A single-frequency diamond single crystal ultraviolet laser

Abstract

The invention discloses a single-frequency diamond single crystal ultraviolet laser, which includes: a laser emitting part, a frequency doubling module, and an "8"-shaped ring cavity Raman and frequency module. The laser emitting part is composed of a pump source, a first beam splitter, and a plane reflector. The pump source is used to emit pump light with a preset power and a preset wavelength; the first beam splitter divides the pump light into two beams; the plane reflector adjusts the optical path direction of the second pump light beam so that it is parallel to and propagates in the same direction as the first pump light beam. The frequency doubling module is composed of a first convex lens, a frequency doubling crystal, and a second convex lens, which realizes the focusing, frequency doubling and shaping of the first pump light beam, and finally injects the frequency doubling light into the ring cavity. The "8"-shaped ring cavity Raman and frequency module is composed of four plano-concave mirrors, a diamond crystal, an F-P standard tool, and a frequency summing crystal, which realizes the Raman conversion of the frequency doubling light, selects the Raman light of the appropriate mode, and frequency sums the Raman light with the second pump light to output single-frequency ultraviolet light.

Description

Technical Field

[0001] The invention relates to the field of all-solid-state ultraviolet lasers, and in particular to a single-frequency diamond single crystal ultraviolet laser. Background Art

[0002] Ultraviolet lasers are widely used in lithography, precision material processing, medical cosmetology, national defense and aerospace, and a variety of advanced technology fields. Among them, solid-state ultraviolet lasers have the advantages of compact structure, good stability, and high output power, which are more conducive to commercialization.

[0003] At present, high-power ultraviolet lasers are mainly generated by nonlinear frequency conversion technology, which requires the pump light to pass through nonlinear crystals multiple times, resulting in low power conversion efficiency and poor beam quality of ultraviolet lasers, which have become common problems. In addition, except for a few ultraviolet laser bands such as 266nm and 355nm, which can produce high-power lasers, many ultraviolet lasers in other bands are generated by tunable pump sources, which makes it difficult to achieve high-power output. Existing lasers are far from achieving full coverage of the ultraviolet light band, and more new ultraviolet wavelength high-power lasers need to be developed.

[0004] In addition, the nonlinear frequency conversion of traditional solid-state ultraviolet lasers makes it difficult to simultaneously achieve high-efficiency, single-frequency and ultraviolet laser output. Summary of the invention

[0005] The present invention provides a single-frequency diamond single crystal ultraviolet laser. The present invention realizes the output of single-frequency ultraviolet wavelength, uses diamond with high thermal stability as Raman gain medium, realizes high beam quality Raman light output, and combines extracavity frequency doubling and intracavity frequency summing technology to finally realize single-frequency ultraviolet laser output. See the following description for details:

[0006] A single-frequency diamond single crystal ultraviolet laser, comprising: a laser emitting unit, a frequency doubling module, an "8"-shaped ring cavity Raman sum frequency module,

[0007] The laser emission part is composed of a pump source, a first beam splitter, and a plane reflector. The pump source is used to emit pump light with a preset power and a preset wavelength. The first beam splitter splits the pump light into two beams. The plane reflector adjusts the optical path direction of the second pump light beam so that it is parallel to the first pump light beam and propagates in the same direction.

[0008] The frequency doubling module is composed of a first convex lens, a frequency doubling crystal, and a second convex lens, which realizes the focusing, frequency doubling, and shaping of the first pump light, and finally injects the frequency doubling light into the annular cavity;

[0009] The "8"-shaped ring cavity Raman sum frequency module consists of four plano-concave mirrors, a diamond crystal, a FP etalon and a sum frequency crystal. It realizes Raman conversion of the doubled frequency light, selects the Raman light of the appropriate mode, sums the Raman light with the second pump light, and outputs single-frequency ultraviolet light.

[0010] Among them, in the "8"-shaped annular cavity, the first input mirror, diamond crystal, FP etalon, and the first plano-concave reflector constitute the upper half of the annular cavity; the second input mirror, sum frequency crystal, and output mirror constitute the lower half of the annular cavity;

[0011] The pump light is split into two beams at the first beam splitter. One beam enters the frequency doubling crystal for frequency doubling, enters the upper part of the ring cavity, causes the diamond crystal to produce stimulated Raman scattering, and outputs first-order Stokes light. It then passes through the FP etalon for mode selection, enters the sum frequency crystal in the lower part of the ring cavity, sums with the other pump light, and is finally output through the output mirror of the ring cavity.

[0012] The second plano-concave reflector reflects the residual pump light to achieve double-pass pumping of the sum frequency crystal;

[0013] The output mirror is coated with a high-reflection film for Raman light, so that the residual Raman light incident on the output mirror circulates in the "8"-shaped ring cavity. The residual Raman light acts as seed light when passing through the diamond crystal, thereby improving the Raman conversion efficiency of the diamond. The output mirror adopts a laser resonant cavity mirror made of piezoelectric ceramics, and utilizes the expansion and contraction characteristics of the ceramic crystal under the action of voltage. The cavity length of the resonant cavity is adjusted through the servo-controlled PDH frequency stabilization technology to achieve single-frequency output.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] 1. The laser uses CVD (chemical vapor deposition) diamond single crystal as Raman crystal, and utilizes the excellent photothermal properties and Raman gain advantages of diamond to efficiently generate Raman light with excellent beam quality in the designed "8" ring cavity, and then combines the extracavity frequency doubling and intracavity sum frequency technology to achieve efficient ultraviolet light output;

[0016] 2. The present invention uses two different special nonlinear crystals, which are used for extracavity frequency doubling and intracavity frequency summing respectively; diamond single crystal is also used for Raman frequency conversion. The above three nonlinear effects are combined to realize the conversion of infrared band to ultraviolet band laser, generating single-frequency ultraviolet light with a specific wavelength;

[0017] 3. The present invention adopts an "8"-shaped ring cavity structure to realize intracavity Raman and intracavity frequency doubling; multiple beam waists are formed in the cavity, so that the diamond crystal used for Raman conversion and the sum frequency crystal used for sum frequency effect can be located at different beam waist positions of the ring cavity, thereby improving the laser power density on the crystal and realizing the improvement of Raman conversion efficiency and sum frequency efficiency;

[0018] 4. The present invention provides a Raman-locked cavity frequency-doubling laser with a ring cavity structure. The structure achieves single-frequency narrow-linewidth ultraviolet output by precisely fine-tuning the cavity length and combining the mode selection of the FP etalon (Fabry-Perot etalon) inserted in the cavity. The present invention achieves narrow-linewidth 372nm ultraviolet wavelength output based on the structure, as described in Examples 1 and 2 for details.

[0019] 5. The present invention adopts a scheme of simultaneously coupling the extracavity pump light and the intracavity Raman light to the nonlinear crystal to realize sum frequency conversion. By accurately adjusting the polarization state of the extracavity pump light through a half-wave plate, better phase matching of the two laser beams can be achieved, thereby enhancing the sum frequency conversion efficiency. In addition, the residual Raman light passing through the nonlinear crystal can be repeatedly circulated in the "8"-shaped ring cavity, which greatly enhances the utilization rate of the Raman light in the sum frequency conversion process and improves the sum frequency conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of a single-frequency diamond single crystal ultraviolet laser.

[0021] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0022] 1: Pump source; 2: First beam splitter;

[0023] 3: first convex lens; 4: frequency doubling crystal;

[0024] 5: second convex lens; 6: first input mirror;

[0025] 7: Diamond crystal; 8: FP etalon;

[0026] 9: first plano-concave reflector; 10: plane reflector;

[0027] 11: half wave plate; 12: third convex lens;

[0028] 13: second input mirror; 14: sum frequency crystal;

[0029] 15: output mirror; 16: fourth convex lens;

[0030] 17: Second plano-concave reflector; 18: Low-pass filter. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0032] In order to overcome the disadvantages of low ultraviolet laser conversion efficiency and poor beam quality in the prior art, the embodiment of the present invention adopts the following technical solution.

[0033] As a Raman crystal, diamond has the advantages of high Raman gain coefficient, wide transmission spectrum range and good thermal stability, and can efficiently generate Stokes photons with a frequency lower than the pump light. In addition, diamond Raman lasers can optimize the beam quality of the pump light, achieving the effects of beam purification and brightness enhancement.

[0034] Laser frequency doubling technology uses the second-order nonlinear effect of nonlinear crystals under strong light to convert laser light with a frequency of ω into frequency doubling light with a frequency of 2ω after passing through the crystal. By selecting nonlinear crystals with large effective frequency doubling polarization coefficients, satisfying the phase matching conditions of nonlinear crystals, and increasing the power density of fundamental frequency light, a higher frequency doubling conversion efficiency can be achieved. In addition, the laser uses active frequency stabilization technology to compare the real-time output frequency with the reference frequency. If the frequency drifts, the error signal is sent to the servo system for feedback control of the laser, so that the output frequency is locked at a certain value. At present, the technology of using a laser resonant cavity mirror composed of PZT (piezoelectric ceramics) through the ring cavity output mirror, using the expansion and contraction characteristics of ceramics under voltage to adjust the resonant cavity length, and realizing single-frequency laser output has been widely used.

[0035] Diamond, which has a beam purification effect, is used as a Raman gain medium to improve the beam quality of the Raman light, thereby improving the beam quality of the output ultraviolet and frequency light.

[0036] Different from the traditional standing wave cavity structure Raman laser, the embodiment of the present invention adopts an "8" ring cavity structure to form multiple beam waists in the cavity, so that both the diamond crystal and the nonlinear crystal can be located at the beam waist position, thereby improving the power density on the crystal and achieving improved Raman conversion efficiency and sum frequency efficiency.

[0037] The scheme of simultaneously coupling the extracavity pump light and the intracavity Raman light to the nonlinear crystal to realize the sum frequency conversion is adopted. By adjusting the polarization state of the extracavity pump light by a half-wave plate, a better match with the intracavity Raman light can be achieved, and the sum frequency conversion efficiency can be enhanced. In addition, the residual Raman light passing through the nonlinear crystal can be repeatedly circulated in the "8" ring cavity, which greatly enhances the utilization rate of Raman light in the sum frequency process and improves the sum frequency conversion efficiency. The structure of the "8" ring cavity also makes the laser system more compact, which is conducive to the miniaturization application of lasers.

[0038] In addition, through the FP standard tool mode selection, the "8" ring cavity output mirror is connected to the servo-controlled frequency locking system to ensure the single-frequency output of ultraviolet light from two aspects.

[0039] Example 1

[0040] See also Figure 1The embodiment of the present invention is provided with a pump source 1, a first beam splitter 2, a first convex lens 3, a frequency doubling crystal 4, a second convex lens 5, a first input mirror 6, a diamond crystal 7, an FP etalon 8, a first plano-concave reflector 9, a plane reflector 10, a half-wave plate 11, a third convex lens 12, a second input mirror 13, a sum frequency crystal 14, an output mirror 15, a fourth convex lens 16, a second plano-concave reflector 17, and a low-pass filter 18.

[0041] The single-frequency diamond single crystal ultraviolet laser of the present invention mainly comprises three parts: a laser emitting part, a frequency doubling module and an "8"-shaped ring cavity Raman and frequency module.

[0042] The laser emitting part is composed of a pump source 1, a first beam splitter 2, and a plane reflector 10. The pump source 1 is used to emit pump light with a preset power and a preset wavelength; the first beam splitter 2 splits the pump light into two beams; the plane reflector 10 adjusts the optical path direction of the second pump light beam so that it is parallel to and propagates in the same direction as the first pump light beam.

[0043] The frequency doubling module is composed of a first convex lens 3, a frequency doubling crystal 4, and a second convex lens 5. It realizes focusing, frequency doubling and shaping of the first pump light, and finally injects the frequency doubling light into the annular cavity.

[0044] The "8"-shaped ring cavity Raman sum frequency module is composed of four plano-concave mirrors (first input mirror 6, first plano-concave reflector 9, second input mirror 13 and output mirror 15), a diamond crystal 7, a FP etalon 8 and a sum frequency crystal 14. It realizes Raman conversion of double frequency light, selects Raman light of appropriate mode, sums Raman light with second pump light, and outputs single-frequency ultraviolet light. The output mirror 15 is connected to an external servo-controlled frequency locking system, which includes PZT piezoelectric ceramics and PDH (Pound–Drever–Hall) controller.

[0045] In the "8"-shaped annular cavity, the first input mirror 6, diamond crystal 7, FP etalon 8, and first plano-concave reflector 9 constitute the upper half of the annular cavity; the second input mirror 13, sum frequency crystal 14, and output mirror 15 constitute the lower half of the annular cavity.

[0046] The pump light is split into two beams at the first beam splitter 2. One beam enters the frequency doubling crystal 4, undergoes frequency doubling, and then enters the upper half of the ring cavity to cause the diamond crystal 7 to produce stimulated Raman scattering and output first-order Stokes light. Then, it is selected by the FP etalon 8 and enters the sum frequency crystal 14 in the lower half of the ring cavity to sum frequency with the other pump light and finally output through the output mirror 15 of the ring cavity.

[0047] The pump source 1 outputs 1064nm near-infrared light, which is split into two beams by the first beam splitter 2. One beam is focused by the first convex lens 3 to the frequency doubling crystal 4 and converted into 532nm frequency doubling light, and then focused by the second convex lens 5, and enters the "8"-shaped ring cavity from the first input mirror 6, and is Raman-converted into 573nm Raman light in the diamond crystal 7. The 573nm Raman light is precisely frequency-selected by the FP etalon 8, and then reflected twice by the first plano-concave reflector 9 and the second input mirror 13, and enters the sum frequency crystal 14.

[0048] Another 1064nm pump light, after changing the transmission direction by the plane reflector 10 and adjusting the polarization direction by the half wave plate 11, is directly focused by the third convex lens 12 to the second input mirror 13, enters the lower half of the ring cavity from the second input mirror 13, and is summed with the 573nm Raman light on the sum frequency crystal 14 to generate 372nm ultraviolet sum frequency light, and finally outputs through the output mirror 15. The remaining 1064nm pump light is reflected by the second plano-concave reflector 17 to achieve double-pass pumping of the sum frequency crystal 14. The output mirror 15 reflects the remaining 573nm Raman light into the "8"-shaped ring cavity, so that the 573nm Raman light passes through the diamond again as the seed light, increasing the Raman conversion efficiency of the diamond single crystal to the 532nm doubled frequency light.

[0049] The fourth convex lens 16 focuses the output light to make it propagate horizontally along a straight line, and the low-pass filter 18 absorbs other residual light except the single-frequency ultraviolet light.

[0050] Example 2

[0051] This embodiment has the same structure as the above-mentioned embodiment 1, and is a supplementary explanation of the parameters of the components in the above-mentioned embodiment 1:

[0052] The pump source 1 outputs a pulsed 1064nm pump light with high peak power; the first beam splitter 2 divides the pump light into two beams; the first convex lens 3 is used to focus the pump light; the frequency doubling crystal 4 is an angle phase-matched LBO (lithium triborate) crystal with a cutting angle θ=90.0° and Φ=11.6°, and both end faces are coated with a broadband dielectric film with a transmittance of >99% for 1064nm and 532nm; the second convex lens 5 focuses the 532nm frequency doubling light so that its beam waist is located at the center of the diamond crystal; the first input mirror 6 is a plano-concave mirror, with a 532nm anti-reflection film coated on the flat surface and a 532nm anti-reflection and 573nm high-reflection film coated on the concave surface; the diamond crystal 7 is a CVD diamond single crystal with a size of 2×2×7mm3, and both end faces are coated with a broadband dielectric film with a transmittance of >99.5% for the 532-573nm band, using <110> The FP standard tool 8 selects 573nm single-frequency Raman light; the first plano-concave reflector 9 is coated with 532nm anti-reflection and 573nm high-reflection film on the concave surface; the plane reflector 10 is coated with 1064nm high-reflection film; the half-wave plate 11 realizes the adjustment of the polarization state of the second pump light; the third convex lens 12 is used to focus the pump light so that its waist position is at the center of the sum frequency crystal; the second input mirror 13 is a plano-concave mirror, the plane is coated with 1064nm anti-reflection film, and the concave surface is coated with 573nm high-reflection and 1064nm anti-reflection film; the sum frequency crystal 14 is an angle phase-matched LBO crystal with a cutting angle of θ = 90.0° and Φ = 34.0°, and the two end faces are coated with broadband dielectric films with a transmittance of > 99% for 1064nm, 573nm and 372nm; the output mirror 15 is a plano-concave mirror, the plane is coated with 1064 The output mirror 15 is a laser resonant cavity mirror made of piezoelectric ceramics, and the cavity length of the resonant cavity is controlled by the expansion and contraction characteristics of the ceramic crystal under the action of voltage, thereby realizing frequency locking; the fourth convex lens 16 is used for output beam shaping; the second plano-concave reflector 17 is coated with a 372nm anti-reflection film on the flat surface, and a 1064nm high-reflection film and a 372nm anti-reflection film on the concave surface, so that the residual 1064nm pump light returns to the annular cavity, realizing double-pass pumping of the sum frequency crystal; the low-pass filter 18 has a transmittance of >90% for wavelengths below 400nm and an absorptivity of >99% for wavelengths above 400nm, and is used to filter out residual lasers of other bands and allow 372nm single-frequency ultraviolet light to pass.

[0053] The embodiment of the present invention uses two LBO crystals as the frequency doubling crystal and the sum frequency crystal respectively, and both adopt type I angle phase matching. Therefore, the angle between the intracavity beam and the LBO crystal will have a significant impact on the phase matching effect. The LBO crystal is placed in a temperature control support to keep the LBO crystal at a constant temperature during laser operation. The angle between the intracavity beam and the LBO crystal can be adjusted by rotating the temperature control support. When adjusted to the optimal position for phase matching, the frequency doubling and sum frequency efficiency can be significantly improved.

[0054] In summary, the embodiment of the present invention proposes a single-frequency ultraviolet Raman laser based on an "8"-shaped ring cavity, which divides the 1064nm laser output by the pump source into two beams, realizes efficient nonlinear frequency conversion through two special LBO crystals and CVD diamond single crystals with different cutting angles, and then combines the FP standard tool and the servo control frequency locking system to achieve high conversion efficiency 372nm single-frequency ultraviolet laser output.

[0055] Unless otherwise specified, the models of the components in the embodiments of the present invention are not limited, and any device that can perform the above functions may be used.

[0056] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A single-frequency diamond single crystal ultraviolet laser, characterized in that: The laser comprises: a laser emitting unit, a frequency doubling module, and an "8"-shaped ring cavity Raman and frequency module. The laser emission part is composed of a pump source, a first beam splitter, and a plane reflector. The pump source is used to emit pump light with a preset power and a preset wavelength. The first beam splitter splits the pump light into two beams. The plane reflector adjusts the optical path direction of the second pump light beam so that it is parallel to the first pump light beam and propagates in the same direction. The frequency doubling module is composed of a first convex lens, a frequency doubling crystal, and a second convex lens, which realizes the focusing, frequency doubling, and shaping of the first pump light, and finally injects the frequency doubling light into the annular cavity; The "8"-shaped ring cavity Raman sum frequency module consists of four plano-concave mirrors, a diamond crystal, a FP etalon and a sum frequency crystal. It realizes Raman conversion of the doubled frequency light, selects the Raman light of the appropriate mode, sums the Raman light with the second pump light, and outputs single-frequency ultraviolet light.

2. The single-frequency diamond single crystal ultraviolet laser according to claim 1, characterized in that: In the "8"-shaped annular cavity, the first input mirror, diamond crystal, FP etalon, and the first plano-concave reflector constitute the upper half of the annular cavity; the second input mirror, sum frequency crystal, and output mirror constitute the lower half of the annular cavity; The pump light is split into two beams at the first beam splitter. One beam enters the frequency doubling crystal for frequency doubling, enters the upper part of the ring cavity, causes the diamond crystal to produce stimulated Raman scattering, and outputs first-order Stokes light. It then passes through the FP etalon for mode selection, enters the sum frequency crystal in the lower part of the ring cavity, sums with the other pump light, and is finally output through the output mirror of the ring cavity.

3. The single-frequency diamond single crystal ultraviolet laser according to claim 1, characterized in that: The second plano-concave reflector reflects the residual pump light to achieve double-pass pumping of the sum frequency crystal; The output mirror is coated with a high-reflection film for Raman light, so that the residual Raman light incident on the output mirror circulates in the "8"-shaped ring cavity. The residual Raman light acts as seed light when passing through the diamond crystal, thereby improving the Raman conversion efficiency of the diamond. The output mirror adopts a laser resonant cavity mirror composed of piezoelectric ceramics, and utilizes the expansion and contraction characteristics of the ceramic crystal under the action of voltage. The cavity length of the resonant cavity is adjusted through the servo-controlled PDH frequency stabilization technology to achieve single-frequency output.

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