JP2738038B2 - Solid-state laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device, and more particularly to stabilization of the quality of a laser beam generated from the solid-state laser device.

[Prior Art] FIG. 12 shows, for example, a laser handbook (Ohm,
FIG. 1 is a cross-sectional configuration diagram showing a conventional solid-state laser device shown in (Showa 57). In the figure, (1) is a solid-state device, for example, Y _3-x Nd _x Al ₅ O when a YAG laser is taken as an example. _A rod-shaped crystal made of ₁₂ ; (3) a flash lamp; (4) a power supply for lighting the flash lamp (3); (5) a condensing and reflecting mirror; and (6) an outlet made of, for example, glass. A mirror, (7) provided on the inner surface of the exit mirror (6), for example, a partially reflective film made of TiO ₂ ; (8) provided on the outer surface of the exit mirror and on both side surfaces of the solid state element (1), An anti-reflection film made of SiO ₂ , (9) a laser beam in the laser resonator, (10) a laser beam taken out, (12) an outside work, and (20) a total reflection mirror.

Next, the operation will be described. The solid state element (1) is excited by direct light from a flash lamp (3) turned on by a power supply (4) and reflected light from a converging / reflecting mirror (5) to form a laser medium. On the other hand, a laser beam (9) confined in a so-called stable resonator composed of an exit mirror (6) having a partial reflectance and a total reflection mirror (20) by a partial reflection film (7) provided on the inner surface. Is amplified by this laser medium each time it goes back and forth between both mirrors,
When the size becomes a certain size or more, a part thereof is emitted to the outside as a laser beam (10) through an exit mirror (6).

FIG. 13 shows an example of the oscillation output characteristic. Here, the solid state element (1) is made of Y _2.4 Nd _0.6 Al ₅ O _{12 and} has a cross-sectional diameter of 8 m.
m, length 150mm, exit mirror (6) and total reflection mirror (20)
The inner surface curvature is both 0.4m, and the distance between both mirrors is 0.45
m, the reflectivity of the exit mirror is 70%. The power consumed and the power consumed to light the flash lamp,
About 100W laser output is obtained with the input power of.

[Problem to be Solved by the Invention] As described above, the conventional solid-state laser device includes one rod (solid-state element), and changes the laser output by changing the input power to the light source that excites the solid-state element. Therefore, there has been a problem that the divergence angle of the generated laser beam varies depending on the power applied to the light source, that is, the laser output, as shown in FIG. This is because the degree of thermal lensing of the solid-state element (1) changes due to a temperature gradient generated in the solid-state element (1) due to a change in the power supplied to the solid-state element, thereby changing the resonance state.

The divergence angle of the laser beam can be said to be the laser beam focusing performance itself. This means that the converging spot system φ _s by the converging lens having the focal length f is approximately represented by φ _s = f · θ with respect to the divergence angle θ, and therefore the converging spot diameter is proportional to the divergence angle. This is because the size is determined.

Therefore, a change in the divergence angle due to the laser output means a change in the light-collecting characteristics, and there has been a problem that stable laser processing cannot be performed. Furthermore, a phenomenon was observed in which the input power was increased, and the thermal lensing of the solid-state element became remarkable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a laser device capable of generating a high-power laser beam with a constant divergence angle.

[Means for Solving the Problems] A laser device according to the present invention includes a plurality of solid-state elements in series on an optical path, and a light source for exciting at least one of the plurality of solid-state elements. Is turned on so that the average input power is constant, and the light source that excites other solid-state elements is turned on by changing the input power so that a desired laser output is obtained, and further, the at least one solid-state element is turned on. The thermal lens value of the element is compensated.

In pulse oscillation, pulsed power is applied to the solid-state device, the laser power is controlled by changing the pulse power waveform, and base power is applied to the light source in response to the pulse power waveform change. It is preferable to perform control such that the average value of the power is changed so as to be kept constant.

In order to reduce the change in the thermal lens value of the solid state element, the power waveform applied to the light source that irradiates the solid state element that is liable to cause thermal lensing should be changed to the thermal lens state of another solid state element. Adjustment may be made to compensate for the change in value, so that the thermal lens value of the entire solid-state device is constant with respect to the change in laser output.

[Operation] The solid-state laser device according to the present invention turns on a light source that excites at least one solid-state element of a plurality of solid-state elements so that the average input power is constant, and sets a light source that excites other solid-state elements. If the power supplied to change the power so that a desired laser output is obtained is turned on, the at least one solid state element shows a constant thermal lens state, and the change in the thermal lens value indicates that the solid state element other than this solid state element has a thermal lens state. It can be reduced only by the change of the thermal lens value.

In the case of pulsed power, the same applies if the base power is changed so as to keep the average value of the power applied to the light source constant in accordance with the change in the pulse power waveform as a constant input power. Thus, a change in the thermal lens value can be reduced.

Furthermore, the power waveform of each light source is controlled so as to compensate for the thermal lens values of the solid state elements using different solid lens elements, so that the thermal lens value of the entire solid element is constant with respect to the change of the laser output. , The change in the divergence angle is reduced.

Embodiment An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, (1) is a plurality of solid-state devices arranged in series on an optical path. For example, taking a YAG laser as an example,
_{3-x Nd x Al 5 O} 12 rods shaped crystals composed of, (2) is a total reflection mirror provided on the rod end surface, it forms a magnifying mirror. (3) is a plurality of excitation light sources for exciting the plurality of solid state elements (1), for example, an arc lamp and a flash lamp. (4) is a power supply for turning on the excitation light source (3), (5) is a condensing and reflecting mirror, and (6) is an exit mirror made of, for example, glass, which forms a collimating mirror.
(7) is a partial reflection film made of, for example, TiO ₂ provided at the center of the inner surface of the exit mirror (6). (8) is on the periphery of the partial reflection film (7) on the inner surface of the exit mirror and the exit mirror (6).
And a non-reflective film made of, for example, SiO ₂ provided on the outer surface of the solid-state device (1), and inside a laser resonator composed of an exit mirror (6) and a total reflection mirror (2), (9) and (11). (10) is a laser beam extracted outside the laser resonator, and (12) is an outer laser beam.

 Next, the operation will be described.

The solid-state element (1) is excited by direct light from an excitation light source (3) turned on by a power supply (4) and reflected light from a converging / reflecting mirror (5) to form a laser medium. on the other hand,
A laser beam (9) (1) generated in a so-called unstable resonator comprising an exit mirror (6) and a total reflection mirror (2)
1) is amplified by this laser medium each time the laser beam reciprocates between the two mirrors, and when it becomes a certain size or more, a part thereof is emitted to the outside as a laser beam (10).

The power supply to the light source will be described in more detail. FIG. 2 is a characteristic diagram showing the oscillation characteristics of the solid-state laser device according to one embodiment of the present invention. Here, the solid-state element (1) is Y _2.4 Nd _0.6 Al ₅ O ₁₂ excited by a lamp. The diameter of the cross section is 6 mm, the length is 100 mm, the distance between the exit mirror (6) and the total reflection mirror (2) is 0.44 mm, and the reflectance of the partial reflection film (7) provided at the center of the inner surface of the exit mirror (6) Is 90%. In FIG. 1, the input power is the sum of the power input to the right light source and the power input to the left light source. Third
Figures (a) and (b) show the case where the same power is applied to two light sources and the laser output is controlled (control A), and a constant power of 5 kW is applied to the light source in front of the left exit mirror. The laser output is adjusted by changing the power to the light source on the front surface of the total reflection mirror on the right side, and controlling the laser output by supplying different powers to the two light sources (control B). FIG. 9 is a characteristic diagram illustrating a change in a divergence angle with respect to a laser output. FIG. 3 shows that the change in the divergence angle is more gradual with respect to the laser output in the case of the control B in which different powers are supplied to the two light sources to control the laser output. Here, in the case of control B, the curvature of the inner surface of the exit mirror was arranged so as to compensate for the thermal lensing of the solid state element excited by the left light source operating at a constant power.

The reason why the change in the divergence angle is small in the case of the control B will be described. In the case of control A, a change in laser output requires changing the total input power to both light sources by 5 to 8 kW. In response to this change, the power of lensing due to temperature gradient generated in the left solid-state element The change of the component (1 / f) is (1 / f) = 7.5m
^It can be explained that a large change in the divergence angle was brought about as shown in FIG. 3 (a) in response to this change. On the other hand, in the case of the control B, the laser output can be changed only by changing the input power to the right light source by 0 to 3 kW. In response to this change, the lens is formed by a temperature gradient generated in the right solid element. The change of the power component (1 / f) is (1 / f) = 1.
0m ^-1 , which is sufficiently smaller than the case of the control A.
As shown in the figure, it can be explained that the change in the divergence angle was reduced.

Considering further the practical advantages of the present invention, the life of the light source changes with the operating condition of the laser, since the average input power to the light source has conventionally changed in accordance with the operating condition of the laser, and therefore, its replacement It was necessary to determine the timing by observing the actual state of the laser output. On the other hand, in the device according to the present invention, the average input power to at least one light source is substantially constant, and the life thereof is also constant irrespective of the operating state of the laser. In addition, it is possible to easily determine the replacement time of the light source.

In the above embodiment, the curvature of the exit mirror (6) is set so as to compensate for the thermal lens formation of the fixed element. However, as shown in FIG. This may be performed by a concave lens (100) disposed before and after the element, or a substantially concave lens may be formed by forming a curve at the end of the solid element. Alternatively, although the light-collecting property is deteriorated, the change in the light-collecting property can be reduced without providing various means for compensating the thermal lens formation as described above.

Further, in the above embodiment, an example in which the average power to at least one light source is kept constant, but the total sum of thermal lenses to a plurality of light sources may be kept constant. If a lens that easily generates a thermal lens is used as compared with the other rods, it is possible to easily control only the power supplied to the rod mainly. For example, YA
When a G rod is used as one of the solid-state elements, a GGG rod that is apt to cause thermal lens formation by about three times with the same power irradiation compared to the YAG rod should be inserted in series with the other one. In response to the decrease in the irradiation power to the YAG rod, the irradiation power to the GGG rod is increased only by about 1/3 as compared with the case of using the YAG rod as the other one. Can be kept constant.

In the above-described embodiment, a case where steady oscillation is performed is described as an example. However, pulse oscillation may be performed. In this case, for example, as shown in FIGS. 5 (a) and 5 (b), at least one rod If the base power is changed in response to the change in the peak power to control the average power to be constant, the same effect as in the above embodiment can be obtained. That is, in FIG. 5, the dotted line is the oscillation threshold, and the shaded portion corresponds to the laser output. Therefore, the laser power may be controlled by changing the peak power, and the base power may be changed and controlled so that the average value of the power applied to the light source is constant in accordance with the waveform change of the peak power. .

Further, in the above embodiment, an example in which the average power is kept constant is shown, but it is not necessary to be strictly constant depending on the configuration of the resonator, and even if a certain degree of deviation occurs, the deviation of the divergence angle is small,
A stable laser beam can be obtained.

Further, in the above embodiment, an example in which an unstable type resonator is used is shown, but it is needless to say that the same effect can be obtained with a stable type resonator as in the conventional case.

Although the exit mirror has a partial reflectivity at the center of the inner surface of the exit mirror, it may have a total reflectivity. In this case, a ring-shaped laser beam is generated, and diffraction caused by the ring-like laser beam is generated. Light condensing performance deteriorates,
Similarly, a laser beam having a stable divergence angle can be generated.

In the above embodiment, the phase difference between the laser beams passing through the central portion and the peripheral portion of the inner surface of the exit mirror was small and did not cause any problem. However, depending on the configuration of the partial reflection film (7), this may cause a problem. In this case, means for canceling the phase difference between the two laser beams may be provided. For example, a step (70) may be provided on the outer surface of the exit mirror as shown in FIG.

In the above embodiment, the total reflection mirror (2) is formed on the side surface of the solid state device. However, as shown in FIGS. 7 and 8, it may be separated from the solid state device. FIG. 8 shows an example in which the exit mirror is formed integrally with the solid-state element.

Further, in the above embodiment, an example is shown in which a converging laser beam is reflected from the total reflection mirror (2). However, a parallel laser beam may be reflected.
9, FIG. 7, and FIG. 8, corresponding to FIG. 9, FIG.
And a modification as shown in FIG. 11 is conceivable.

[Effects of the Invention] As described above, according to the present invention, a plurality of solid-state elements are provided in series on an optical path, and a plurality of light sources are provided for exciting the plurality of solid-state elements, respectively. A light source that excites at least one solid-state element is turned on so that the average input power is constant, and a light source that excites the other solid-state elements is changed in power to be input so that a desired laser output is obtained. Since it is made to light up and further compensate for the thermal lens value of the at least one solid-state element,
There is an effect that a change in the divergence angle of the output laser light can be reduced and stable laser oscillation can be realized. Further, there is an effect that the time for replacing the light source can be easily determined.

In addition, by applying pulsed power to the solid-state device and changing the pulse power waveform to control the laser output,
If control is performed to change the base power in accordance with the pulse power waveform change so that the average value of the power applied to the light source is kept constant, even in pulse oscillation, the laser output of the divergence angle can be changed. Change can be made small, and there is an effect that stable laser oscillation can be realized.

In order to reduce the change in the thermal lens value of the solid state element, the power waveform applied to the light source that irradiates the solid state element that is liable to cause thermal lensing should be changed to the thermal lens state of another solid state element. Adjustment may be made to compensate for the change in value, so that the thermal lens value of the entire solid-state device is constant with respect to the change in laser output.

[Brief description of the drawings]

1 is a sectional view showing a solid-state laser device according to one embodiment of the present invention, FIG. 2 is a characteristic diagram showing oscillation characteristics of the solid-state laser device according to one embodiment of the present invention, and FIG.
(B) is a characteristic diagram for explaining a divergence angle characteristic in the solid-state laser device according to one embodiment of the present invention, FIG. 4 is a sectional configuration diagram showing a solid-state laser device according to another embodiment of the present invention, and FIG. a) and (b) are waveform diagrams showing power waveforms applied to a light source according to another embodiment of the present invention, and FIGS. 6 to 11 each show a solid-state laser device according to still another embodiment of the present invention. FIG. 12 is a cross-sectional configuration diagram showing a conventional solid-state laser device, FIG. 13 is a characteristic diagram showing oscillation characteristics in a conventional solid-state laser device, and FIG. 14 is a divergence angle characteristic in a conventional solid-state laser device. FIG. (1) solid state element, (2), (20) total reflection mirror, (3) light source, (4) power supply, (6) exit mirror, (9) (10) ( 11) Laser beam In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

(57) [Claims] 1. A plurality of solid state devices arranged in series on an optical path,
A plurality of light sources for exciting the plurality of solid state elements, a laser resonator for extracting a laser beam from the plurality of solid state elements excited by the plurality of light sources, and exciting at least one solid state element of the plurality of solid state elements Light source
A power source that is turned on so that the average input power is constant, and that turns on a light source that excites other solid-state devices by changing the power input so that a desired laser output is obtained, and the at least one solid-state device A solid-state laser device provided with a compensating means for compensating for the thermal lens value. 2. A plurality of solid state devices arranged in series on an optical path,
A plurality of light sources for exciting the plurality of solid-state elements, a laser resonator for extracting a laser beam from the plurality of solid-state elements excited by the plurality of light sources, and at least one solid-state element of the plurality of solid-state elements, The pulsed power is applied to the light source to be excited, the laser output is controlled by changing the pulse power waveform, and the base power corresponding to the pulse power waveform change is set to the average value of the power applied to the light source. A solid-state laser device provided with a power supply for turning on the light source by changing the light source to be constant. 3. A plurality of solid state elements arranged in series on an optical path and having a thermal lens value, a plurality of light sources for exciting the plurality of solid state elements, and the plurality of solid states excited by the plurality of light sources. A laser resonator that extracts a laser beam from the element, and a power waveform applied to a light source that excites a solid-state element having a large thermal lens value among the plurality of solid-state elements, a change in the thermal lens value of a solid-state element with a small thermal lens value. A solid-state laser device comprising a power supply for adjusting the compensation so as to make each of the plurality of light sources turn on so that the thermal lens value of the entire solid-state element becomes constant with respect to a change in laser output.