A UV laser

Abstract

The present invention discloses a self-frequency doubling ultraviolet laser, comprising a pump source, a laser resonant cavity, a self-frequency doubling laser crystal, a λ / 4 wave plate and a total reflection mirror arranged in sequence; the laser resonant cavity comprises an input cavity mirror and an output cavity mirror, and the self-frequency doubling laser crystal is located between the input cavity mirror and the output cavity mirror; the light passing direction of the self-frequency doubling laser crystal is the best frequency doubling direction and the best triple frequency or quadruple frequency direction, and the two directions are not on the same straight line, and the light path is overlapped by making the light path totally reflected on one side of the self-frequency doubling laser crystal, so that the two directions form the light passing direction. The present invention adopts the above-mentioned self-frequency doubling ultraviolet laser, and only one crystal is needed to realize the triple frequency or quadruple frequency process to obtain the self-frequency doubling ultraviolet laser output, which has the advantages of small size, simple and compact structure, light weight, integration, high beam quality, high reliability, low cost, etc.

Description

Technical Field

[0001] The invention relates to the technical field of laser and nonlinear crystal devices, in particular to an ultraviolet laser. Background Art

[0002] Ultraviolet lasers are widely used in laser secure communications, spark ignition, material processing and laser therapy due to their short wavelength, easy focusing, high resolution and high photon energy. For example, in the electronics industry, PCB through-hole processing, large-capacity storage optical disc processing and higher resolution in microscopes can be achieved.

[0003] However, the current method of obtaining self-frequency doubling ultraviolet lasers is mostly to use two nonlinear crystals to perform frequency conversion on the 1μm-band infrared laser, which consists of two phase matching processes: frequency doubling and sum frequency. The cutting angles of the crystals for the frequency doubling and sum frequency processes are different, and the required polarization states are different, so two self-frequency doubling laser crystals are required accordingly. Since nonlinear optical crystals are the core components of optical frequency converters and are also the most expensive components in optical frequency converters, they are more expensive and more complicated to adjust than traditional lasers made of two crystals. Summary of the invention

[0004] The purpose of the present invention is to provide an ultraviolet laser, which only needs one crystal to realize the frequency tripling process and thus obtain self-frequency doubling ultraviolet laser output, and has the advantages of small size, simple and compact structure, light weight, integration, high beam quality, high reliability, low cost, etc.

[0005] To achieve the above-mentioned purpose, the present invention provides an ultraviolet laser, comprising a pump source, a laser resonant cavity, a self-frequency doubling laser crystal, a λ / 4 wave plate and a total reflection mirror arranged in sequence; the laser resonant cavity comprises an input cavity mirror and an output cavity mirror, and the self-frequency doubling laser crystal is located between the input cavity mirror and the output cavity mirror; the self-frequency doubling laser crystal is a laser crystal that can simultaneously realize near-infrared band fundamental frequency laser oscillation, fundamental frequency laser frequency doubling, fundamental frequency laser and frequency doubling laser frequency to generate triple frequency, or frequency doubling light to generate quadruple frequency light; the light transmission direction of the self-frequency doubling laser crystal is the optimal frequency doubling direction and the optimal triple frequency or quadruple frequency direction, the two directions are not on the same straight line, and the light path is overlapped by causing the light path to be totally reflected on one side of the self-frequency doubling laser crystal, so that the two directions constitute the light transmission direction.

[0006] Preferably, the pump source is a diode laser, a fiber laser or a solid laser with an emission center wavelength in the 940-980 nm band.

[0007] Preferably, the self-doubling laser crystal is an irregular polyhedron; the light transmission length of the self-doubling laser crystal in the frequency doubling direction (the distance from the incident point to the total reflection point) is 1mm-30mm, and the light transmission length in the triple or quadruple frequency direction (the distance from the total reflection point to the exit point) is 1mm-30mm.

[0008] Preferably, the self-doubling laser crystal is an irregular hexahedral structure, the length L1 of the self-doubling laser crystal is 3-40mm, L2 is 1-20mm, the hypotenuse W1 is 1-25mm, W2 is 1-25mm, the thickness H1 is 0.5-10mm, and the width between the lengths L1 and L2 is specifically determined according to different phase matching angles.

[0009] Preferably, the self-frequency doubling laser crystal is Yb 3+ :YAl(BO3)4 crystal.

[0010] Preferably, the optimal phase matching direction of the self-frequency doubling laser crystal is the direction with the largest effective nonlinear coefficient. When the laser propagates in the self-frequency doubling laser crystal, it is totally reflected on one side of the self-frequency doubling laser crystal and propagates in a V-shape, thereby ensuring that the propagation directions of the fundamental frequency light, the doubled frequency light, the tripled frequency light or the quadrupled frequency light remain consistent. This propagation direction is the optimal phase matching direction.

[0011] Preferably, the side of the self-frequency doubling laser crystal that undergoes total reflection is polished or coated with a reflective film after polishing; the self-frequency doubling laser crystal is wrapped on a heat sink, the material of the heat sink is copper or brass, and the heat sink has circulating coolant or is connected to a TEC cooling plate.

[0012] Preferably, the reflective film is a reflective film that highly reflects pump light in the 940-980nm band, fundamental frequency light in the 1000-1100nm band, doubled frequency light in the 500-550nm band, tripled frequency light in the 330-370nm band, or quadrupled frequency light in the 250-275nm band.

[0013] Preferably, the input cavity mirror is coated with a dielectric film A which is highly transmittant to the pump light and the tripled frequency light and highly reflective to the fundamental frequency light and the doubled frequency light, and the output cavity mirror is coated with a dielectric film B which is highly reflective to the pump light, the tripled frequency light and the fundamental frequency light and highly transmittant to the doubled frequency light; the dielectric film A is a dielectric film which is highly transmittant to the pump light in the 940-980nm band and the tripled frequency light in the 330-370nm band and highly reflective to the fundamental frequency light in the 1000-1100nm band and the doubled frequency light in the 500-550nm band; the dielectric film B is a dielectric film which is highly reflective to the pump light in the 940-980nm band, the tripled frequency light in the 330-370nm band and the fundamental frequency light in the 1000-1100nm band and highly transmittant to the doubled frequency light in the 500-550nm band.

[0014] Preferably, the input cavity mirror is coated with a dielectric film C that is highly transmittant to the pump light and the quadrupled frequency light and highly reflective to the fundamental frequency light and the doubled frequency light, and the output cavity mirror is coated with a dielectric film D that is highly reflective to the pump light, the quadrupled frequency light and the fundamental frequency light and highly transmittant to the doubled frequency light; the dielectric film C is a dielectric film that is highly transmittant to the pump light in the 940-980nm band and the quadrupled frequency light in the 250-275nm band and highly reflective to the fundamental frequency light in the 1000-1100nm band and the doubled frequency light in the 500-550nm band; the dielectric film D is a dielectric film that is highly reflective to the pump light in the 940-980nm band, the quadrupled frequency light in the 250-275nm band and the fundamental frequency light in the 1000-1100nm band and highly transmittant to the doubled frequency light in the 500-550nm band.

[0015] Therefore, the present invention adopts the above-mentioned ultraviolet laser, which has the following beneficial effects:

[0016] (1) Structurally, the present invention adopts a crystal structure to obtain a self-frequency doubling ultraviolet laser. The frequency doubling process and the sum frequency process in the self-frequency doubling ultraviolet laser occur in a crystal, which not only solves the problem of inconsistent phase matching directions, but also solves the problem of inconsistent polarization states, reduces the number of crystals used in the process of generating ultraviolet lasers, reduces costs, and improves the stability of the system. It has the advantages of small size, simple and compact structure, light weight, and integration.

[0017] (2) The light transmission direction in the self-frequency doubling laser crystal of the present invention is the optimal phase matching direction of the frequency doubling and sum frequency, which can ensure the maximum conversion efficiency while minimizing the volume, and is easy to produce and promote the use of the product.

[0018] (3) The laser structure design of the present invention has the advantages of being simple, easy to operate, stable in structure, and easy to replace and debug.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a first embodiment of an ultraviolet laser of the present invention;

[0021] Figure 2 It is a top view schematic diagram of a first embodiment of an ultraviolet laser of the present invention;

[0022] Figure 3 It is a schematic diagram of the cutting direction of a self-frequency doubling laser crystal of an ultraviolet laser embodiment of the present invention;

[0023] Figure 4 It is a schematic diagram of the structure of a self-frequency doubling laser crystal of an ultraviolet laser embodiment of the present invention;

[0024] Figure 5 This is a self-frequency doubling ultraviolet laser spectrum diagram of a first embodiment of an ultraviolet laser of the present invention;

[0025] Figure 6 It is a structural schematic diagram of a second embodiment of an ultraviolet laser of the present invention;

[0026] Figure 7 It is a structural schematic diagram of a third embodiment of an ultraviolet laser of the present invention;

[0027] Figure 8 is a top view schematic diagram of a third embodiment of an ultraviolet laser of the present invention;

[0028] Fig. 9 This is a self-frequency doubling ultraviolet laser spectrum diagram of a third ultraviolet laser embodiment of the present invention.

[0029] Reference numerals

[0030] 1. Pump source; 2. Input cavity mirror; 3. Self-frequency doubling laser crystal; 4. Output cavity mirror; 5. λ / 4 wave plate; 6. Total reflection mirror. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0032] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0033] The relevant terms mentioned in the preceding or subsequent sections are explained as follows:

[0034] High transmittance: refers to the transmittance of light of a specific wavelength or band being greater than 99%.

[0035] High reflection: refers to the reflectivity of light of a specific wavelength or band being greater than 99%.

[0036] Phase matching: The so-called phase matching condition actually means that the fundamental frequency light and the double frequency light have the same refractive index when propagating in the crystal. Among all phase matching angles, there is an angle that can achieve the highest double frequency efficiency, which is called the best phase matching direction.

[0037] Embodiment 1

[0038] like Figure 1 and Figure 2 As shown, the present invention provides an ultraviolet laser, comprising a pump source 1, a laser resonant cavity, a self-frequency doubling laser crystal 3, a λ / 4 wave plate 5 and a total reflection mirror 6 arranged in sequence, the laser resonant cavity comprising an input cavity mirror 2 and an output cavity mirror 4, and the self-frequency doubling laser crystal 3 is located between the input cavity mirror 2 and the output cavity mirror 4. The self-frequency doubling laser crystal 3 is a laser crystal that can simultaneously realize near-infrared band fundamental frequency laser oscillation, fundamental frequency laser frequency doubling, and fundamental frequency laser and frequency doubling laser frequency tripled generation, the light transmission direction of the self-frequency doubling laser crystal 3 is the best frequency doubling direction and the best frequency tripled direction, the two directions are not on the same straight line, and the light path is overlapped by causing the light path to be totally reflected on one side of the self-frequency doubling laser crystal 3, so that the two directions constitute the light transmission direction.

[0039] like Figure 3 and Figure 4 As shown, in this embodiment, the self-frequency doubling laser crystal 3 is Yb 3+ :YAl(BO3)4(Yb:YAB) crystal, the emission wavelength of pump source 1 is 940-980nm, the type I phase matching angle of the frequency doubling of the Yb:YAB crystal at 1030nm is θ1=31.35°, and the type I phase matching angle of the frequency tripling is θ2=42.63°, Figure 3 Wherein k1 and k2 are the phase matching directions of the doubled frequency light, k3 and k4 are the phase matching directions of the tripled frequency light, the direction of L1 is -5.64°, that is, θ3=5.64°, k1 and k4 are the propagation directions of the light in the crystal, the angle between the two is 106.02°, k1 is perpendicular to the W1 side, k4 is perpendicular to the W2 side, the angle between L1 and W1 is θ4=53.01°, the length L1 of the self-doubling laser crystal 3 is 10mm, L2 is 6mm, the hypotenuse W1=W2 is 3.32mm, the thickness H1 is 3mm, the width between L1 and L2 is 2.66mm, and the incident angle of the light on the self-doubling laser crystal 3 when propagating in the self-doubling laser crystal 3 is 106.02° / 2≈53°, and total reflection can occur to achieve 343nm tripled frequency self-doubling ultraviolet laser output.

[0040] In this embodiment, the input cavity mirror 2 is coated with a dielectric film A which has high transmittance to the pump light in the 940-980nm band and the tripled frequency light in the 330-370nm band, and high reflectivity to the fundamental frequency light in the 1000-1100nm band and the doubled frequency light in the 500-550nm band; the output cavity mirror 4 is coated with a dielectric film B which has high reflectivity to the pump light in the 940-980nm band, the tripled frequency light in the 330-370nm band and the fundamental frequency light in the 1000-1100nm band, and high transmittance to the doubled frequency light in the 500-550nm band.

[0041] When in use, turn on the power of the pump source 1, and control the power output of the pump light by adjusting the current on the pump source 1. The pump light emitted by the pump source 1 is injected into the self-frequency doubling laser crystal 3 after passing through the input cavity mirror 2. Under the joint action of the input cavity mirror 2 and the output cavity mirror 4, the fundamental frequency light is generated in the cavity, and the doubled frequency light is generated under the frequency doubling action of the self-frequency doubling laser crystal 3. After the fundamental frequency light and the doubled frequency light are totally reflected on the L1×H1 plane, they are emitted from the self-frequency doubling laser crystal 3 to the output cavity mirror 4. The fundamental frequency light is reflected, and the doubled frequency light passes through the output cavity mirror 4 and then passes through λ / After passing through the λ / 4 wave plate 5, the polarization state rotates 90° after passing through the λ / 4 wave plate 5 again through the total reflection mirror 6. At this time, the polarization states of the fundamental frequency light and the doubled frequency light are parallel. After returning to the self-doubling laser crystal 3, the fundamental frequency light and the doubled frequency light are summed to produce a tripled self-doubling ultraviolet laser. Subsequently, after total emission occurs at the L1×H1 surface, the fundamental frequency light, the doubled frequency light and the tripled frequency light are emitted from the incident surface of the self-doubling laser crystal 3. When passing through the input cavity mirror 2, the fundamental frequency light and the doubled frequency light are highly reflected, and the tripled frequency light is transmitted, thereby obtaining a tripled self-doubling ultraviolet laser output. The spectrum of the output self-doubling ultraviolet laser is shown as follows: Figure 5 shown.

[0042] In this embodiment, the self-frequency-doubling laser crystal 3 is wrapped with a heat sink, and circulating cooling water flows through the heat sink, so that the temperature of the self-frequency-doubling laser crystal 3 can be stabilized within a certain range.

[0043] In this embodiment, the two light-passing surfaces of the self-doubling laser crystal 3 are polished, and the total reflection L1×H1 surface is polished and then coated with a reflective film. The reflective film is a reflective film that highly reflects the pump light in the 940-980nm band, the fundamental frequency light in the 1000-1100nm band, the doubled frequency light in the 500-550nm band, and the tripled frequency light in the 330-370nm band.

[0044] Embodiment 2

[0045] like Figure 6 As shown, the structure of this embodiment is different from that of the first embodiment in that the input cavity mirror 2 in this embodiment is formed by coating a dielectric film A on the input surface of the self-frequency doubling laser crystal 3, and the output cavity mirror 4 is formed by coating a dielectric film B on the output surface of the self-frequency doubling laser crystal 3.

[0046] Embodiment 3

[0047] like Figure 7 and Figure 8 As shown, the structure of this embodiment is different from that of the first embodiment in that this embodiment finally realizes the output of 1030nm quadruple frequency laser 257.5nm ultraviolet laser. The type I phase matching angle of the quadruple frequency of Yb:YAB crystal in the 1030nm band is θ2=47.63°, Figure 3 Wherein k1 and k2 are the phase matching directions of the doubled frequency light, k3 and k4 are the phase matching directions of the quadrupled frequency light, the direction of L1 is -12.425°, that is, θ3=12.425°, k1 and k4 are the propagation directions of the light in the self-doubling laser crystal 3, the angle between them is 109.59°, k1 is perpendicular to the W1 side, k4 is perpendicular to the W2 side, the angle between L1 and W1 is θ4=46.225°, the length L1 of the self-doubling laser crystal 3 is 10mm, L2 is 6mm, the hypotenuse W1=W2 is 2.89mm, the thickness H1 is 3mm, the width between L1 and L2 is 2.09mm, and the incident angle of the light on the L1×H1 surface on the self-doubling laser crystal 3 when propagating in the self-doubling laser crystal 3 is 109.59° / 2≈54.8°, and total reflection can occur.

[0048] The input cavity mirror 2 is coated with a dielectric film C which has high transmittance to the pump light in the 940-980nm band and the quadrupled frequency light in the 250-275nm band, and high reflectivity to the fundamental frequency light in the 1000-1100nm band and the doubled frequency light in the 500-550nm band. The output cavity mirror 4 is coated with a dielectric film D which has high reflectivity to the pump light in the 940-980nm band, the quadrupled frequency light in the 250-275nm band and the fundamental frequency light in the 1000-1100nm band, and high transmittance to the doubled frequency light in the 500-550nm band.

[0049] In this embodiment, the two light-transmitting surfaces H1×W1 and H1×W2 of the self-doubling laser crystal 3 are polished, and the total reflection surface L1×H1 is only polished.

[0050] Finally, a quadruple frequency ultraviolet laser output with a wavelength of 257.5nm can be obtained. The spectrum of the output self-frequency doubled ultraviolet laser is as follows: Fig. 9 shown.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A self-frequency doubling ultraviolet laser, characterized in that: The invention comprises a pump source, a laser resonant cavity, a self-frequency doubling laser crystal, a λ / 4 wave plate and a total reflection mirror arranged in sequence; the laser resonant cavity comprises an input cavity mirror and an output cavity mirror, and the self-frequency doubling laser crystal is located between the input cavity mirror and the output cavity mirror; the self-frequency doubling laser crystal is a laser crystal capable of simultaneously realizing near-infrared band fundamental frequency laser oscillation, fundamental frequency laser frequency doubling, fundamental frequency laser and frequency doubling laser frequency generation of triple frequency, or frequency doubling light to generate quadruple frequency, the light transmission direction of the self-frequency doubling laser crystal is the best frequency doubling direction and the best triple frequency or quadruple frequency direction, the two directions are not on the same straight line, and the light path is overlapped by causing the light path to be totally reflected on one side of the self-frequency doubling laser crystal, so that the two directions constitute the light transmission direction; The light transmission length of the self-frequency doubling laser crystal in the frequency doubling direction is 1mm-30mm, and the light transmission length in the triple frequency or quadruple frequency direction is 1mm-30mm; The self-frequency doubling laser crystal is an irregular hexahedral structure, the length L1 of the self-frequency doubling laser crystal is 3-40 mm, L2 is 1-20 mm, the hypotenuse W1 is 1-25 mm, W2 is 1-25 mm, the thickness H1 is 0.5-10 mm, and the width between the lengths L1 and L2 is specifically determined according to different phase matching angles; The optimal phase matching direction of the self-frequency doubling laser crystal is the direction with the largest effective nonlinear coefficient. When the laser propagates in the self-frequency doubling laser crystal, it is totally reflected on one side of the self-frequency doubling laser crystal and propagates in a V-shape, thereby ensuring that the propagation directions of the fundamental frequency light, the doubled frequency light, the tripled frequency light or the quadrupled frequency light remain consistent. This propagation direction is the optimal phase matching direction.

2. A self-frequency doubling ultraviolet laser according to claim 1, characterized in that: The pump source is a diode laser, a fiber laser or a solid laser with an emission center wavelength in the 940-980nm band.

3. The self-frequency doubling ultraviolet laser according to claim 1, characterized in that: The self-frequency doubling laser crystal is Yb 3+ :YAl(BO3)4 crystal.

4. The self-frequency doubling ultraviolet laser according to claim 1, characterized in that: The side of the self-frequency doubling laser crystal that undergoes total reflection is polished or coated with a reflective film after polishing; the self-frequency doubling laser crystal is wrapped on a heat sink, the heat sink is made of copper or brass, and circulating coolant is passed through the heat sink or the heat sink is connected to a TEC cooling plate.

5. A self-frequency doubling ultraviolet laser according to claim 4, characterized in that: The reflective film is a reflective film that highly reflects pump light in the 940-980nm band, fundamental frequency light in the 1000-1100nm band, doubled frequency light in the 500-550nm band, tripled frequency light in the 330-370nm band, or quadrupled frequency light in the 250-275nm band.

6. The self-frequency doubling ultraviolet laser according to claim 1, characterized in that: The input cavity mirror is plated with a dielectric film A which has high transmittance to pump light and tripled frequency light and high reflection to fundamental frequency light and doubled frequency light, and the output cavity mirror is plated with a dielectric film B which has high reflection to pump light, tripled frequency light and fundamental frequency light and high transmittance to doubled frequency light; the dielectric film A is a dielectric film which has high transmittance to pump light in a band of 940-980nm and tripled frequency light in a band of 330-370nm and high reflection to fundamental frequency light in a band of 1000-1100nm and doubled frequency light in a band of 500-550nm; the dielectric film B is a dielectric film which has high reflection to pump light in a band of 940-980nm, tripled frequency light in a band of 330-370nm and fundamental frequency light in a band of 1000-1100nm and high transmittance to doubled frequency light in a band of 500-550nm.

7. The self-frequency doubling ultraviolet laser according to claim 1, characterized in that: The input cavity mirror is plated with a dielectric film C that has high transmittance to pump light and quadrupled frequency light and high reflection to fundamental frequency light and frequency doubled frequency light; the output cavity mirror is plated with a dielectric film D that has high reflection to pump light, quadrupled frequency light and fundamental frequency light and high transmittance to frequency doubled frequency light; the dielectric film C is a dielectric film that has high transmittance to pump light in the 940-980nm band and quadrupled frequency light in the 250-275nm band and high reflection to fundamental frequency light in the 1000-1100nm band and frequency doubled frequency light in the 500-550nm band; the dielectric film D is a dielectric film that has high reflection to pump light in the 940-980nm band, quadrupled frequency light in the 250-275nm band and fundamental frequency light in the 1000-1100nm band and high transmittance to frequency doubled frequency light in the 500-550nm band.

Images