A high-energy solid-state ultraviolet laser

Abstract

This application discloses a high-energy solid-state ultraviolet laser, relating to the field of solid-state laser technology. It not only achieves high-energy fundamental frequency light output but also improves frequency doubling efficiency, simplifies the optical path, reduces losses, and enhances system stability and reliability. The laser includes a seed light module, a beam splitter, a first total reflection mirror, a first amplification module, a second amplification module, a second plano-convex mirror, a first half-wave plate, a second half-wave plate, a beam combiner prism, a frequency doubling crystal, and a beam splitter prism. The P-polarized seed light output from the seed light module is split into two paths by the beam splitter. The first path undergoes traveling-wave amplification and polarization state transformation simultaneously through the first total reflection mirror, the first amplification module, the second plano-convex mirror, and the first half-wave plate. The second path undergoes only traveling-wave amplification through the second amplification module and the second half-wave plate. The resulting two orthogonally polarized beams synchronously enter the beam combiner prism. The combined fundamental frequency light then outputs a high-energy ultraviolet laser after passing through the frequency doubling crystal and the beam splitter prism.

Description

Technical Field

[0001] This application relates to the field of solid-state laser technology, and more particularly to a high-energy solid-state ultraviolet laser. Background Technology

[0002] The 300-320nm ultraviolet laser band combines high photon energy with moderate penetration characteristics, making it a core operating band for high-end equipment and cutting-edge scientific research. Its applications cover key scenarios in multiple fields: in medicine, 308nm is the standard wavelength for precise phototherapy of skin diseases such as vitiligo and psoriasis, and it is also used in minimally invasive interventional treatments such as thrombolysis; in industry, it can be used for semiconductor wafer inspection, laser lift-off of flexible devices, high-precision micromachining and grating writing, and is compatible with low-temperature polycrystalline silicon annealing and functional thin film pulsed laser deposition; in scientific research and life sciences, this band is used for ultraviolet Raman spectroscopy, flow cytometry nucleic acid fluorescence excitation, DNA sequencing and precision spectral analysis, and is also indispensable in ultraviolet lithography, material modification, environmental monitoring and optical metrology. The acquisition of 300-320nm ultraviolet laser light mainly involves the following technical approaches: XeCl excimer lasers, with an output wavelength of 308nm, can cover this band, but they have inherent drawbacks such as large size, short lifespan, and high maintenance costs. Meanwhile, multi-stage cascaded nonlinear frequency conversion based on near-infrared laser sources, a solid-state solution, suffers from numerous stages, high energy loss, and poor system stability, making it difficult to achieve high-energy, narrow-pulse-width output at the millijoule level. Furthermore, conventional single-path laser amplification techniques are limited by the thermal lensing effect of the gain medium and the damage threshold of optical components, resulting in limited power enhancement potential. External beam splitting and combining for power expansion easily introduces polarization mismatch and phase fluctuations, further reducing system reliability and hindering the engineering and practical development of 300–320nm ultraviolet laser systems. Summary of the Invention

[0003] The embodiments of this application provide a high-energy solid-state ultraviolet laser, which adopts a scheme of local oscillator beam splitting + independent amplification + polarization beam combining to construct a solid-state 311nm ultraviolet pulsed laser system, realizing high-energy 622nm fundamental frequency light output at the hundred millijoules level, while improving frequency doubling efficiency, simplifying the optical path, reducing loss, and improving system stability and reliability, thus achieving stable output of 311nm ultraviolet laser with narrow pulse width and high energy.

[0004] To achieve the above objectives, embodiments of this application provide a high-energy solid-state ultraviolet laser, comprising a seed light module, a beam splitter, a first total reflection mirror, a first amplification module, a second amplification module, a second plano-convex mirror, a first half-wave plate, a second half-wave plate, a beam combiner prism, a frequency doubling crystal, and a beam splitter prism; the seed light module is capable of outputting 622nm P-polarized seed light; the P-polarized seed light is split into two beams by the beam splitter, and the first beam is reflected by the first total reflection mirror and then sequentially passes through the first amplification module, the second plano-convex mirror, and... The first half-wave plate; the second beam splitter passes sequentially through the second amplification module and the second half-wave plate; the first amplification module can realize the two-way traveling-wave amplification of the first beam splitter and reflect and output its polarization state after flipping from P polarization to S polarization; the second amplification module can realize the two-way traveling-wave amplification of the second beam splitter; the S polarized light emitted from the first half-wave plate and the P polarized light emitted from the second half-wave plate enter the beam combining prism simultaneously; the fundamental frequency light after beam combining passes sequentially through the frequency doubling crystal and the beam splitter prism and outputs high-energy ultraviolet laser.

[0005] Furthermore, the seed light module includes a pump source, a coupling lens group, a first cavity mirror, a gain medium, a Q-switched crystal, a first quarter-wave plate, and a second cavity mirror arranged in sequence. The pump light output from the pump source is shaped and focused by the coupling lens group, then generates fundamental frequency light through the gain medium, is passively Q-switched by the Q-switched crystal to form a narrow pulse, and then becomes P-polarized light through the first quarter-wave plate, which is then output by the second cavity mirror.

[0006] Furthermore, the pump source is a 488nm semiconductor laser; the gain medium is a Pr:YAP crystal; and the Q-switching crystal is a Cr:YAP crystal.

[0007] Furthermore, the first amplification module includes a P-polarization thin film polarizer, a first pump module, a second quarter-wave plate, and a second total reflection mirror arranged sequentially; the first pump module includes a first pump LD bar pair; the first pump LD bar pair is provided with a first amplification crystal; the first amplification crystal is capable of amplifying the seed light generated by the seed light module by a traveling wave.

[0008] Furthermore, the first beam splitter of the beam splitter is perpendicular to the incident light, and the second beam splitter is coaxial with the incident light; the reflected light of the first total reflection mirror is parallel to the incident light of the beam splitter; and the reflected light of the second total reflection mirror is perpendicular to the emitted light of the second magnification module.

[0009] Furthermore, the second amplification module includes a second pump module, a third total reflection mirror, a fourth total reflection mirror, a first plano-convex mirror, and a third pump module arranged sequentially; the second pump module is disposed on the second beam-splitting optical path of the beam splitter, and the third and fourth total reflection mirrors constitute a folding optical path; the second pump module includes a second pump LD bar pair; a second amplification crystal is disposed within the second pump LD bar pair; the third pump module includes a third pump LD bar pair; a third amplification crystal is disposed within the third pump LD bar pair; both the second and third amplification crystals are capable of performing traveling-wave amplification of the seed light generated by the seed light module.

[0010] Furthermore, the first, second, and third amplifying crystals are all Pr:YAP crystals; the operating wavelengths of the first, second, and third pump LD bar pairs are 488 nm.

[0011] Furthermore, the frequency doubling crystal is a BBO crystal; the light-transmitting surface of the BBO crystal is coated with 622nm and 311nm antireflection films, and a type II phase matching method is used to directly generate a 311nm ultraviolet second harmonic through a single nonlinear frequency conversion.

[0012] Furthermore, the aperture of the P-polarized thin film polarizer is Φ30mm; the transmittance of 622nm P-polarized light is >97%; and the reflectance of 622nm S-polarized light is >99%.

[0013] Furthermore, the beam splitter utilizes the dispersion effect to separate the 311nm ultraviolet light from the remaining 622nm fundamental frequency light.

[0014] This application has the following advantages over the prior art: 1. The high-energy solid-state ultraviolet laser in this application splits the laser output from the local oscillator into two independently amplified beams, which are then combined using a specific beam-combining method to ultimately obtain a high-energy 311nm ultraviolet laser. This technical approach can achieve integrated completion of laser beam energy amplification and polarization state conversion without the need for additional polarization control devices, which simplifies the system structure and reduces energy loss and debugging difficulty introduced by the devices.

[0015] 2. The high-energy solid-state ultraviolet laser in this application embodiment has a unique traveling-wave amplification structure. This structure can precisely process the single-polarization laser beam output from the local oscillator: firstly, the single-polarization laser beam is split into two perpendicular beams. One beam undergoes traveling-wave amplification while simultaneously completing a synchronous polarization state conversion; the other beam retains its original polarization state and only undergoes traveling-wave amplification. Through this design, two mutually orthogonal laser beams are ultimately obtained, and the two beams achieve a high degree of matching in terms of spot size, mode, and optical path, laying the foundation for subsequent beam combining and frequency doubling.

[0016] 3. The high-energy solid-state ultraviolet laser in this application embodiment has only one nonlinear frequency doubling, which is simple in structure, easy to debug, highly reliable, and has strong anti-interference ability.

[0017] 4. The high-energy solid-state ultraviolet laser in this application adopts a solid structure, has a long lifespan and small size, and can be directly used in medical, photolithography, precision machining and other scenarios. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the planar structure of a high-energy solid-state ultraviolet laser according to an embodiment of this application.

[0020] Figure 2 This is a three-dimensional structural diagram of a high-energy solid-state ultraviolet laser according to an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "joining" should be interpreted broadly, for example, they can refer to fixed connections, detachable connections, or integral connections; those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" can explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0025] The high-energy solid-state ultraviolet laser of this application adopts a technical approach of splitting and independently amplifying the local oscillator laser beam before combining it. Through the cooperation of various modules and components, a traveling-wave amplification structure is formed, which can split the single-polarized laser beam output from the local oscillator into two beams. One beam undergoes traveling-wave amplification and polarization state conversion at the same time, while the other beam maintains its original polarization state and only undergoes traveling-wave amplification. The orthogonally polarized light formed by the two amplified beams is combined by a beam combining prism to meet the second-type phase matching condition. Then, a high-energy 311nm ultraviolet laser is directly output through a frequency doubling crystal, realizing the integrated completion of laser beam energy amplification and polarization state conversion without the need for additional polarization devices.

[0026] Reference Figure 1 and Figure 2 The high-energy solid-state ultraviolet laser in this application embodiment includes a seed light module 1, a beam splitter 2, a first total reflection mirror 3, a first amplification module 4, a second amplification module 5, a second plano-convex mirror 6, a first half-wave plate 7, a second half-wave plate 8, a beam combiner prism 9, a frequency doubling crystal 10, and a beam splitter prism 11.

[0027] The seed light module 1 is the local oscillator light source of the system, including a pump source 101, a coupling lens group 102, a first cavity mirror 103, a gain medium 104, a Q-switched crystal 105, a first quarter wave plate 106, and a second cavity mirror 107 arranged in sequence.

[0028] The pump source 101 is a 488nm semiconductor laser. The coupling lens group 102 is made of K9 glass with a diameter of Φ20mm and a focal length of f=30mm. The gain medium 104 is a Pr:YAP crystal. The crystal size of the Pr:YAP crystal is 4mm×4mm×25mm. The Q-switching crystal 105 is a Cr:YAP crystal. The crystal size of the Cr:YAP crystal is 4mm×4mm×3mm. The Cr:YAP crystal is a saturable absorber, which can realize passive Q-switching and output nanosecond-level pulses.

[0029] The 488nm laser output from pump source 101 is efficiently coupled to gain medium 104 via coupling lens group 102. The first cavity mirror 103 and the second cavity mirror 107 form a resonant cavity, providing positive feedback. Under pump excitation, gain medium 104 generates a 622nm fundamental frequency laser. The laser is passively Q-switched by Q-switched crystal 105 to form a narrow pulse (stable nanosecond-level pulsed laser). The laser is then calibrated to P-polarization state by the first quarter-wave plate 106. The second cavity mirror 107 outputs a stable 622nm P-polarized seed light, which serves as the common local oscillator source for the two amplified paths. It should be noted that the seed light module can adopt either a resonant cavity structure or a traveling wave oscillation structure, and the output pulse width can be adjusted within a certain range to adapt to different processing and application scenarios.

[0030] Beam splitter 2 is positioned at the output end of seed light module 1 and is coaxial with it. Beam splitter 2 splits the single beam of seed light (P-polarized seed light) into two beams according to a set ratio, forming two independent transmission optical paths. The first beam splitter is perpendicular to the incident light, and the second beam splitter is coaxial with the incident light.

[0031] Beam splitter 2 can be a broadband beam splitter, a polarization-independent beam splitter, or an energy-equalizing beam splitter element to ensure balanced output energy after amplification of the two paths.

[0032] The first beam splitter, after being reflected by the first total reflection mirror 3, passes sequentially through the first magnification module 4, the second plano-convex mirror 6, and the first half-wave plate 7. The second beam splitter passes sequentially through the second magnification module 5 and the second half-wave plate 8. The two beams maintain synchronized timing, consistent mode, and matched optical path.

[0033] The reflected light from the first total reflection mirror 3 is parallel to the incident light from the beam splitter 2. The first amplification module 4 adopts a folded-back two-way amplification structure, which can realize two-way traveling-wave amplification of the first beam splitter and reflect and output its polarization state after flipping it from P polarization to S polarization.

[0034] The first amplification module 4 specifically includes a P-polarization thin film polarizer 401, a first pump module 402, a second quarter-wave plate 403, and a second total reflection mirror 404 arranged sequentially.

[0035] The P-polarized thin-film polarizer 401 exhibits high transmission of P-polarized light and high reflection of S-polarized light, enabling double-pass amplification and polarization state separation. Specifically, the P-polarized thin-film polarizer 401 has an aperture of Φ30mm; its transmittance for 622nm P-polarized light is >97%; and its reflectance for 622nm S-polarized light is >99%.

[0036] The first pump module 402 includes a first pump LD bar pair; the first pump LD bar pair contains a first amplifying crystal 405. The operating wavelength of the first pump LD bar pair is 488nm. The first amplifying crystal 405 is a Pr:YAP crystal with a crystal size of 4mm×4mm×25mm, capable of amplifying the first seed light generated by the seed light module 1 using a traveling wave method. The reflected light from the second total reflection mirror 405 is perpendicular to the incident light from the beam splitter 2.

[0037] P-polarized seed light passes through the P-polarized thin-film polarizer 401 and enters the first amplifying crystal 405. Pump energy is provided by the first pump LD bar to complete the first gain amplification. After being reflected by the second quarter-wave plate 403 and the second total reflection mirror 404, it passes through the first amplifying crystal 405 again to complete the second gain amplification. During the round trip, the polarization state is automatically flipped from P-polarized to S-polarized light and reflected by the P-polarized thin-film polarizer 401, realizing the integration of amplification and polarization conversion.

[0038] It should be noted that the first amplification module 4 can be configured with a single or multiple-stage double-pass amplification structure according to energy requirements, and the number of pump LD bar pairs can be increased or decreased according to gain requirements.

[0039] The second amplification module 5 is a two-way traveling-wave amplification structure, which can realize two-way traveling-wave amplification of the second beam splitter.

[0040] Specifically, the second amplification module 5 includes a second pump module 501, a third total reflection mirror 502, a fourth total reflection mirror 503, a first plano-convex mirror 504, and a third pump module 505 arranged sequentially along the optical path.

[0041] The second pump module 501 is disposed on the second beam-splitting optical path of the beam splitter 2. The second pump module 501 includes a second pump LD bar pair, and a second magnifying crystal 506 is disposed within the second pump LD bar pair.

[0042] The third total reflection mirror 502 and the fourth total reflection mirror 503 form a refracting optical path, that is, the incident light of the third total reflection mirror 502 is parallel to the outgoing light of the fourth total reflection mirror 503.

[0043] The first plano-convex mirror 504 has a diameter of Φ20mm and a focal length of f=60mm.

[0044] The third pump module 505 includes a third pump LD bar pair, and a third amplifying crystal 507 is provided inside the third pump LD bar pair.

[0045] The operating wavelengths of both the second and third pump LD bar pairs are 488nm. The second amplifying crystal 506 and the third amplifying crystal 507 are both Pr:YAP crystals with a crystal size of 4mm×4mm×25mm, capable of amplifying the second seed light generated by the seed light module 1 using a traveling wave amplification.

[0046] The second beam splitter directly enters the second amplification module 5, passing sequentially through the second amplification crystal 502, the third total reflection mirror 503, and the fourth total reflection mirror 504 to form a two-way traveling-wave amplification. Pump energy is provided by the second pump LD bar pair 501 and the third pump LD bar pair 506. Beam coupling, spot shaping, divergence angle calibration, and thermal lensing effect compensation are achieved through the first plano-convex mirror 505 positioned between the two amplification stages, ensuring a high degree of matching between the output beam and the first beam splitter in terms of aperture, mode, and position. This optical path maintains its original P-polarization characteristics unchanged during the amplification process.

[0047] It should be noted that the first plano-convex lens 504 in the second magnification module 5 can be replaced with a cemented lens, an aspherical lens, or a lens group to further improve beam quality and coupling efficiency.

[0048] The second plano-convex mirror 6 has a diameter of Φ25mm and a focal length of f=50mm.

[0049] The S-polarized light output from the first amplification module 4 is adjusted in beam width and divergence angle by the second plano-convex mirror 6, and then polarized locked by the first 1 / 2 wave plate 7 to ensure that the output is stable S-polarized light.

[0050] The P-polarized light output from the first amplification module 5 is polarized locked by the second half-wave plate 8 to ensure that the output is stable P-polarized light.

[0051] After polarization locking, the two beams form strictly orthogonal linearly polarized beams, satisfying the injection conditions for type II phase matching in BBO.

[0052] It should be noted that the first half-wave plate 7 and the second half-wave plate 8 can both be zero-level wave plates, multi-level wave plates, or temperature-controlled wave plates to adapt to different working environments and long-term stability requirements.

[0053] Two orthogonally polarized beams are simultaneously incident on the beam combiner prism 9. Utilizing polarization selection characteristics, efficient and lossless beam combining is achieved, synthesizing a high-energy, high-brightness 622nm fundamental frequency beam. It should be noted that because the spot size, mode, and optical path of the two beams are highly matched before beam combining, the beam combining efficiency is high and there is no additional loss.

[0054] The combined fundamental frequency light is directly incident on the frequency doubling crystal 10. The frequency doubling crystal 10 is a BBO crystal, which operates in a type II phase-matched state. It directly converts the 622nm fundamental frequency light into 311nm ultraviolet light through a single nonlinear frequency doubling, without going through multiple cascaded frequency conversions.

[0055] Specifically, the light-transmitting surface of the BBO crystal is coated with a 622nm / 311nm anti-reflection film, and the dimensions of the BBO frequency doubling crystal 10 are 6mm×6mm×12mm.

[0056] It should be noted that BBO frequency doubling crystals can be selected with different cutting angles, different light transmission lengths, and different temperature control schemes according to power level and matching conditions to achieve the best frequency doubling efficiency.

[0057] The frequency-doubled mixed light enters the beam splitter 11, which uses wavelength dispersion characteristics to separate the 311nm ultraviolet light from the remaining 622nm fundamental frequency light, and finally outputs a pure, high-energy, narrow-pulse 311nm ultraviolet pulsed laser.

[0058] The beam splitting output section can be equipped with filters, apertures, beam pointing stabilization components, or energy monitoring modules to improve the purity, stability, and safety of the output laser.

[0059] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-energy solid-state ultraviolet laser, characterized in that, It includes a seed light module, a beam splitter, a first total reflection mirror, a first magnification module, a second magnification module, a second plano-convex mirror, a first half-wave plate, a second half-wave plate, a beam combiner prism, a frequency doubling crystal, and a beam splitter prism; The seed light module can output 622nm P-polarized seed light; the P-polarized seed light is split into two beams by a beam splitter. The first beam is reflected by the first total reflection mirror and then passes through the first amplification module, the second plano-convex mirror and the first half-wave plate in sequence. The second beam splitter passes through the second amplification module and the second half-wave plate in sequence; the first amplification module can realize the two-way traveling wave amplification of the first beam splitter and reflect and output its polarization state after flipping it from P polarization to S polarization. The second amplification module can realize two-way traveling-wave amplification of the second beam splitter; The S-polarized light emitted from the first half-wave plate and the P-polarized light emitted from the second half-wave plate enter the beam combiner prism simultaneously. After the fundamental frequency light is combined, it passes through a frequency doubling crystal and a beam splitter in sequence before being output as a high-energy ultraviolet laser.

2. The high-energy solid-state ultraviolet laser according to claim 1, characterized in that, The seed light module includes a pump source, a coupling lens group, a first cavity mirror, a gain medium, a Q-switched crystal, a first quarter-wave plate, and a second cavity mirror arranged in sequence. The pump light output from the pump source is shaped and focused by the coupling lens group, then generates fundamental frequency light through the gain medium, is passively Q-switched by the Q-switched crystal to form a narrow pulse, and then becomes P-polarized light through the first quarter-wave plate, which is then output by the second cavity mirror.

3. The high-energy solid-state ultraviolet laser according to claim 2, characterized in that, The pump source is a 488nm semiconductor laser; the gain medium is a Pr:YAP crystal; and the Q-switching crystal is a Cr:YAP crystal.

4. The high-energy solid-state ultraviolet laser according to claim 1, characterized in that, The first amplification module includes a P-polarization thin film polarizer, a first pump module, a second quarter-wave plate, and a second total reflection mirror arranged sequentially; the first pump module includes a first pump LD bar pair; the first pump LD bar pair contains a first amplification crystal; the first amplification crystal is capable of amplifying the seed light generated by the seed light module by a traveling wave.

5. The high-energy solid-state ultraviolet laser according to claim 4, characterized in that, The first beam splitter of the beam splitter is perpendicular to the incident light, and the second beam splitter is coaxial with the incident light; the reflected light of the first total reflection mirror is parallel to the incident light of the beam splitter; the reflected light of the second total reflection mirror is perpendicular to the output light of the second magnification module.

6. The high-energy solid-state ultraviolet laser according to claim 5, characterized in that, The second amplification module includes a second pump module, a third total reflection mirror, a fourth total reflection mirror, a first plano-convex mirror, and a third pump module arranged sequentially. The second pump module is located on the second beam-splitting optical path of the beam splitter, and the third and fourth total reflection mirrors form a folding optical path. The second pump module includes a second pump LD bar pair. A second amplifying crystal is disposed within the second pump LD bar pair. The third pump module includes a third pump LD bar pair. A third amplifying crystal is disposed within the third pump LD bar pair. Both the second and third amplifying crystals can amplify the seed light generated by the seed light module using a traveling wave amplification.

7. The high-energy solid-state ultraviolet laser according to claim 6, characterized in that, The first, second, and third amplifying crystals are all Pr:YAP crystals; the operating wavelengths of the first, second, and third pumped LD bar pairs are 488 nm.

8. The high-energy solid-state ultraviolet laser according to claim 1, characterized in that, The frequency doubling crystal is a BBO crystal; the light-transmitting surface of the BBO crystal is coated with 622nm and 311nm anti-reflection films, and a type II phase matching method is used to directly generate the 311nm ultraviolet second harmonic through a single nonlinear frequency conversion.

9. The high-energy solid-state ultraviolet laser according to claim 4, characterized in that, The P-polarized thin film polarizer has an aperture of Φ30mm; the transmittance of 622nm P-polarized light is >97%; and the reflectance of 622nm S-polarized light is >99%.

10. The high-energy solid-state ultraviolet laser according to claim 1, characterized in that, The beam splitter uses the dispersion effect to separate the 311nm ultraviolet light from the remaining 622nm fundamental frequency light.

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