CN100470968C - Pulsed Lasers for Improved Output Beam Quality - Google Patents

Abstract

A pulsed laser for improving the quality of an output beam belongs to the technical field of lasers, and is characterized in that the laser includes a pump source, a laser gain medium, a saturable absorbing device, and a cavity mirror. By changing the loss of the saturable absorbing device along the radial direction, the high-order transverse mode can be effectively suppressed, and the laser output with high beam quality can be obtained. Specifically, it can be realized by changing the absorption factor in the radial direction of the saturable absorbing device, or plating a variable reflectivity film on the light-transmitting surface of the saturable absorbing device. The invention has the advantages of being simple and effective, stable and reliable in operation, and solves the problems of increased system complexity and decreased stability caused by the traditional technology.

Description

Pulsed Lasers for Improved Output Beam Quality

technical field

The invention relates to a laser, in particular to a pulse laser with high beam quality, and belongs to the technical field of lasers.

Background technique

Pulsed lasers play an important role in industrial processing, information transmission, remote sensing and other fields. At present, Q-switching technology is commonly used to obtain laser pulses with high peak power and short duration. In many industrial and military applications, laser output beams are required to have high beam quality. At present, measures such as diaphragm mode selection, special stable cavity or unstable cavity are generally used, and these measures either reduce the efficiency of the laser, increase the complexity of the resonator, or reduce the stability of the system. However, under the same laser operating parameters, the output beam quality of passively Q-switched lasers is better than that of actively Q-switched lasers, which is mainly due to the dynamic aperture characteristics of saturable absorbing devices.

The effect of the dynamic aperture characteristics of saturable absorbing devices on improving the quality of laser output beams has been discussed in many optical professional works (such as: Lan Xinju, Laser Technology, Science Press, second edition, 2005, 125 Page). As early as 1965, W.R. Sooy theoretically analyzed the mode selection characteristics of saturable absorption devices (see W.R. Sooy, The natural selection of modes in a passive q-switched laser, Applied Physics Letters, v 7, p36-37 for details ). In 2002, Zheng Quan and others reported the effect of Cr:YAG on the selection of transverse mode and longitudinal mode when used as a passive Q-switching element (see Zheng Quan, Chen Yingxin, Zhao Ling, Qian Longsheng, Saturable absorbing material Cr:YAG The role of mode selection in passive Q-switching components, Acta Photonica Sinica, Vol. 31, pp. 550-552). In 2006, Junewen Chen et al. reported the cross-mode selection characteristics of various saturable absorbing materials used as slow Q switches (see Junewen Chen, Jun-Ting Linand Ou-Yang Mang, Smaller output beam divergence in the slowly opened Q-switch operation, Optical Review, v13, p69-76).

In addition, the use of variable reflectivity mirrors as output coupling mirrors can also improve the quality of the output beam. This point has also been discussed in many optical professional works (such as: written by W. Kirchner, translated by Sun Wen, Jiang Zewen, Cheng Guoxiang , Solid Laser Engineering, Science Press, 2002, 243 pages).

In order to further improve the transverse mode selection characteristics of the passively Q-switched laser, the present invention proposes a pulsed laser for improving the quality of the output beam.

Contents of the invention

The object of the present invention is to provide a pulsed laser device for improving the quality of the output beam. The laser has the advantages of high output beam quality, simple structure, stable and reliable operation, and strong practicability.

The present invention is characterized in that: a pulsed laser for improving the output beam quality, comprising: a pump source, a laser gain medium, a saturable absorbing device, and a cavity mirror, and the cavity mirror at least includes a rear cavity mirror and an output mirror The rear cavity mirror is highly reflective to the laser; the emission spectrum of the pump source matches the absorption spectrum of the laser gain medium; the laser gain medium produces laser output, and the saturable absorption device has a saturable emission wavelength for the laser gain medium Solid laser working material with absorption characteristics; the pump light emitted by the pump source can be directly or incident on the laser gain medium after passing through the coupling device. The doping concentration changes along the radial direction, the center doping concentration is low, and the edge doping concentration is high; the transmittance of the coating of the output mirror to the laser wavelength is set.

The rear cavity mirror can be plated on the end surface of the laser gain medium facing the pump source in the form of an optical dielectric film to increase the transmission of the pump light. The pump light emitted by the pump source can be coupled through an optical fiber, and the lens is focused and incident On the laser gain medium, the coating on the light-transmitting surface facing the output of the laser gain medium is anti-transmissive to the laser wavelength.

The output mirror can be an optical thin film coated on the light-transmitting surface of the saturable absorbing device, whose reflectivity changes along the radial direction.

The optical film whose reflectivity changes along the radial direction is plated on the transparent surface of the saturable absorbing device.

The pumping sources are various pumping sources including semiconductor lasers and flash lamps, and the pumping methods are various pumping methods including end pumping and side pumping.

The laser adopts various cavity structures including straight cavity, folded cavity and ring cavity.

The laser gain medium can be combined with a saturable absorption device to form a composite medium.

Laser gain elements and saturable absorption elements can be doped into the laser gain medium at the same time to form a self-saturated absorption laser medium.

The back cavity mirror may be a separate back cavity mirror.

Compared with the prior art, the present invention has the following advantages and outstanding effects: the present invention proposes to change the reflectance film by changing the radial absorption factor of the saturable absorbing device, or on the light-transmitting surface of the saturable absorbing device The method of improving the quality of the output beam has the advantages of being simple, effective, stable and reliable, and solves the problems of increasing system complexity and reducing stability caused by traditional technologies.

Description of drawings

FIG. 1 is a schematic structural diagram of a first embodiment of a pulsed laser for improving output beam quality provided by the present invention.

Fig. 2 is a schematic structural diagram of a second embodiment of a pulsed laser for improving output beam quality provided by the present invention.

Fig. 3 is a schematic structural diagram of a third embodiment of a pulsed laser for improving output beam quality provided by the present invention.

Fig. 4 is a schematic structural diagram of a fourth embodiment of a pulsed laser for improving output beam quality provided by the present invention.

Fig. 5 is a schematic structural diagram of a fifth embodiment of a pulsed laser for improving output beam quality provided by the present invention.

In Figures 1 to 5, 1—semiconductor laser, 2—coupling fiber, 3—coupling lens, 4—back cavity mirror plated on the gain medium in the form of an optical dielectric film, 5—laser gain medium, 6—optical surface The saturable absorbing device processed into a concave surface, 7—output mirror, 8—the saturable absorbing device whose doping concentration of the saturable absorbing element changes along the radial direction, 9—the output plated on the saturable absorbing device in the form of a variable reflectivity film Mirror, 10—laser medium with self-saturated absorption processed into concave surface

Detailed ways

Fig. 1 is the first embodiment of the pulsed laser for improving the output beam quality provided by the present invention. The idea of the present invention can be applied to lasers of various cavity types, such as straight cavity, folded cavity, ring cavity, etc. Various pumping sources and various pumping methods such as semiconductor lasers and flash lamps can be used. Here, the choice of straight cavity and semiconductor laser end-pumping method is only used as a convenient embodiment of the present invention.

In the first embodiment, the light-passing surface of the saturable absorbing device 6 is processed into a concave surface, and the two light-passing end faces are coated with an anti-reflection film corresponding to the laser wavelength. The pumping light emitted by the semiconductor laser 1 is coupled through the optical fiber 2 and focused by the lens 3 to enter the laser gain medium 5 . The emission spectrum of the semiconductor laser 1 matches the absorption spectrum of the gain medium 5 . The rear cavity mirror 4 is anti-reflective to pump light and highly reflective to laser light. In this embodiment, the rear cavity mirror 4 is plated on the end face of the gain medium 5 facing the pump in the form of an optical dielectric film, of course, a separate rear cavity mirror can also be used. The laser gain medium 5 is a solid-state laser working material that can generate laser output and the saturable absorption device 6 has saturable absorption characteristics for its emission wavelength, such as Nd:YAG, Yb:YAG, Nd:YVO ₄ , Nd:glass, etc. . The coating on the light-transmitting surface of the laser gain medium 5 facing the output is anti-transmissive to the laser wavelength. The coating of the front cavity mirror 7 has a certain transmittance to the laser wavelength.

In the first embodiment, the saturable absorbing device 6 itself has a dynamic aperture characteristic, mainly because the oscillating light beam has the highest intensity near the central axis, so that the position of the saturable absorbing device 6 at and near the center of the axis is first bleached, For the position farther from the axis, because of the low incident light power density, it is not easy to be bleached, so the loss is large, which makes it difficult for the high-order transverse mode to form oscillation, thereby improving the quality of the output beam. By processing the light-passing surface of the saturable absorbing device 6 into a concave surface or a convex surface, the central absorption is weak and the edge absorption is strong. Since the mode radius of the high-order transverse mode is generally larger than that of the fundamental transverse mode, the absorption of the high-order transverse mode is stronger than that of the fundamental transverse mode. Therefore, the high-order transverse mode is less likely to oscillate, which further enhances the dynamic aperture characteristics of the saturable absorbing device 6 , thereby further improving the quality of the output beam.

Fig. 2 is the second embodiment of the pulsed laser for improving the quality of the output beam provided by the present invention, wherein, in the saturable absorbing device 8, the doping concentration of the saturable absorbing element changes along the radial direction, and simultaneously it moves towards the output A variable reflectivity film 9 is plated on the light-transmitting surface as an output mirror. Set the doping concentration of the saturable absorbing element to be high in the center and low in the edge. The variable reflectivity film 9 is an optical film with variable radial reflectivity, generally with high reflectivity at the center and low at the edge. Considering that the mode radius of the high-order transverse mode is generally larger than that of the fundamental transverse mode, the loop loss of the high-order transverse mode is higher than that of the fundamental transverse mode. Therefore, the high-order transverse mode is not easy to vibrate, thereby improving the quality of the output high beam.

Fig. 3 is the third embodiment of the pulsed laser used to improve the output beam quality provided by the present invention. It is characterized in that the end face of the saturable absorbing device 6 is processed into a concave surface, and the surface of the saturable absorbing device facing the output is plated The variable reflectivity film 9 serves as an output mirror. Therefore, the mode selection effect of the saturable absorbing device is further enhanced, thereby improving the quality of the output high beam.

Fig. 4 is the 4th embodiment of the pulsed laser that is used to improve output beam quality that the present invention provides, it is characterized in that, laser gain medium 5 and saturable absorption device 6 are combined into a kind of composite medium, its implementation principle is the same as that of the present invention The first embodiment is basically the same.

Fig. 5 is the fifth embodiment of the pulsed laser used to improve the quality of the output beam provided by the present invention, which is characterized in that laser gain elements and saturable absorption elements are simultaneously mixed in the laser gain medium to form a self-saturated absorption laser The implementation principle of the medium 10 is basically the same as that of the first embodiment of the present invention.

Claims (9)

1. The pulsed laser for improving the output beam quality is characterized in that it contains at least: pumping source (1), laser gain medium (5), saturable absorbing device (6, 8), cavity mirror (4, 7, 9), the cavity mirror at least includes a rear cavity mirror (4) and an output mirror (7, 9); the rear cavity mirror (4) is highly reflective to laser light; the emission spectrum of the pump source (1) and the laser gain medium The absorption spectrum of (5) matches; Laser gain medium (5) is to produce laser output, and described saturable absorption device (6,8) has the solid-state laser of saturable absorption characteristic to the emission wavelength of this laser gain medium (5) Working substance; the pumping light emitted by the pumping source (1) is incident on the laser gain medium (5) directly or through the coupling device (2, 3), and the light-passing surface of the saturable absorbing device (6, 8) is processed into Concave or convex, or the doping concentration of saturable absorbing ions changes along the radial direction, with low doping concentration at the center and high doping concentration at the edge; the transmittance of the output mirrors (7, 9) to the laser wavelength is set. 2. the pulsed laser that is used to improve output beam quality according to claim 1, is characterized in that, described rear cavity mirror (4) is plated on laser gain medium (5) towards pumping source ( On the end face of 1), the pump light is enhanced, the pump light emitted by the pump source (1) is coupled through the optical fiber (2), the lens (3) is focused and incident on the laser gain medium (5), the laser The coating film on the light-transmitting surface of the gain medium (5) facing the output is anti-transmissive to the laser wavelength. 3. The pulse laser for improving the output beam quality according to claim 1, characterized in that, the output mirror (7, 9) is a kind of mirror plated on the light-passing surface of the saturable absorbing device (6, 8). The optical film (9) whose reflectivity changes along the radial direction has high reflectivity at the center and low reflectivity at the edges. 4. the pulsed laser that is used to improve output beam quality according to claim 1, is characterized in that, the optical thin film ( 9), the center reflectivity is high and the edge reflectivity is low. 5. The pulse laser for improving output beam quality according to claim 1, characterized in that, the pumping source (1) is a laser or a flash lamp, and the pumping mode is one of end pumping and side pumping kind. 6 . The pulsed laser for improving the output beam quality according to claim 1 , wherein the laser adopts one of straight cavity, folded cavity and ring cavity structures. 7 . 7. The pulsed laser for improving the output beam quality according to claim 1, characterized in that the laser gain medium (5) and the saturable absorption device (6) are combined into a composite medium. 8. The pulsed laser for improving output beam quality according to claim 1, characterized in that, in the laser gain medium (5), doping laser gain elements and saturable absorption elements simultaneously constitutes a self-saturated absorption Laser media (10). 9. The pulsed laser for improving output beam quality according to claim 1, characterized in that, the rear cavity mirror (4) is a separate rear cavity mirror.

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