JP2550499B2 - Solid-state laser device - Google Patents

Description

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

[Prior Art] FIG. 13 is a cross-sectional configuration diagram showing a conventional solid-state laser device described in, for example, Laser Handbook (Ohmsha, 1982, pages 220 to 225). In the figure, (1)
Is a solid-state element, for example, Y _3-X Nd _X Al
_A rod-shaped crystal composed of ₅ O ₁₂ (0 <x <3), (3) is a light source for exciting the solid state element (1), for example, a flash lamp, and (4) is for lighting the flash lamp (3). A power source, (5) a condenser reflection mirror, (6) an exit mirror made of, for example, glass, (7) a partial reflection film made of, for example, TiO ₂ provided on the inner surface of the exit mirror (6), (8)
Is a non-reflective film made of, for example, SiO ₂ provided on the outer surface of the exit mirror (6) and both side surfaces of the solid state element (1), (9) is a laser beam in a laser resonator, and (10) is extracted to the outside. Laser beam, (12) an outer frame, and (20) a total reflection mirror.

Next, the operation will be described. The solid-state element (1) is excited by the direct light from the flash lamp (3) turned on by the power source (4) and the reflected light from the condensing reflection mirror (5) to form a laser medium. On the other hand, a laser beam (9) confined in a so-called stable resonator consisting 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 the laser medium every time it goes back and forth between both mirrors, and when it reaches a certain size or more, a part of it is emitted as a laser beam (10) to the outside through the exit mirror (6).

As an example of the oscillation output characteristics, FIG. 14 shows the applied power (kW) on the horizontal axis and the laser output (W) on the vertical axis. here,
The solid-state device (1) is made of Y _2.4 Nd _0.6 Al ₅ O ₁₂ , the cross-sectional diameter is 8 mm, the length is 150 mm, the exit mirror (6) and the total reflection mirror (20) both have an inner curvature of 0.4 m, both mirrors. The distance between
0.45 m, the reflectance of the exit mirror (6) is 70%. Further, the input power is the power consumed for lighting the flash lamp (3), and as shown in the figure, a laser output of about 100 W is obtained with an input power of 6 kW.

[Problems to be Solved by the Invention] As described above, the conventional solid-state laser device changes the input power to the light source to change the laser output, and the divergence angle (mrad) of the generated laser beam and the input power are changed. Figure 15 shows the relationship of (kW). As shown in the figure, there is a problem that the divergence angle changes depending on the electric power supplied to the light source and thus the laser output. This is because the degree of lensing of the solid-state element (1) due to the temperature gradient generated in the solid-state element (1) changes with a change in the electric power applied to the solid-state element (1), thereby changing the resonance state. .

By the way, the size of the divergence angle of the laser beam can be said to be the focusing performance of the laser beam itself. This is because the focused spot diameter φs by the focusing lens with the focal length f is roughly represented by φs = f · θ with respect to the divergence angle θ, and the focused spot diameter is proportional to the divergence angle. This is because it is decided. Therefore, the fact that the divergence angle changes according to the laser output means that the converging characteristics change, and there is a problem that stable laser processing cannot be performed. Further, if the input power is increased, the solid lens becomes a thermal lens. For example, it was also observed that the oscillation becomes extremely unstable at 7kW or more.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a solid-state laser device capable of stably generating a high-power laser beam with a constant divergence angle.

[Means for Solving the Problems] A solid-state laser device according to the present invention includes a solid-state element, a light source for exciting the solid-state element, a resonator for extracting a laser beam from the solid-state element, and a power supply for supplying pulsed power to the light source. The laser output is controlled by changing the pulsed power waveform and changing the base power in response to the change in the waveform to keep the average value of the input power to the light source constant. It is a thing.

Further, the peak value of the pulsed electric power is changed to control the laser output, and the base electric power is changed correspondingly to keep the average value of the electric power supplied to the light source constant.

[Operation] Since the power supply in the present invention applies pulsed power to the light source to excite the solid-state element, it alleviates the change of the thermal lens in the solid-state element and stabilizes the resonator state. The laser output is changed by the change in the waveform of the pulsed power.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional configuration diagram showing a solid-state laser device according to an embodiment of the present invention. In the figure, (1) is a solid-state element, for example, Y _3-X Nd _X Al ₅ O ₁₂ (0
A rod-shaped crystal of <X <3), and (2) a total reflection mirror provided on the end face of the rod, which constitutes a magnifying mirror. (3) is an excitation light source, for example, an arc lamp or a flash lamp, (4) is a power source for turning on the excitation light source (3), (5) is a condensing reflection mirror, and (6) is, for example, glass. The exit mirror forms a collimating mirror. (7) is a partial reflection film made of, for example, TiO ₂ provided in 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 outer surface of the exit mirror (6) And a non-reflective film made of, for example, SiO ₂ provided on the side surface of the solid-state device (1), (9) and (11) are generated in the laser resonator including the exit mirror (6) and the total reflection mirror (2). A laser beam, (10) is a laser beam taken out of the laser resonator, and (12) is an outer frame.

Next, the operation will be described. The solid-state element (1) is excited by the direct light from the excitation light source (3) turned on by the power source (4) and the reflected light from the condensing reflection mirror (5),
It forms the laser medium. On the other hand, the laser beams (9) and (11) generated in a so-called unstable resonator composed of the exit mirror (6) and the total reflection mirror (2) are amplified by this laser medium every time the laser beams reciprocate between the two mirrors. When a certain size or more is reached, a part of it becomes an external laser beam (1
It is released as 0).

Power supply to the light source (3) will be described in more detail. FIG. 2 (a) shows a ramp (3) with respect to time (horizontal axis).
2 (b) is a waveform diagram showing the laser output (vertical axis) corresponding to FIG. 2 (a). Here, the borrowing frequency of power input to the lamp is 100 Hz, while the average power input is kept almost constant by changing the base power within the range not reaching the oscillation threshold value as the peak power increases. For example, the duty cycle is 33%, the threshold of oscillation is 10kW,
Assuming that the average input power is kept constant at 16.5kW, the base power should be 0kW when the peak power is 50kW, and the base power should be 10kW when the peak power is 30kW. FIG. 3 shows the relationship between the peak value (Kw) of input power on the horizontal axis and the average laser output (W) on the vertical axis. It can be seen that the laser output is controlled by the change in the peak value of the input power and a maximum laser output of 100 W is obtained. Here, the solid-state element (1) is Y _2.4 Nd _0.6 Al ₅ O ₁₂ excited by the lamp (3), the diameter of its cross section is 8 mm, the length is 150 mm, the exit mirror (6), the total reflection mirror (2). The inner surface curvatures of) are 0.48 m and 0.8 m, the distance between both mirrors is 0.44 m, the reflectance of the partial reflection film (7) at the center of the inner surface of the exit mirror (6) is 80%, and the average input power is about 6 kW. Is.

On the other hand, FIG. 4 shows the relationship between the total divergence angle (mrad) of the laser beam and the average laser output (W). The total divergence angle was approximately 1 mrad, which was almost constant regardless of the laser output value. This is because the peak value of the input power was changed and the laser output was controlled while the average input power to the solid-state element (1) was kept constant. That is, since the response time for forming a thermal lens in the solid-state element (1) is generally several seconds, for a pulsed power of several 100 Hz, a thermal lens determined only by its average value is generated in the solid-state element (1). Is.

Considering further the practical advantage, since the average equal input power to the lamp (3) has conventionally been changed corresponding to the operating state of the laser, the life of the lamp (3) changes depending on the operating state of the laser. Therefore, it is necessary to determine the replacement time by observing the actual laser output state. On the other hand, in the device according to the invention, the average power applied to the lamp (3) is substantially constant and therefore its life is also constant irrespective of the operating state of the laser. Therefore, for example, if the total operation time of the laser is recorded, the replacement time of the lamp (3) can be easily determined.

In the above embodiment, an example in which the average power is kept constant is shown, but it does not have to be strictly constant depending on the configuration of the resonator, and even if some deviation occurs, the deviation of the divergence angle may be small. Also in this case, a much more stable laser beam was obtained when compared with the case where the base power was not controlled at all.

In addition, in the above-mentioned embodiment, the example using the unstable resonator is shown, but it goes without saying that the same effect can be obtained with the stable resonator as in the conventional case.

In addition, although the center of the inner surface of the exit mirror has a partial reflectance, this may be one having a total reflection property. In this case, a ring-shaped laser beam is generated and diffraction due to the ring-shaped is generated. Although the light-collecting performance deteriorates due to light, a laser beam with a stable divergence angle can be generated as in the above-described embodiment.

Further, in the above-mentioned 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 was not a problem, but this may be a problem due to the structure of the partial reflection film (7). It is conceivable, and in that case, means for canceling the phase difference between the two laser beams may be provided. For example, as shown in FIG. 5, it can be realized by providing a step (70) on the outer surface of the exit mirror.

Further, although the total reflection mirror (2) is formed on the side surface of the solid-state element in the above-mentioned embodiment, both may be separated as shown in FIG.

The solid state element (1) may also be arranged near the exit mirror as shown in FIGS. 7 and 8.

Further, in the above-described embodiment, an example in which the condensed laser beam is reflected from the total reflection mirror (2) has been shown, but a parallel laser beam may be reflected.
FIG. 9 corresponds to FIG. 6, FIG. 7, FIG.
Embodiments as shown in FIGS. 10, 11 and 12 are possible.

[Advantages of the Invention] As described above, the solid-state laser device according to the present invention includes a solid-state element, a light source for exciting the solid-state element, a resonator for extracting a laser beam from the solid-state element, and a power supply for supplying pulsed power to the light source. The laser output is controlled by changing the pulsed power waveform and changing the base power corresponding to the change in the waveform to keep the average value of the input power to the light source constant. As a result, there is an effect that a solid-state laser device capable of generating a laser beam with stable quality can be obtained regardless of the magnitude of the laser output.

In addition to the above invention, the peak value of the pulsed power is changed to control the laser output, and the base power is changed correspondingly so as to keep the average value of the input power to the light source constant. By doing so, there is an effect that a solid-state laser device capable of generating a laser beam with more stable quality can be obtained.

Further, there is an effect that the replacement time of the lamp can be easily determined.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a solid-state laser device according to an embodiment of the present invention, and FIG. 2 (a) is a waveform diagram showing input power (vertical axis) to a lamp (3) with respect to time (horizontal axis), FIG. 2 (b) is a waveform diagram showing the laser output (vertical axis) corresponding to FIG. 2 (a), FIGS. 3 and 4 are diagrams showing the operating characteristics, and FIG. 3 is the horizontal axis. Fig. 4 shows the relation between the peak value (Kw) of input power and the average laser output (W) on the vertical axis, and Fig. 4 shows the relation between the total divergence angle (mrad) of the laser beam and the average laser output (W). FIG. 5 is a sectional view showing the other embodiment of the present invention, FIG. 13 is a sectional view showing a conventional solid-state laser device, FIG. 14 and FIG.
The figure is an operating characteristic diagram of a conventional solid-state laser device. Fig. 14 is a characteristic diagram showing the input power (kW) on the horizontal axis and the laser output (W) on the vertical axis, and Fig. 15 is the divergence of the generated laser beam. Corner (mr
It is a characteristic view which shows the relationship between ad) and input electric power (kW). (1) ... Solid element, (2), (20) ... Total reflection mirror, (3) ... Light source, (6) ... Exit mirror, (7) ...
… Partially reflective film, (8) …… Non-reflective film, (9), (10),
(11) …… Laser beam. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

(57) [Claims] 1. A solid-state device, a light source for exciting the solid-state device,
A resonator for extracting a laser beam from the solid-state element and a power supply for supplying pulsed power to the light source are provided, and the waveform of the pulsed power is changed, and the base power is changed in response to the change in the waveform. The solid-state laser device is configured to control the laser output by keeping the average value of the electric power supplied to the light source constant. 2. The laser output is controlled by changing the peak value of the pulsed electric power, and the base electric power is changed correspondingly to keep the average value of the electric power supplied to the light source constant. 2. A solid-state laser device according to claim 1.