CN2901640Y - Double stick serial connection high power solid laser - Google Patents

Abstract

A high-power solid-state laser connected in series with two rods belongs to the technical field of high-power solid-state lasers. At present, the output power of the existing Nd:YAG laser in China is only 500-700W when two 400W single-rod laser modules are connected in series, and the electro-optical conversion efficiency is only 3%. The utility model is characterized in that the following conditions are met at the same time: two high-power laser modules with the same average effective thermal focal length f, radial thermal focal length fr, and tangential thermal focal length fθ are selected for two rods to be connected in series; the laser resonator is selected to be symmetrically parallel Planar structure; the distance between the rods of the laser is selected to be twice the distance between the rod and the cavity mirror, and the range of the distance between the rods is 1 to 2 times the average thermal focal length f; two apertures with the same aperture are selected to be symmetrically placed between the two series connected laser rods Both ends; adjust the coaxiality of the rod centers of the two serially connected laser rods. The maximum output power of the laser of the utility model can reach 1100-1200W, the beam quality is 21-25mm·mrad, and the overall electro-optic conversion efficiency is 3.8%-4.1%.

Description

Double-rod cascaded high-power solid-state laser

Technical field:

A high-power solid-state laser connected in series with two rods belongs to the technical field of high-power solid-state lasers.

Background technique

Applications in industrial laser material processing require high power, high beam quality laser output. There are currently two main types of lasers, namely CO2 gas lasers and Nd:YAG solid-state lasers. Compared with CO2 gas lasers, solid-state lasers have obvious advantages: solid-state lasers have short wavelength (compared to CO2 lasers), high material absorption rate, small size, and can be transmitted by optical fibers. They are competitive laser light sources in industrial applications.

The application of industrial laser material processing requires solid-state lasers to output kilowatts or even higher power. Usually, the output power of a 200mm long single-rod Nd:YAG laser module is limited to a single module output of 400-600W. There are two ways to achieve greater output power requirements. One is to use a multi-rod oscillation amplification structure. Since the intensity of the output laser in the amplifier stage is much lower than the saturation intensity of the laser rod, the efficiency of the amplifier stage is low; for high-power laser In terms of vibration amplification system, due to the influence of thermal lens effect, the quality of the output beam will be reduced, and the deviation of optical path collimation will easily cause damage to the laser rod; Realize that the output power of the laser is accumulated according to the power of a single rod, while the beam quality remains approximately unchanged, avoiding the problem of the oscillation amplification structure. Industrial high-power YAG lasers generally adopt a modular structure with multiple rods connected in series.

The output characteristics of multi-rod high-power YAG lasers, including output power and beam quality, are not only related to the characteristics of single-rod lasers, but also related to the matching between serially connected multi-rod laser modules. For two single-rod laser modules with the same characteristics, the output power can be accumulated according to the power of the two modules only under the conditions of matching parameters such as structure, thermal focal length and birefringence, critical stability and stable region between the two rod laser modules, and Beam quality maintains the beam quality of a single rod laser module. Due to the matching problem between laser modules, the output power is limited. At present, the output power of the existing Nd:YAG lasers in China is only 500-700W when two 400W single-rod laser modules are connected in series, and the electro-optical conversion efficiency is only 3%. The mode is a mixed mode composed of the base mode and the lower order mode.

Utility model content:

The purpose of this utility model is to increase the output power of the laser system by matching parameters such as the structure, thermal focal length, critical point and stable area between the two laser modules, so that the power of the laser system is accumulated according to the power of the two laser modules, and the beam Quality maintains the beam quality of a single rod laser module.

The double-rod serial connection high-power solid-state laser of the present invention is characterized in that it satisfies the following conditions at the same time:

Select two high-power laser modules with the same average effective thermal focal length f, radial thermal focal length fr, and tangential thermal focal length fθ for two-rod serial connection;

The laser resonator chooses a symmetrical parallel plane structure;

The distance between the rods 3 of the laser is selected to be twice the distance between the rods 3 and the cavity mirror, and the distance between the rods 3 ranges from 1 to 2 times the average thermal focal length f;

Choose two diaphragms 4 with the same aperture and place them symmetrically at both ends of the two serially connected laser rods 3;

Adjust the rod center coaxiality of the two serially connected laser rods 3 .

Two high-power laser modules with the same average effective thermal focal length f, radial thermal focal length fr, and tangential thermal focal length fθ are selected for two rods to be connected in series.

The resonant cavity adopts a symmetrical parallel plane structure, that is, a resonant cavity structure in which two plane mirrors are symmetrically placed on both sides of the laser crystal rod 3 . Compared with other resonators, the symmetrical parallel planar resonant cavity can be equivalent to a resonant cavity when the high-power laser module is connected in series with two rods in a symmetrical structure, and it is easy to match the high-power laser module connected in series with two rods. At the same time, the symmetrical parallel plane resonator has the advantages of large mode volume, small misalignment sensitivity, and the beam waist is located at the output mirror, which is convenient for fiber coupling output. Therefore, the parallel plane resonator is used for the high-power solid-state laser with two rods connected in series.

The distance between the rods 3 and the distance between the rods 3 and the cavity mirror is selected, that is, the distance between the rods is twice the distance between the rods and the cavity mirror, so that the laser works in a stable region. Therefore, the laser can work stably in a wide range of pump power, and the output power increases steadily with the increase of pump power, which is beneficial to obtain the maximum output power. The boundary of the stable working area should be taken into consideration during design, and the distance between the rods 3 ranges from 1 to 2 times the average thermal focal length f.

Two apertures 4 with the same aperture are chosen to be placed symmetrically at both ends of the two serially connected laser rods, so that the radial thermal focal length fr and the tangential thermal focal length fθ match at and near the critical point. Since the radial thermal focal length fr and the tangential thermal focal length fθ of the laser crystal do not pass through the critical point at the same time, it is necessary to select the diaphragm 4 with an aperture size of 0.85-0.95 times the diameter of the laser rod to match the critical point and its vicinity.

The radial matching of the two rods connected in series is adjusted, even if the rod centers of the two rods 3 of the series connected lasers are coaxial. Although the laser rod can be equivalent to a positive lens element, it is also a working substance. High power output requires a large working mode volume. Only when the two rods of the two series connected lasers are radially matched can there be high power output.

To sum up, if the above five-point matching method is satisfied, the matching of the two laser modules is adjusted according to these five points. The maximum output power of the laser can reach 1100-1200W, the beam quality is 21-25mm·mrad, and the overall electro-optical conversion efficiency is 3.8%-4.1%.

Description of drawings:

Figure 1. The schematic structure diagram of the laser

Figure 2. Power supply pump power and output laser power diagram

Figure 3. The power density of the output laser beam is measured

In the figure, 1 is a total reflection mirror, 2 is a partial reflection coupling output mirror, 3 is a rod, and 4 is an aperture.

Detailed ways:

The specific embodiment of the utility model is described below in conjunction with accompanying drawing:

Please refer to Figure 1 for the principle structure of the laser. The parameters of the laser module connected in series by two rods are: the laser crystal rod 3, that is, the Nd:YAG rod, has a size of φ9mm×155mm, and the pump lamp is a krypton lamp of φ8mm×150mm; glaze. The reflectivity of the ceramic body to the absorption band of the gain medium is greater than 97%; the laser cavity adopts full-cavity water cooling, and the cooling is provided by a double-circulation water cooling system, and the temperature is 20°C (±1°C); the laser is implemented with double lamp pumping, and the power supply The maximum pump power is 16kW. This matching method is also applicable to lasers pumped by a single lamp.

The thermal focal length of the two power laser modules connected in series is measured. When the maximum pump power is 16kW, the average thermal focal length f is 150mm, and the corresponding radial thermal focal length fr and tangential thermal focal length fθ are respectively 170mm (± 2mm), 130mm (±2mm).

A symmetrical parallel plane resonant cavity structure is adopted, the distance between the rods 3 is 230mm, and the distance between the main surface of the rods 3 and the cavity mirror is 115mm; the cavity mirror is composed of a total reflection mirror 1 and a partial reflection coupling output mirror 2 with a reflectivity of 80%; Two diaphragms 4 are placed symmetrically between the rod 3 and the cavity mirror, the distance from the end face of the rod is 60 mm, and the aperture of the diaphragm 4 is 8.5 mm; the centers of the rods of the two serially connected laser modules are coaxial.

Measure the power of the output laser. The output power of the laser increases nearly linearly with the pump power. When the maximum power pump power is 30kW, the output power is 1176W. The power pump power and output laser power are shown in Figure 2. Use a high-power beam spot quality diagnostic instrument to measure the power density of the output laser beam, as shown in Figure 3. Since the beam waist of the laser output laser is at the output mirror, the output laser beam is focused by the lens, and the output laser beam quality is measured by the "hole method", that is, the high-power beam spot quality diagnostic instrument is used to measure the laser beam at the focus beam waist and the focal length of the lens. The radius of the light intensity of 86% and the corresponding distance are obtained to obtain the beam quality of the output laser beam as 23mm·mrad. The highest output power and the injected electric power are measured under the condition of high beam quality, and the overall electro-optical conversion efficiency of the laser is found to be 4%.

Claims (1)

1. A double-rod cascaded high-power solid-state laser, characterized in that it satisfies the following conditions simultaneously: Select two high-power laser modules with the same average effective thermal focal length f, radial thermal focal length fr, and tangential thermal focal length fθ for two-rod serial connection; The laser resonator chooses a symmetrical parallel plane structure; The distance between the rods (3) of the laser is selected to be twice the distance between the rods (3) and the cavity mirror, and the distance between the rods (3) ranges from 1 to 2 times the average thermal focal length f; Select two diaphragms (4) with the same aperture and place them symmetrically at both ends of the two serially connected laser rods (3); Adjust the rod centers of the two serially connected laser rods (3) to be coaxial.

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