CN100511881C - Four-time harmonic solid laser - Google Patents

Abstract

A fourth harmonic solid-state laser, including a second harmonic generation cavity, a fourth harmonic generation cavity, a modular independent design of the second harmonic generation cavity and the fourth harmonic generation cavity, in the fourth harmonic The optical devices that the fourth harmonic passes through in the wave generation cavity are equipped with motors, and these motors are connected to the computer. When the fourth harmonic laser makes the film on the surface of the optical device that it passes through begin to degrade, the computer controls the motor to move each optical device. Device, pass the fourth harmonic laser through the undegraded part of the remaining film layers of the optical device. The modular design of the second harmonic laser generating part and the fourth harmonic laser generating part makes the installation and adjustment simple and the maintenance and replacement easy. The optical components passed by the fourth harmonic adopt computer-controlled motor displacement technology. The displacement trajectory includes linear movement and rotational movement. Move to make the fourth harmonic laser pass through the undegraded part of the remaining film layers of the optical device, so that the final life of the laser is equal to the service life of a single point of the optical component multiplied by the total number of movable points.

Description

Fourth harmonic solid-state laser

Technical field

The invention relates to a fourth harmonic solid laser.

Background technique

In recent years, with the rapid development of the laser processing industry, laser processing has penetrated into various fields. Especially in laser fine processing, compared with mechanical processing equipment, laser processing has no consumables, no vibration, no cooling fluid, and can process any shape. In fine processing, laser processing equipment is replacing traditional laser processing equipment step by step. mechanical processing equipment. The short-wavelength high-power ultraviolet laser has become an important development direction of laser fine processing due to its high resolution, high absorption, and cold processing.

Coherent Corporation of the United States has developed a Nd:YAG Q-switched quadruple frequency laser with an average laser power of 1-3w, which is mainly used for laser marking and TFT cutting; a continuous quadruple frequency laser with a laser power of 200mw has been developed, which is mainly used for semiconductor silicon wafers. Quality inspection and microlithography.

American Spectra-Physics company has developed laser average power 1~2w Q-switched Nd:YVO ₄ and 1w continuous quadruple frequency laser, which can be used for wafer cutting, gem substrate scribing, micro-hole, FBG manufacturing and DVD disc engraving system.

In order to generate high-power fourth harmonic laser, it is usually used to focus the harmonics onto the quadruple frequency nonlinear crystal outside the laser cavity to obtain sufficient second harmonic power density to improve the frequency doubling efficiency, such as Sony's US patent No. As shown in US 6249371 and Acuhighr US Patent No. US 6741620 B2, Spectra-Physics and Coherent also use this method of extracavity one-way frequency doubling. This method is simple and stable, but in order to achieve a higher four times The frequency conversion efficiency must be refocused on the quadruple frequency nonlinear crystal with the second harmonic, so the high power density fourth harmonic laser generated on the quadruple frequency nonlinear crystal is easy to cause the damage of the nonlinear medium. In addition, the second harmonic that is not converted to the fourth harmonic will be wasted through the nonlinear crystal, so the conversion efficiency of the fourth harmonic laser is also limited.

Another method for generating the fourth harmonic of laser Q-switching is the method of cascading harmonic crystals in the fundamental resonator cavity. Lightwave Electronics US Patent No. US 6697391 B2 and Photonics Industries International Company US Patent No. US 6229829. This method takes advantage of the high power density of the fundamental wave in the cavity and improves the conversion efficiency of harmonics. In order to avoid damage to components in the cavity by ultraviolet light, a prism or oblique nonlinear crystal end face is used to guide the fourth harmonic laser out of the cavity. , the method is based on one-way harmonic action, and the second harmonic laser that has not been converted to the fourth harmonic is still wasted, thus limiting the fourth harmonic output power. In order to improve efficiency and achieve high power output, Kigre Company US Patent No. US5278852 and Quantronix Company US Patent No. US 5943351 proposed intra-cavity sub-cavity and multiple reflection methods respectively. The second harmonic frequency doubling light in the cavity is used to double the frequency on the fourth harmonic crystal multiple times to generate high-efficiency and high-power fourth harmonic laser output. The problem with this method is that the ultraviolet laser output is a double beam, so that Output power and laser mode are limited.

The commonly used fourth harmonic crystal mentioned above is BBO, and the second harmonic laser is frequency-multiplied on BBO to obtain the ultraviolet band. US Patent No. US 6249371 of sony company uses the fundamental wave and the third harmonic to mix on the LBO crystal to obtain the fourth harmonic laser output; in addition, the new nonlinear crystal CLBO has high harmonic conversion efficiency and excellent deep ultraviolet transparency Optical performance, Japan Research Development uses CLBO to produce fourth harmonic and fifth harmonic deep ultraviolet laser. However, CLBO is easy to deliquescence and the material is soft and fragile, so it can be used in industrial products after gradually increasing.

The fourth harmonic ultraviolet laser in China is still in the basic research stage. Nanjing University and Shandong Normal University jointly researched and obtained 63mw/266nm laser output by using extracavity focusing frequency doubling method ("Acta Physica", He Jingliang et al., Vol. 49, No. 10, 2000, pp. 2106-2108). Xi'an Institute of Optics and Mechanics detected continuous 266nm laser signals by the external cavity resonance method ("Acta Photonica Sinica", by Chen Guofu et al., Vol. 28, No. 8, 1999, pp. 684-687). Tsinghua University and Peking University jointly researched and used CLBO nonlinear crystal frequency doubling to obtain 78mw/266nm laser ("Journal of Synthetic Crystals", Sun Tongqing et al., Vol. 33, No. 2, 2004, pp. 133-135).

Contents of the invention

The technical problem to be solved by the present invention is to provide a stable fourth harmonic solid-state laser output with high light conversion efficiency, the fourth harmonic cavity and the second harmonic cavity are designed as independent modules, which is convenient for installation and adjustment Replacement fourth harmonic solid-state lasers with long UV device life.

The technical solution adopted by the present invention to solve the technical problem is: a fourth harmonic solid-state laser, including a second harmonic generation cavity, a fourth harmonic generation cavity, a second harmonic generation cavity and a fourth harmonic The wave generation cavity is modular and independently designed. In the fourth harmonic generation cavity, the optical devices that the fourth harmonic passes through are equipped with motors. These motors are connected to the computer. When the fourth harmonic laser makes it pass through the surface of the optical device When the film layer begins to degrade, the computer controls the motor to move each optical device, so that the fourth harmonic laser passes through the undegraded part of the remaining film layers of the optical device.

The second harmonic cavity includes a pump module, Q switch, double frequency nonlinear crystal, end reflector, angle reflector and shaping system. The pump module generates high power density fundamental wave light, which is reflected by the end reflector Incident to the double-frequency nonlinear crystal, the second harmonic laser is transmitted through the angle mirror and the shaping system to output.

The fourth harmonic cavity includes an angle reflector, an end reflector, and a quadruple frequency nonlinear crystal. The second harmonic laser shaped by the shaping system is injected into the quadruple frequency nonlinear crystal. Under the reflection, the fourth harmonic solid-state laser is output by the angle reflector for multiple accumulations.

The double frequency nonlinear crystal used can be LBO, BBO or CLBO nonlinear crystal.

The frequency quadrupling nonlinear crystal used may be a type I LBO, a type I BBO or a type I CLBO nonlinear crystal.

The fundamental solid-state laser medium used in the pump module can be: Nd:YAG, Nd:YVO4, Nd:YLF, Nd:Glass, Yb:YAG or Er:YAG.

The Q switch used can be an acousto-optic switch, an electro-optic switch or a saturated excitation type passive Q switch.

The pumping light source used can be high-power semiconductor laser diode end pumping, diode side pumping, or krypton lamp or xenon lamp side pumping.

The second harmonic generation cavity adopts a 45° angle folded cavity structure, a small angle folded cavity structure or a Brewster angle folded cavity structure.

The fourth harmonic generation cavity adopts a 45° angle folded cavity structure, a small angle folded cavity structure or a Brewster angle folded cavity structure.

The motor that moves the fourth harmonic laser device can be a stepper motor, a servo motor, a piezoelectric motor.

The moving track of moving the fourth harmonic laser device can be straight line or rotation.

The movement of the fourth harmonic laser device can be independent movement or simultaneous movement.

The technical effect produced by the present invention is: in the fourth harmonic solid-state laser of the present invention, the infrared fundamental wave resonant cavity is designed to balance the high power density stable cavity structure with the laser medium thermal lens, forming a high linearly polarized laser oscillation. Under these conditions, a high power density fundamental wave is generated.

A semiconductor-pumped solid-state laser resonator with high power density fundamental wave and high harmonic conversion efficiency are designed by matrix optics. The high power density fundamental wave is applied to the double frequency nonlinear crystal to generate the second harmonic. After the second harmonic is output, the beam is shaped and injected into the quadruple frequency nonlinear crystal. The multiple reflection method makes the second harmonic form a closed-circuit multiple total reflection, and generates multiple accumulated fourth harmonic solid-state laser output, and the second harmonic that has not been converted into the fourth harmonic passes through the nonlinear crystal for many times. Frequency doubling makes full use of the second harmonic power to achieve high conversion efficiency; the method of unfocused beam after beam shaping is used to prolong the service life of the single-point coating on the surface of fourth harmonic optical components.

The fourth harmonic solid-state laser of the present invention carries out mechanical modular design on the second harmonic and the fourth harmonic cavity, so that the installation and adjustment are simple, and the maintenance and replacement are easy.

The fourth harmonic solid-state laser of the present invention adopts computer-controlled motor displacement technology for all optical components passing by the fourth harmonic, wherein the mechanical design is stable and compact, and the computer control is precise, including linear and rotational displacement tracks, and has displacement recording functions. Make the final life of the laser equal to the life of a single point of optical components multiplied by the total number of movable points.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of the principle of the optical path of the fourth harmonic solid-state laser of the present invention.

Fig. 2 is a schematic diagram of the general opto-mechanical principle of the fourth harmonic solid-state laser of the present invention.

Fig. 3 is an experimental result diagram of the fourth harmonic solid-state laser power and pulse width variation curves corresponding to different input currents in the experiment of the fourth harmonic solid-state laser of the present invention (F=14KHZ).

Fig. 4 is an experiment result diagram (I=34A) of fourth harmonic solid-state laser power and pulse width variation curves corresponding to different repetition frequencies in the experiment of the fourth harmonic solid-state laser of the present invention.

Fig. 5 is a pulse waveform diagram (F=14KHZ, I=34A) of the fourth harmonic solid-state laser generated in the experiment of the fourth harmonic solid-state laser generation method of the present invention.

Detailed ways

The optical principle of the fourth harmonic solid-state laser of the present invention is shown in Figure 1, using a fundamental wave oscillator, which includes a high-power laser diode array end pump module 3, Q switch 2, end total reflection mirrors 1, 5 , 10, nonlinear crystals 4, 9, angle mirrors 6, 8 and shaping system 7, wherein angle mirrors 6, 8 are 45-degree reflectors in the cavity. By calculating and measuring the thermal lens effect of the pump module 3 under different pump powers, and using the optical matrix method to calculate the spatial distribution of the Gaussian mode transfer in the cavity, the cavity length and the curvature of the end mirror are designed to make the infrared laser cavity thermally It still maintains stable oscillation under a wide range of lens changes. A frequency-doubled nonlinear crystal 4 is placed near the light waist of the total reflection mirror 5 at the end. Since the infrared laser cavity is a closed internal total reflection oscillation, which is balanced with the thermal lens effect of high-power pumping, a high intra-cavity power density can be achieved.

The components for generating the second harmonic include a nonlinear crystal 4, a total end reflection mirror 1, a total end reflection mirror 5, and an angle mirror 6, wherein the nonlinear crystal 4 is used as a double frequency crystal. Angle mirror 6 is coated with two-color film with high reflection of fundamental wave and high transmission of second harmonic. The second harmonic constitutes a closed low-consumption polarization coupling internal total reflection, and the formation process is as follows: the fundamental wave light coming from the direction of the end total reflection mirror 5 generates horizontally polarized second harmonic light in the double frequency crystal 4, and the second harmonic The light is output through the angle mirror 6.

The components that generate the fourth harmonic include a nonlinear crystal 9, an angle mirror 8 and a total end reflection mirror 10, which is a single-ended open reflective cavity structure and has the characteristics of low loss and single beam output. Among them, the nonlinear crystal 9 is used as a quadruple frequency crystal. The formation process of the fourth harmonic is as follows: the horizontally polarized second harmonic light from the angle mirror 6 is transmitted through the shaping system 7 and the angle mirror 8 and then incident on the quadruple frequency doubling crystal 9 to generate a vertically polarized fourth harmonic Laser, the quadruple frequency harmonic laser is reflected by the end total reflection mirror 10 and returns from the original path, and is output through the angle mirror 8. After reflection, it acts on the quadrupling frequency crystal 9, and the fourth harmonic light generated again is coupled out through the angle mirror 8. In this way, the frequency is multiplied in the quadrupling frequency crystal 9 for many times, thus generating a very efficient fourth harmonic Laser output.

According to the fourth harmonic solid-state laser of the present invention, a high-power diode laser array end-pumped laser cavity quadruple frequency experimental device is used for testing. Fig. 3 is the experimental result of the fourth harmonic laser power and pulse width variation curve corresponding to different input currents (F=14KHZ), and Fig. 4 is the fourth harmonic solid-state laser power and pulse width variation curve corresponding to different repetition frequencies Figure 5 shows the pulse waveform of the fourth harmonic laser (F=14KHZ, I=34A).

The optomechanical principle of the fourth harmonic solid-state laser of the present invention is as shown in Figure 2, which includes a second harmonic laser generating module 11 for generating second harmonic laser, a fourth harmonic laser generating module 12 for generating fourth harmonic, and also includes Electrically controlled displacement motors 13, 15, 16, and a mechanical connection frame 14 connecting quadruple frequency doubling crystal 9 and end total reflection mirror 10, industrial computer 17 controls the movement of electrically controlled displacement motors 13, 15, 16.

First, the second harmonic laser generation module 11 outputs the second harmonic laser after being shaped by the shaping system 7, and then the fourth harmonic laser generation module 12 is coupled to the second harmonic laser generation module 11 through a mechanical device. A fourth harmonic laser output can be obtained.

The long-term operation of the fourth harmonic solid-state laser will cause the degradation of the surface film layers of the angle mirror 8, the frequency quadrupling crystal 9 and the end total reflection mirror 10, resulting in a decrease in the fourth harmonic laser power. At this time, the software sends commands to the industrial computer 17, and the industrial computer 17 sends signals and controls the operation of the electric control displacement motors 13, 15, and 16 to move the angle mirror 8 and the mechanical connecting frame 14 to a position, wherein the movement of the mechanical connecting frame 14 drives The simultaneous movement of the quadrupling frequency crystal 9 and the end total reflection mirror 10 is realized. After the movement, the fourth harmonic laser passes through the new position of the angle mirror 8, the quadrupling frequency crystal 9 and the end total reflection mirror 10, avoiding the point where the film layer has degraded, so the fourth harmonic laser power rises back to the highest power.

In order to ensure that the output optical path of the fourth harmonic laser remains unchanged, the movement of the angle mirror 8 is vertical, rotated or moved laterally along the angle direction where the angle mirror 8 is placed. Because the positions of the quadruple frequency doubling crystal 9 and the end total reflection mirror 10 are parallel, so the electric control displacement motors 15 and 16 control the quadruple frequency doubling crystal 9 and the end total reflection mirror 10 to move in the vertical and lateral directions simultaneously.

According to the principle of the fourth harmonic solid-state laser of the present invention, it is not difficult to infer that the double frequency nonlinear crystal used can be LBO, BBO or CLBO nonlinear crystal; the used quadruple frequency nonlinear crystal can be Class I LBO, Type I BBO or Type I CLBO nonlinear crystal; the fundamental solid-state laser medium used can be: Nd:YAG, Nd:YVO4, Nd:YLF, Nd:Glass, Yb:YAG or Er:YAG; the Q switch used It can be an acousto-optic switch, an electro-optic switch or a saturated excitation type passive Q switch. In addition, the pumping light source used can be high-power semiconductor laser diode end pumping, diode side pumping, or krypton lamp or xenon lamp side pumping. Small-angle folded cavity structures, 45°-angle folded cavity structures, or Brewster-angle folded cavity structures can be used. The displacement motor used may be a stepper motor, a servo motor, a piezoelectric motor, or the like. The movement of the angle mirror is vertical, rotating or moving laterally along the angle direction where the angle mirror is placed. The frequency quadrupling crystal and the total end reflection mirror can move vertically and laterally at the same time, or move separately. When moving independently, the end total reflection mirror can rotate and move.

Claims (12)

1. A fourth harmonic solid-state laser, comprising a second harmonic generation cavity and a fourth harmonic generation cavity, characterized in that: the second harmonic generation cavity and the fourth harmonic generation cavity are modular and independent Design, in the fourth harmonic generation cavity, the optical devices that the fourth harmonic passes through are equipped with motors, and these motors are connected to the computer. When the fourth harmonic laser causes the film on the surface of the optical device to pass through to degrade, The computer controls the motor to move each optical device, so that the fourth harmonic laser passes through the undegraded part of the remaining film layers of the optical device. 2. The fourth harmonic solid-state laser according to claim 1, characterized in that: the second harmonic generating cavity includes a pump module, a Q switch, a double frequency nonlinear crystal, an end reflector, an angle reflector and Shaping system, the pump module generates high power density fundamental wave light, the fundamental wave light is reflected by the end reflector and then enters the double frequency nonlinear crystal, and the second harmonic laser is transmitted through the angle reflector and the shaping system. 3. The fourth harmonic solid-state laser according to claim 2, characterized in that: the fourth harmonic generating cavity includes angle reflectors, end reflectors, quadruple frequency nonlinear crystals, and the second wave after being shaped by the shaping system The sub-harmonic laser is injected into the quadruple-frequency nonlinear crystal, and the angle reflector outputs the fourth-harmonic solid-state laser accumulated multiple times under the multiple reflections of the end reflector. 4. The fourth harmonic solid-state laser according to claim 2, characterized in that: the double frequency nonlinear crystal used is LBO, BBO or CLBO nonlinear crystal. 5. The fourth harmonic solid-state laser according to claim 3, characterized in that: the quadrupling frequency nonlinear crystal used is a type I LBO, type I BBO or type I CLBO nonlinear crystal. 6. The fourth harmonic solid-state laser according to claim 2, characterized in that: the fundamental solid-state laser medium used in the pump module is: Nd:YAG, Nd:YVO4, Nd:YLF, Nd:Glass, Yb :YAG or Er:YAG. 7. The fourth harmonic solid-state laser according to claim 2, characterized in that: the Q switch used is an acousto-optic switch, an electro-optic switch or a saturated excitation type passive Q switch. 8. The fourth harmonic solid-state laser according to claim 2, characterized in that: the second harmonic generation cavity adopts a 45° angle folded cavity structure, a small angle folded cavity structure or a Brewster angle folded cavity structure. 9. The fourth harmonic solid-state laser according to claim 3, characterized in that: the fourth harmonic generation cavity adopts a 45° angle folded cavity structure, a small angle folded cavity structure or a Brewster angle folded cavity structure. 10. The fourth harmonic solid-state laser according to claim 1, wherein the motor for moving the optical device is a stepper motor, a servo motor or a piezoelectric motor. 11. The fourth harmonic solid-state laser according to claim 1, characterized in that: the movement of the optical device is a linear movement or a rotational movement. 12. The fourth harmonic solid-state laser according to claim 1, characterized in that: the movement of the optical devices is either individually or simultaneously.

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