JP3214056B2 - Optically pumped solid-state laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically pumped laser apparatus for generating a high-quality laser beam of high quality.

[0002]

2. Description of the Related Art FIG. 22 is a sectional view showing a conventional laser apparatus shown in, for example, "Laser Handbook" edited by The Laser Society of Japan, Ohmsha, p. 222.
(B) is a cross-sectional view. In FIG. 22, 1 is a total reflection mirror, 2 is a partial reflection mirror, 3 is a solid-state element including an active solid medium. In the case of a yag laser, for example, Nd-doped Nd: YAG (Yttrium Aluminum Garne) is used as an active solid medium.
t), 4 is a light source, for example, an arc lamp, 5 is a power supply for turning on the light source 4, 6 is a condenser of the light source 4, for example, has an elliptical cross section and an inner surface formed of a light reflecting surface. Reference numeral 7 denotes a laser beam generated in the laser resonator constituted by the mirrors 1 and 2, 8 denotes a light source 4, a cylindrical tube for adjusting the flow of a medium 60 for cooling the periphery of the solid element 3 including an active solid medium, and 9 denotes O. Sealing materials such as rings, 81 and 82 are inlets and outlets of the cooling medium 60, 70 is a laser beam taken out, and 100 is a base.

The conventional light-pumped solid-state laser device is configured as described above. The light source 4 and the solid-state element 3 are arranged at the focal point of a condensing device 6 having an elliptical cross-section, and are turned on by a power source 5. The light emitted from is collected in the solid-state device 3. The solid state element 3 is excited by the collected light and becomes a laser medium. Spontaneous emission light generated from the laser medium is amplified while reciprocating between the resonators constituted by the mirrors 1 and 3, and when it reaches a certain size or more, is emitted to the outside as a laser beam 70 having good directivity. You. Further, the light source 4 and the solid state element 3 are cooled from the surroundings by a cooling medium 60 circulating around the inside of the cylindrical tube 8.

[0004]

In the conventional laser device as described above, the light from the light source 4 is condensed on the solid-state element 3, and the condensed light is further packed in the concentrator. 23, due to the refractive index difference between the cooling medium 60 and the solid-state element 3, the vicinity of the center of the solid-state element 3 is strongly excited. Therefore, a distribution occurs in the excitation, and the quality of the generated laser medium is reduced in the cross section. Therefore, it was not possible to obtain a high-quality beam having a good condensing property. For example, FIG. 24 shows an example of observing spontaneous emission light from the axial direction of the solid-state element 3 without forming an optical resonator. FIG. 25 shows a thermal lens degree in a cross section generated by a temperature distribution in the solid-state element 3. Here is an example of actual measurement of the distribution. FIG. 26 shows a divergence angle of a laser beam obtained by performing laser oscillation using the solid state element 3 in comparison with a theoretical limit value. Here, a Nd: YAG rod with a diameter of 4 mm capable of generating the highest quality laser beam at present was used and excited by a Kr arc lamp. When the input to the lamp was increased, the laser output was increased, but the distribution shown in FIG. 25 was also increased, and as a result, the quality of the laser beam was deteriorated.
For the above reasons, high-quality beams of 50 W or more have not been obtained using Nd: YAG rods at present, nor have they been industrialized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and uniformly guides light into a solid-state device, obtains a uniform laser medium, and generates a high-output and high-quality laser beam. It is an object of the present invention to obtain a light-pumped solid-state laser device capable of performing the above-mentioned operations.

[0006]

According to the present invention, there is provided an optically-pumped solid-state laser device according to the present invention, wherein a periphery of a first solid-state element including an active solid medium is covered with a second solid-state element having a refractive index larger than that of the medium . Excite the thickness of the second solid state device
The light that excites the weak side is thicker than the strong side .

[0007]

Further, in the light-pumped solid-state laser device of each of the above configurations, the inner surface of the light collector may be constituted by a diffuse reflection surface.

In the above-described optically pumped solid-state laser device, the first solid-state element including the active solid-state medium has a circular cross section, and the second solid-state element having a large refractive index covering the periphery thereof is cylindrical. The outer diameter of the second solid state element, or the sum of the thickness of the second solid state element and the radius of the first solid state element,
The outer diameter of the first solid state element may be larger than the ratio of q = (refractive index of the material of the second solid state element / refractive index of the medium packed in the light collector).

It is preferable that a thin-film medium sufficiently thinner than the thickness of the second solid-state element is inserted between the first solid-state element and the second solid-state element.

Further, it is preferable that the optically pumped solid-state laser device of each of the above structures uses an unstable type resonator.

Further, the optical resonator of the optically pumped solid-state laser device having the above-mentioned configuration includes an enlarged exit mirror having a partial reflection mirror at the center and a non-reflection portion at the periphery thereof, and a collimating total reflection mirror. It is preferable to use a resonator.

Further, it is preferable to use, as the enlarged exit mirror, one provided with means for canceling the phase difference between the laser beam passing through the central partial reflection portion and the surrounding non-reflection portion.

[0014]

In the photo-pumped solid-state laser device configured as described above, the thickness of the second solid-state element is given a distribution,
Make the weaker exciting light thicker than the stronger exciting light.
Light from the surroundings to the first solid-state element
Irradiate the first solid-state device to photoexcit
Therefore, a homogeneous laser medium can be obtained .

[0015]

Further, the light collector formed of the diffuse reflection surface uniformly distributes and guides the light from the light source around the second solid-state element, and excites the light.

Further, the sum of the outer diameter or the thickness thereof and the radius of the first solid state element is at least q = (refractive index of material of second solid state element / light collecting element). The refractive index of the medium packed in the vessel) is larger than the ratio of the second solid-state element, the light incident on its surroundings spread fan-shaped in the cross section,
The fan is uniformly excited by including a solid-state element including an active solid medium in the fan.

The thin-film medium inserted between the first solid-state element and the second solid-state element disperses heat from the periphery of the first solid-state element uniformly around the second solid-state element. Lead to the element,
Therefore, the heat distribution of the first solid state element is made uniform in the circumferential direction.

Further, the flat laser beam generated from the unstable resonator maintains uniformity in the first solid-state device.

A resonator composed of an enlarged exit mirror having a partial reflection mirror at the center and a non-reflection portion at the periphery and a collimated total reflection mirror generates a flat laser beam inside the resonator. In addition to maintaining uniformity in the first solid-state element, a flat beam with good condensing properties is generated outside, and the intensity of the laser beam in the resonator is reduced to reduce the first solid-state laser beam. Reduces deformation of the element.

Further, by providing a means for canceling the phase difference between the laser beams passing through the partial reflection portion and the non-reflection portion in the enlarged exit mirror having the above-described configuration, a laser beam having a uniform phase and a middle jam is generated.

[0022]

[Embodiment 1] 1A and 1B are cross-sectional views showing one embodiment of the present invention, in which FIG. 1A is a longitudinal section, and FIG. In FIG. 1, 1, 2, 3, 4, 5, 6, 7,
8, 9, 60, 70, 81, 82 and 100 are exactly the same as the above-mentioned conventional apparatus. Reference numeral 30 denotes a second solid-state element arranged so as to cover the solid-state element (first solid-state element) 3 containing an active solid medium, for example, YA not doped with Nd.
G (Yttrium Aluminum Garnet), which has a higher refractive index than the cooling medium 60.

In the laser device configured as described above, the light source 4 and the first solid medium 3 are disposed at the focal point of the light collector 6 having an elliptical cross-sectional shape. The emitted light is converged on the first solid state element 3 after being bent on the surface of the second solid state element 30. The solid state element 3 is excited by the collected light and becomes a laser medium. Spontaneous emission light generated from the laser medium is amplified while reciprocating between the resonators constituted by the mirrors 1 and 2, and when it reaches a certain size or more, is emitted to the outside as a laser beam 70 having good directivity. You.

The operation of the bending action of the second solid state element 30 will be described. A second solid state element 30 arranged around the first solid state element 3 spreads light coming from various directions in a fan shape as shown in FIG. When the first solid state element 3 is arranged in this fan, light reaches each point uniformly. FIG. 2 shows a calculation example of the radial distribution of the intensity of light reaching the second solid element 30 in the middle. From this example, the outer diameter of the first solid state element 3 is
The ratio q0 = (refractive index of the material of the second solid-state element / refractive index of the medium packed in the light collector) is smaller by a factor of q0, and it is necessary to adopt an arrangement as shown in FIG. As a result, it is possible to remove a dark portion generated in a peripheral portion in the cross section of the solid-state element, and to obtain a uniform light intensity pattern. Further, as shown in FIG. 4, if the outer diameter of the second solid state element 30 is made larger than this condition, a part of the light passes through the first solid state element 3 and the efficiency is reduced, but the light is more uniform. An intensity pattern is obtained.

Embodiment 2 FIG. FIG. 5 is a cross-sectional configuration diagram of the first and second solid state devices according to the second embodiment of the present invention, in which the thickness of the second solid state device is changed on the periphery and distributed over the thickness of the second solid state device 30. The upper side in the figure on the side facing the light source 4 and the lower side in the figure on the side opposite to the light source 4 where the solid element is shadowed.
The configuration is such that the asymmetrical quantity of light incident thereon is corrected so that the light distribution gradient at the center does not occur up to the high output range.

Next, the operation will be described. FIG. 24 shows a spontaneous emission light distribution in a cross section from the axial direction of the solid-state element 3 to the direction perpendicular to the paper without forming an optical resonator. As shown in FIG. The occurrence of dark areas was observed, and the light distribution in the center was not constant.
It can be seen that the right side of the paper close to is strongly excited. This is because the amount of light incident thereon becomes asymmetric on the side facing the light source 4 and on the side opposite to the side where the solid-state element is shadowed, and a light distribution gradient also occurs at the center. This is particularly noticeable in the case of a strong excitation state pursuing output power, and a low-quality laser beam having an asymmetric and non-uniform beam quality has been generated. FIG. 5 shows a structure in which such asymmetry and non-uniformity do not occur. The thickness of the second solid-state element 30 on the lower side is larger than that on the upper side, and as a result, as shown in FIG. The upper part receives the light of the part B and the lower part of the light of the part A having a larger area, and the distribution of the amount of light incident on the first solid-state element 3 is generated due to the density distribution of the light on the upper and lower sides. It is configured not to. FIG. 7 shows an example of a result obtained by observing the spontaneous emission light distribution in a cross section of the first solid-state element 3 configured as described above from the axial direction to the vertical direction on the paper under the same excitation conditions as the conventional example. It can be seen that uniform irradiation was maintained up to high-power excitation in the cross section.

Embodiment 3 FIG. In each of the above embodiments, the reflection inner surface shape of the light collector 6 was not specified.
With the diffuse reflection shape, the light around the second solid-state element 30 is uniformly incident from all directions, and the effect of the invention described in the first and second embodiments is further enhanced.

FIG. 8 shows an example of the light emission distribution when a diffuse reflection condenser is used, and FIG. 9 shows an example of the actual measurement of the distribution of the degree of the thermal lens in the cross section generated by the temperature distribution in the solid-state device. . It can be seen that uniform light emission was obtained and uniform thermal deformation occurred. This uniform thermal lens can be easily corrected by, for example, a normal optical lens arranged outside. FIG. 10 shows a laser beam obtained under the same conditions as those used in the conventional example from the laser medium thus obtained, and the quality thereof. It can be seen that a laser beam with a small divergence angle and a good condensing property is obtained up to a high output region.

Embodiment 4 FIG. In the examples shown in FIGS. 11 and 12, between the first solid state element 3 and the second solid state element 30, a thin film medium (for example, optically transparent medium) that is sufficiently smaller than the thickness of the second solid state element 30. (Adhesive) 61 is inserted. When there is no thin film, the distribution of the gap between the solid-state elements may occur, but the gap is made constant by the thin film. Further, needless to say, the uniformity is increased if the thin film is formed into a liquid such as gel or water.

Embodiment 5 FIG. In the example shown in FIG. 13, an unstable resonator using an enlarged reflection mirror 20 and a collimated total reflection mirror 21 instead of the partial reflection mirror 2 is used. When an unstable resonator is used, a generated laser beam can be generated with a substantially uniform intensity distribution, for example, as shown in FIG. Since the cross-sectional shape of the laser beam is uniform, even in a high-power region where a part of the laser beam is absorbed by the first solid-state element 3 and heated, the uniform laser beam uniformly irradiates the first solid-state element. As a result, the laser beam is heated, so that the uniformity of the laser medium is not disturbed, and as a result, a high-quality laser beam can be stably generated even in a high power range. In FIG. 15, using a 6 mm diameter Nd: YAG rod, Kr
An example of characteristics of a laser beam obtained by excitation by an arc lamp will be described. It can be seen that the unstable resonator generates a laser beam with a large cross-sectional area, and a 6 mm-diameter rod efficiently and stably produces a laser beam with a small divergence angle and good condensing properties.

Embodiment 6 FIG. In the embodiment shown in FIG. 16, further, instead of the magnifying reflection mirror 20 of the fifth embodiment, the center is a partial reflection mirror 22 and the periphery thereof is a magnified exit mirror 24 composed of a non-reflection portion 23 and a collimating mirror. A resonator constituted by the reflection mirror 21 is used.
With this structure, a laser beam having a hollow shape as shown in FIG. Further, as compared with the fifth embodiment, the intensity of the laser beam 7 necessary for obtaining the same light-collecting property can be reduced, and the amount of heat generated when the first solid-state element 3 absorbs the laser beam can be reduced. Therefore, heat generation is reduced, and as a result, a high-quality laser beam can be stably generated even in a high-power region. Figure 18 shows a 6 mm diameter Nd:
An example of the characteristics of a laser beam obtained by excitation with a Kr arc lamp using a YAG rod is shown. A laser beam having a smaller divergence angle and better condensing properties than that of the fifth embodiment is obtained. You can see that.

Embodiment 7 FIG. In the embodiment shown in FIG. 19, in the sixth embodiment, the phase difference between the laser beam passing through the central partial reflection mirror portion 22 and the laser beam passing through the non-reflection portion 23 in the peripheral portion is further added to the mirror outer surface, for example. The configuration is such that a stepped laser beam is canceled by the provided step 25 to obtain a middle-packed laser beam having the same phase. In this case, the light condensing property of the laser beam is further improved. FIG.
Figure 6 shows an example of the characteristics of a laser beam obtained by using a 6 mm diameter Nd: YAG rod and exciting with a Kr arc lamp. It can be seen that a good laser beam is obtained more stably.

In each of the above embodiments, a cross section is described as being circular. However, the present invention is not limited to a circular cross section, but may be a rectangle or an ellipse.

Although not particularly described in any of the above embodiments, the non-reflective thin film, such as a normal optical element, is used for a part of the optical element which is not particularly indicated and a part where the laser beam passes. By doing so, the loss in the resonator is reduced, and efficient laser oscillation can be realized.

Embodiment 8 FIG. Further, in Example 2,
The thickness of the second solid state element 30 is varied on the circumference to give a distribution to the thickness of the second solid state element. However, the distribution of the thickness of the second solid state element is not limited to the cross section, but may be in the axial direction. For example, as shown in FIG. 21, the thickness of the second solid state element 30 is increased at the end, and a small amount of incident light at the end is collected and guided to the first solid state element 3. Then, the end portion can be irradiated with the same amount of light as that of the central portion, so that uniform irradiation can be performed in the axial direction. As a result, deformation such as mechanical bulging of the first solid state element 3 can be reduced in the axial direction. Since the first solid-state element can be made uniform, it is possible to prevent a deformation effect due to a so-called end effect in which the first solid-state element end surface swells and the first solid-state element turns into a lens, and as a result, a stable operation can be realized.

[0036]

As described above, according to the present invention, the periphery of the first solid state element is covered with the second solid state element, and the side on which the light for exciting the thickness of the second solid state element is weak is excited.
Since the light to be emitted is thicker than the strong side, a laser medium that emits light more uniformly in the cross section of the first solid-state element is obtained, and there is an effect that a high-quality laser beam can be stably obtained.

[0037]

Further, if the inner surface of the light collector is constituted by a diffuse reflection surface, the light from the light source can be uniformly distributed and guided around the second solid-state element, and the laser can emit light more uniformly in the cross section. A medium can be obtained, and an extremely high-quality laser beam can be stably obtained.

The sum of the outer diameter of the second solid state element or the thickness of the second solid state element and the radius of the first solid state element is q = (the second solid state element) larger than the outer diameter of the first solid state element. If it is configured to be larger than the ratio of (the refractive index of the material of the element / the refractive index of the medium packed in the light collector), the light incident on the periphery spreads out in a fan shape in the cross section, and the fan The first solid-state element can be included in the laser medium, and the first solid-state element can be uniformly excited, and a laser medium that emits light almost uniformly in a cross section can be obtained. Is obtained stably.

When a thin-film medium sufficiently smaller than the thickness of the second solid state element is inserted between the first solid state element and the second solid state element, heat from the surroundings of the first solid state element is dissipated. The radiation is uniformly guided on the circumference to the second solid-state element, so that the heat distribution of the first solid-state element is made uniform in the circumferential direction, and a laser medium that emits light stably and almost uniformly in the cross section is obtained. A high-quality laser beam can be stably obtained by using the detector.

If the optical resonator is constituted by an unstable resonator that generates a flat laser beam, a part of the laser beam is uniformly absorbed by the first solid-state element uniformly excited by the light source. As a result, the laser beam uniformly heats the first solid-state element, so that a high-quality laser beam can be stably extracted even in a high-power region without disturbing the uniformity of the laser medium.

In the above-mentioned optically pumped solid-state laser device, if an optical resonator is constituted by an enlarged exit mirror composed of a partial reflection mirror at the center and a non-reflection part at the periphery thereof, a resonator is provided. Generates a flat laser beam inside, maintains the uniformity within the first solid-state device, generates a flat beam with good condensing properties outside, and further increases the intensity of the laser beam inside the resonator. By lowering, the deformation caused by the absorption of the laser beam into the first solid-state element uniformly excited by the light source can be reduced, and a high-quality laser beam can be stably extracted even in a high-power region.

Further, if the enlarged exit mirror having the above structure is provided with means for canceling the phase difference between the laser beam passing through the central partial reflection portion and the surrounding non-reflection portion, it is possible to obtain a good external light-collecting property. A flat beam having the same phase difference is generated, and a high-quality laser beam can be taken out stably even in a high-power region.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view and a horizontal sectional view showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional configuration diagram illustrating first and second solid-state elements according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the second embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the second embodiment of the present invention.

FIG. 8 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the third embodiment of the present invention.

FIG. 9 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the third embodiment of the present invention.

FIG. 10 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the third embodiment of the present invention.

FIG. 11 is a sectional view showing a main part of an optically pumped solid-state laser device according to a fourth embodiment of the present invention.

FIG. 12 is a sectional view showing a main part of another optically pumped solid-state laser device according to Embodiment 4 of the present invention.

FIG. 13 is a longitudinal sectional view and a transverse sectional view showing a fifth embodiment of the present invention.

FIG. 14 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the fifth embodiment of the present invention.

FIG. 15 is an explanatory diagram illustrating an operation of a photo-excitation solid-state laser device according to a fifth embodiment of the present invention.

FIG. 16 is a vertical sectional view and a horizontal sectional view showing a sixth embodiment of the present invention.

FIG. 17 is an explanatory diagram illustrating the operation of the photoexcitation solid-state laser device according to Embodiment 6 of the present invention.

FIG. 18 is an explanatory diagram illustrating the operation of the photoexcitation solid-state laser device according to Embodiment 6 of the present invention.

FIG. 19 is a longitudinal sectional view and a transverse sectional view showing a seventh embodiment of the present invention.

FIG. 20 is an explanatory diagram illustrating an operation of the photoexcitation solid-state laser device according to the seventh embodiment of the present invention.

FIG. 21 is a longitudinal sectional view and a transverse sectional view showing Example 8 of the present invention.

FIG. 22 is a longitudinal sectional view and a transverse sectional view showing a conventional photo-excitation solid-state laser device.

FIG. 23 is an explanatory diagram illustrating an operation of a conventional photoexcitation solid-state laser device.

FIG. 24 is an explanatory diagram illustrating the operation of a conventional photoexcitation solid-state laser device.

FIG. 25 is an explanatory diagram illustrating an operation of a conventional photoexcitation solid-state laser device.

FIG. 26 is an explanatory diagram illustrating the operation of a conventional photoexcitation solid-state laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Total reflection mirror 2 Partial reflection mirror 3 1st solid-state element 4 Light source 6 Condenser 7 Laser beam 20 Magnification reflection mirror 21 Collimation total reflection mirror 22 Partial reflection mirror 23 Non-reflection part 24 Expansion exit mirror 25 Step 30 Second Solid element 60 Cooling medium 61 Medium 70 Laser beam

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-11992 (JP, A) JP-A-60-239076 (JP, A) JP-A-2-202077 (JP, A) 73568 (JP, U) Japanese Utility Model Showa 52-124670 (JP, U) Japanese Patent Publication No. 41-175 (JP, B1) Japanese Patent Publication No. 1-500786 (JP, A) (58) Field surveyed (Int. ⁷ , DB name) H01S 3/00-3/30 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A first solid-state device including an active solid medium, a concentrator arranged so as to surround the first solid-state device, and an inner surface formed of a light reflecting surface; In a light-pumped solid-state laser device including a light source that emits light for exciting the first solid-state element, a medium packed in the light collector, and an optical resonator that extracts light from the excited first solid-state element, Around the solid state element is covered with a second solid state element having a refractive index larger than that of the medium, and the side where the light for exciting the thickness of the second solid state is weak is excited.
A light- pumped solid-state laser device characterized in that the light is thicker than the strong light . 2. A photoexcitation solid laser device constructed according to claim 1, wherein the inner surface of the collector is a diffusion-type light reflecting surface. 3. The cross section of the first solid state device is circular, the second solid state device is cylindrical, the outer diameter of the second solid state device, or the thickness of the second solid state device and the first solid state device. Is larger than the outer diameter of the first solid state element by at least the ratio of q = (refractive index of the material of the second solid state element / refractive index of the medium packed in the light collector). 3. An optically pumped solid-state laser device according to claim 1, wherein: Wherein any one of claims 1 to 3, characterized in that the insertion of the thin-film medium sufficiently smaller than the thickness of the second solid element between the first solid element and a second solid state device 3. The optically pumped solid-state laser device according to item 1. 5. The optical resonator optically pumped solid-state laser apparatus according to any one of claims 1 to 4, characterized in that it is unstable resonator. 6. The optical resonator has a partially reflecting mirror at the center,
And the peripheral portion is enlarged exit mirror consists nonreflective portion thereof, optically pumped solid-state laser apparatus according to any one of claims 1, characterized in that it is composed of a collimating the total reflection mirror 5. 7. An optically pumped solid-state laser device according to claim 6 , wherein the enlarged exit mirror includes means for canceling a phase difference between a laser beam passing through a central partial reflection portion and a surrounding non-reflection portion. .