JPH0412576A - Solid laser oscillating apparatus - Google Patents

Abstract

PURPOSE:To effectively obtain laser output by cutting out slab containing crystal distortion part inside crystal from Nd-YAG single crystal, and projecting laser light on the slab through the part except the crystal distortion part. CONSTITUTION:A laser oscillating apparatus is constituted by using a slab 3 which is cut out from Nd-YAG single crystal 1, so as to contain a crystal distortion part 2 at a cutting-out surface. The volume of the cut-out slab 3 of the Nd-YAG single crystal 1 is twice that of a slab which is cut out so as to avoid the crystal distortion part 2. Both end surfaces 4a, 4b of the slab 3 are parallel to each other, and cut out at an inclination angle of alpha away from the upper surface 5a and the lower surface 5b. Both of the end surfaces 4a, 4b and the upper and the lower surfaces 5a, 5b are polished to be optical mirror surfaces. Hence laser light can travel two times in one crystal, so that the laser output is doubled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses neodymium (Ndj), which is a laser active ion.
”) added yttrium aluminum garnet (Nd”: Ys All s 012, hereinafter referred to as Nd
-Abbreviated as YAG. ) A slab-type solid-state laser oscillator using a single crystal.

[Prior Art] In a laser oscillation device in which a resonator is configured by providing excitation mirrors before and after a plate-shaped laser medium, an NdYAG single crystal is used as a plate-shaped crystal (hereinafter referred to as a slab).

Nd-YAG single crystal is yttrium aluminum garnet (Nd”) doped with neodymium (Nd):
Y, AQ, O, □).

Nd'+ ions are one of the few ions in a laser oscillation device, and YAG is generally used as a carrier to which Nd is added. The Nd-YAG single crystal doped with Nd'+ ions becomes a laser solid-state waxy substance (also referred to as a laser solid-state element).

Nd-YAG single crystals are usually manufactured by the Czyochlaski method, but this manufacturing method produces crystal strained areas in the center and periphery of the single crystal.

In this crystal strained portion, since the crystal is irregular, optical distortion occurs. Therefore, rods (round bar-shaped elements) and slabs (flat plate-shaped elements) used as laser media were collected while avoiding this area.

That is, as shown in FIG. 7, Nd-YAG single crystal 1
There are crystal strained parts 2 in the center and peripheral parts, and the conventional method of cutting out a slab is to cut out a slab 3 from the NdYAG single crystal 1 while avoiding the crystal strained parts 2.

FIG. 8 shows the configuration of a conventional slab-type solid-state laser oscillator.

A slab 3 of Nd-YAG single crystal and an excitation lamp 6 are arranged in a reflection box 7, with the lamp 6 sandwiching the slab 3 from above and below, and both ends of the slab 3 and the lamp 6 are separated from the reflection box 7. It's sticking out. A total reflection mirror 8 and an output mirror 9 are arranged facing each other in the long axis direction of the slab 3.

Both end surfaces 4a and 4b of the Nd-YAG single crystal slab 3 are:
They are cut out parallel to each other and at an inclined angle α with respect to the upper and lower surfaces 5a and 5b of the slab 3. And this slab 3
Both end surfaces 4a, 4b and upper and lower surfaces 5a, 5b are polished to optical mirror surfaces.

The excitation lamp 6 and slab 3 housed in the reflection box 7 are cooled by water introduced into the reflection box 7.

A total reflection mirror 8 is disposed on one end surface 4alIll of the slab 3 exposed to the outside of the reflection II 7, and an output mirror 9 is disposed on the other end surface 4b, thereby forming a resonant system.

When the excitation lamp 6 is turned on and excitation light is transmitted through the slab 3, the Nd'+ ions within the slab 3 are excited to a higher energy level.

Laser light is emitted when the energy level falls from this high energy level to a low energy level, and this laser light further becomes stimulation light and causes stimulated emission of laser light.

In the above-mentioned resonant system, the laser beam reflected by the total reflection mirror 8 travels along the optical path, is refracted at the end surface 4a, enters the slab 3, is totally reflected at the lower surface 5b and the upper surface 5a, and then reaches the end surface 4b. The beam reaches the end surface 4b and is refracted again toward the output mirror 9.

Adjustment is made so that the laser beam reflected from the output mirror 9 passes through the optical path again. Therefore, while the laser light travels back and forth on the optical path, the laser light is amplified and a portion of the laser light is taken out from the output mirror 9.

According to such a slab-type solid-state laser oscillator, the laser light is totally reflected by the upper and lower surfaces of the element, that is, the laser medium, and propagates in a zigzag pattern throughout the laser medium, so it is not affected by the thermal lens effect caused by optical excitation. , it is possible to obtain laser light with a small divergence angle.

[Problems to be Solved by the Invention] In the prior art as described above, the slab was cut out avoiding crystal strain, which is a defect in the Nd-YAG single crystal, so the dimensions of the slab were small, and therefore it was difficult to use high power. The laser oscillation device could not be built.

In other words, when cutting a slab from an NdYAG single crystal pulled from a single crystal production device, the slab is cut avoiding the central part of the crystal where optical distortion is large and the crystal strained part extending from there to the periphery, so that the pulled Nd- Only a slab with a small volume could be obtained compared to the volume of the YAG single crystal. And since the laser output is proportional to the slab volume,
There was a limit to the laser output for small volume slabs.

Therefore, the present invention provides an oscillator configuration in which a slab is cut out from an Nd-YAG single crystal including the crystal strained part inside the crystal, and the laser beam is passed through the part outside the crystal strain part to the slab. The purpose is to obtain laser output efficiently.

[Means for solving the problem] In the solid-state laser oscillation device of the present invention, neodymium (Nd)
A plate-shaped laser medium cut out from a yttrium aluminum cartridge single crystal (Nd''; Ys The laser beam passes through the laser medium while avoiding the crystal strain area.

[Function] The present invention cuts out a slab including the crystal strain part from the NdYAG single crystal pulled with a single crystal production device, and allows the laser beam to pass through the same slab twice.
It has the effect of producing twice the laser output as a conventional slab that does not contain crystal strained parts, making it possible to achieve a high-output laser.

Examples] The present invention will be described in detail with reference to the drawings.

The laser oscillation device of the present invention is constructed using a slab 3 cut out from an Nd-YAG single crystal 1 including a crystal strained portion 2 at a cutting plane as shown in FIG.

As shown in FIG. 1, the Nd-YAG single crystal slab 3 cut out can have twice the volume of the slab cut out avoiding the crystal strained portion 2 using the conventional technique.

Both end surfaces 4a and 4b of the slab 3 are parallel to each other and are cut out at an inclined angle α with respect to the upper and lower surfaces 5a and 5b of the slab.

Both end surfaces 4a, 4b and upper and lower surfaces 5a, 5 of this slab
b is polished to an optical mirror surface.

By adopting the configuration shown in FIGS. 2 and 3, it becomes possible for laser light to pass through the crystal twice in one crystal. As a result, the laser output is doubled.

The slab 3 and the excitation lamp 6 are housed in a reflection box 7, and the slab 3 and the excitation lamp 6 are cooled by water introduced into the reflection box 7. Both ends of the slab 3 and the excitation lamp 6 are exposed to the outside of the reflection box 7. Two total reflection mirrors 8a and 8b are arranged facing each other at an angle of 45 degrees with respect to the laser beam #IL on one end surface 4a side of the slab 3, and on the other end surface 4b side. , a total reflection mirror 8C, and an output mirror 9 are arranged at right angles to the laser beam RL, thereby forming a resonant system.

The slab 3 has a crystal strained part 2 in the center, and the total reflection mirrors 8a, 8b, 8c and the output mirror 9 are arranged so that the laser beam path avoids the crystal strained part 2 and extends as shown in FIG. It is located in

The principle of stimulated emission of laser light is as described above in the conventional example, and in the configuration of the present invention, the laser light reflected by the total reflection mirror 8c is refracted at the end surface 4b and enters the slab 3, and enters the slab 3 on its lower surface 5b and upper surface. 5a, the light reaches the end surface 4b, is reflected from the total reflection mirror 8a to the total reflection mirror 8b, enters the slab 3 again from the end surface 4b, is refracted again, and reaches the output mirror 9.

Each of the mirrors 8a, 8b, 8c, and 9 is adjusted so that the laser beam reflected from the output mirror 9 passes through the optical path again, and while the laser beam travels back and forth on this light F#IL, it is amplified. A part of the amplified laser light is emitted from the output mirror 9.

By configuring a resonator as described above and driving four lamps 6 with a pulse @ source, a laser output of 410 W can be obtained under the conditions of a pulse width of 7 ms (milliseconds), a repetition frequency of 10 ppS, and an input of 12 kW.

By employing the configuration of the present invention, it is possible for the laser light to pass through the slab twice, thereby doubling the laser output.

A diamond-shaped slab 3 with a width of 55 mm, a total length of 147 mm, a thickness of 8 mm, and an end face angle of 30.6 degrees, with a 7 mm wide crystal distortion in the center of the width, and three total reflection mirrors with a reflectance of 100% 8
A, 8b, 8c and an output mirror 9 with a reflectance of 50% constituted the oscillation device shown in FIGS. 2 and 3.

A total of four excitation lamps 6 were used, two on the upper surface 5a side of the slab 3 and two on the lower surface 5b side.

A pulse power supply (not shown) inputs power to the lamp 6 at 12 kW, pulse 41i7 milliseconds, and pulse repetition number 1.
An average laser output of 410 W was obtained under the condition of 0 pps.

As described above, by oscillating the laser with the configuration of the present invention, a laser output of 410 W was obtained with an input of 12 kW, which was about twice the output of the conventional system.

The slab 3 was cooled by the cooling water flow A as shown in FIG. 4(a), and the internal temperature distribution in the width direction of the slab became as shown in FIG. 4(b).

As a comparative example of the present invention, as shown in FIG. 5(a), a laser oscillation device was constructed in the same manner as the present invention by arranging two slabs 3 having no crystal strain portions in parallel. In this case, 2
In order to avoid a decrease in output due to mutual interference of the laser beams passing through the book slabs 3, each slab 3 had to be arranged at a certain distance L:M.

Figure 5(a)
When the slab is cooled by the cooling water flow A as shown in Fig. 5, the internal temperature distribution in the width direction of the slab becomes as shown in Fig. 5 (b), and as shown in Fig. 4 (a) and (b). The temperature gradient was steeper than that of a single slab. Therefore, the ratio of refractive index n to temperature t is d n / d t
became large, and the beam quality of the emitted laser light deteriorated. Therefore, this configuration was found to be undesirable.

As a comparative example of the present invention, as shown in FIG.
A laser oscillation device was constructed in the same manner as the present invention by sandwiching the d-YAG material 3a and bonding it with adhesive 10. However, this laser oscillation device was found to be undesirable for the following two reasons.

1) Polish each of the two slabs 3, and polish them to a homogeneous Nd-YAG
When the slabs 3a are sandwiched and bonded together using adhesive 10 as shown in Fig. 6, it is difficult to make the upper and lower surfaces completely parallel.If the parallelism is not good, each slab will have a zigzag pattern. The optical axis of the path blurs, making it difficult to adjust the mirror.

2) When the slabs 3 are bonded together with adhesive 10 as shown in FIG. 6, a temperature gradient occurs between the adhesive 10 and the slabs 3, and the ratio of refractive index to temperature t is d n / d
t becomes large, resulting in uneven intensity distribution of the emitted beam.

[Effects of the Invention] With the configuration of the present invention, it was possible to obtain an oscillation output approximately twice that of the oscillation output produced by the slab sampled while avoiding the strained portion in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an Nd-YAG single crystal showing a cut surface of a slab used in the oscillation device of the present invention. FIG. 2 is a perspective view showing the relationship between the slab and the mirror in the configuration of the oscillation device of the present invention. FIG. 3 is a schematic cross-sectional plan view showing the configuration of the oscillation device of the present invention. FIG. 4(a) is an explanatory diagram showing the slab and the flow of cooling water in the oscillation device of the present invention. FIG. 4(b) is a graph showing the internal temperature distribution in the width direction of the slab in the arrangement of FIG. 4(a). FIG. 5(a) is an explanatory plan view showing the slabs and the flow of cooling water in the generator in which the slabs are placed side by side. FIG. 5(b) is a graph showing the internal temperature distribution in the width direction of the slab in the arrangement of FIG. 5(a). FIG. 6 is a schematic cross-sectional view showing a structure in which two slabs are polished and bonded together with an adhesive. FIG. 7 is a perspective view showing a crystal strained portion of a YAG single crystal and a cut surface of a conventional slab. FIG. 8 is a schematic cross-sectional plan view showing the configuration of a conventional slab-type solid-state laser oscillation device. In the figures, reference symbols indicate the following: 1: YAG crystal, 2: Crystal cracks formed inside the single crystal, 3 varnish slab, 4a, 4b end faces of varnish slab, 5a upper surface of varnish slab, 5b lower surface of varnish slab, 6 2 excitation lamps, 7: reflection box, 8: Reflection mirror 9: Output mirror 10: Adhesive

Claims (1)

[Claims] It consists of a plate-shaped laser medium cut out from an Nd-YAG single crystal including the crystal strained part, and a pair of mirrors arranged on both sides of the laser medium in the long axis direction, so that the laser beam avoids the crystal strained part. A solid-state laser oscillation device characterized in that the laser beam passes through a laser medium.