Macroenergy inner cavity stimulated Raman laser based on batten structure

Abstract

The invention discloses a large-energy inner cavity stimulated Raman laser based on a batten structure, and belongs to the technical field of lasers. The laser comprises a pumping source, a pumping shaping system, a mixed resonant cavity, a conventional laser medium with a lath structure, a polarization control element, an electro-optic Q-switching element, a stimulated Raman back cavity mirror and a stimulated Raman medium with a lath structure. The laser crystal and the Raman crystal both adopt lath structures, and are welded to the high-heat-dissipation-rate heat sink through gold plating on the upper and lower large surfaces, so that efficient heat dissipation and one-dimensional temperature field distribution are realized, and thermally induced birefringence and depolarization loss are effectively eliminated. The mixing cavity structure is a thermal stable cavity in the thickness direction and an unstable cavity in the width direction, high-efficiency stimulated Raman conversion is achieved by combining the high peak power characteristic in the cavity, the repetition frequency, the light beam quality, the output power and the single pulse energy are remarkably improved, and the laser is suitable for various Raman laser configurations.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lasers, and particularly relates to a high-energy intracavity stimulated Raman laser based on a slab structure. BACKGROUND

[0002] The all-solid-state stimulated Raman laser technology can produce Stokes light with a specific frequency shift through the inelastic scattering of optical phonons and pump photons, thereby significantly expanding the spectral coverage of traditional solid-state lasers. This technology has unique advantages such as Raman beam purification and pulse shortening, and has high conversion efficiency, and has broad application prospects in the fields of laser radar and photoelectric countermeasure. Among them, the intracavity stimulated Raman configuration places the Raman medium in the resonant cavity of the pump laser, and uses the extremely high peak power in the cavity to effectively drive the Raman scattering process, which is a common and efficient technical solution.

[0003] However, the stimulated Raman scattering process is essentially inelastic scattering, and the energy difference between the pump light and the Stokes light will be deposited in the Raman medium in the form of heat. Commonly used stimulated Raman media, such as potassium gadolinium tungstate (KGW), strontium tungstate (SrWO4) and barium nitrate (Ba(NO3)2), etc., have generally low thermal conductivity, which is much lower than that of conventional laser crystals such as Nd:YAG. This low thermal conductivity causes heat to accumulate in the medium, forming a serious temperature gradient and refractive index distribution, i.e. a thermal lens effect. The focal length of this thermal lens is closely coupled with the laser power density in the cavity, making the mode size of the resonant cavity extremely sensitive to parameters such as pump power, and the design is complex and the stability is poor. At the same time, the thermal effect also causes beam distortion, leading to deterioration of the output beam quality.

[0004] In the existing intracavity stimulated Raman laser implementation scheme, the conventional laser medium and the Raman medium usually adopt the traditional rod structure. This structure has limited heat dissipation area, further exacerbating the heat management problem. In order to compensate for the thermal lens effect, existing technologies often need to introduce complex shaping lenses in the resonant cavity, which increases the instability and design difficulty of the system. Therefore, the existing technologies generally have obvious shortcomings such as difficulty in improving the output power and single-pulse energy (usually difficult to break through the level of tens of millijoules), poor beam quality, and poor system stability. Using a rod-shaped medium and a symmetric stable resonant cavity structure, it is difficult to overcome the above inherent defects, which seriously limits the development of high-power, high-energy, and high-beam quality stimulated Raman lasers. SUMMARY

[0005] To address the aforementioned technical problems, this invention provides a high-energy internal cavity stimulated Raman laser based on a slat structure. This successfully eliminates the thermal birefringence of conventional rod-shaped laser media and stimulated Raman media, greatly improving beam quality. Simultaneously, the gold plating on the upper and lower surfaces of the slat structure significantly increases the heat dissipation surface area of ​​the laser and stimulated Raman media. Welding to a high-efficiency heat sink achieves ultra-high heat dissipation efficiency, greatly reducing the difficulty of resonant cavity design and eliminating the need for additional thermally stabilizing lenses.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-energy intracavity stimulated Raman laser based on a slat structure includes the following components arranged sequentially along the optical path:

[0008] Pump source, used to emit pump light;

[0009] A pump-shaping optical system is used to shape the pump light to form an elongated light spot that matches the slat structure;

[0010] The hybrid cavity rear end mirror is used to transmit the shaped pump light;

[0011] A conventional laser medium with a slat structure is used to receive transmitted pump light and generate a 1μm fundamental frequency laser.

[0012] A polarization control element is used to select the polarization of the 1μm fundamental frequency laser.

[0013] Electro-optic Q-switching crystals are used to Q-switch polarization-selected 1μm fundamental frequency lasers to form giant pulses;

[0014] Stimulated Raman spectroscopy is used to transmit the 1μm giant pulse;

[0015] A slatted structured stimulated Raman medium is used to receive transmitted 1μm giant pulses and generate stimulated Raman lasers;

[0016] The hybrid cavity output cavity mirror is used to form a resonant cavity for a 1μm fundamental frequency laser with the hybrid cavity post cavity mirror, and to form a resonant cavity for a stimulated Raman laser with the stimulated Raman post cavity mirror, and to simultaneously output a 1μm fundamental frequency laser and a stimulated Raman laser.

[0017] Both the conventional laser medium and the stimulated Raman medium have a lath structure.

[0018] Furthermore, the pump source is an 808nm diode array.

[0019] Furthermore, the pump-shaping optical system includes a first cylindrical microlens, a second cylindrical microlens, and a Fourier lens arranged sequentially along the optical path, wherein the first cylindrical microlens and the second cylindrical microlens constitute a Kohler illumination array.

[0020] Further, the upper and lower large faces of the conventional laser medium and the stimulated Raman medium are plated with gold and welded to a copper heat sink.

[0021] Further, the resonant cavity formed by the mixed cavity rear mirror and the mixed cavity output mirror is a thermal stable cavity in the direction of the thickness of the slab and a non-stable cavity in the direction of the width of the slab.

[0022] Further, in the direction of the thickness of the slab, the mixed cavity rear mirror and the mixed cavity output mirror are both plane mirrors; in the direction of the width of the slab, the mixed cavity rear mirror is a concave mirror and the mixed cavity output mirror is a convex mirror.

[0023] Further, the polarization control element is a slab structure α-BBO birefringent crystal.

[0024] Further, the electro-optical Q-switching crystal is a slab structure unipolar electro-optical Q-switching crystal, and a voltage reduction type Q-switching working mode is adopted.

[0025] Further, the stimulated Raman rear mirror is plated with a film layer having high transmittance to 1 μm laser and high reflectivity to stimulated Raman laser.

[0026] Further, the ratio of the width to the thickness of the conventional laser medium is 10:1, and the light passing surface is plated with high transmittance films for 808 nm and 1 μm.

[0027] The present application has the following beneficial effects:

[0028] The present application is directed to the technical problems of low thermal conductivity and weak heat load capacity of the stimulated Raman medium, and innovatively proposes a large energy intracavity stimulated Raman laser based on a slab structure. The stimulated Raman material is placed inside the laser resonant cavity, and the high peak power characteristics in the cavity are used to overcome the defect that the 1 μm output power is lower than the stimulated Raman threshold and the wavelength cannot be realized. The laser crystal and the stimulated Raman crystal both adopt a slab structure, and the upper and lower large faces are plated with gold and welded to a high thermal conductivity copper heat sink. The pumping is based on a uniform shaping diode stack, which simultaneously ensures efficient partial end face pumping and one-dimensional temperature field of the laser crystal / stimulated Raman crystal, successfully eliminates thermal induced birefringence and depolarization loss, greatly weakens the thermal lens effect in the thickness direction of the slab, and combines with the one-dimensional mixed cavity structure. The output mirror can synchronously output 1 μm and stimulated Raman laser. This design greatly improves the upper limit of the diode stack pumping injection, overcomes the major defects of the traditional rod intracavity stimulated Raman, greatly improves the repetition frequency, beam quality, output power and single pulse energy (up to dozens of mJ) of the stimulated Raman laser, and can be used as a high reliability, super high volume compactness and excellent performance stimulated Raman light source.

[0029] The present application is applicable to diode stack pulse pumping or continuous pumping condition, although it is a cavity structure, but applicable to all stimulated Raman laser configuration, such as single pass stimulated Raman amplifier, external cavity stimulated Raman or other stimulated Raman coupling form. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a large energy intracavity stimulated Raman laser based on the present application based on the structure of the board view;

[0031] Figure 2 It is a large energy intracavity stimulated Raman laser based on the present application based on the structure of the board side view;

[0032] Figure 3 It is a schematic diagram of diode stack pumping shaping;

[0033] Figure 4 (a) is based on the present application to the slow axis direction of the conventional laser medium pumping shaping profile;

[0034] Figure 4 (b) is based on the present application to the fast axis direction of the conventional laser medium pumping shaping profile.

[0035] Reference signs:

[0036] Diode stack 1, pumping shaping optical system 2, mixed cavity back mirror 3, laser medium 4, α-BBO birefringent crystal 5, single polarity electro-optic Q switching crystal 6, stimulated Raman back mirror 7, stimulated Raman medium 8, mixed cavity output mirror 9, first cylindrical microlens 2-1, second cylindrical microlens 2-2, Fourier lens 2-3. DETAILED DESCRIPTION

[0037] The present application is further illustrated below in conjunction with the drawings and examples.

[0038] The present application is directed to the technical problems of low thermal conductivity and weak thermal load capacity of stimulated Raman medium, and innovatively provides a large-energy intracavity stimulated Raman laser based on a slab structure, wherein the stimulated Raman material is arranged in the laser resonant cavity, and the cavity high peak power characteristics are used to overcome the defect that the 1-micron output power is lower than the stimulated Raman threshold and the wavelength cannot be realized, the laser crystal and the stimulated Raman crystal both adopt the slab structure, the upper and lower large surfaces are gold-plated and welded on the high-heat-dissipation copper heat sink, the diode stack is injected into the laser crystal to realize partial end-pumped laser crystal after homogenization and shaping based on the microlens in the slow axis direction, not only ensuring efficient matching of the diode stack and the resonant cavity mode, but also changing the two-dimensional temperature field distribution into one-dimensional temperature field distribution, which successfully eliminates the thermal birefringence and depolarization loss, the slab structure greatly weakens the thermal lens effect, and the thermal lens only exists in the thickness direction of the slab medium, combined with the one-dimensional hybrid cavity structure, the conventional stimulated emission laser generated by the laser crystal propagates back and forth in the resonant cavity, the power density in the resonant cavity is extremely high, as a new pump source, the stimulated Raman medium is pumped back and forth for many times, which greatly improves the repetition frequency, beam quality, output power and single-pulse energy of the stimulated Raman laser, and the laser has high reliability and super-high volume compactness, and can be used as an excellent stimulated Raman light source.

[0039] As shown in Figures 1-2 The present application provides a large-energy intracavity stimulated Raman laser based on a slab structure, and the overall optical path flow is as follows:

[0040] The 808nm diode stack 1 emits laser as a pump source, and the light beam is shaped by the pump shaping optical system 2 composed of the first cylindrical microlens 2-1, the second cylindrical microlens 2-2 and the Fourier lens 2-3, forming a long strip-shaped spot matched with the slab structure. The shaped pump light passes through the hybrid cavity rear mirror 3, is injected into the slab structure conventional laser medium 4, excites particle inversion, and thus can generate 1-micron wavelength fundamental laser.

[0041] In the resonant cavity composed of the hybrid cavity rear mirror 3 and the hybrid cavity output mirror 9, the 1-micron fundamental laser starts to establish from quantum noise and oscillates back and forth. The 1-micron fundamental laser obtains gain by passing through the slab structure conventional laser medium 4 in turn, is polarized by the slab structure alpha-BBO birefringent crystal 5, is Q-switched by the slab structure unipolar electro-optic Q-switching crystal 6, passes through the stimulated Raman rear mirror 7, and finally enters the slab structure stimulated Raman medium 8.

[0042] When the electro-optic Q-switching crystal 6 works, a 1 μm giant pulse is formed in the cavity. The 1 μm giant pulse laser with high peak power acts as a stimulated Raman pump source, and the stimulated Raman laser is generated in the stimulated Raman resonant cavity composed of the stimulated Raman rear cavity mirror 7 and the mixed cavity output cavity mirror 9 through round-trip oscillation. The pump slab structure stimulated Raman medium 8 is used for generating stimulated Raman scattering, and the stimulated Raman laser passes through the stimulated Raman medium 8 round-trip, and finally the 1 μm fundamental laser and the stimulated Raman laser are synchronously output at the mixed cavity output cavity mirror 9.

[0043] The diode stack 1 is composed of hundreds of diode single tubes arranged in space, and the beam quality in the fast axis direction is better and presents Gaussian distribution, and the beam quality in the slow axis direction is poor and presents incoherent superposition distribution.

[0044] As shown in Figure 3 The pump shaping optical system 2 is used for shaping the outgoing beam of the diode stack 1 into a long strip-shaped spot. The first cylindrical microlens 2-1 and the second cylindrical microlens 2-2 constitute a Kohler illumination array to segment and superimpose the light beams in the slow axis direction; and the Fourier lens 2-3 finally images the spot on the end face of the conventional laser medium 4. After shaping by the system, a uniform flat-top distribution is formed in the slow axis direction at the conventional laser medium 4, and a Gaussian distribution is maintained in the fast axis direction.

[0045] The mixed cavity rear cavity mirror 3 and the mixed cavity output cavity mirror 9 jointly constitute the resonant cavity of the 1 μm fundamental laser. The resonant cavity adopts a special one-dimensional mixed cavity design: in the thickness direction of the slab (the direction in which the thermal lens effect is significant), both the rear cavity mirror and the output cavity mirror are plane mirrors, and the thermal lens effect forms a thermally stable cavity, and the beam waist is located on the surface of the cavity mirror, and the high-order mode is suppressed through diffraction; in the width direction of the slab, the rear cavity mirror 3 is a concave mirror (with a curvature radius R1), and the output cavity mirror 9 is a convex mirror (with a curvature radius R2), and a non-stable cavity structure is formed, and the equivalent output reflectivity is |R2 / R1|.

[0046] The slab structure conventional laser medium 4 adopts a slab configuration with a width to thickness ratio of about 10:1, and the light transmission surface is coated with 808 nm and 1 μm high transmission films. The upper and lower large surfaces are plated with gold and welded to a copper heat sink to achieve high-efficiency heat dissipation.

[0047] The slab structure α-BBO birefringent crystal 5 generates e light walk-off through the birefringent effect, and after being blocked by a mechanical diaphragm, the 1 μm fundamental laser in the resonant cavity becomes linearly polarized light, and the polarization direction matches the optimal polarization direction of the stimulated Raman medium 8.

[0048] The slab structure unipolar electro-optic Q-switching crystal 6 adopts a voltage reduction type Q-switching working mode, and can form a 1 μm giant pulse in tens of nanoseconds to provide a high peak power pump source for the stimulated Raman process.

[0049] The stimulated Raman medium 8 of the slab structure and the stimulated Raman back cavity mirror 7 and the mixed cavity output cavity mirror 9 jointly constitute a stimulated Raman resonant cavity. The stimulated Raman back cavity mirror 7 is plated with a 1 μm high-transparency and stimulated Raman laser high-reflection film layer. The medium also adopts a slab structure, and the upper and lower large surfaces are plated with gold and welded to a copper heat sink.

[0050] The core innovation of the present application is that the conventional laser medium 4 and the stimulated Raman medium 8 both adopt a slab structure, and the uniformization and shaping of the pump light make the temperature field change from three-dimensional distribution to one-dimensional distribution, successfully eliminating the thermal birefringence and depolarization loss, and greatly weakening the thermal lens effect. At the same time, the slab structure provides a large heat dissipation surface area, and the non-steady cavity design ensures that the laser is fully extracted in the gain direction of the slab width. By increasing the slab width, the output energy can be increased to the order of tens of millijoules, while ensuring high beam quality and high reliability.

[0051] As shown in FIGS. 4(a)-4(b), the pump light intensity distribution formed on the end face of the slab structure conventional laser medium 4. In the direction corresponding to the slow axis of the diode stack array, the light intensity distribution is successfully uniformized and shaped into a flat top (flat top) distribution, which ensures that the pump energy is uniformly injected in the slab width direction, which is the key to realizing one-dimensional temperature field distribution in the laser medium and thus eliminating thermal birefringence. In the fast axis direction, the light intensity maintains the original Gaussian distribution, which can achieve good matching with the cavity mode in the slab thickness direction (heat-stable cavity direction) of the resonant cavity, which is beneficial to obtaining high beam quality of the fundamental frequency laser output. This one-dimensional uniformization and one-dimensional Gaussian light field profile is an important basis for realizing the high-performance output of the present application.

[0052] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A high-energy intracavity stimulated Raman laser based on a slat structure, characterized in that, Including those arranged sequentially along the optical path: Pump source, used to emit pump light; A pump-shaping optical system is used to shape the pump light to form an elongated light spot that matches the slat structure; The hybrid cavity rear end mirror is used to transmit the shaped pump light; A conventional laser medium with a slat structure is used to receive transmitted pump light and generate a 1μm fundamental frequency laser. A polarization control element is used to select the polarization of the 1μm fundamental frequency laser. Electro-optic Q-switching crystals are used to Q-switch polarization-selected 1μm fundamental frequency lasers to form giant pulses; Stimulated Raman spectroscopy is used to transmit the 1μm giant pulse; A slatted structured stimulated Raman medium is used to receive transmitted 1μm giant pulses and generate stimulated Raman lasers; The hybrid cavity output cavity mirror is used to form a resonant cavity for a 1μm fundamental frequency laser with the hybrid cavity post cavity mirror, and to form a resonant cavity for a stimulated Raman laser with the stimulated Raman post cavity mirror, and to simultaneously output a 1μm fundamental frequency laser and a stimulated Raman laser. Both the conventional laser medium and the stimulated Raman medium have a lath structure.

2. The high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The pump source is an 808nm diode array.

3. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The pump-shaping optical system includes a first cylindrical microlens, a second cylindrical microlens, and a Fourier lens arranged sequentially along the optical path. The first cylindrical microlens and the second cylindrical microlens constitute a Kohler illumination array.

4. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The conventional laser medium and the stimulated Raman medium are gold-plated on their upper and lower surfaces and soldered to a copper heat sink.

5. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The resonant cavity formed by the hybrid cavity rear mirror and the hybrid cavity output mirror is a thermally stable cavity in the slab thickness direction and an unstable cavity in the slab width direction.

6. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 5, characterized in that, In the thickness direction of the slats, both the rear cavity mirror and the output cavity mirror of the mixing chamber are plane mirrors; in the width direction of the slats, the rear cavity mirror of the mixing chamber is a concave mirror, and the output cavity mirror of the mixing chamber is a convex mirror.

7. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The polarization control element is an α-BBO birefringent crystal with a lath structure.

8. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The electro-optic Q-switching crystal is a unipolar electro-optic Q-switching crystal with a slab structure, and it adopts a step-down Q-switching mode.

9. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The stimulated Raman lasing mirror is coated with a film that is highly transparent to 1μm lasers and highly reflective to stimulated Raman lasers.

10. A high-energy intracavity stimulated Raman laser based on a slat structure according to claim 1, characterized in that, The conventional laser medium has a width-to-thickness ratio of 10:1, and its light-transmitting surface is coated with a high-transmittance film of 808nm and 1μm.

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