JPH0936462A - Solid state laser and pumping method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an edge pumping system solid state laser in which both high output and high quality are realized. SOLUTION: A parallel pumping light 1 is converted through a Bessel beam optical system 10 into a Bessel beam which is then directed to the solid state laser medium 40 in an edge pumping system solid state laser. The Bessel beam can have a longer depth of focus for fixed beam diameter and when the oscillation mode region of solid state laser medium 40 is confined in a pumping region determined by the depth of focus and the beam diameter, both high output and high quality can be realized.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to laser processing, measurement,
The present invention relates to a solid-state laser excitation method and a solid-state laser device capable of generating high-power, high-efficiency laser light used for wavelength conversion and the like.

[0002]

2. Description of the Related Art A solid-state laser using a semiconductor laser as an excitation light source has been proposed as a method for realizing a high-quality, high-efficiency and high-output solid-state laser. However, in particular, it is possible to increase the laser output without degrading the beam quality. There is a desire for an excitation system that can be obtained. The pumping method for this purpose can be roughly classified into an end face pumping method in which pumping light is made incident on the laser oscillation optical path and is incident, and a side surface pumping method in which pumping light is incident in a direction orthogonal to the laser oscillation optical path.

In the lateral pumping method, a rod-shaped solid-state laser is used and pumping light is dispersed in the lengthwise direction of the rod to disperse heat generation and obtain high output. However, since the excitation region and the oscillation mode region cannot be sufficiently overlapped with each other, there is a problem that high-efficiency oscillation cannot be performed, and higher-order mode oscillation is likely to occur and the beam quality is deteriorated. On the other hand, the end-face excitation method has an advantage that the excitation region and the low-order oscillation mode can be overlapped with each other at a high level, and laser light with high efficiency and high beam quality can be emitted.

[0004]

However, in the conventional end face excitation method, in order to obtain a high laser output of 50 W or more, the effective excitation length determined by the absorption length of the laser beam and the divergence angle of the excitation beam. Is shorter than that of the lateral excitation method, a large thermal lens effect that is difficult to correct occurs, and there is a problem that the rod causes stress fracture due to excessive excitation density. Therefore, there is a problem that it is difficult to increase the efficiency of laser output for pumping and obtain a high-quality laser output in a low-order mode. It is an object of the present invention to provide a solid-state laser pumping method and a solid-state laser device capable of increasing the efficiency of laser output and obtaining a high-quality laser output.

[0005]

A solid-state laser pumping method of the present invention is a solid-state laser end-face pumping method, wherein pumping light is a Bessel beam, and a solid-state laser is provided within a pumping region determined by a focal depth and a beam diameter of the Bessel beam. The oscillation mode region of the medium is included.

Further, the solid-state laser device of the present invention is a solid-state laser device that collects and inputs pumping light from a pumping light source to an end face of a solid-state laser medium, and uses a focusing optical system for collecting the pumping light. A Bessel beam optical system is used. Here, the solid-state laser medium is preferably composed of a composite material in which a layer of only the base material containing no laser-active ions is bonded around the solid-state laser material containing laser-active ions in the base material.

The solid-state laser device of the present invention has a structure in which one end face of the solid-state laser medium is a high-reflecting mirror of the laser resonator, or a Bessel beam optical system is provided between the high-reflecting mirror and the solid-state laser medium. And a dichroic mirror for synthesizing the excitation light and the laser oscillation light is arranged between the excitation light source and the Bessel beam optical system by providing an optical path for transmitting the laser light with low loss at the center of the Bessel beam optical system. Is preferred.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing the configuration of a first example of an embodiment of the present invention. The collimated light 1 emitted from an excitation light source 3 such as a semiconductor laser light source is converted into a Bessel beam 20 by a conical lens 10 which is a Bessel beam optical system.
Has a portion 41 containing Nd ions composed of Nd: YAG at the center, and a YAG crystal 42 around the portion 41.
The solid-state laser medium 40 made of a composite material surrounded by is focused and irradiated from the end face 46.

Here, in the conical lens 10 as the Bessel beam optical system, the incident parallel excitation light 1 is converted into a Bessel beam 20 by the conical lens 10 as shown in FIG. At this time, when the incident beam diameter R, the conical lens inclination angle are α, the distance from the tip of the conical lens in the optical path direction is L, and ρ is the exit angle from the conical lens, the maximum depth of focus is Lmax = R [ tan (π / 2−ρ + α) -tan α].

As described above, the Bessel beam can obtain a depth of focus about 30 times deeper than that of a Gaussian beam or the like condensed by a normal lens. Further, as shown in FIGS. 3A and 3B, which show typical intensity distributions of the Bessel beam in the optical axis direction and the radial direction, in the Bessel beam, the central depth is proportional to the distance in the traveling direction of the optical axis. Becomes stronger, and a strong beam-like intensity distribution is obtained at the center in the radial direction. The above is the case where the space in which the Bessel beam propagates is a free space without absorption.However, when used for pumping a solid-state laser medium that has absorption of pumping light, intensity attenuation due to absorption of pumping light occurs, The intensity in the optical axis direction changes at a gentler gradient than the gradient shown in FIG. However, since the long depth of focus characteristic of the Bessel beam is maintained, it becomes possible to excite the solid-state laser medium over a long absorption length even in the edge-pumped configuration, and as a result, the heat per unit length of the solid-state laser medium is increased. The load can be reduced and the thermal lens effect and the like can be suppressed to a small value.

A high reflection coat 80 is formed on the end surface 46 of the solid-state laser medium 40.
With 0, it becomes possible to highly transmit the excitation light and highly reflect the laser light. The other end surface of the solid-state laser medium 40 is cut at an angle of 45 degrees with respect to the axis of the rod, the cut surface 45 is coated with a highly reflective laser beam, and this surface is bonded to the heat sink 32. ing. The second heat sink 30 is also adhered to the side surface of the solid-state laser medium 40, so that the cooling efficiency can be improved by radiating heat from both directions.

The laser light reflected by the cut surface 45 exits from the flat portion of the solid-state laser medium 40 having the antireflection coating and is directed to the output mirror 70. A laser resonator is formed between the coat 80 and the output mirror 70, and as a result,
The laser oscillation light 60 output from the output mirror 70 can be obtained.

Here, the incident beam diameter is 5 mm and the cut angle is 4
The depth of focus of the Bessel beam from the 1-degree synthetic quartz conical lens 10 corresponds to 8 mm in free space, so the length of the solid-state laser medium 40 was set to 20 mm in consideration of the refractive index. Further, the laser oscillation mode diameter inside the solid-state laser medium 40 is designed to be 600 μm, the diameter of the portion 41 containing Nd ions is set to 900 μm, and the Bessel beam light is efficiently absorbed only in the laser oscillation mode region. Is taking. The diameter of the solid-state laser medium 40 is 1.5 m
m.

When the pump input is set to about 50 W using this configuration, the output of about 20 W can be obtained by optimizing the output mirror transmittance. In this configuration, since the heat load on the solid-state laser medium 40 is dispersed in the length direction, there is no risk of destruction, and the heat sink 32 is not.
Since the excitation light intensity is maximized in the vicinity of, the distance between the strong heat generating region and the heat sink can be shortened and the cooling efficiency can be increased, as compared with the normal end face excitation by the Gaussian beam.

FIG. 4 is a schematic configuration diagram of the second embodiment of the present invention, in which the reflecting mirror 71 is arranged outside the Bessel beam optical system. End face 46 of solid-state laser medium 40
Has a non-reflective coating for excitation light and laser light,
A hole 100 that allows laser light to be transmitted with low loss is provided at the center of the optical axis of the conical lens 10, and a dichroic mirror 90 that transmits the excitation light 1 and reflects the laser oscillation light separates the laser optical path and the excitation light optical path, and provides high reflection. The mirror 71 is one reflection mirror of the laser resonator. With this configuration, the effect of the thermal lens effect due to heat generation on the resonator mode is smaller than in the case where the end surface 46 of the solid-state laser medium 40 is one reflecting mirror, and there is an advantage that the stable oscillation of the laser oscillation characteristics is improved. . Further, there is an advantage that there is a high degree of freedom in selecting the curvatures of the high-reflecting mirror 71 and the output mirror 60 and the distance between the high-reflecting mirror 71 and the solid-state laser medium 40 so as to optimize the mode matching with the excitation beam.

FIG. 5 is a schematic configuration diagram of the third embodiment of the present invention. Here, the excitation beam can be introduced from both sides of the solid-state laser medium 40. First excitation light 1
And the second excitation light 2 is the first conical lens 10 and the second conical lens 1 which constitute the Bessel beam optical system, respectively.
1, and enters from each end face of the solid-state laser medium 40.
The high reflection mirror 71 and the output mirror 70 of the laser resonator are separated from the pumping light optical path by the first dichroic mirror 90 and the second dichroic mirror 91 to form a laser resonator. According to this configuration, the pumping intensity distribution in the length direction of the solid-state laser medium 40 can be made more uniform as compared with the pumping from only one direction, and the pumping density per unit volume can be increased.

FIG. 6 is a schematic configuration diagram of a fourth embodiment of the present invention. Here, a plurality of amplifying units excluding the resonator of the oscillator shown in FIG. It is a thing. First amplification unit 150, second
The amplification unit 151 and the third amplification unit 152 are coupled by the first and second coupling lenses 200 and 201, respectively, and form a laser resonator between the high reflection mirror 70 and the output mirror 71. The first and second coupling lenses 200 and 201 are used to compensate the influence of the thermal lens effect of the laser resonance mode. With this configuration, a pump power of 150W in total is applied to each amplification unit,
It is possible to obtain 60 W as the output.

In each of the above-mentioned embodiments, an example in which a conical lens is used as the Bessel beam optical system is shown. However, instead of the conical lens, two opposite conical lenses, a concentric zone plate, a concentric mask and a condenser lens are used. The effect of the present invention can be obtained by using a combination of the above. Needless to say, a semiconductor laser array, a surface emitting semiconductor laser, or a fiber output semiconductor laser may be used as the excitation light source.

[0019]

As described above, according to the present invention, since the Bessel beam is used as the condensing optical system of the edge pumping type solid state laser device, the focal depth of the pumping light is long and the laser oscillation mode and the pumping mode are used. It is possible to realize a solid-state laser device with good mode matching. As a result, it is possible to obtain a solid-state laser device having a high efficiency laser output for pumping and a high-quality laser output in a low-order mode.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram for explaining a method of generating a Bessel beam.

FIG. 3 is a diagram showing intensity distributions of a Bessel beam in an optical axis direction and a radial direction.

FIG. 4 is a schematic configuration diagram of a second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a third embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a fourth embodiment of the present invention.

[Explanation of symbols]

 3 Excitation Light Source 10 Cone Lens 20 Bessel Beam 30 Second Heat Sink 32 Heat Sink 40 Solid Laser Medium 41 Part Containing Laser Ion 42 YAG Crystal 45 Cut Surface 46 End Face (Injection Surface) 70 Output Mirror 80 High Reflection Coat 90 Dichroic Mirror

Claims (7)

[Claims] 1. A method of pumping an end surface of a solid-state laser, wherein pumping light is a Bessel beam, and an oscillation mode region of a solid-state laser medium is included in a pumping region determined by a focal depth and a beam diameter of the Bessel beam. Solid-state laser excitation method. 2. A solid-state laser medium, and a high-reflection mirror and an output mirror arranged on both sides of the solid-state laser medium constitute a laser resonator, and pumping light from a pumping light source is condensed and incident on an end face of the solid-state laser medium. In the solid-state laser device, a Bessel beam optical system is used as a focusing optical system for focusing the excitation light. 3. The solid-state laser medium is composed of a composite material in which a layer of only the base material containing no laser-active ions is bonded around a solid-state laser material containing laser-active ions in the base material. Solid-state laser device. 4. The solid-state laser device according to claim 3, wherein one end face of the solid-state laser medium is a high reflection mirror of a laser resonator. 5. A Bessel beam optical system is disposed between a high-reflecting mirror and a solid-state laser medium, an optical path for transmitting laser light with low loss is provided in the center of the Bessel beam optical system, and an excitation light source and a Bessel beam optical system are provided. 4. The solid-state laser device according to claim 3, wherein a dichroic mirror for synthesizing the pumping light and the laser oscillation light is arranged between the two. 6. The method according to claim 4, wherein the end surface of the solid-state laser medium opposite to the Bessel beam optical system is formed obliquely with respect to the central axis, and the end surface is provided with a high-reflection coating and a heat sink is adhered. Solid-state laser device. 7. The Bessel beam optical system comprises a conical lens,
3. A lens comprising two inverted conical lenses, a concentric zone plate, a concentric mask and a condenser lens.
The solid-state laser device according to any one of 1 to 6.