate the pulse to trigger self-starting of the mid-infrared laser.

[0018] In the above mid-infrared laser, the pulse is generated by the saturable absorption mirror to power on the electro-optic switch, and then trigger self-starting of the mid-infrared laser to generate a picosecond pulse laser.

[0019] In a possible implementation, the mid-infrared laser further includes a first collimating lens and a second collimating lens; the first collimating lens is arranged between the first pump source and the second high-reflectivity mirror along the first optical axis and is configured to convert the first initial light beam into a first collimated parallel light; and the second collimating lens is arranged between the second pump source and the third high-reflectivity mirror along the first optical axis and is configured to convert the second initial light beam into a second collimated parallel light.

[0020] In the above mid-infrared laser, the first initial light beam and the second initial light beam are converted into collimated parallel light by the first collimating lens and the second collimating lens, which can improve the propagation stability of the light beam and further improve the light energy utilization.

[0021] In a possible implementation, the mid-infrared laser further includes a first focusing lens and a second focusing lens; the first focusing lens is arranged between the first collimating lens and the second high-reflectivity mirror along the first optical axis and is configured to focus the first collimated parallel light; and the second focusing lens is arranged between the second collimating lens and the third high-reflectivity mirror along the first optical axis and is configured to focus the second collimated parallel light.

[0022] In the above mid-infrared laser, the light beam is focused by the first focusing lens and the second focusing lens, which further improves the light energy utilization.

[0023] In a possible implementation, the mid-infrared laser further includes a third focusing lens; the third focusing lens is arranged between the polarization beam splitter and the fourth high-reflectivity mirror along the third optical axis and is configured to focus the second linearly polarized light beam.

[0024] In the above mid-infrared laser, the second linearly polarized light beam is focused by the third focusing lens, which reduces the scattering of the second linearly polarized light beam output by the resonant cavity and improves the light energy utilization.

[0025] According to the technical scheme, the application provides a mid-infrared laser, comprising: a pumping module, the pumping module comprising a first pumping source and a second pumping source; the first pumping source is configured to emit a first initial light beam, and the second pumping source is configured to emit a second initial light beam; the first initial light beam and the second initial light beam propagate along a first optical axis, and the propagation directions of the first initial light beam and the second initial light beam are opposite; a resonant cavity, the resonant cavity comprising a first crystal, a second crystal, an optical rotator, a first quarter-wave plate, a first high-reflection mirror, a polarization beam splitter prism, an electro-optic switch, a first saturable absorption mirror, a second high-reflection mirror and a third high-reflection mirror; the first crystal and the second crystal are the same and are isotropic gain media; the first crystal and the second crystal are arranged on the first optical axis; the first crystal is configured to be excited by the first initial light beam emitted by the first pumping source to generate a first light beam; the second crystal is configured to be excited by the second initial light beam emitted by the second pumping source to generate a second light beam; the optical rotator is arranged between the first crystal and the second crystal along the first optical axis and is configured to couple the first light beam and the second light beam to generate an initial state light beam; the first quarter-wave plate is arranged perpendicularly to a second optical axis and is configured to change the phase of the initial state light beam; the second optical axis is perpendicular to the first optical axis; the first high-reflection mirror is arranged on the second optical axis and is configured to cooperate with the optical rotator to generate a first linearly polarized light beam; the polarization beam splitter prism is arranged perpendicularly to a third optical axis and is configured to reflect the first linearly polarized light beam; the third optical axis is perpendicular to the first optical axis; the second high-reflection mirror and the third high-reflection mirror are arranged on the first optical axis at a preset angle; the second high-reflection mirror is configured to reflect the first linearly polarized light beam to the polarization beam splitter prism; the third high-reflection mirror is configured to reflect the initial state light beam to the first quarter-wave plate; the electro-optic switch is arranged on the third optical axis and is configured to change the polarization direction of the first linearly polarized light beam to generate a second linearly polarized light beam; the polarization beam splitter prism is also configured to transmit the second linearly polarized light beam; and the first saturable absorption mirror is arranged on the third optical axis and is configured to reflect the first linearly polarized light beam or the second linearly polarized light beam.

[0026] The mid-infrared laser provided by the application emits two initial light beams through two pumping sources, irradiates the first initial light beam and the second initial light beam to the first crystal and the second crystal respectively to generate first and second light beams with fixed wavelengths, couples the first and second light beams through the optical rotator to offset the thermal-induced birefringence of the first and second crystals, adjusts the phase difference of the coupled light beams through the quarter-wave plate, and forms the first linearly polarized light beam after reflection by the first high-reflection mirror; at this time, the polarization beam splitter prism reflects the first linearly polarized light beam, and the first saturable absorption mirror, the second high-reflection mirror and the third high-reflection mirror cooperate to enable the first linearly polarized light beam to continuously oscillate in the resonant cavity; when the electro-optic switch is started, the first linearly polarized light beam is converted into the second linearly polarized light beam, which is output in one time through the polarization beam splitter prism, so that the mid-infrared laser can output the mid-infrared laser with high efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, for those skilled in the art, other drawings can also be obtained based on these drawings without any creative effort.

[0028] Figure 1 A schematic diagram of a mid-infrared laser;

[0029] Figure 2 A schematic diagram of a mid-infrared laser provided by the embodiments of the present application;

[0030] Figure 3 A schematic diagram of a multi-periodic crystal moving direction provided by the embodiments of the present application.

[0031] Reference signs:

[0032] 101 - first pump source; 102 - second pump source;

[0033] 201 - first crystal; 202 - second crystal; 203 - optical rotator; 204 - first quarter wave plate; 205 - first high reflection mirror; 206 - polarization beam splitter prism; 207 - electro-optical switch; 208 - first saturable absorption mirror; 209 - second high reflection mirror; 210 - third high reflection mirror; 211 - second quarter wave plate; 212 - first collimating lens; 213 - second collimating lens; 214 - first focusing lens; 215 - second focusing lens;

[0034] 301 - multi-periodic crystal; 302 - fourth high reflection mirror; 303 - output coupling mirror;

[0035] 401 - laser diode; 402 - fifth high reflection mirror; 403 - anisotropic crystal; 404 - polarization controller; 405 - first polarization beam splitter; 406 - second polarization beam splitter; 407 - sixth high reflection mirror; 408 - shaping mirror; 409 - output mirror; 410 - second saturable absorption mirror; 411 - seventh high reflection mirror; 412 - eighth high reflection mirror; 413 - PPLN crystal; 414 - coupling mirror;

[0036] A1 - first line segment; A2 - second line segment. DETAILED DESCRIPTION

[0037] The embodiments will be described in detail below with examples shown in the drawings. When the following description refers to the drawings, identical numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following embodiments do not represent all the embodiments consistent with the present application.

[0038] It should be noted that the brief description of the terms in this application is only for the convenience of understanding the embodiments described below, and is not intended to limit the embodiments of the application. Unless otherwise specified, these terms should be understood according to their ordinary and general meanings.

[0039] The terms "first", "second", "third" and the like in the specification and the above drawings in the specification are used to distinguish similar or similar objects or entities, and do not necessarily mean a specific order or sequence, unless otherwise noted. It should be understood that the terms used in this way can be interchanged under appropriate circumstances.

[0040] In order to facilitate the understanding of the technical solutions of the application, the related terms are first explained as follows.

[0041] Laser: It is a kind of optical device that uses the principle of stimulated radiation amplification to generate laser light, which converts external input energy (electric energy, light energy, chemical energy, etc.) into laser beam output with high directionality, monochromaticity, coherence and high brightness. Its basic structure includes: working substance (i.e. gain medium, determines the wavelength of laser), pump source for exciting working substance to make its particle number reverse, and optical resonant cavity composed of reflecting mirror for light amplification and oscillation.

[0042] Linearly polarized light: In the direction of light propagation, the light vector only vibrates along a fixed direction. This kind of light is called plane polarized light, and since the trajectory of the light vector endpoint is a straight line, it is also called linearly polarized light.

[0043] Resonant cavity: Resonant cavity is a cavity in which light waves are reflected back and forth to provide light energy feedback, which is a necessary component of laser, usually composed of two flat or concave spherical mirrors perpendicular to the axis of the working medium.

[0044] The mid-infrared waveband has important applications in many fields such as basic scientific research, biomedical detection, environmental monitoring, national security, security and safety, communication and industrial application. High-performance mid-infrared laser is the key foundation to realize the above applications.

[0045] The mid-infrared laser mainly includes pump source, gain medium and resonant cavity, and its working principle is as follows:

[0046] When the gain medium placed in the resonant cavity is irradiated by the initial light beam emitted by the pump source, photons propagating along the axis of the resonant cavity are generated. The photons are reflected back and forth in the resonant cavity, repeatedly passing through the gain medium, and each time passing through the gain medium, the photons are amplified by stimulated emission. The resonant cavity effectively amplifies light of a specific wavelength and direction and forms a stable oscillation in the cavity. When the light amplification gain is sufficient to overcome the loss in the resonant cavity (such as mirror transmission / absorption / scattering, medium absorption / scattering), a continuous and powerful laser oscillation is formed. When the laser output is needed, the output coupling mirror of the resonant cavity allows a part of the oscillation laser energy to pass through the mirror and exit the cavity, forming a usable mid-infrared laser beam.

[0047] Figure 1 A schematic diagram of a mid-infrared laser.

[0048] In the mid-infrared laser as shown in Figure 1 The laser diode 401 emits laser light for exciting the anisotropic crystal 403, such as neodymium-doped yttrium vanadate (Nd:YVO4). At this time, the anisotropic crystal 403 emits infrared light waves. The infrared light waves are reflected back and forth between the fifth high-reflection mirror 402 and the second saturable absorption mirror 410, forming a closed light path, i.e., a resonant cavity. The second saturable absorption mirror 410 is arranged in the resonant cavity, forcing the infrared light waves in the resonant cavity to act in unison, generating a series of picosecond laser pulses, so that the mid-infrared laser can emit ultra-short and ultra-strong light pulses. In addition, in order to control the timing of laser emission, the resonant cavity is also provided with a polarization controller 404, a first polarization beam splitter 405 and a second polarization beam splitter 406, a sixth high-reflection mirror 407, a shaping mirror 408, an output mirror 409, and a seventh high-reflection mirror 411. The polarization controller 404 can change the vibration direction of the light in the resonant cavity in a very short time. Since the first polarization beam splitter 405 and the second polarization beam splitter 406 can limit the passage or reflection of light of a specific vibration direction, when the polarization controller 404 quickly changes the vibration direction of the light, the first polarization beam splitter 405 and the second polarization beam splitter 406 can control the output of the laser pulse from the resonant cavity at a specific time. At this time, the laser pulse is input to the OPO composed of an eighth high-reflection mirror 412, a coupling mirror 414, and a PPLN crystal 413. The PPLN crystal in the OPO can change the output laser wavelength by changing its temperature, thereby enabling the mid-infrared laser to output a specific wavelength laser.

[0049] However, the above-mentioned mid-infrared laser uses an anisotropic crystal as a gain medium to improve the conversion efficiency of the OPO. However, due to the limitations of the thermal and mechanical properties of the anisotropic crystal, it is prone to thermal effects and cannot accept high-power laser pumping, which reduces the efficiency of the mid-infrared laser output. Moreover, when the OPO adjusts the wavelength of the output laser according to the change in temperature, a large temperature range is required, and the implementation is complex, time-consuming, and resource-consuming.

[0050] In some embodiments, to solve the problem that anisotropic crystals may cause thermal effects, resulting in reduced laser output efficiency, isotropic crystals with better thermal and mechanical properties can be used as gain media. However, due to the lack of natural birefringence of isotropic crystals, it is difficult to directly output linearly polarized light when using isotropic crystals as gain media, which may cause power loss when the light beam runs in the resonant cavity.

[0051] Therefore, to improve the efficiency of the output laser of the mid-infrared laser and improve the speed and convenience of wavelength adjustment, the present application provides a mid-infrared laser. The mid-infrared laser uses two isotropic crystals as gain media, and uses a rotator to offset the thermal-induced birefringence generated by the two isotropic crystals. In addition, a quarter-wave plate is used to adjust the phase difference of the light beams emitted by the isotropic crystals to form a linearly polarized light beam, so as to improve the efficiency of the laser emitted by the mid-infrared laser and reduce power loss.

[0052] Figure 2 A structural schematic diagram of a mid-infrared laser provided by an embodiment of the present application is shown in FIG. 1.

[0053] As shown in FIG. 1, the mid-infrared laser includes a first isotropic crystal 1, a second isotropic crystal 2, a rotator 3, a quarter-wave plate 4, and a wavelength tuning device 5. Figure 2As shown, the mid-infrared laser includes: a pump module, the pump module includes a first pump source 101 and a second pump source 102; the first pump source 101 is configured to emit a first initial light beam, and the second pump source 102 is configured to emit a second initial light beam; the first initial light beam and the second initial light beam propagate along a first optical axis, and the propagation directions of the first initial light beam and the second initial light beam are opposite; a resonant cavity, the resonant cavity includes a first crystal 201, a second crystal 202, an optical rotator 203, a first quarter-wave plate 204, a first high-reflection mirror 205, a polarization beam splitter prism 206, an electro-optical switch 207, a first saturable absorption mirror 208, a second high-reflection mirror 209, and a third high-reflection mirror 210; the first crystal 201 and the second crystal 202 are the same and are isotropic gain media; the first crystal 201 and the second crystal 202 are arranged on the first optical axis; the first crystal 201 is configured to be excited by the first initial light beam emitted by the first pump source 101 to generate a first light beam; the second crystal 202 is configured to be excited by the second initial light beam emitted by the second pump source 102 to generate a second light beam; the optical rotator 203 is arranged between the first crystal 201 and the second crystal 202 along the first optical axis and is configured to couple the first light beam and the second light beam to generate an initial state light beam; the first quarter-wave plate 204 is arranged vertically on a second optical axis and is configured to change the phase of the initial state light beam; the second optical axis is perpendicular to the first optical axis; the first high-reflection mirror 205 is arranged on the second optical axis and is configured to cooperate with the optical rotator 203 to generate a first linearly polarized light beam; the polarization beam splitter prism 206 is arranged vertically on a third optical axis and is configured to reflect the first linearly polarized light beam; the third optical axis is perpendicular to the first optical axis; the second high-reflection mirror 209 and the third high-reflection mirror 210 are arranged on the first optical axis at a preset angle; the second high-reflection mirror 209 is configured to reflect the first linearly polarized light beam to the polarization beam splitter prism 206; the third high-reflection mirror 210 is configured to reflect the initial state light beam to the first quarter-wave plate 204; the electro-optical switch 207 is arranged on the third optical axis and is configured to change the polarization direction of the first linearly polarized light beam to generate a second linearly polarized light beam; the polarization beam splitter prism 206 is also configured to transmit the second linearly polarized light beam; and the first saturable absorption mirror 208 is arranged on the third optical axis and is configured to reflect the first linearly polarized light beam or the second linearly polarized light beam.

[0054] In an implementation, the first pump source 101 and the second pump source 102 emit initial light beams with the same wavelength to the first crystal 201 and the second crystal 202 respectively; wherein the first crystal 201 and the second crystal 202 are the same, isotropic gain medium, after receiving the initial light beams, the first crystal 201 and the second crystal 202 generate the same first light beam and second light beam respectively; the optical rotator 203 couples the first light beam and the second light beam, since the two identical isotropic crystals have similar thermal effects under the condition of receiving the same power pumping, therefore, the initial state light beam after the thermal-induced birefringence is offset can be obtained after the first light beam and the second light beam are coupled by the optical rotator 203; the initial state light beam moves along the optical axis to the first quarter-wave plate 204, the first quarter-wave plate 204 changes the phase of the initial state light beam, after being reflected back to the first quarter-wave plate 204 by the first high reflector 205, the light beam propagates according to the O light and the E light with a phase difference, realizing linear polarization; when the light beam is reflected to the polarization beam splitter prism 206 by the second high reflector 209, the cooperation of the third high reflector 210 and the first saturable absorber 208 will preferentially oscillate the first linearly polarized light reflected by the polarization beam splitter prism 206, since the S light of this polarization direction has extremely low loss, most of the S light is reflected through the polarization beam splitter prism 206, generating laser oscillation; while the P light of the other polarization direction cannot form effective oscillation due to excessive loss, which cannot meet the polarization condition; in the process of S light oscillation, the photons generated by amplification will have the same wavelength, phase and polarization state as the original photons; and since the gain medium is an isotropic crystal, the energy in the gain medium will be extracted as photons with the same phase and polarization state in the process of optical amplification, thereby making the resonant cavity operate linearly polarized laser; when the electro-optical switch 207 is turned on, the polarization direction of the light can be changed, so that the P light forms oscillation in the resonant cavity, at this time, the P light can be output through the polarization beam splitter prism 206, forming a laser beam.

[0055] For example, the first pump source 101 and the second pump source 102 are both 808 nm semiconductor laser diode arrays, emitting initial light beams of 808 nm wavelength. The first crystal 201 and the second crystal 202 are both Nd:YAG crystals of the same size, and both sides of the first crystal 201 and the second crystal 202 are coated with a 1064 nm high-transmittance film structure, and are placed along the first optical axis. The optical rotator 203 is a 90° optical rotator, and is placed along the first optical axis between the first crystal 201 and the second crystal 202, and both ends of the optical rotator 203 are also coated with a 1064 nm high-transmittance film structure. The first quarter-wave plate 204 is placed along the second optical axis perpendicular to the first optical axis at an angle of 90°, and adjusts the phase difference between O light and E light to 90°, and both sides of the first quarter-wave plate 204 are also coated with a 1064 nm high-transmittance film structure. The first high-reflection mirror 205 is placed above the first quarter-wave plate 204 along the second optical axis, and is coated with a 1064 nm high-reflection film structure. The third high-reflection mirror 210 is placed below the first quarter-wave plate 204 along the first optical axis at an angle of 45°, and is coated with a 1064 nm high-reflection film structure. The polarization beam splitter 206 can be vertically placed along the third optical axis perpendicular to the first optical axis, and the four light transmission surfaces thereof are coated with a 1064 nm high-transmittance film. The second high-reflection mirror 209 is placed above the polarization beam splitter 206 along the first optical axis at an angle of 45°, and is coated with a 1064 nm high-reflection film structure. The first saturable absorber mirror 208 is placed on one side of the electro-optical switch 207. The above coating method can make the 1064 nm light beam move in the resonant cavity. The electro-optical switch 207 can be a Pockels cell, which can realize the conversion from S light to P light by changing the applied voltage, and control the laser to emit laser.

[0056] In some embodiments, the mid-infrared laser further comprises a parametric oscillator; the parametric oscillator comprises a multi-period crystal 301; the multi-period crystal 301 is movably arranged on one side of the polarization beam splitter 206 along the third optical axis, and is configured to tune the wavelength of the second linearly polarized light beam.

[0057] In one implementation, the parametric oscillator is arranged on one side of the polarization beam splitter 206 outputting the laser, and after the electro-optical switch 207 is turned on, the P light is emitted to the parametric oscillator through the polarization beam splitter 206. The multi-period crystal 301 in the parametric oscillator can change the wavelength of the incident light by selecting different periods or changing the temperature, to generate a laser of a specific wavelength.

[0058] For example, the multi-period crystal 301 has multiple periods in the transverse direction, such as 27.5 μm, 28.5 μm, 29.5 μm, and 31 μm. It should be understood that the multi-period crystal 301 can also have other periods, which are determined by the preparation method of the multi-period crystal 301.

[0059] In some embodiments, the method for preparing a multi-periodic crystal comprises steps S1-S4:

[0060] Step S1: Prepare a polished high-purity lithium niobate crystal.

[0061] Step S2: Perform photolithography on the lithium niobate crystal.

[0062] In one implementation, a uniform thin film of photoresist is spin-coated on the surface of the lithium niobate crystal; a UV photolithography machine is used to expose different regions of the lithium niobate crystal to light through different masks to form a pattern; an alkaline developer (such as KOH) is used to remove the photoresist in the exposed regions, exposing the surface of the crystal; an electron beam evaporation or magnetron sputtering is used to deposit a metal electrode (such as a Cr / Au bilayer, 100 nm thick) on the patterned surface as a conductive layer for polarization.

[0063] Step S3: Perform high-voltage polarization on the lithium niobate crystal.

[0064] In one implementation, the lithium niobate crystal is placed in a high-temperature environment (100-200°C), and a high-voltage power supply is used to apply a pulsed or direct current electric field; under the action of the direct current electric field, the internal domains of the lithium niobate crystal are periodically inverted according to the electrode pattern, forming alternating polarization regions; the leakage current is monitored in real time to control the polarization process and prevent breakdown; after polarization is complete, the temperature is slowly reduced to room temperature before the electric field is removed, preventing the domain structure from reverting.

[0065] Step S4: Perform post-processing.

[0066] In one implementation, a wet etching method (such as gold etching solution: / solution) is used to remove the metal electrode, leaving a clean crystal surface; low-temperature annealing (400°C for several hours) is performed in an oxygen atmosphere to eliminate stress and defects introduced during the polarization process; the crystal is cut to the desired size according to application requirements, and the end face (such as a bevel or anti-reflection coating) is polished to reduce optical loss.

[0067] The multi-periodic crystal 301 prepared using the above method has multiple periods, and different periods can generate different wavelengths of laser light without changing the temperature. For example, at a temperature of 100°C, selecting a portion of the multi-periodic crystal 301 with a period of 29.5μm to receive incident light can generate a mid-infrared laser with a wavelength of 3.7μm; while also at a temperature of 100°C, selecting a portion of the multi-periodic crystal 301 with a period of 28.5μm to receive incident light can generate a mid-infrared laser with a wavelength of 4μm, improving the efficiency and convenience of adjusting the wavelength of the laser.

[0068] In some embodiments, the parametric oscillator further comprises: a driving motor; the driving motor is in transmission connection with the multi-period crystal 301 and is configured to drive the multi-period crystal 301 to move in a direction perpendicular to the second linearly polarized light beam.

[0069] In an implementation manner, since the multi-period crystal 301 has different periods at different positions in the longitudinal direction, by changing the longitudinal position of the multi-period crystal 301, the purpose of selecting different periods to adjust the output laser wavelength can be achieved. The driving motor is in transmission connection with the multi-period crystal 301, and the driving motor drives the multi-period crystal 301 to move in a direction perpendicular to the second linearly polarized light beam output by the polarization beam splitter prism 206.

[0070] Figure 3 A multi-period crystal moving direction schematic diagram provided for the embodiments of the present application.

[0071] As shown in Figure 3 , the arrow direction of the first line segment A1 is the direction of the laser output by the polarization beam splitter prism 206, and the arrow direction of the second line segment A2 is the moving direction of the multi-period crystal 301. The multi-period crystal 301 moves up and down perpendicular to the laser direction, that is, the period can be changed.

[0072] In some embodiments, the parametric oscillator further comprises: a fourth high-reflective mirror 302 and an output coupling mirror 303; the fourth high-reflective mirror 302 is arranged on the third optical axis and is configured to receive the second linearly polarized light beam, and reflect the idler light and the signal light; the output coupling mirror 303 is arranged on the third optical axis and is configured to output the idler light, and reflect the signal light; wherein the idler light is the second linearly polarized light beam of the target wavelength, and the signal light is the second linearly polarized light beam of the non-target wavelength.

[0073] In an implementation manner, the fourth high-reflective mirror 302 and the output coupling mirror 303 are respectively arranged on both sides of the multi-period crystal 301. The fourth high-reflective mirror 302 is placed on the side of the multi-period crystal 301 close to the polarization beam splitter prism 206, and the output coupling mirror 303 is placed on the other side of the multi-period crystal 301. The fourth high-reflective mirror 302 and the output coupling mirror 303 form a resonant cavity structure, so that the incident laser continuously oscillates in the parametric oscillator.

[0074] Exemplarily, the coating parameters of the fourth high reflectivity mirror 302 are AR@1.064 μm, HR@1.4-1.6 μm & 3-4 μm. The coating parameters of the output coupling mirror 303 are AR@1.064 μm, HR@1.4-1.6 μm, and AR@3-4 μm. The coating parameters of the multi-period crystal 301 at both ends are AR@1.064 μm, 1.4-1.6 μm & 3-4 μm. Through the above coating mode, the parametric oscillator can receive the laser with a wavelength of 1064 nm refracted by the polarization beam splitter 206, and generate and amplify the laser with a wavelength of 3-4 μm belonging to the mid-infrared waveband.

[0075] In some embodiments, the resonant cavity further comprises: a second quarter-wave plate 211; the second quarter-wave plate 211 is arranged vertically on the third optical axis and is configured to perform fine adjustment on the polarization direction of the second linearly polarized light beam.

[0076] In an implementation, since the electro-optical switch 207 needs to change the polarization direction of the first linearly polarized light beam by setting the on-voltage, and then generate the second linearly polarized light beam for output. Therefore, when the laser output is turned on, the voltage of the electro-optical switch 207 needs to be adjusted. In actual application, due to the influence of hardware and other objective conditions, the voltage adjustment may deviate, and therefore the fine adjustment on the polarization direction of the second linearly polarized light beam is performed by changing the angle of the second quarter-wave plate 211.

[0077] Exemplarily, the second quarter-wave plate 211 is arranged between the electro-optical switch 207 and the polarization beam splitter 206, and the two sides are coated with a 1064 nm high-transparency film system.

[0078] In some embodiments, the first saturable absorption mirror 208 is further configured to: generate a pulse to trigger the self-starting of the mid-infrared laser.

[0079] In an implementation, the passive mode-locking can be realized through the first saturable absorption mirror 208 to generate ultra-short pulses, and then realize the cavity emptying in the resonant cavity, so that the laser can output laser with high repetition frequency and narrow pulse width.

[0080] Exemplarily, the first saturable absorption mirror 208 is arranged on the right side of the electro-optical switch 207, and is used for controlling the output of the pulsed laser of the mid-infrared laser.

[0081] In some embodiments, the mid-infrared laser further comprises: a first collimating lens 212 and a second collimating lens 213; the first collimating lens 212 is disposed between the first pump source 101 and the second high-reflective mirror 209 along the first optical axis and is configured to convert the first initial light beam into a first collimated parallel light; the second collimating lens 213 is disposed between the second pump source 102 and the third high-reflective mirror 210 along the first optical axis and is configured to convert the second initial light beam into a second collimated parallel light.

[0082] In an implementation, the first collimating lens 212 is disposed at the output end of the first pump source 101 and the second collimating lens 213 is disposed at the output end of the second pump source 102, so that the first initial light beam and the second initial light beam are converted into the first collimated parallel light and the second collimated parallel light, respectively, which can improve the propagation stability of the light beam and further improve the light energy utilization.

[0083] In some embodiments, the mid-infrared laser further comprises: a first focusing lens 214 and a second focusing lens 215; the first focusing lens 214 is disposed between the first collimating lens 212 and the second high-reflective mirror 209 along the first optical axis and is configured to focus the first collimated parallel light; the second focusing lens 215 is disposed between the second collimating lens 213 and the third high-reflective mirror 210 along the first optical axis and is configured to focus the second collimated parallel light.

[0084] In an implementation, the first focusing lens 214 is disposed at the output end of the first collimating lens 212 to focus the first collimated parallel light, and the second focusing lens 215 is disposed at the output end of the second collimating lens 213 to focus the second collimated parallel light, which further improves the light energy utilization.

[0085] In some embodiments, the mid-infrared laser further comprises: a third focusing lens 216; the third focusing lens 216 is disposed between the polarization beam splitter prism 206 and the fourth high-reflective mirror 302 along the third optical axis and is configured to focus the second linearly polarized light beam.

[0086] In an implementation, the third focusing lens 216 is disposed at the output end of the polarization beam splitter prism 206 to focus the second linearly polarized light beam, which reduces the scattering of the second linearly polarized light beam output by the resonant cavity and improves the light energy utilization.

[0087] According to the above technical scheme, the application provides a mid-infrared laser, comprising: a pumping module, the pumping module comprising a first pumping source 101 and a second pumping source 102; the first pumping source 101 is configured to emit a first initial light beam, and the second pumping source 102 is configured to emit a second initial light beam; the first initial light beam and the second initial light beam propagate along a first optical axis, and the propagation directions of the first initial light beam and the second initial light beam are opposite; a resonant cavity, the resonant cavity comprising a first crystal 201, a second crystal 202, an optical rotator 203, a first quarter-wave plate 204, a first high-reflection mirror 205, a polarization beam splitter prism 206, an electro-optical switch 207, a first saturable absorption mirror 208, a second high-reflection mirror 209, and a third high-reflection mirror 210; the first crystal 201 and the second crystal 202 are the same and are isotropic gain media; the first crystal 201 and the second crystal 202 are arranged on the first optical axis; the first crystal 201 is configured to be excited by the first initial light beam emitted by the first pumping source 101 to generate a first light beam; the second crystal 202 is configured to be excited by the second initial light beam emitted by the second pumping source 102 to generate a second light beam; the optical rotator 203 is arranged between the first crystal 201 and the second crystal 202 along the first optical axis and is configured to couple the first light beam and the second light beam to generate an initial-state light beam; the first quarter-wave plate 204 is arranged perpendicularly to a second optical axis and is configured to change the phase of the initial-state light beam; the second optical axis is perpendicular to the first optical axis; the first high-reflection mirror 205 is arranged on the second optical axis and is configured to cooperate with the optical rotator 203 to generate a first linearly polarized light beam; the polarization beam splitter prism 206 is arranged perpendicularly to a third optical axis and is configured to reflect the first linearly polarized light beam; the third optical axis is perpendicular to the first optical axis; the second high-reflection mirror 209 and the third high-reflection mirror 210 are arranged at a preset angle on the first optical axis; the second high-reflection mirror 209 is configured to reflect the first linearly polarized light beam to the polarization beam splitter prism 206; the third high-reflection mirror 210 is configured to reflect the initial-state light beam to the first quarter-wave plate 204; the electro-optical switch 207 is arranged on the third optical axis and is configured to change the polarization direction of the first linearly polarized light beam to generate a second linearly polarized light beam; the polarization beam splitter prism 206 is further configured to transmit the second linearly polarized light beam; and the first saturable absorption mirror 208 is arranged on the third optical axis and is configured to reflect the first linearly polarized light beam or the second linearly polarized light beam.

[0088] The mid-infrared laser provided in the application emits two initial light beams through two pump sources, irradiates the first initial light beam and the second initial light beam to the first crystal 201 and the second crystal 202 respectively, generates the first light beam and the second light beam with a fixed wavelength, and then couples the first light beam and the second light beam by the optical rotator 203 to offset the thermal-induced birefringence of the first crystal 201 and the second crystal 202; and adjusts the phase difference of the coupled light beam through the first quarter wave plate 204, and forms the first linearly polarized light beam after being reflected by the first high reflection mirror 205; at this time, the polarization beam splitter prism 206 reflects the first linearly polarized light beam, and cooperates with the first saturated absorption mirror 208, the second high reflection mirror 209 and the third high reflection mirror 210 to make the first linearly polarized light beam can continuously oscillate in the resonant cavity. When the electro-optical switch 207 is started, the first linearly polarized light beam is converted into the second linearly polarized light beam, and is output all at once through the polarization beam splitter prism 206, so that the mid-infrared laser can output the mid-infrared laser with high efficiency.

[0089] The similar parts among the embodiments provided in the application can be referred to each other, the specific embodiments provided above are only several examples under the general concept of the application, and do not constitute the limitation of the protection scope of the application. For those skilled in the art, any other embodiments extended according to the application scheme without creative labor are within the protection scope of the application.

Claims

1. A mid-infrared laser, characterized by, The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device.

2. The mid-infrared laser of claim 1, wherein, The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. 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The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application relates to a mid-infrared laser device. The application The multi-period crystal (301) is movably arranged on one side of the polarization beam splitter prism (206) along the third optical axis, and is configured to tune the wavelength of the second linearly polarized light beam.

3. The mid-infrared laser of claim 2, wherein, The parametric oscillator further comprises: a driving motor; The driving motor is in driving connection with the multi-period crystal (301), and is configured to drive the multi-period crystal (301) to move perpendicularly to the direction of the second linearly polarized light beam.

4. The mid-infrared laser of claim 3, wherein, The parametric oscillator further comprises: a fourth high-reflective mirror (302) and an output coupling mirror (303); The fourth high-reflective mirror (302) is arranged on the third optical axis, and is configured to receive the second linearly polarized light beam, and reflect idler light and signal light; The output coupling mirror (303) is arranged on the third optical axis, and is configured to output the idler light, and reflect the signal light; wherein the idler light is the second linearly polarized light beam of a target wavelength, and the signal light is the second linearly polarized light beam of a non-target wavelength.

5. The mid-infrared laser of claim 4, wherein: The fourth high-reflective mirror (302) and the output coupling mirror (303) are arranged on two sides of the multi-period crystal (301), respectively.

6. The mid-infrared laser of claim 1, wherein, The resonant cavity further comprises: a second quarter-wave plate (211); The second quarter-wave plate (211) is arranged perpendicularly on the third optical axis, and is configured to perform fine adjustment on the polarization direction of the second linearly polarized light beam.

7. The mid-infrared laser of claim 1, wherein, The first saturable absorption mirror (208) is further configured to: generate a pulse to trigger self-starting of the mid-infrared laser.

8. The mid-infrared laser of claim 6, wherein, The mid-infrared laser further comprises: a first collimating lens (212) and a second collimating lens (213); The first collimating lens (212) is arranged between the first pump source (101) and the second high-reflective mirror (209) along the first optical axis, and is configured to convert the first initial light beam into first collimated parallel light; The second collimating lens (213) is arranged between the second pump source (102) and the third high-reflective mirror (210) along the first optical axis, and is configured to convert the second initial light beam into second collimated parallel light.

9. The mid-infrared laser of claim 8, wherein, The mid-infrared laser further comprises: a first focusing lens (214) and a second focusing lens (215); The first focusing lens (214) is arranged between the first collimating lens (212) and the second high-reflective mirror (209) along the first optical axis, and is configured to focus the first collimated parallel light; The second focusing lens (215) is arranged between the second collimating lens (213) and the third high-reflective mirror (210) along the first optical axis, and is configured to focus the second collimated parallel light.

10. The mid-infrared laser of claim 4, wherein, The mid-infrared laser further comprises: a third focusing lens (216); The third focusing lens (216) is arranged between the polarization beam splitter prism (206) and the fourth high-reflective mirror (302) along the third optical axis, and is configured to focus the second linearly polarized light beam.

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