CN103762490A - Laser resonant cavity method for improving optical beam quality through thermal lenses - Google Patents

Abstract

The invention relates to a method of using a thermal lens to improve the laser resonant cavity of the beam quality, comprising: a resonant cavity composed of a plane total reflection mirror and a concave mirror with a transmittance of 20%, the plane total reflection mirror totally reflects light with a wavelength of 1064nm, and the resonant cavity There are multi-level Nd:YAG crystal rods inside, and the feature is: by adjusting the doping concentration of Nd:YAG in the crystal rod or controlling the output power of the pump source, the pump light output by the pump source is irradiated on the Nd: After the YAG crystal rod, a thermal lens with similar optical parameters is formed inside each level of Nd:YAG crystal rod, and the pump light output by the pump source converges into a waist at the edge of the crystal or outside the crystal, and the position of the waist spot formed by all thermal lenses Symmetry, where the front and rear thermal lenses are on the confocal plane, and the thermal lens of the last crystal is on the confocal plane with the concave mirror, so that the pumping region and the laser low-order mode region overlap, and an undoped crystal is placed between the two doped crystals. A glass rod is used to adjust the distance between the thermal lenses to ensure the control effect on the pump light.

Description

A Method of Laser Resonator Using Thermal Lens to Improve Beam Quality

technical field

The invention belongs to the technical field of lasers, and relates to a diode-pumped solid-state laser resonator device, in particular to a laser resonator method for improving beam quality by using a thermal lens.

technical background

In a solid-state laser, to match the low-order modes of the pump light and the oscillating light, the radius of the pump light is required to be small, but in practice, the pump light has a certain divergence angle. With the propagation of the beam, the radius of the spot in the laser crystal It will increase quickly. If it is not controlled, a large amount of pump light energy will be consumed in the area outside the low-order mode, which will not only seriously reduce the laser efficiency, but also affect the beam quality of the laser due to the increase of high-order mode components. Therefore, We make use of the thermal lens in the crystal and design a suitable thermal lens to control the spot.

When the crystal absorbs the pump light, the energy absorbed by the crystal with different concentrations is different. We control the doping concentration of the crystal to form a thermal lens with a suitable focal length, so that the low-order modes of the pump light and the oscillating light match. The advantage is that the area of the pump light overlaps with the low-order mode area of the laser, which suppresses the generation of high-order modes in the laser crystal, improves the efficiency of the laser, and improves the beam quality of the laser.

Contents of the invention

The purpose of the present invention is to provide a laser resonator that uses a thermal lens to improve the beam quality, and realizes the overlap and matching of the pump region and the laser low-order mode region. Measurement, and through acousto-optic Q-switching, output high-power, high-quality laser.

The object of the present invention is achieved like this, a kind of method that utilizes thermal lens to improve the laser resonant cavity of beam quality, comprises: the resonant cavity that the concave mirror of transmittance 20% and plane total reflection mirror forms, and plane total reflection mirror is to 1064nm wavelength Total reflection of light, multi-level Nd:YAG crystal rods in the resonant cavity, characterized by: by adjusting the doping concentration of Nd:YAG in the crystal rods or controlling the output power of the pump source, the pump output by the pump source After the pump light is irradiated on the Nd:YAG crystal rod, a thermal lens with similar optical parameters is formed inside each level of Nd:YAG crystal rod. The position of the formed waist spot is symmetrical, in which the front and rear thermal lenses are on the confocal plane, and the thermal lens of the last crystal is on the confocal plane with the concave mirror, so that the pumping region and the laser low-order mode region overlap, between the two doped crystals A non-doped glass rod is put in to adjust the distance between the thermal lenses to ensure the control effect on the pump light.

The optical parameter mentioned is the focal length of the thermal lens.

The said output power control is controlled by linear regulation.

There is an acousto-optic Q-switch between the Nd:YAG crystal rod and the concave mirror with a transmittance of 20%.

The pumping light output by the pumping source irradiates the Nd:YAG crystal rod through vertical end face pumping.

The pumping light output by the pumping source is irradiated on the Nd:YAG crystal rod for side-end pumping.

The feature of the present invention is that under the condition of constant pumping power, crystals with different concentrations form thermal lenses with different focal lengths. We select suitable thermal lens focal lengths and crystal positions so that the thermal lenses in each two segments of crystals have a confocal plane, and the output mirror It is a concave mirror, and it is in a confocal plane with the last segment of the crystal, which realizes the overlapping of the pumping area and the low-order mode area of the laser, and improves the beam quality and efficiency of the laser.

The present invention will be further described below in conjunction with embodiment

Description of drawings

Fig. 1 is a schematic structural view of Embodiment 1 of the present invention;

Fig. 2 is a schematic structural view of Embodiment 2 of the present invention;

Fig. 3 is a schematic structural diagram of Embodiment 3 of the present invention.

In the figure: 1. Pump source; 2. Planar total reflection mirror; 3. Nd:YAG crystal rods with different concentrations; 4. Thermal lens; 5. Glass rod without doping; 6. Acousto-optic Q switch; 20% concave mirror.

Detailed ways

Example 1

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;k</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; dn</span>}}{\mathrm{<span\; class="notranslate">\; dT</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; [</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

为随温度变化的折射率变化量，η为晶体热转换系数，p₀泵浦光功率，σ₂₁为晶体的受激发射截面，n_i为晶体的掺杂浓度，l_i为激光晶体长度。In the above formula, f _n is the thermal lens focal length of the laser medium, k _c is the thermal conductivity of the laser medium, ω _p is the Gaussian beam radius,

is the change of refractive index with temperature, η is the thermal conversion coefficient of the crystal, p ₀ is the pump light power, σ ₂₁ is the stimulated emission cross section of the crystal, n _i is the doping concentration of the crystal, and l _i is the length of the laser crystal.

As shown in Figure 1, a design method of a laser resonator using a thermal lens to improve beam quality, including: a resonator composed of a plane total reflection mirror 2 and a concave mirror 7 with a transmittance of 20%, and a plane total reflection mirror 2 pair 1064nm Total reflection of wavelength light, multi-level Nd:YAG crystal rods 3 in the resonant cavity are combined together by bonding, and there is a pump source 1 outside the plane total reflection mirror 2, and the output optical axes of the pump source 1 coincide. The formula ( 1) It can be seen that, in the case of knowing the appropriate doping concentration of each crystal and the length of the laser crystal, as well as the output power of the pump light and the radius of the spot, we can obtain the appropriate thermal lens focal length of the crystal by numerical calculation. By adjusting the Nd :YAG doping concentration in the crystal rod, so that the pump light output by the pump source 1 is irradiated on the Nd:YAG crystal rod, and a thermal lens with similar optical parameters or a suitable focal length is formed inside each level of Nd:YAG crystal rod 4. Nd:YAG crystals with different concentrations absorb different pump light and form thermal lenses with different focal lengths. We can adjust the focal length relationship between each stage of crystals by adjusting the doping concentration of the crystals, or make each stage Properly adjust the length of the stage crystal to meet the focal length requirements of each stage crystal, so that the pump light output by the pump source 1 will converge into a waist at the edge of the crystal after passing through the thermal lens, and make the waist spot formed by all thermal lenses The positions are symmetrical, where two thermal lenses are on the confocal plane, and the thermal lens of the last crystal is on the confocal plane with the concave mirror, so that the pumping area and the laser low-order mode area overlap.

There is an acousto-optic Q switch 6 between the Nd:YAG crystal rod and the concave mirror with a transmittance of 20%.

Example 2

As shown in Figure 2, a design method of a laser resonator using a thermal lens to improve beam quality, including: a resonator composed of a plane total reflection mirror 2 and a concave mirror 7 with a transmittance of 20%, and a plane total reflection mirror 2 for 1064nm Total reflection of wavelength light, multi-level Nd:YAG crystal rods 3 in the resonant cavity, pump source 1 outside the plane total reflection mirror 2, and the output optical axes of pump source 1 coincide. It can be seen from formula (1) that when each In the case of the appropriate doping concentration and laser crystal length of the first-grade crystal, as well as the output power of the pump light and the radius of the spot, we can obtain the appropriate thermal lens focal length of the crystal by numerical calculation. By adjusting the Nd:YAG in the crystal rod The doping concentration is such that the pump light output by the pump source 1 is irradiated on the Nd:YAG crystal rod, and a thermal lens 4 with similar optical parameters or a suitable focal length is formed inside each level of Nd:YAG crystal rod. Different concentrations of Nd: YAG crystals absorb different pump light and form thermal lenses with different focal lengths. We can adjust the focal length relationship between each stage of crystals by adjusting the doping concentration of the crystals, or adjust the distance between each stage of crystals appropriately. Adjustment to meet the focal length requirements of each level of crystals, put an undoped glass rod 5 between the two doped crystals to adjust the distance between the thermal lenses to ensure the control effect on the pump light , so that the pump light output by the pumping source 1 converges into a waist at the edge of the crystal or outside the crystal, and the positions of the waist spots formed by all the thermal lenses are symmetrical, where two thermal lenses are in the same focal plane, and the thermal lens of the last crystal is in the same concave surface as The confocal plane of the mirror realizes the overlapping of the pump region and the laser low-order mode region.

There is an acousto-optic Q switch 6 between the Nd:YAG crystal rod and the concave mirror with a transmittance of 20%.

The difference between embodiment 2 and embodiment 1 is that an undoped glass rod 5 is placed between two doped crystals to adjust the distance between the thermal lenses.

Example 3

A method for designing a laser resonant cavity using a thermal lens to improve beam quality, comprising: a resonant cavity formed by a plane total reflection mirror 2 and a concave mirror 7 with a transmittance of 20%, the plane total reflection mirror 2 totally reflects and resonates light with a wavelength of 1064nm There are multiple levels of Nd:YAG crystal rods 3 in the cavity, and there is a pump source 1 on one side of each Nd:YAG crystal rod 3. It can be seen from formula (1) that when the appropriate doping concentration and laser crystal length of each level of crystal are known, , and the pump light output power and spot radius, we can obtain the appropriate thermal lens focal length of the crystal by numerical calculation, by adjusting the doping concentration of Nd:YAG in the crystal rod or controlling the pump light power output, After the pump light output by the pump source 1 is irradiated on the Nd:YAG crystal rod, a thermal lens 4 with similar optical parameters or a suitable focal length is formed inside each level of Nd:YAG crystal rod, and Nd:YAG crystals with different concentrations absorb The focal length of the thermal lens formed is different with the different pump light. We can adjust the focal length relationship between each stage of crystals by adjusting the doping concentration of the crystals, or properly adjust the distance between each stage of crystals to meet The requirements of the focal length required for each stage of crystal make the oscillating light converge into a waist at the edge of the crystal or outside the crystal, and the positions of the waist spots formed by all the thermal lenses are symmetrical, where two thermal lenses are in the same focal plane, and the thermal lens of the last crystal is the same as that of the thermal lens. Confocal plane of the concave mirror.

Example 3 differs from Example 2 in that it is side pumped.

The components and structures not described in detail in this embodiment are known components and common structures or common means in this industry, and are not described here one by one.

Claims (6)

1. A method of using a thermal lens to improve the laser resonant cavity of the beam quality, comprising: a resonant cavity composed of a flat total reflection mirror (2) and a concave mirror (7) with a transmittance of 20%, and the flat total reflection mirror (2) is Total reflection of 1064nm wavelength light, multi-level Nd:YAG crystal rods (3) in the resonant cavity, characterized by: adjusting the doping concentration of Nd:YAG in the crystal rods or controlling the output power of the pump source (1) , after the pump light output by the pump source (1) irradiates the Nd:YAG crystal rod, a thermal lens (4) with similar optical parameters is formed inside each level of Nd:YAG crystal rod, and the output of the pump source (1) The pumping light converges into a waist on the edge of the crystal or at the outer edge of the crystal, and the positions of the waist spots formed by all the thermal lenses are symmetrical. The area overlaps with the laser low-order mode area, and an undoped glass rod (5) is placed between the two doped crystals to adjust the distance between the thermal lenses to ensure the control effect on the pump light. 2. A method of using a thermal lens to improve the beam quality of a laser cavity according to claim 1, characterized in that: said optical parameter is the focal length of the thermal lens (4). 3. A method of using a thermal lens to improve the laser resonator of beam quality according to claim 1, characterized in that: said output power control is controlled by linear adjustment. 4. a kind of method utilizing thermal lens to improve the laser cavity of beam quality according to claim 1, it is characterized in that: there is acousto-optic modulation between the described Nd:YAG crystal rod and the concave mirror of transmittance 20%. Q switch (6). 5. A method of using a thermal lens to improve the beam quality of a laser resonator according to claim 1, characterized in that: the pump light output by the pump source (1) is irradiated on the Nd:YAG crystal rod Pumped through a vertical end face. 6. A method of using a thermal lens to improve the beam quality of a laser resonator according to claim 1, characterized in that: the pump light output by the pump source (1) is irradiated on the Nd:YAG crystal rod Side pumped.

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