CN205405031U - Have ultraviolet laser converter of non -critical phase matching doubling of frequency, frequency tripling performance concurrently - Google Patents

Abstract

The utility model relates to an ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance, comprising a fundamental frequency light source, a beam shrinking system, a first reflector, a nonlinear optical crystal, and a quarter wave plate , the second reflector and the filter plate, the angle bisector of the X-axis and the Z-axis of the nonlinear optical crystal, and the included angle of the polarization direction of the fundamental frequency light is 0-5°, and the direction of the optical axis of the quarter-wave plate and The included angle of the polarization direction of the fundamental frequency light is 0-5°; the included angle between the first reflector and the central axis of the optical path is 35-55°; the nonlinear optical crystal is Gd _x Y _1-x COB crystal, when the fundamental frequency When the light wavelength is 1064nm, the value range of x is 0.18-0.22, and when the fundamental frequency light wavelength is 1053nm, the value range of x is 0.11-0.15. The utility model enables a piece of Gd _x Y _1-x COB to be used as a frequency doubling and triple frequency crystal at the same time, and the production cost is low.

Description

An Ultraviolet Laser Frequency Converter with Non-Critical Phase Matching Frequency Doubling and Tripling Performance

technical field

The utility model relates to an ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performances, which belongs to the technical field of laser and nonlinear optics.

Background technique

Lasers play an increasingly important role in modern technology. Among them, all-solid-state ultraviolet lasers have very important applications in the fields of laser micromachining (drilling, cutting and corrosion), laser chemistry, optical engraving, rapid prototyping, laser printing and spectroscopy. Since the wavelengths of practical solid-state lasers are mostly in the infrared spectral region, in order to obtain ultraviolet light, it is necessary to use nonlinear optical crystals to convert the frequency of infrared lasers. This method has high efficiency, good beam quality, small volume, high stability and long life. Etc. At present, the most commonly used technical route is to triple the frequency of Nd-doped YAG or Nd glass laser (1064nm/1053nm) to obtain 355nm/351nm UV output. This process consists of two steps: first, use a nonlinear optical The crystal doubles the frequency of the infrared fundamental frequency light, and the generated frequency doubled green light (532nm/526nm) and the remaining fundamental frequency light are then neutralized in another nonlinear optical crystal to finally achieve 355nm/351nm ultraviolet light output. As shown in Fig. 1(a), two crystals are used as frequency-doubling and frequency-tripling crystals respectively. At present, commonly used frequency-doubling crystals are KH ₂ PO4 (KDP), KTiOPO ₄ (KTP) and LiB ₃ O ₅ (LBO), and frequency-tripling crystals are KDP, LBO and β-BaB ₂ O ₄ (BBO). Even if the same crystal is used for frequency doubling and frequency tripling, since the phase matching directions are different, the space cutting angles are different. Therefore, it is inevitable to use two crystals, which greatly increases the cost of raw materials and processing.

In order to realize a nonlinear crystal directly output tripled frequency light, two key problems must be solved. (1) Find a suitable Gd _x Y _1-x COB crystal, that is, determine the composition parameter x. (2) Satisfy the requirements of the phase matching method on the polarization state. From a theoretical point of view, even if a suitable crystal composition is found to adjust the phase matching direction of frequency doubling and triple frequency to the Y axis of the Gd _x Y _1-x COB crystal, if the polarization state of the frequency doubling light is not adjusted, the Triple frequency light cannot be output. The reason is that the polarization direction of the frequency-doubled light generated by type II non-critical phase matching is along the X-axis (fast axis direction) of the crystal, while the triple frequency of type I non-critical phase matching requires the polarization direction of the frequency-doubled light to be along the Z-axis (slow axis) of the crystal. axis direction).

Gd _x Y _1-x Ca ₄ O(BO ₃ ) ₃ (Gd _x Y _1-x COB) series borate crystals are a substitutional solid solution whose refractive index can change continuously, and thus can realize non-critical phase matching wavelength Continuously adjustable. This type of crystal has the advantages of moderate effective nonlinear optical coefficient, wide light transmission band, high laser damage threshold, large phase matching range, no deliquescence and stable physical and chemical properties. It is a kind of nonlinear optical crystal with excellent performance and has wide applications. prospect. The research shows that along the Y axis of Gd _x Y _1-x COB series crystals, that is, the (90°, 90°) phase matching direction, non-critical phase matching type II frequency doubling and I Tripling-like and very close to crystal compositions that achieve non-critical phase-matched frequency doubling and tripling.

Contents of the invention

Aiming at the deficiencies of the prior art, the utility model provides an ultraviolet laser frequency converter with non-critical phase-matching frequency doubling and frequency tripling performances.

The utility model uses a crystal to first realize non-critical frequency multiplication and then non-critical triple frequency to obtain 355nm/351nm ultraviolet light output. The utility model has low cost, small volume, convenient processing, and is convenient for large-scale popularization.

Terminology Explanation

1. Phase matching: In the process of nonlinear optical frequency conversion, the incident light wave generates harmonic polarized waves where it passes. These harmonic polarized waves propagate in the crystal and interfere with each other. The result is the measured harmonic total strength. This intensity is related to the harmonic phase difference generated by each position. If the phase difference is zero, that is, the phase is consistent, the harmonics will be effectively strengthened; if the phase difference is inconsistent, the harmonics will cancel each other out; even no harmonics can be observed at all. output. Obviously, only when the propagation speed of the incident light wave is equal to the propagation speed of the harmonic, the harmonics generated at each position in the crystal can strengthen each other because of the phase coincidence, which is called phase matching. In principle, there are two types of phase matching for the three-wave interaction in nonlinear optical crystals: the light wave with frequency ω ₁ and the light wave with frequency ω ₂ have the same linear polarization, and the phase matching is type I; otherwise, the light wave ω ₁ With an orthogonal linear polarization to the light wave ω, the phase match is type _II .

2. Non-critical phase matching (NCPM): For biaxial crystals, it refers to the phase matching along the main axis of the refractive index, and the phase matching in other cases is called critical phase matching (CPM). Compared with CPM, NCPM has the advantages of large tolerance angle, zero walk-off angle and high crystal utilization, so it is also called optimal phase matching.

3. Frequency doubling (SHG): Optical frequency doubling, also known as optical second harmonic, refers to the transformation of the fundamental frequency light with a frequency of ω into a frequency doubled light of 2ω due to the interaction between light and a nonlinear medium (usually a crystal). The phenomenon.

4. Triple frequency (THG): Triple frequency is also called optical third harmonic, which refers to the interaction between the fundamental frequency light with a frequency of ω and the frequency doubled light with a frequency of 2ω in the crystal to become light with a frequency of 3ω. Phenomenon.

5. Wave plate: An optical device that can generate an additional optical path difference (or phase difference) between two mutually perpendicular optical vibrations. Usually made of a birefringent wafer of precise thickness, such as quartz, calcite, or mica, with the optical axis parallel to the wafer surface.

6. Quarter wave plate: a birefringent single crystal sheet with a certain thickness. When the normal incident light passes through, the phase difference between ordinary light (o light) and extraordinary light (e light) is equal to π/2 or its odd multiple, such a wafer is called a quarter wave plate or 1/ 4 wave plates. When the angle θ between the incident vibration plane of the polarized light and the optical axis of the wave plate is 45°, the linearly polarized light passing through the quarter wave plate becomes circularly polarized light, otherwise, when the circularly polarized light passes through the quarter wave plate After the film, it becomes linearly polarized light. When light passes through the quarter-wave plate twice, it acts like a half-wave plate.

7. Half-wave plate: a birefringent crystal sheet with a certain thickness. When the normal incident light passes through, the phase difference between ordinary light (o light) and extraordinary light (e light) is equal to π or its odd multiple, such a wafer is called a half wave plate or 1/2 wave film, referred to as half-wave film. After the linearly polarized light passes through the half-wave plate, it is still linearly polarized light, but the vibration plane of the outgoing polarized light and the vibration plane of the incident polarized light are rotated by 2θ. If θ=45°, the vibration plane of the outgoing light is perpendicular to the vibration plane of the original incident light, that is, when θ=45°, the half-wave plate can rotate the polarization state by 90°.

The technical scheme of the utility model is:

An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance, including fundamental frequency light source, beam shrinking system, first reflector, nonlinear optical crystal, quarter wave plate, second reflector mirror and filter, the beam shrinking system, the first reflector, the nonlinear optical crystal, the quarter-wave plate, and the second reflector are arranged along the optical path from left to right, and the filter is arranged on the first Directly below a reflecting mirror; the angle bisector of the X-axis and Z-axis of the nonlinear optical crystal and the polarization direction of the fundamental-frequency light produced by the fundamental-frequency light source are at an angle of 0-5°, and the quarter The angle between the optical axis direction of the wave plate and the polarization direction of the fundamental frequency light produced by the fundamental frequency light source is 0-5 °; the angle between the first reflector and the central axis of the optical path is 35-55 °; The linear optical crystal is Gd _x Y _1-x COB crystal. When the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1064nm, the value range of x is 0.18-0.22. When the fundamental frequency light wavelength emitted by the fundamental frequency light source is 1053nm , the value range of x is 0.11-0.15.

The fundamental frequency light source generates fundamental frequency light, and the fundamental frequency light passes through the beam shrinkage system to increase the power density of the incident fundamental frequency light, and the incident fundamental frequency light passes through the first reflector and enters the nonlinear optical crystal, where Type II frequency doubling effect occurs in the middle, the generated frequency doubling light and the remaining fundamental frequency light pass through the quarter wave plate, enter the second reflector, return according to the original optical path after total reflection, and pass through the quarter wave plate for the second time The wave plate enters the nonlinear crystal again, through the polarization rotation of the quarter wave plate, the frequency doubled light interacts with the Z-axis component of the remaining fundamental frequency light, and a type I triple frequency occurs, resulting in triple frequency ultraviolet light It is reflected by the first reflector, and then the remaining fundamental frequency light and frequency doubled light are filtered out by a filter, and a pure ultraviolet laser is output. In this way, the polarization direction of the frequency-doubled light is adjusted by the introduction of the quarter-wave plate, while the polarization direction of the fundamental frequency light remains unchanged, thereby realizing ultraviolet laser output.

Gd _x Y _1-x COB crystals have consistent melting properties, can be grown in large size by pulling method, and have high optical quality. After batching according to the stoichiometric ratio, the materials are mixed and fired, and then the sintered polycrystalline material is put into an iridium crucible, and a high-temperature single crystal pulling furnace is used for growth to grow into a Gd _x Y _1-x COB single crystal. Crystals are oriented along the optical axis, cut, polished, and coated along the Y axis. Therefore, the quasi-crystal grows with the seed crystal in the Y direction, so the utilization rate of the crystal is high.

Preferably according to the present invention, the angle bisector of the X-axis and the Z-axis of the nonlinear optical crystal is parallel to the polarization direction of the fundamental-frequency light generated by the fundamental-frequency light source, and the direction of the optical axis of the quarter-wave plate is parallel to The polarization direction of the fundamental frequency light generated by the fundamental frequency light source.

Preferably according to the present invention, the included angle between the first reflecting mirror and the central axis of the optical path is 45°.

Preferably according to the present invention, when the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1064nm, x=0.2; when the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1053nm, x=0.13.

Preferably according to the present invention, the ultraviolet laser frequency converter also includes a temperature control system and an electric rotating platform, the temperature control system includes a temperature control box, the nonlinear optical crystal is arranged in the temperature control box, and the The electric rotating platform is arranged under the temperature control box.

The advantage of the design here lies in the setting of the temperature control system and the electric rotating platform in order to find the best temperature and the best phase matching direction to obtain greater UV light output.

Preferably according to the utility model, the temperature control accuracy of the temperature control system is ±0.1°C, and the two optical end faces of the temperature control box are provided with quartz glass with high transparency to the ultraviolet-infrared wide spectrum; the electric rotating platform The rotation accuracy is 0.00125°. Quartz glass prevents heat from spreading and acts as an insulator.

Preferably according to the present invention, the beam reduction system includes a first plano-convex lens and a second plano-convex lens with different focal lengths;

The fundamental frequency light source is a Nd:YAG mode-locked laser;

The first reflector is coated with a dielectric film that is highly transparent to 1064nm and 532nm lasers and highly reflective to 355nm ultraviolet light;

The second mirror is coated with a dielectric film that fully reflects the 1064nm and 532nm lasers;

The nonlinear optical crystal is a Y-cut Gd _0.2 Y _0.8 COB. The nonlinear optical crystal is oriented according to the axis X, Y, and Z of the refractive index, and the size is 10mm×10mm×5mm. The two Y-direction light-transmitting surfaces are polished and Coated with 1064nm, 532nm, 355nm triple frequency anti-reflection coating; Y-cut Gd _0.2 Y _0.8 COB means: the direction of light transmission is the Y-axis, cutting and polishing along the plane perpendicular to the Y-axis of the crystal;

The quarter-wave plate is a 532nm mica quarter-wave plate;

The filter is made of quartz, coated with a dielectric film with high reflection to 1064nm and 532nm lasers and high transparency to 355nm lasers.

Preferably, according to the present invention, a Faraday rotator is arranged between the fundamental frequency light source and the beam reduction system;

The beam reduction system includes a first plano-convex lens and a second plano-convex lens with different focal lengths;

The fundamental frequency light source is a neodymium glass mode-locked laser;

The first mirror is coated with a dielectric film with high transparency to 1053nm and 526nm lasers and high reflection to 351nm ultraviolet light;

The second mirror is coated with a dielectric film that fully reflects the 1053nm and 526nm lasers;

The nonlinear optical crystal is a Y-cut Gd _0.13 Y _0.87 COB. The nonlinear optical crystal is oriented according to the X, Y, and Z axes of the main axes of refractive index, and the size is 12nm×16mm×29mm. The two Y-direction light-transmitting surfaces are polished and Coated with 1053nm fundamental frequency, 526nm frequency doubling, 351nm triple frequency anti-reflection coating; Y-cut Gd _0.13 Y _0.87 COB means: the direction of light transmission is the Y-axis, cutting and polishing along the plane perpendicular to the Y-axis of the crystal;

The quarter-wave plate is a 526nm mica quarter-wave plate;

The filter is made of quartz, coated with a dielectric film with high reflection to 1053nm and 526nm lasers and high transparency to 351nm lasers.

The working method of the above-mentioned ultraviolet laser frequency converter, the specific steps include:

(1) The fundamental-frequency light source generates fundamental-frequency light; ensure that its polarization direction is parallel to the angle bisector of the X-axis and Z-axis of the crystal and the direction of the optical axis of the quarter-wave plate.

(2) The fundamental frequency light passes through the beam shrinkage system, passes through the first reflector, enters the nonlinear optical crystal, and class II frequency doubling occurs in the nonlinear optical crystal, resulting in a polarization direction located at X The frequency doubled light of the axis and the remaining fundamental frequency light pass through the quarter wave plate, because the polarization direction of the fundamental frequency light is parallel to the optical axis of the wave plate, so the polarization direction of the fundamental frequency light remains unchanged, and the frequency doubled light is due to its polarization direction The included angle with the optical axis of the wave plate is 45°, from linearly polarized light to circularly polarized light, incident to the second reflector, and returning according to the original optical path after total reflection;

(3) After passing through the quarter-wave plate for the second time, the polarization direction of the fundamental frequency light remains unchanged, but the frequency-doubled light passes through the quarter-wave plate twice, and the quarter-wave plate acts as a half-wave plate at this time function, the polarization direction of the frequency-doubled light rotates 90° on the Z axis of the crystal, the frequency-doubled light and the fundamental frequency light enter the nonlinear crystal again, and through the polarization rotation of the quarter-wave plate, the Z of the frequency-doubled light and the remaining fundamental frequency light The axial components interact to generate a class I triple frequency, and the generated triple frequency ultraviolet light is reflected by the first mirror, and then the remaining fundamental frequency light and frequency double light are filtered out by a filter, and a pure ultraviolet laser is output.

The beneficial effects of the utility model are:

The utility model solves the polarization matching problem of triple frequency through a quarter wave plate, so that a piece of Gd _x Y _1-x COB can be used as a frequency double and triple frequency crystal at the same time. The optical components such as the quarter-wave plate used have been developed and mature, and are easy to purchase in the market, and the price is far lower than that of nonlinear crystals. Therefore, the production cost is far lower than three times that of using two nonlinear crystals at present. Frequency devices, and more convenient processing and assembly. At the same time, the characteristics of non-critical phase matching also make the crystal material utilization rate of the device high, and the large tolerance angle reduces the requirements on the quality of the fundamental frequency light beam, improves the output stability, and is conducive to large-scale production and application.

Description of drawings

Figure 1(a) is a schematic diagram of an existing triple frequency implementation;

In Figure 1(a), a nonlinear optical crystal is used to double the frequency of the infrared fundamental frequency light ω first, and the frequency doubled light 2ω generated and the remaining fundamental frequency light ω are neutralized in another nonlinear optical crystal, and finally Achieve UV 3ω output.

Fig. 1 (b) is the schematic diagram of the triple frequency realization mode of the present invention;

In Figure 1(b), after the frequency doubling occurs, the polarization state of the frequency-doubled light is changed through the quarter-wave plate, and then passes through the quarter-wave plate and the crystal again after total reflection by the second mirror, so that all The doubled frequency light (2ω) and the remaining fundamental frequency light (ω) components in the required polarization state are summed in the crystal, and reflected by the first mirror to finally realize the output of ultraviolet light (3ω).

Figure 2(a) is a schematic diagram of the polarization of fundamental frequency light and frequency doubled light when type II frequency doubling occurs;

In Figure 2(a), after the fundamental frequency light enters the crystal, it undergoes orthogonal decomposition to realize Type II frequency doubling, and the polarization direction of the generated frequency doubling light is located on the X-axis of the crystal.

Fig. 2(b) is a schematic diagram of polarization of fundamental frequency light, frequency doubled light and tripled frequency ultraviolet light when type I triple frequency occurs.

In Figure 2(b), after the action of the quarter-wave plate and the reflection of the second mirror, the fundamental frequency light and the polarization direction are rotated by 90° to the frequency-doubled light on the Z axis to enter the crystal again, and the frequency-doubled light and the fundamental frequency The Z-axis component of the light acts to realize Class I triple frequency, and the polarization direction of the generated triple-frequency ultraviolet light is located on the X axis.

FIG. 3 is a schematic structural view of the ultraviolet laser frequency converter described in Embodiment 1 of the present invention;

Fig. 4 is a schematic structural diagram of the ultraviolet laser frequency converter described in Embodiment 2 of the present invention;

Fig. 5 is a schematic structural diagram of the ultraviolet laser frequency converter described in Embodiment 3 of the present invention;

FIG. 6 is a measured output spectrum diagram of the ultraviolet laser converter described in Embodiment 3 of the present invention.

Among them, 1. fundamental frequency light source; 2. first plano-convex lens; 3. second plano-convex lens; 4. first reflector; 5. nonlinear optical crystal; 6. quarter-wave plate; 7. second reflector Mirror; 8. Filter; 9. Temperature control box; 10. Electric rotating platform; 11. Faraday rotator.

detailed description

The utility model will be further limited below in conjunction with the accompanying drawings and embodiments, but not limited thereto.

Example 1

An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance, including a fundamental frequency light source 1, a beam shrinking system, a first mirror 4, a nonlinear optical crystal 5, and a quarter-wave plate 6 , the second reflector 7 and the filter plate 8, the beam shrinking system, the first reflector 4, the nonlinear optical crystal 5, the quarter wave plate 6, and the second reflector 7 are placed along the optical path in sequence from left to right , the filter 8 is arranged directly below the first reflector 4; the bisector of the angle of the X axis and the Z axis of the nonlinear optical crystal 5 is parallel to the polarization direction of the fundamental frequency light generated by the fundamental frequency light source 1, so The direction of the optical axis of the quarter wave plate 6 is parallel to the polarization direction of the fundamental frequency light generated by the fundamental frequency light source 1 . The included angle between the first reflecting mirror 4 and the central axis of the optical path is 45°.

The fundamental frequency light source 1 generates fundamental frequency light, and the fundamental frequency light passes through the beam shrinkage system to increase the power density of the incident fundamental frequency light, and the incident fundamental frequency light passes through the first reflector 4 and enters the nonlinear optical crystal 5, where The type II frequency doubling effect occurs in the linear optical crystal 5, and the generated frequency doubling light and the remaining fundamental frequency light pass through the quarter-wave plate 6 and are incident on the second reflector 7. After total reflection, they return according to the original optical path. After passing through the quarter-wave plate 6 for the first time, it enters the nonlinear crystal 5 again, and through the polarization rotation of the quarter-wave plate 6, the frequency doubled light interacts with the Z-axis component of the remaining fundamental frequency light, and a type I triple frequency, the generated triple frequency ultraviolet light is reflected by the first reflector 4, and then the remaining fundamental frequency light and frequency doubled light are filtered out by the filter plate 8, and a pure ultraviolet laser is output. In this way, the introduction of the quarter-wave plate 6 adjusts the polarization direction of the frequency-doubled light, while the polarization direction of the fundamental-frequency light remains unchanged, thereby realizing ultraviolet laser output. A schematic diagram of an implementation manner of triple frequency in the present invention is shown in FIG. 1( b ). The schematic diagram of polarization of fundamental frequency light and doubled frequency light when type II frequency doubling occurs is shown in Figure 2(a); the schematic diagram of polarization of fundamental frequency light, frequency doubled light and tripled frequency ultraviolet light when type I triple frequency occurs is shown in Figure 2 ( b) shown;

Gd _x Y _1-x COB crystals have consistent melting properties, can be grown in large size by pulling method, and have high optical quality. After batching according to the stoichiometric ratio, the materials are mixed and fired, and then the sintered polycrystalline material is put into an iridium crucible, and a high-temperature single crystal pulling furnace is used for growth to grow into a Gd _x Y _1-x COB single crystal. Crystals are oriented along the optical axis, cut, polished, and coated along the Y axis. Therefore, the quasi-crystal grows with the seed crystal in the Y direction, so the utilization rate of the crystal is high.

The beam reduction system includes a first plano-convex lens 2 and a second plano-convex lens 3 with different focal lengths;

The fundamental-frequency light source 1 is a Nd:YAG mode-locked laser, and the wavelength of the fundamental-frequency light emitted by the Nd:YAG mode-locked laser is 1064 nm, and x=0.2.

The first reflector 4 is coated with a dielectric film that is highly transparent to 1064nm and 532nm lasers and highly reflective to 355nm ultraviolet light;

The second mirror 7 is coated with a dielectric film that fully reflects the 1064nm and 532nm lasers;

The nonlinear optical crystal 5 is a Y-cut Gd _0.2 Y _0.8 COB, and the nonlinear optical crystal 5 is oriented according to the axis X, Y, and Z of the main axis of the refractive index, with a size of 10mm×10mm×5mm, and two Y-directed light-passing surfaces Polished and coated with 1064nm, 532nm, 355nm triple-frequency anti-reflection coating; Y-cut Gd _0.2 Y _0.8 COB means: the direction of light transmission is the Y-axis, and the crystal is cut and polished along the plane perpendicular to the Y-axis of the crystal;

The quarter-wave plate 6 is a 532nm mica quarter-wave plate;

The filter 8 is made of quartz, coated with a dielectric film that is highly reflective to 1064nm and 532nm lasers and highly transparent to 355nm lasers.

The structural schematic diagram of the ultraviolet laser frequency converter described in this embodiment is shown in FIG. 3 .

Example 2

According to embodiment 1, an ultraviolet laser frequency converter with non-critical phase matching frequency doubling and triple frequency performance, the difference is that the ultraviolet laser frequency converter also includes a temperature control system and an electric rotating platform 10, so The temperature control system includes a temperature control box 9 , the nonlinear optical crystal 5 is set inside the temperature control box 9 , and the electric rotating platform 10 is set under the temperature control box 9 .

The advantage of the design here is that the temperature control system and the setting of the electric rotating platform 10 are expected to find the best temperature and the best phase matching direction to obtain greater output of ultraviolet light.

The temperature control accuracy of the temperature control system is ±0.1°C, and the two optical end faces of the temperature control box 9 are provided with quartz glass that is highly transparent to the ultraviolet-infrared wide spectrum; the rotation accuracy of the electric rotating platform 10 is 0.00125° . Quartz glass prevents heat from spreading and acts as an insulator.

A schematic structural diagram of the ultraviolet laser frequency converter described in this embodiment is shown in FIG. 4 .

Example 3

An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance, including a fundamental frequency light source 1, a beam shrinking system, a first mirror 4, a nonlinear optical crystal 5, and a quarter-wave plate 6 , the second reflector 7 and the filter plate 8, the beam shrinking system, the first reflector 4, the nonlinear optical crystal 5, the quarter wave plate 6, and the second reflector 7 are placed along the optical path in sequence from left to right , the filter 8 is arranged directly below the first reflector 4; the bisector of the angle of the X axis and the Z axis of the nonlinear optical crystal 5 is parallel to the polarization direction of the fundamental frequency light generated by the fundamental frequency light source 1, so The direction of the optical axis of the quarter wave plate 6 is parallel to the polarization direction of the fundamental frequency light generated by the fundamental frequency light source 1 . The included angle between the first reflecting mirror 4 and the central axis of the optical path is 45°.

The fundamental frequency light source 1 generates fundamental frequency light, and the fundamental frequency light passes through the beam shrinkage system to increase the power density of the incident fundamental frequency light, and the incident fundamental frequency light passes through the first reflector 4 and enters the nonlinear optical crystal 5, where The type II frequency doubling effect occurs in the linear optical crystal 5, and the generated frequency doubling light and the remaining fundamental frequency light pass through the quarter-wave plate 6 and are incident on the second reflector 7. After total reflection, they return according to the original optical path. After passing through the quarter-wave plate 6 for the first time, it enters the nonlinear crystal 5 again, and through the polarization rotation of the quarter-wave plate 6, the frequency-doubled light interacts with the Z-axis component of the remaining fundamental frequency light, and a type I triple frequency, the generated triple frequency ultraviolet light is reflected by the first reflector 4, and then the remaining fundamental frequency light and frequency doubled light are filtered out by the filter plate 8, and a pure ultraviolet laser is output. In this way, the introduction of the quarter-wave plate 6 adjusts the polarization direction of the frequency-doubled light, while the polarization direction of the fundamental-frequency light remains unchanged, thereby realizing ultraviolet laser output.

Gd _x Y _1-x COB crystals have consistent melting properties, can be grown in large size by pulling method, and have high optical quality. After batching according to the stoichiometric ratio, the materials are mixed and fired, and then the sintered polycrystalline material is put into an iridium crucible, and a high-temperature single crystal pulling furnace is used for growth to grow into a Gd _x Y _1-x COB single crystal. Crystals are oriented along the optical axis, cut, polished, and coated along the Y axis. Therefore, the quasi-crystal grows with the seed crystal in the Y direction, so the utilization rate of the crystal is high.

A Faraday rotator 11 is arranged between the fundamental frequency light source 1 and the beam reduction system;

The beam reduction system includes a first plano-convex lens 2 and a second plano-convex lens 3 with different focal lengths;

The fundamental frequency light source 1 is a neodymium glass mode-locked laser, and the wavelength of the fundamental frequency light emitted by the neodymium glass mode-locked laser is 1053nm;

The first mirror 4 is coated with a dielectric film with high transparency to 1053nm and 526nm lasers and high reflection to 351nm ultraviolet light;

The second mirror 7 is coated with a dielectric film that fully reflects the 1053nm and 526nm lasers;

The nonlinear optical crystal 5 is a Y-cut Gd _0.13 Y _0.87 COB, and the nonlinear optical crystal 5 is oriented according to the axis X, Y, and Z of the main axis of the refractive index, with a size of 12nm×16mm×29mm, and two Y-direction light-passing surfaces Polished and coated with 1053nm fundamental frequency, 526nm frequency multiplier, and 351nm triple frequency anti-reflection coating; Y-cut Gd _0.13 Y _0.87 COB means: the direction of light transmission is the Y-axis, and the plane is cut and polished along the vertical crystal Y-axis;

The quarter-wave plate 6 is a 526nm mica quarter-wave plate;

A schematic structural diagram of the ultraviolet laser frequency converter described in this embodiment is shown in FIG. 5 .

The measured output spectrogram of the ultraviolet laser frequency converter described in the present embodiment is as shown in Figure 6; in Fig. 6, when 1053nm triple frequency is realized, the spectrogram of output ultraviolet light is measured by the spectrometer, and the center wavelength is positioned at 351 nanometers , proving that triple frequency can be achieved.

Claims (8)

1. An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance, characterized in that it includes a fundamental frequency light source, a beam reduction system, a first reflector, a nonlinear optical crystal, a quarter A wave plate, a second mirror and a filter, the beam shrinking system, the first mirror, a nonlinear optical crystal, a quarter wave plate, and the second mirror are arranged along the optical path from left to right in sequence, and the filter The sheet is arranged directly below the first reflecting mirror; the angle bisector of the X-axis and the Z-axis of the nonlinear optical crystal and the polarization direction of the fundamental-frequency light generated by the fundamental-frequency light source are at an angle of 0-5°, The included angle between the optical axis direction of the quarter wave plate and the polarization direction of the fundamental frequency light generated by the fundamental frequency light source is 0-5°; the included angle between the first reflector and the central axis of the optical path is 35- 55°; the nonlinear optical crystal is Gd _x Y _1-x COB crystal, when the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1064nm, the value range of x is 0.18-0.22, when the fundamental frequency light emitted by the fundamental frequency light source When the frequency light wavelength is 1053nm, the value range of x is 0.11-0.15. 2. An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance according to claim 1, characterized in that the bisectors of the X-axis and the Z-axis of the nonlinear optical crystal are parallel Based on the polarization direction of the fundamental frequency light generated by the fundamental frequency light source, the direction of the optical axis of the quarter wave plate is parallel to the polarization direction of the fundamental frequency light generated by the fundamental frequency light source. 3. A UV laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance according to claim 1, characterized in that the angle between the first reflector and the central axis of the optical path is 45° °. 4. A kind of ultraviolet laser converter with non-critical phase matching frequency multiplication and triple frequency performance according to claim 1, characterized in that, when the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1064nm, x= 0.2; when the wavelength of the fundamental frequency light emitted by the fundamental frequency light source is 1053nm, x=0.13. 5. An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance according to claim 1, characterized in that, the ultraviolet laser frequency converter also includes a temperature control system and an electric rotating platform, The temperature control system includes a temperature control box, the nonlinear optical crystal is arranged in the temperature control box, and the electric rotating platform is arranged under the temperature control box. 6. An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance according to claim 5, characterized in that, the temperature control accuracy of the temperature control system is ±0.1°C, and the The two optical ends of the temperature control box are equipped with quartz glass that is highly transparent to the ultraviolet-infrared wide spectrum; the rotation accuracy of the electric rotating platform is 0.00125°. 7. An ultraviolet laser frequency converter with non-critical phase-matching frequency doubling and frequency tripling performance according to claim 1, characterized in that the beam shrinking system includes a first plano-convex lens and a second plano-convex lens with different focal lengths plano-convex lens; The fundamental frequency light source is a Nd:YAG mode-locked laser; The first reflector is coated with a dielectric film that is highly transparent to 1064nm and 532nm lasers and highly reflective to 355nm ultraviolet light; The second mirror is coated with a dielectric film that fully reflects the 1064nm and 532nm lasers; The nonlinear optical crystal is a Y-cut Gd _0.2 Y _0.8 COB. The nonlinear optical crystal is oriented according to the axis X, Y, and Z of the refractive index, and the size is 10mm×10mm×5mm. The two Y-direction light-transmitting surfaces are polished and Coated with 1064nm, 532nm, 355nm triple frequency anti-reflection coating; The quarter-wave plate is a 532nm mica quarter-wave plate; The filter is coated with a dielectric film that is highly reflective to 1064nm and 532nm lasers and highly transparent to 355nm lasers. 8. An ultraviolet laser frequency converter with non-critical phase matching frequency doubling and frequency tripling performance according to claim 1, characterized in that a Faraday optical rotator; The beam reduction system includes a first plano-convex lens and a second plano-convex lens with different focal lengths; The fundamental frequency light source is a neodymium glass mode-locked laser; The first mirror is coated with a dielectric film with high transparency to 1053nm and 526nm lasers and high reflection to 351nm ultraviolet light; The second mirror is coated with a dielectric film that fully reflects the 1053nm and 526nm lasers; The nonlinear optical crystal is a Y-cut Gd _0.13 Y _0.87 COB. The nonlinear optical crystal is oriented according to the X, Y, and Z axes of the main axes of refractive index, and the size is 12nm×16mm×29mm. The two Y-direction light-transmitting surfaces are polished and Coated with 1053nm fundamental frequency, 526nm frequency doubling, 351nm triple frequency anti-reflection coating; The quarter-wave plate is a 526nm mica quarter-wave plate; The filter is coated with a dielectric film that is highly reflective to 1053nm and 526nm lasers and highly transparent to 351nm lasers.