JPH0362581A - Solid-state laser equipment - Google Patents

Abstract

PURPOSE:To miniaturize an optical resonator and unnecessitate the optical axis adjustment, by arranging a laser gain part and a Q-switching part in a body in solid-state laser medium, and installing a function curved surface minimizing the laser medium dimension on a laser optical axis. CONSTITUTION:When a semiconductor laser 15 is operated and laser light L1 is made to enter from a first coating 14 of solid-state laser medium 12, a part A adjacent to the coating 14 of the medium 12 is excited. YAG laser light L2 oscillates between coatings 14, 16, and emitted from the coating 16. When ultrasonic signal is turned ON, and ultrasonic wave U is generated in the medium 12 by an ultrasonic wave transducer 19, the laser light L2 is diffracted and the oscillation is interrupted. When the ultrasonic wave signal is turned OFF, the laser light L2 oscillates. By a pair of function curved surfaces 17 in the vicinity of an optical axis, the thickness of the medium 12 is reduced to about 1/5. By a convex surface 18, the width is reduced to about 1/3. Hence the intensity of the ultrasonic wave is amplified 15 times, and the diffraction efficiency is increased 4 times.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a solid-state laser device equipped with an ultrasonic Q-switch.

(Prior art) For example, in the processing of semiconductor elements and thin films, in order to locally process the surface layer, a short pulse with a small energy of μJ but a very short pulse width of several ns is required. be. In such cases, the solid-state laser device Y
In an AG laser, a YAG rod is excited by a continuously lit lamp, and a pulse output is generated by operating a Q switch installed in a resonator. Elements that have the property of diffracting light by ultrasonic waves are widely used as Q-switch elements.

Conventionally, a YAG laser having such a structure has been constructed as shown in FIG. That is, numeral 1 in the figure is a YAG rod as a solid laser medium.

A high-reflection mirror 2 is disposed to face one end face of the YAG rod 1, and an output mirror 3, which forms a resonator with the high-reflection mirror 2, is disposed to face the other end face.

A Q-switch cable 5 connected to a high-frequency power source 4 is arranged between one end face of the YAG rod 1 and the high-reflection mirror 2. Furthermore, an excitation lamp 6 for continuously optically exciting this YAG rod 1 is provided on the side of the upper 2 YAC rod 1.

Then, if the high frequency power source 4 is controlled on/off while the YAG rod 1 is optically excited by the excitation lamp 6,
The output mirror 3 can output pulsed laser light.

However, according to the conventional YAG laser with such a configuration, the Q switch element etc. are separate from the YAG rod 1,
Since this Q switch 5 is provided between the end face of the YAG rod 1 and the high reflection mirror 2, it is inevitable that the total length of the optical resonator will be large. As the total length of the optical resonator increases, even if a large output can be obtained, the pulse width of the pulsed laser beam inevitably increases.

Therefore, as described above, it may not be possible to precisely perform local processing of semiconductor elements, thin films, and the like.

Furthermore, if the Q-switch element 5 is separate from the YAG rod 1, the optical axes of these elements must be precisely adjusted, which not only requires a lot of effort, but also requires a lot of time and effort for each mirror and the Q-switch rod 5. The stability of the optical resonator may be impaired due to a decrease in the particle size of the optical resonator.

(Problem to be solved by the invention) As described above, in the conventional solid-state laser device, the solid-state laser medium and the Q-switch element were separate, so the total length of the optical resonator became large and the pulse width could not be sufficiently controlled. There have been cases where it has not been possible to oscillate a short laser beam, and it has taken a lot of effort to adjust the optical axis of the Q-switch element.

This invention was made based on the above circumstances, and its purpose is to reduce the size of an optical resonator by integrating a solid-state laser medium and a Q-switch element, and to improve optical axis adjustment. Means and operation for solving the problem without unnecessary) In order to solve the above problem, the present invention includes a solid-state laser medium, an optical resonator provided on a pair of opposing end faces of the solid-state laser medium, and a solid-state laser medium. an excitation means for optically exciting a laser medium; an ultrasonic generation means for generating an ultrasonic wave in a direction in which an ultrasonic wavefront forms a Bragg angle with respect to an optical axis in an optical resonance direction of a laser beam generated by the excitation means; The laser medium is provided with a functional curved surface formed along the traveling direction of the ultrasonic wave and minimizing the thickness dimension of the solid laser medium at a location of the optical axis of the laser beam.

With this configuration, the part with laser gain and the part that performs Q-switch operation can be integrated into the solid-state laser medium, so the overall size can be reduced, and the optical axis 21 This eliminates the need for adjustment, and furthermore, high diffraction efficiency can be obtained by using a functional curved surface.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 shows a YAG laser as a solid-state laser device, and this YAG laser is equipped with a cooling plate 11. As shown in FIG. On this cooling plate 11, a YAG crystal is formed to have a thickness of, for example, 5 mns to 10 mm.

A solid laser medium 12 formed into a rectangular plate shape with a length of about 20 mm is installed. One end face in the longitudinal direction of this solid-state laser medium 12 is formed into a concave surface 13 with a curvature of several tens of degrees, and a first coating 14 is applied to this convex surface 13. This first coating 14 has a wavelength of 810rv.
It transmits light (semiconductor laser light) and the wavelength is 1.
．． 06μ "n light (YAG laser light) is designed to be reflected.

At a position facing the convex surface 13, a semiconductor laser 15 as an excitation means is located at its emission surface 15. A is placed in the χ1 direction. As shown in FIG. 2, the semiconductor laser light L1 output from the output surface 15a is focused by the lens action of the convex surface 13 and enters the solid laser medium 12. Thereby, the solid-state laser medium 12 is optically excited by the semiconductor laser light output from the semiconductor laser 15. That is, the first coating 1 shown as A in FIG. 2 of the solid-state laser medium 12
The portion near 4 is a portion with laser gain that is optically excited by the semiconductor laser light L1 incident on the solid-state laser medium 12.

A second coating 16 is applied to the other end face of the solid-state laser medium 12. This second coating 1
6 is designed to transmit light having a wavelength of 1.06 μm in a range of 98 to 95%. Therefore, this second coating 16 and the first coating 14 combine two YAG laser beams with a wavelength of 1.06 μm to form the second
The coating 16 forms an optical resonator that outputs light.

On the upper and lower surfaces of the portion of the solid-state laser medium 12 that is closer to the second coating 16 than the portion A, a cosh
A smooth function curved surface 17 such as a 2x curved surface (hyperbolic cosine curved surface) or a squared curved surface is formed along the width direction by means such as polishing. These pair of function surfaces 17
Therefore, as shown in FIG. 3, the solid-state laser medium 12 has a minimum cross-sectional thickness near the two axes of YAG laser beam L beam combination.

On one side of the portion of the solid-state laser medium 12 where the function curved surface 17 is formed, there is, for example, 10 mm along the longitudinal direction.
A convex portion 1i1i18 curved with a certain degree of curvature is formed. An ultrasonic transducer is attached to this convex surface 18 so as to form a Bragg angle with respect to the wavefront of an ultrasonic wave forming a compressional wave generated in the solid-state laser medium 12 by this single transducer, as will be described later. The convex surface 18 is configured to converge the width of the ultrasonic wave U to about 1/3 near the two axes of the YAG laser beam L by its lens action, as shown in FIG. 2.

One of the above ultrasonic transducers has a high frequency matching circuit 2.
A high frequency power source 22 that generates a high frequency of 150 to 200 MHz is connected through the power source 1 . If the high frequency of this high frequency power supply 22 is applied to the ultrasonic transducer 19 via the high frequency matching circuit 21, this transducer 1
The wavefront changes to YAG laser beam L due to the ultrasonic vibration generated in step 9.
Ultrasonic waves are generated in the width direction of the solid-state laser medium 12 at a Bragg angle with respect to the two axes of optical coupling, that is, the optical axis in the optical resonance direction. Therefore, when the ultrasonic transducer 19 is activated to generate an ultrasonic wave, a refractive index distribution is generated in a lattice pattern in the two paths of the YAG laser beam L, so that the YAG laser beam L is refracted into the second path. There is no output from the coating 16. That is, by continuously turning on and off the ultrasonic transducer 19, highly repetitive Q-switched laser pulses can be obtained.

Note that the side surface of the solid-state laser medium 12 opposite to the side surface to which one ultrasonic transducer is attached is formed into a slope 23 to prevent ultrasonic waves from directly returning due to reflection. An elastic plate 24 made of rubber or the like is joined. Further, the temperature of the cooling plate 11 is controlled by a cooling means (not shown), so that the solid-state laser medium 1
2 is maintained at a predetermined temperature.

According to the YAG laser having such a configuration, when the semiconductor laser 15 is operated to cause the semiconductor laser beam L1 to enter from the first coating 14 of the solid-state laser medium 12, the semiconductor laser beam L1 causes the first coating of the solid-state laser medium 12 to be incident. 1
A portion A near the coating 14 of is photoexcited. Thereby, the coating 1 of the YAG laser beam L beam combination 21 is
4 and the second coating 16, and is output from the second coating 16.

Here, if the ultrasonic signal is turned on and the ultrasonic transducer 19 generates a superwave U in the solid-state laser medium 12, a lattice-like refractive index distribution will be generated in the solid-state laser medium 12, so that the YAG laser beam L The light is combined and folded into two and no longer oscillates. Also, if you quickly turn off the ultrasound signal,
YAG laser beam L beam 2 rises to high peak pulse YA
G laser light L2 will be oscillated.

The ultrasonic wave U emitted from one ultrasonic transducer is produced by reducing the thickness of the solid-state laser medium 12 to about 115 by a pair of function curved surfaces 17 near the optical axis, and attaching one ultrasonic transducer to the solid-state laser medium 12. Since the width dimension is reduced by about 1/3 by the convex surface 18, the ultrasonic intensity effective for diffraction efficiency is amplified by about 15 times. Therefore, even if the input from the high frequency power source 22 is small, high diffraction efficiency can be obtained.

The above diffraction efficiency can be determined as follows. That is, if the incident light to the solid-state laser medium 12 is 11, the diffracted light refracted by the ultrasound is 2, and the acoustic power density of one ultrasound transducer is I, then I 2
The diffraction efficiency determined by /I r is...Equation (1), where p is the interaction length, λ is the optical wavelength, and M is the material constant, which is 0.467 for quartz and 0.467 for YAG laser medium. The case is 0.073.

Since the coefficient α in sin 2 in the above equation (1) is small, the above equation (1) can be changed to the equation (2), and the diffraction efficiency is proportional to the square root of the acoustic power density I3. will be the value.

Therefore, if the ultrasonic density is amplified 15 times as described above, the diffraction efficiency will be JR5=4. In other words, a pair of functional curved surfaces 17 are formed in the solid-state laser medium 12, and the ultrasonic transducer 19
By making the surface to which is attached a convex surface 18, the diffraction efficiency can be quadrupled.

Further, a portion with laser gain excited by the semiconductor laser 15 and a portion that generates a Q-switch operation due to ultrasonic vibration are integrally provided in the solid-state laser medium 12, and furthermore, a pair of opposing end surfaces of the solid-state laser medium 12 A first coating 14 and a second coating 16 forming an optical resonator are formed. Therefore, since the total length of the optical resonator can be sufficiently shortened, the pulse width determined by the caddy length of the optical resonator can also be shortened.

In the above embodiment, the functional curved surface is formed on both the upper and lower surfaces of the solid-state laser medium, but the intensity of the ultrasonic wave, which is effective for diffraction efficiency, can be amplified even if the functional curved surface is formed on only one of the surfaces. In this case, it goes without saying that the optical axis of the YAG laser beam L2 is set to be centered in the thickness direction of the portion where the functional curved surface of the solid-state laser medium is formed.

Further, even without a convex surface to which an ultrasonic transducer for converging ultrasonic waves in the width direction is attached, it is possible to amplify the intensity of ultrasonic waves effective for diffraction efficiency only by the function curved surface.

Furthermore, it goes without saying that the solid-state laser medium may be other than the YAG laser medium. Furthermore, the means for exciting the solid-state laser medium may be a Kr arc lamp or the like instead of a semiconductor laser, and in that case, the excitation light from the Kr arc lamp may be made to enter the solid-state laser medium through a fiber end. good.

Further, a laser oscillation photovoltaic system using excitation light as described above is also effective.

[Effects of the Invention] As described above, the present invention integrates a portion with a laser gain in a solid-state laser medium, a portion that causes a Q-switch operation, and an optical resonance means, and also allows the oscillation optical axis of the laser beam to be A functional curved surface is formed that minimizes the thickness of the laser medium at the location, thereby making it possible to increase the intensity of the ultrasonic wave for producing the Q-switch operation at the location of the oscillation optical axis. Therefore, not only is it unnecessary to adjust the optical axis of each optical component, which is required when Q-switch elements and optical resonators are provided separately, but the total length of the optical resonator can be shortened to output short-pulse laser light. can be done. Furthermore, the above-mentioned functional curved surface allows high diffraction efficiency to be obtained even at low frequency waves.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the general structure of a YAG laser showing an embodiment of the present invention, FIG. 2 is a plan view of the solid-state laser medium, FIG. 3 is a cross-sectional view, and FIG. 4 is a conventional solid-state laser. FIG. 2 is a schematic diagram of the device. 12...Solid laser medium, 13.14...First and second coatings (optical resonance means) 15...Semiconductor laser (excitation means) 17...Function curved surface, 19...Ultrasonic transducer (Ultrasonic generation means).

Claims (1)

[Claims] a solid-state laser medium, an optical resonance means provided on a pair of opposing end surfaces of the solid-state laser medium, an excitation means for optically exciting the solid-state laser medium, and an optical axis in the optical resonance direction of the laser light generated by the excitation means. an ultrasonic generating means for generating an ultrasonic wave in a direction in which an ultrasonic wavefront is at a Bragg angle; A solid-state laser device comprising: a functional curved surface that minimizes the thickness of the solid-state laser medium at a certain point.