JPH0414279A - Semiconductor excitation solid-state laser - Google Patents

Abstract

PURPOSE:To stably oscillate a high-quality laser beam at a high output by fetching the laser beam output from an oscillating section which oscillates laser light by injecting excitation light into a small area in a solid-state laser medium and an amplifying section which amplifies the laser light under a non-oscillating condition by receiving the oscillated laser light by means of another solid-state laser medium and injecting the excitation light from the side. CONSTITUTION:At an oscillating section 10, excitation light EL is injected at a high density into a small area in a solid-state laser medium 11 and, at the same time, laser oscillation can be started highly efficiently at a low threshold level even though the injected amount of the light EL is small, since the injecting direction of the light EL is equal to the direction of laser resonance. Oscillated laser light L is fetched from the section 10 via a partial reflecting mirror 14 and given to an amplifier section 20 below the section 10 via total reflecting mirrors 31 and 32. The laser light L given to the section 20 from the section 10 is reflected between both reflecting mirrors 22 and 23 and fetched as an laser light output Lo after the light L passes through a solid-state laser medium 21 plural times, for example, three times in this example, along an optical path which is shifted at every reflection and is amplified whenever the light L passes through the medium 21.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a solid-state laser device that optically excites an active substance in a solid-state laser medium such as YAG using excitation light emitted by a semiconductor laser device, especially a high-output basic device. The present invention relates to a device suitable for extracting laser light oscillated in a mode.

[Prior Art] As is well known, a solid-state laser that uses a laser medium in which a loft or slab is formed of an optical crystal such as YAG or glass containing an active substance such as Nd is generally optically excited. Tungsten halogen lamps and krypton discharge lamps are often used as excitation light sources for this purpose, but within the wide emission spectrum of these lamps ranging from ultraviolet to near-infrared, very little light is absorbed by the laser medium and contributes to laser oscillation. Since it is limited to a narrow wavelength range, not only does the laser oscillation efficiency decrease, but also component light that does not contribute to excitation turns into heat within the laser medium, so the laser beam is Problems such as quality deterioration and thermal destruction of the solid-state laser medium are likely to occur.

On the other hand, a semiconductor laser has a very narrow emission spectrum. For example, a GaAlAs laser diode is suitable for excitation of YAG containing Nd. It has an emission wavelength around m, and has the advantage that this wavelength can be finely adjusted by changing the mixed crystal ratio of AI.

For this reason, semiconductor lasers are attracting attention as light sources because they are advantageous for optical excitation of solid-state laser media, although there are rjIMs that emit a small amount of light. A solid-state laser device using this semiconductor laser as an excitation light source will be described below with reference to FIGS.

FIG. 2 shows an example in which the laser medium 11 is excited from its end face 11a. The excitation light EL from the semiconductor laser 12 is projected into the laser medium 11 from the end face 11a and focused at the focal point F by the focusing means 13 consisting of a collimator lens 13a and a focusing lens 13b. This end face 11a has 0.81-
A coating is applied that has high transmittance for the excitation light EL and high reflectivity and wavelength selectivity for the 1.06-wave oscillation laser light. The other end face 11b is coated with a coating that is highly transparent to laser light, and has a reflectance of, for example, 0.
About 95 partial reflections and 1114 are arranged facing each other. The laser resonant system includes the end face 11a of the laser medium 11 and the partial reflecting mirror 1.
4, and is synchronized with the laser oscillation by finely adjusting the position of the partial reflecting mirror 12. Of course, the laser beam output O is taken out via the partial reflecting mirror 14.

The conventional example shown in FIG. 2 is a so-called end-pumping type in which the excitation light EL is injected from the end surface 11a side of the laser medium 11.
The conventional technique shown in FIG. 3 is of the side-pumping type, which is particularly suitable for oscillation of a fundamental mode called the o-mode, which is used to increase the output of the laser beam.

That is, as shown in FIG. 3(a), the excitation light E from the semiconductor laser array 24 placed on the side surface of the laser medium 11
This is excited from the side by L. Semiconductor laser chips are small, about 11 cubic meters in size, and during manufacturing, they are separated into chips from a wafer through bars arranged in a row. The semiconductor laser array 24 as an excitation light source utilizes the bar state as it is, and is placed on the side of the rod-shaped laser medium 11 as shown in FIG. The laser medium 11 is injected into the interior of the laser medium 11 using the lens effect. The laser resonant system in the conventional example shown in FIG. 3 is formed between a partial reflection mirror 14 as an output mirror and a total reflection mirror 15 placed on the opposite side of the laser medium 11, as shown in FIG. 3(a). be done.

In the second side pumping type, by arranging multiple semiconductor lasers along the laser medium 1rllO axis direction, the amount of pumping light can be increased and the output can be increased, but the injection density of the pumping light EL is not very high (only the fundamental mode Since oscillation is difficult, it is not as good as the end-pumped type in terms of oscillation efficiency and laser beam quality.

FIG. 4 shows a conventional example suitable for fundamental mode oscillation and high output oscillation. In this prior art, a so-called slab shape having a flat rectangular cross section is used as the laser medium 16, and a pair of side surfaces 16
a with a highly reflective coating and place it on the slope 16.
The laser beam entering and exiting the laser medium 16 from b is reflected by both side surfaces 16a as shown in the figure, and travels in a zigzag pattern inside the medium.

A partial reflection mirror 14 and a total reflection mirror 15 are arranged so as to face the slope 16b, respectively, to form a laser resonant system. The excitation light BL is guided from a semiconductor laser (not shown) through an optical fiber 25, and is connected to a Selfox lens 2.
6, and is injected into the laser medium 16 from each reflection point of the laser beam on both side surfaces 16a into its very shallow surface at high density.

The conventional example shown in FIG. 5 is a simplified version of the structure shown in FIG. 4 to improve its practicality. The laser medium 17 has a rectangular cross section similar to that shown above, and a partial reflection mirror 14 and a total reflection mirror are used so that the laser beam travels inside in a zigzag shape while being reflected on both sides at a more acute angle than in the case of FIG. 15, the reflection points on the side surface 17a are brought close to each other, and the excitation light EL from the semiconductor laser array 24 is focused by the cylindrical lens 27 on the surface area of the laser medium 17 where these reflection points are lined up. inject.

[Problems to be Solved by the Invention] In all of the conventional techniques described above, while taking advantage of the above-mentioned advantages of exciting a solid-state laser device with semiconductor laser light, the laser oscillation efficiency is maximized and the laser beam is as high as possible. Efforts have been made to improve the quality of the laser beam by increasing the output power and oscillating the fundamental mode, but unfortunately each has its advantages and disadvantages.
At present, there are few products that can satisfy these requirements sufficiently or simultaneously.

That is, in the end-pumped solid-state laser device shown in FIG. 2, the excitation light EL can be concentrated in a small region near the focal point F in the laser medium 11, so it has the advantage of a low lasing threshold and high lasing efficiency. In addition, it is easy to oscillate only the fundamental mode, so the quality of the laser beam is excellent. However, since the total amount of excitation light EL that can be injected from the narrow end face 11a of the laser medium [11] is limited, this end-pumped solid-state laser device has the drawback that it is essentially unsuitable for oscillating a high-power laser beam. be.

In this regard, in the side-pumped solid-state laser device shown in FIG. 3, a large number of semiconductor lasers are arranged in the form of an array 24 along the axial direction of the laser medium 11, as described above, to control the total amount of pumping light EL. However, the injection density of the pumping light EL into the laser medium 11 is considerably lower than that of the end-pumped type, and in reality, only the fundamental mode Since oscillation is often difficult, there are still problems to be improved in terms of oscillation efficiency and quality of the laser beam.

The conventional example shown in FIG. 4 can overcome the drawbacks of the end-pumped type and the side-pumped type, and can easily achieve high output because the excitation light EL can be injected into the laser medium 16 from a large number of semiconductor lasers. Since the excitation light EL can be injected at high density into each reflection point of the laser beam on the side surface of the laser medium 16, the advantage of high oscillation efficiency and suitability for oscillation in only the fundamental mode can be obtained.

However, since a large number of SELFOX lenses 26 are used, the structure becomes complicated, and their positions and angles must be adjusted one by one to match each reflection point, which tends to cause errors during operation. Therefore, although it is excellent in principle, its practicality is not very high.

In the conventional technique shown in FIG. 5, the structure and optical adjustment are simple, high output is possible, the injection density of pumping light is quite high, the oscillation efficiency is high, and fundamental mode oscillation is also possible. However, in practice, it is still quite difficult to apply a highly reflective coating to the laser beam reflecting part 17a on the right side of the laser medium 17 in the figure, and to apply another highly transparent coating to the entrance and exit part 17b. It's troublesome.

In addition, in both the conventional examples shown in Fig. 4 and Fig. 5, there is a problem that the laser light in the laser medium is attenuated each time it is repeatedly reflected on the side surface. Applying reflective coatings to the sides of the laser medium is quite difficult in practice, and the reflective properties of such coatings are susceptible to deterioration during operation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art and provide a semiconductor laser pumped solid-state laser device that can stably oscillate a high-output, high-quality laser beam.

[Means to solve the problem]

According to the present invention, this purpose is to provide an oscillation section that injects excitation light into a small region within a solid-state laser medium placed in an optical resonant system and oscillates a laser beam in the same direction as the oscillation section, and a separate section that separates this oscillation laser beam. an amplifying section that amplifies the laser beam under non-oscillation conditions by injecting excitation light from the side into the optical path of the laser beam received in the solid-state laser medium and passing through the solid-state laser medium, and extracting the laser beam output from the amplifying section. This is achieved by

Note that a laser diode is most suitable as the semiconductor laser for the excitation light source, and it is preferable to use a single laser diode in the oscillation section and the above-mentioned laser diode bars arranged in an array in the amplification section.

A rod-shaped laser medium is suitable for the oscillating section, and it is desirable to configure this oscillating section as an end-pumped laser oscillator to oscillate in the fundamental mode.

On the other hand, a slab type is suitable for another laser medium for the amplification section, and it is desirable to configure this amplification section as a side-pumping type laser optical amplifier that injects pumping light from the large-area side surface of the slab. Furthermore, in this case, the laser beam is passed through the slab-shaped laser medium multiple times in the axial direction of the slab while sequentially shifting its optical path, and excitation light is injected from the semiconductor laser array into each optical path from the side of the slab. It's advantageous. In addition, in this way, the laser beam is emitted into the laser medium multiple times i! 1ij4, for example, by combining a pair of reflecting mirrors with a laser medium, and in order to sequentially shift the path of the laser beam, the directions of both reflecting mirrors may be shifted from each other.

[Function] In the present invention, the oscillation section in the above configuration has the role of generating high-quality laser light, and the amplification section has the role of amplifying this laser light into a high-output laser beam. While utilizing optical excitation by a semiconductor laser, the laser beam extracted from the latter is made to have both high quality and high output by assigning specialized functions to each part.

In other words, in order to improve the quality of the laser beam, it is desirable to include only the fundamental mode, and for that purpose it is necessary to oscillate the laser beam in the fundamental mode. It is advantageous for fundamental mode oscillation not to increase the oscillation output in the part. In other words, in low-output laser oscillation, the excitation light can be focused and injected into a small region of the laser medium at high density, and the thermal lens effect caused by temperature rise can be minimized, making it easy to oscillate only the fundamental mode and excitation light. Complicated structure and deviation from fundamental mode oscillation when light is injected into multiple locations in the laser medium can also be prevented.

In the present invention, the high-quality laser beam oscillated in this way is given to the amplification section to amplify it into a high-output laser beam, but this amplification section generates a non-resonant laser beam in a separate solid-state laser medium as described above. Since this laser light is amplified under certain conditions, there is no room for its fundamental mode to go out of order, and it can be amplified while maintaining its original good properties. Furthermore, in this amplification section, excitation light is injected from the side into the optical path of the laser beam passing through the laser medium, so a large number of semiconductor lasers or arrays thereof can be arranged along this optical path, increasing the amplification factor. It is possible to obtain a high-power laser beam.

It should be noted that the oscillation section and the amplification section only have different functional assignments as described above, and the optical relationship between them, such as optical axis alignment, does not need to be particularly strict.

In this way, the present invention solves the above-mentioned problems of increasing the quality and output of a laser beam by having the oscillation section and the amplification section perform their respective specialized functions. This has succeeded in making it unnecessary.

[Example] Hereinafter, an example of the semiconductor laser pumped solid-state laser device of the present invention will be described with reference to FIG. The figure shows an example of the configuration in a perspective view.

The oscillation unit 10 of this embodiment shown in the upper part of the figure is an end-pumped laser oscillation device similar to that shown in FIG. For example, several to tens of optical crystals such as YAG containing
A rond with a diameter of about
A wavelength-selective coating that is highly reflective to the oscillated laser beam having a wavelength of - is applied, and a coating that is highly transparent to the oscillated laser beam is applied to the other end face 11b.

Opposed to this other end surface 11b, a partial reflection #L having a reflectance of, for example, 0.95 with respect to laser light is used as an output mirror.
14 is disposed, and by finely adjusting its position, for example, a laser resonant system for the wavelength of the oscillated laser beam is formed between the partial reflecting mirror 14 and one end surface 11a of the laser medium 11.

The semiconductor laser 12 in the figure is a single laser diode or the like, and the excitation light EL emitted from it is projected onto the end face 11a of the laser medium 11 via the condensing means 13, and the focal point of the condensing means 13 inside the laser medium 11 is projected. It is implanted at a high density in a small area nearby. Note that the condensing means 13 is, for example, a combination lens consisting of a collimator lens and a condensing lens, as in the previous case of FIG. 2.

In this oscillation section 10, the excitation light EL is injected at high density into a small area in the solid-state laser medium 11 as described above, and the injection direction is the same as the laser resonance direction, so the amount of the excitation light EL injected is very small. However, laser oscillation can be started with a low threshold and high efficiency. In addition, since the amount of excitation light is small, the solid-state laser medium I
Since there is almost no temperature rise in II, and therefore almost no thermal lens effect based on it, the generation of multi-modes is suppressed, and although the output level is low, it is possible to easily oscillate high-quality laser light purely in the fundamental mode. This oscillated laser light is extracted from the oscillating section 10 via a partial reflecting mirror 14 as usual, and in this example is applied to the amplifying section 20 below it via total reflecting mirrors 31 and 32 in the figure.

The amplification section 20 in this embodiment is a YAG
A slab-type solid-state laser medium 21 made of an optical crystal or the like;
It is composed of reflecting mirrors 22 and 23 placed opposite to each other on the end faces 21a and 21b, and a semiconductor laser array 24 placed below the large-area side surface of the laser medium 21.
Both end surfaces 21a and 21b are coated with a coating that is highly transparent to laser light in order to prevent parasitic oscillation between reflections 922 and 23 and to minimize reflection loss. A so-called sanding treatment is applied to the three side surfaces except for the 3 sides to prevent parasitic oscillation. Furthermore, in this embodiment, the pair of reflecting mirrors 22, 23 are inclined at an angle θ with respect to both end surfaces 21a, 21b of the laser medium 21, and are therefore arranged so that they form an angle twice that of each other.

As a result, the laser light given from the oscillating part 10 to the amplifying part 20 is reflected between the two mirrors 22 and 23 as shown in the figure, and the solid laser medium 2 follows the optical path that is shifted each time it is reflected.
1 multiple times (in this example, 3 times), and after being amplified each time, it is output as a laser beam and taken out as O.

The semiconductor laser array 24 thus provides excitation light for amplification to the laser medium 21 within the range through which the laser light passes.For example, a bar in which the aforementioned laser diodes are arranged is attached on top of the Berthier element for cooling. Then,
On the other hand, the laser medium 21 is disposed with its lower side surface in close contact with the laser medium 21 . Note that the above-mentioned angle θ of the reflecting mirrors 22 and 23 is set to be sufficiently small, so that the multiple optical paths of the laser light in the laser medium 21 are shifted only slightly.
Even if the semiconductor laser array 24 is a single laser diode bar, the laser medium 21 in a plurality of optical path ranges can be optically excited.

When using the array 24 in which about 10 or more semiconductor lasers are arranged in this way, the laser light passing through the laser medium 21 can be amplified several times each time it passes, so it can be made to pass about three times as in this example. For example, the laser light of about 0.1 W given from the oscillation unit 10 can be amplified several tens of times to increase the laser light output Lo to several W. Of course, the output level can be further increased by increasing the number of passes. can.

Furthermore, in this amplification section 20, the above-described amplification effect on the laser light is performed under non-resonant conditions by preventing parasitic oscillation as described above and shifting the laser light optical path in the laser medium 21 each time it passes through. Therefore, there is no room for another mode to be added to the laser light oscillated in the fundamental mode by the oscillation unit 10, and the above-mentioned high-output laser light can be output and amplified to O while maintaining the original good properties.

The present invention is not limited to the embodiments described above, and can be implemented in various embodiments. For example, although the oscillation section is of an end-pump type, it is possible to oscillate a laser beam with good properties such as fundamental mode oscillation. If so, you can replace it accordingly. As for the amplifying section, the solid-state laser medium therein does not necessarily have to be slab-shaped, and a laser medium with a rectangular cross section or the like can be used. The optical path of the laser beam in the laser medium may also be a simpler zigzag-shaped optical path than in the embodiments so that the number of passes can be adjusted, and the means for specifying such an optical path is not limited to the reflecting mirror as in the embodiments. Of course.

〔Effect of the invention〕

As described above, in the present invention, a solid-state laser device pumped by a semiconductor laser is configured with an oscillation section dedicated to generating high-quality laser light and an amplification section dedicated to increasing the output of the laser light,
In the oscillation section, excitation light is injected into the booth area of a laser medium placed in an optical resonant system to oscillate laser light in the same direction as the injection, and in the amplification section, this laser light is passed through another laser medium and its By injecting excitation light from the side into the optical path, amplifying it under non-oscillation conditions, and then extracting it as laser light output,
You can get the following effects.

(a) Separate the functions of improving the quality and output of the laser beam, and assigning separate sections to the oscillation section, amplification section, and laser beam, respectively, and fully utilizing their respective specialized functions to achieve high quality. It is possible to extract a laser beam that has both high power and high power.

(b) The utilization efficiency of excitation light can be increased more than ever for both laser oscillation in the oscillation section and amplification of laser light in the amplification section, and the oscillation efficiency of the solid-state laser device can be significantly improved.

(C) No particular density is required for optical axis alignment between the oscillation section and the amplification section, and optical adjustment is easy.

As described above, the present invention provides a highly practical means for solving the conventional problems related to semiconductor laser excitation of solid-state laser devices, and is expected to contribute to further improvements in efficiency and performance.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of an embodiment of a semiconductor laser pumped solid-state laser device of the present invention. Figure 2 and subsequent figures relate to the prior art; Figure 2 is a configuration diagram of an end-pumped solid-state laser device;
Figure 3 (a) is a block diagram of a side-pumped solid-state laser device, Figure 3 (b) is a partial cross-sectional view, and Figure 4 is a diagram of a solid-state laser device that injects excitation light into multiple locations on the surface of a laser medium. FIG. 5 is a block diagram of an improved solid-state laser device. 10: Oscillation part, 11: Solid laser medium (Rondo), 12
: semiconductor laser, 20: amplification section, 21: solid laser medium (slab), 24: semiconductor laser array, εL: excitation light, L: laser light generated by oscillation section, 21st! ]

Claims (1)

[Claims] A solid-state laser device that uses a semiconductor laser as a light source for optical excitation, which injects excitation light into a small region of a solid-state laser medium placed in an optical resonant system and oscillates laser light in the same direction as the injection. an oscillating section; and an amplifying section that receives laser light from the oscillating section into another solid-state laser medium and injects excitation light from the side into the optical path of the laser light passing through the solid-state laser medium to amplify the laser light under non-oscillation conditions. A solid-state laser device pumped by a semiconductor laser, in which laser light output is extracted from an amplifying section.