WO2008014640A1

WO2008014640A1 - Fourth harmonic generating solid laser device

Info

Publication number: WO2008014640A1
Application number: PCT/CN2006/002077
Authority: WO
Inventors: Yunfenq Gao; Yuchao Zhou; Junhul Zheng; Jun Li; Shuzhen Ma
Original assignee: Shenzhen Han's Laser Technology Co., Limited
Priority date: 2006-07-08
Filing date: 2006-08-16
Publication date: 2008-02-07
Also published as: CN100511881C; CN101102033A

Abstract

A fourth harmonic generating solid laser device includes a second harmonic generating cavity (11), a fourth harmonic generating cavity (12), the two cavities are designed independently, each of the optic devices in the fourth harmonic generating cavity (12) is connected with a motors (15,16) respectively, the motor (15,16) is connected with a computer. When one of a film of the surface of the optic devices is deteriorated, the optic device is displaced to another place by the motor. Therefore, the laser has long life.

Description

Fourth harmonic solid state laser

The invention relates to a fourth harmonic solid state laser. Background technique

In recent years, with the rapid development of the laser processing industry, laser processing has penetrated into various fields. Especially in the field of laser fine processing, compared with machining equipment, no consumables in laser processing, no vibration, no need for coolant, and the ability to process any shape, laser processing equipment is replacing the tradition step by step in fine processing. 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 Company of the United States has developed a laser average power of l~3wNd: YAG Q-quad four-frequency laser, mainly used for laser marking and TFT cutting; developed a laser power 200mw continuous quadruple-frequency laser, mainly used for semiconductor silicon wafers. Quality inspection and microlithography.

Spectra-Physics has developed a laser average power of l~2w Q-switched Nd: YV0 ₄ and lw continuous quadruple-frequency lasers, which can be used for wafer cutting, gem substrate dicing, drilling microvia, FBG manufacturing and DVD disc engraving. system.

In order to generate high-power fourth-order harmonic lasers, the harmonics are usually focused outside the laser cavity to a quadruple-frequency nonlinear crystal, and sufficient second-harmonic power density is obtained to improve the frequency-doubling efficiency, such as the US patent of Sony Corporation. US Pat. No. 6,249,371 and Acuhighr, US Pat. No. 6,716,620 B2, and Spectra-Physics and Coherent also use this method of single-pass frequency over the cavity. This method is simple and stable, but in order to achieve a four times higher The frequency conversion efficiency must be refocused on the quadruple-frequency nonlinear crystal by the second harmonic. Therefore, the high-power density fourth-order harmonic laser generated on the quadruple-frequency nonlinear crystal is liable to cause nonlinear medium damage. In addition, the second harmonic that is not converted to the fourth harmonic will be wasted through the nonlinear crystal. Therefore, the conversion efficiency of the fourth harmonic laser is also limited.

Another laser Q-switched fourth-order harmonic generation method is a harmonic wave series method in a fundamental wave cavity. U.S. Patent No. 6,697,391 B2 to Lightwave Electronics and U.S. Patent No. 6,229,829 to Photonics Industries International. This method utilizes the high power density of the fundamental wave in the cavity to improve the conversion efficiency of the harmonics. In order to avoid the damage of the components in the cavity by the ultraviolet light, the fourth harmonic laser is extracted out of the cavity by using a prism or a non-linear crystal end face. The method is based on the one-way harmonic action, and the second harmonic laser that is not converted to the fourth harmonic is still wasted, thereby limiting the fourth harmonic output power. In order to increase efficiency and achieve high power output, U.S. Patent No. 5,278,852 to Kigre and U.S. Patent No. 5,943,351 to Quantronix, respectively, disclose intracavity subcavities and Multiple reflection method. Using the intracavity second harmonic frequency doubling light to multiply and multiply multiple times on the fourth harmonic crystal to produce a high efficiency, high power fourth harmonic laser output. The problem with this method is that the ultraviolet laser output is a double beam, Output power and laser mode are limited.

The above-mentioned commonly used fourth harmonic crystal is BBO, and the second harmonic laser is doubled to obtain the ultraviolet band on the BBO. US Patent No. 6,249,371 of the sony company uses the fundamental wave and the third harmonic to mix 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 transmission. Optical performance, Japan Research Development used CLBO to generate fourth harmonic and fifth harmonic deep ultraviolet laser. However, CLBO is easy to deliquesce and the material is soft and brittle, and needs to be gradually improved to be used in industrial products.

The domestic fourth-order harmonic ultraviolet laser is still in the basic research stage. The cooperation between Nanjing University and Shandong Normal University is to obtain 63mw/266mn laser output by the out-of-cavity focusing frequency multiplication method (《Journal of Physics》, He Jingliang, et al., Volume 49, No. 10, 2000, 2106~2108). The continuous 266 nm laser signal was detected by the external cavity resonance method used by Xi'an Opto-mechanics (Journal of Photonics, Chen Guofu et al., Vol. 28, No. 8, 1999, p. 684 687). Tsinghua University and Peking University jointly studied the use of CLBO nonlinear crystal frequency doubling to obtain a 78mw/266nm laser (Journal of Synthetic Crystals, Sun Tongqing et al., Vol. 33, No. 2, 2004, pp. 133-135). Summary of the invention

The problem to be solved by the present invention is to provide a stable fourth harmonic harmonic solid laser output, and the light conversion efficiency is high. The fourth harmonic cavity and the second harmonic cavity are designed as independent modules, which are convenient to be replaced. Fourth-order harmonic solid-state laser with long life of UV devices.

The technical solution adopted by the present invention to solve the technical problem thereof is: a fourth harmonic solid laser comprising a second harmonic generating cavity, a fourth harmonic generating cavity, a second harmonic generating cavity and a fourth harmonic The wave generating cavity is modularly designed independently. The optical components passing through the fourth harmonic of the fourth harmonic generating cavity are correspondingly equipped with motors, which are connected to the computer, when the fourth harmonic laser passes through the surface of the optical device. As the film begins to degrade, the computer controls the motor to move the optics so that the fourth harmonic laser passes through the undegraded portion of the remaining layers of the optic.

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

The fourth harmonic cavity includes an angle mirror, an end mirror, and a quadruple frequency nonlinear crystal. The second harmonic laser shaped by the shaping system is injected into the quadruple frequency nonlinear crystal, and is repeatedly applied to the end mirror. Reflected by The angle mirror outputs a quadratic harmonic solid laser that is accumulated multiple times.

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

The quadruple-frequency nonlinear crystal used may be a class I LBO, a class I BBO or a class I CLBO nonlinear crystal.

The fundamental solid-state laser medium used in the pump module can be ^(1 _: ¥8 0^±^04, :¥1^, Nd: Glass, Yb: YAG or Er: YAG.

The Q switch used can be an acousto-optic switch, an electro-optic switch, or a saturation-activated passive Q-switch.

The pump source can be used for high power semiconductor laser diode end pumping, diode side pumping, or xenon lamp, xenon lamp side pumping.

The second harmonic generation cavity is 45. Angle folded cavity structure, small angle folded cavity structure or Brewster angle folded cavity structure.

The fourth harmonic generation cavity adopts a 45 ^Q angle folding cavity structure, a small angle folding cavity structure or a Brewster angle folding cavity structure.

The motor that moves the fourth harmonic laser device can be a stepping motor, a servo motor, or a piezoelectric motor. The moving trajectory of the moving fourth harmonic laser device can be straight or rotated.

The movement of the fourth harmonic laser device can be either moving alone or simultaneously.

The technical effect produced by the present invention is: In the fourth harmonic solid-state laser of the present invention, the infrared fundamental wave resonator is designed to balance the high power density stable cavity structure with the laser medium thermal lens, and form a high linear polarization laser oscillation. Under these conditions, a high power density fundamental wave is generated.

A semiconductor pumped solid-state laser cavity with high power density fundamental wave and efficient harmonic conversion efficiency are designed by matrix optics. The high power density fundamental wave is applied to the second frequency nonlinear crystal to generate the second harmonic, and the second harmonic output is then optically shaped and injected into the quadruple frequency nonlinear crystal, and the second harmonic cavity is used. The external multiple reflection method causes the second harmonic to form a closed circuit multiple total reflection, and generates a quadratic harmonic solid laser output that is accumulated multiple times, and the second harmonic that is not converted into the fourth harmonic passes through the nonlinear crystal multiple times. The frequency multiplication is utilized to make full use of the second harmonic power to achieve high conversion efficiency. The method of beam shaping and non-focusing beam is used to extend the service life of the single-point film layer on the surface of the fourth harmonic optical component.

The fourth harmonic solid-state laser of the invention modularly designs the second harmonic and the fourth harmonic cavity, which makes the assembly adjustment simple and easy to repair and replace.

The fourth harmonic solid-state laser of the invention adopts computer-controlled motor displacement technology for all optical components passing through the fourth harmonic, wherein the mechanical design is stable and compact, the computer control is precise, and the displacement track such as straight line and rotation is included, and the displacement recording function is provided. , so that the life of the laser is equal to the final optical components multiplied by the total number of single points of life ^_ a movable point. DRAWINGS

The invention will now be further described with reference to the drawings and embodiments.

1 is a schematic view showing the principle of an optical path of a fourth harmonic solid laser according to the present invention.

2 is a schematic diagram of the general principle of opto-mechanical electromechanical of a fourth harmonic solid laser according to the present invention

Fig. 3 is a graph showing the experimental results of the fourth harmonic solid 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 a graph showing the experimental results of the four-order harmonic solid 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 (I = 34A).

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

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

The element generating the second harmonic includes a nonlinear crystal 4, an end total reflection mirror 1, an end total reflection mirror 5, and an angle mirror 6, wherein the nonlinear crystal 4 is used as a double frequency crystal. Angle mirror 6 plated wave high reflection and secondary harmonic high transmission two-color film. The second harmonic constitutes a closed low-loss polarization coupled total reflection, and the formation process is as follows: The fundamental wave from the direction of the total reflection mirror 5, the horizontally polarized second harmonic light is generated in the double frequency crystal 4, the second harmonic The light is output through the angle mirror 6.

The elements producing the fourth harmonic include a nonlinear crystal 9, an angle mirror 8 and an end total reflection mirror 10, which are single-ended open-type reflective cavity structures with low loss, single beam output characteristics, wherein the nonlinear crystal 9 is quadrupled Frequency crystal. The fourth harmonic generation process 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 crystal 9 to generate a fourth harmonic of vertical polarization. The laser, the quadruple-frequency harmonic laser is reflected back from the original path by the end-reflecting mirror 10, and is output through the angle mirror 8. The second harmonic that is not converted is again formed by the shaping system 7, the angle mirror 6, and the total reflection mirror 5 After reflection, it acts on the quadruple frequency crystal 9, and the regenerated fourth harmonic light is coupled out through the angle mirror 8. Thus, multiple round trips are multiplied in the quadruple frequency crystal 9, thus producing 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 four-frequency experimental device is used for the test. Figure 3 shows the experimental results of the fourth harmonic laser power and pulse width curve corresponding to different input currents (F=14KHZ). Figure 4 shows the fourth harmonic solid laser power and pulse width variation curves corresponding to different repetition frequencies. Experimental results, Figure 5 is the pulse waveform of the fourth harmonic laser (F=14KHZ, I=34A) o

The optomechanical principle of the fourth harmonic solid laser of the present invention is as shown in FIG. 2, which includes a second harmonic laser generating module 11 for generating a second harmonic laser, a fourth harmonic laser generating module 12 for generating fourth harmonics, and The electronically controlled displacement motors 13, 15, and 16, and the mechanical connector 14 connecting the quadruple frequency crystal 9 and the end total reflection mirror 10, the industrial computer 17 controls the movement of the electronically controlled displacement motors 13, 15, 16.

First, the second harmonic laser generating module 11 outputs the second harmonic laser shaped by the shaping system 7, and then the fourth harmonic laser generating module 12 is coupled to the second harmonic laser generating module 11 by mechanical means. Can get the fourth harmonic laser output.

Long-term operation of the fourth-order harmonic solid-state laser causes degradation of the surface film of the angle mirror 8, the quadruple-frequency crystal 9 and the end total reflection mirror 10: "causes the fourth-order harmonic laser power to drop. At this point, the command is sent by software. The industrial computer 17, the industrial computer 17 sends a signal and controls the operation of the electronically controlled displacement motor 13, 15, 16 to move the angle mirror 8 and the mechanical connector 14 to a position, wherein the movement of the mechanical connector 14 drives the quadruple frequency crystal 9 and Simultaneous movement of the end total reflection mirror 10. After the movement, the fourth harmonic laser passes through the new positions of the angle mirror 8, the quadruple frequency crystal 9 and the end total reflection mirror 10, avoiding the point where the film layer has degraded, thus four The subharmonic laser power is re-elevated to the highest power.

In order to ensure that the fourth harmonic laser output light path is unchanged, the movement of the angle mirror 8 is vertical, rotated or laterally moved along the angular direction of the angle mirror 8. Since the positions of the quadruple-frequency crystal 9 and the end total reflection mirror 10 are in a parallel relationship, the electrically-controlled displacement motors 15, 16 control the quadruple-frequency crystal 9 and the end total reflection mirror 10 to move in both the vertical and lateral directions.

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 may be an LBO, BBO or CLBO nonlinear crystal; the quadruple-frequency nonlinear crystal used may be a class I LBO, Class I BBO or Class I CLBO nonlinear crystal; the fundamental solid-state laser medium used may be: Nd: YAG, Nd: YV04, Nd: YLF, Nd: Glass, Yb: YAG or Er: YAG; Q switch used It can be an acousto-optic switch, an electro-optic switch or a saturation-activated passive Q-switch. In addition, the pump source used may be a high power semiconductor laser diode end pump, a diode side pump, or a xenon lamp or a xenon lamp side pump. The cavity structure can be folded at a small angle, 45. An angular folded cavity structure or a Bruce angle folded cavity structure. The displacement motor used may be a stepping motor, a servo motor, a piezoelectric motor or the like. The movement of the angle mirror is vertical, rotated or laterally moved along the angular direction in which the angle mirror is placed. The quadruple-frequency crystal and the end-to-end mirror can be moved simultaneously in the vertical and lateral directions, or individually. When moving alone, the end-reflecting mirror can be rotated.

Claims

1. A fourth harmonic solid state laser comprising a second harmonic generating cavity and a fourth harmonic generating cavity, wherein: the second harmonic generating cavity and the fourth harmonic generating cavity are modularly independent. Designed, the optics passing through the fourth harmonic of the fourth harmonic generation cavity are equipped with motors, which are connected to the computer. When the fourth harmonic laser passes through the surface of the optical device that begins to degrade, The computer controlled motor moves the optics such that the fourth harmonic laser passes through the undegraded portion of the remaining layers of the optic.

2. The fourth harmonic solid state laser according to claim 1, wherein: the second harmonic cavity comprises a pump module, a Q switch, a double frequency nonlinear crystal, an end mirror, an angle mirror and In the shaping system, the pump module generates high-power density fundamental light, and the fundamental wave is reflected by the end mirror and then incident on the second-frequency nonlinear crystal, and the second harmonic laser is transmitted through the angle mirror and the shaping system.

3. A fourth harmonic solid state laser according to claim 2, wherein: the fourth harmonic cavity comprises an angle mirror, an end mirror, a quadruple frequency nonlinear crystal, and a quadratic harmonic after being shaped by the shaping system. The wave laser is incident on the quadruple-frequency nonlinear crystal, and the fourth-order harmonic solid laser that is accumulated multiple times by the angle mirror is outputted under the multiple reflection of the end mirror.

4. A fourth harmonic solid state laser according to claim 2, wherein: the double frequency nonlinear crystal used may be an LBO, BBO or CLBO nonlinear crystal.

The fourth harmonic solid state laser according to claim 3, wherein the quadruple frequency nonlinear crystal used is a class I LBO, a class I BBO or a class I CLBO nonlinear crystal.

6. The fourth harmonic solid state laser according to claim 2, wherein: the fundamental solid laser medium used in the pumping module can be: Nd _: YAG, Nd: YV04, Nd: YLF, Nd: Glass. Yb: YAG or Er: YAG. -

7. A fourth harmonic solid state laser according to claim 2, wherein: the Q switch used can be an acousto-optic switch, an electro-optical switch or a saturation-excited passive Q-switch.

8. The fourth harmonic solid state laser according to claim 2, wherein the pumping light source is a high power semiconductor laser diode end pump, a diode side pump, or a xenon lamp, or a xenon lamp side pump. One-

9. The fourth harmonic solid state laser according to claim 2, wherein: the second harmonic generating cavity adopts a 45 ^Q angle folding cavity structure, a small angle folding cavity structure or a Brewster angle folding cavity structure.

10. The fourth harmonic solid state laser according to claim 3, wherein: the fourth harmonic generating cavity adopts a 45 ^Q angle folding cavity structure, a small angle folding cavity structure or a Brewster angle folding cavity structure.

11. The fourth harmonic solid state laser according to claim 1, wherein the motor for moving the fourth harmonic laser device is a stepping motor, a servo motor, and a piezoelectric motor.

12. The fourth harmonic solid state laser according to claim 1, wherein: moving the fourth harmonic The moving trajectory of the wave laser device can be straight or rotated.

13. A fourth harmonic solid state laser according to claim 1, wherein: the movement of the fourth harmonic laser device can be moved individually or simultaneously.