JPH06112577A - Solid-state laser - Google Patents

Abstract

PURPOSE:To provide a solid laser which stably operates even when the intensity of an exciting light source is increased and is excited by a high-output lamp which oscillates in a single basic mode. CONSTITUTION:In order to suppress the temperature rise of a laser element 9 caused by absorption so as to obtain high-output laser oscillation in a single basic mode, the element 9 is constituted of a core 7 containing a laser medium and clad 8 containing no laser medium. In addition, fluoride glass which well transmits infrared ray is used as the base material of the element 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser using a tungsten lamp or an arc lamp as an excitation light source.

[0002]

2. Description of the Related Art A solid-state laser using a lamp as an excitation light source is
It is the smallest laser device that can obtain a high-power laser beam among the laser devices currently in practical use, and is used in a wide range of fields from physicochemical research to industrial fields. FIG. 4 is a cross-sectional view of the most commonly used solid-state laser,
Reference numeral 1 is a lamp light source for excitation, 2 is a cylindrical laser element to which a laser medium is evenly added, 3 is an elliptic reflecting mirror for concentrating the lamp light on the laser element 2, and 4 is a cooling water flowing flow. Pipes 5 are cooling water. The characteristic of this solid-state laser is that a large output can be obtained in the case of multimode oscillation with a relatively simple device. In the conventional solid-state laser, in order to avoid the temperature rise of the laser element 2 due to the heat generation of the excitation lamp,
As shown in FIG. 4, cooling water 5 is flowed around the laser element 2 to cool the laser element 2. Due to the effect of the cooling water 5, the temperature of the surface of the laser element 2 is kept at the temperature of the cooling water, and part of the energy radiated from the lamp 1 is absorbed to suppress an excessive rise in the temperature of the laser element 2. There is.
FIG. 5 is an enlarged cross-sectional view of the laser device 2 of FIG.
Reference numeral 6 indicates the oscillation region of the excited laser. The shaded area indicates the region containing the laser medium.

[0003]

In the conventional laser element, since the laser medium is added to the entire laser element as shown in FIG. 5, the energy of the incident pumping light is absorbed in the entire laser element. However, the diameter of the laser beam, that is, the oscillation region of the laser is smaller than the diameter of the laser element, and in particular, the diameter of the laser beam in the single fundamental mode is about 1/5 to 1/10 of the diameter of the laser element. The energy of the excitation light absorbed by other components does not contribute to laser oscillation at all, and most of it becomes heat, which causes the temperature rise of the laser element. In addition, since the conventional solid-state laser using a lamp as a pumping light source has a small beam diameter of laser light in the case of single fundamental mode oscillation, the energy of pumping light contributing to single fundamental mode laser oscillation is multimode. It is smaller than the energy that contributes to oscillation. Moreover, the oscillation becomes unstable when the intensity of the excitation light is increased due to the lens effect caused by the temperature rise of the laser element, and the output of the single fundamental mode laser light is the output of the multimode laser light even with the same excitation light intensity. There is a drawback that less than one tenth of
The reason why the temperature of the laser element rises despite the cooling effect of the cooling water is that the radiant energy of the exciting lamp that is not absorbed by the cooling water and is transmitted is absorbed by the laser element. In this absorption, there are one in which the laser medium added for laser oscillation absorbs the radiant energy and the other in which the laser element itself absorbs the radiant energy. Furthermore, since the energy of the excitation light incident on the laser element is also absorbed by the portion outside the laser region, the energy of the excitation light reaching the laser oscillation region is less than the energy of the incident excitation light, and the luminous efficiency is improved. Is reduced.

The present invention has been made in view of these drawbacks of a solid-state laser pumped by a lamp, and operates stably even if the intensity of a pumping light source is increased. To provide a solid-state laser.

[0005]

SUMMARY OF THE INVENTION The present invention is for suppressing the temperature rise of a laser element due to these absorptions and obtaining stable high output single fundamental mode laser oscillation. The laser element is composed of a core containing a laser medium and a clad not containing the laser medium. The second feature is that fluoride glass having a high infrared transmittance is used as a base material of the laser element.

[0006]

The laser device as the first feature of the present invention will be described first. FIG. 1 is a cross-sectional view of a laser device 9 used in the present invention, 7 is a core containing a laser medium and corresponds to a laser oscillation region 6 shown by 6 in FIG. Reference numeral 8 denotes a clad that does not include the laser medium, and the core 7 indicates that the laser medium is included by hatching. When excitation light with a uniform energy density is irradiated from the periphery of the laser element toward the center of the laser element, the laser element used in the present invention has a laser medium added to the portion other than the laser oscillation region as shown in FIG. Therefore, there is no heat generation due to absorption of radiant energy in this portion, and the temperature rise of the laser element can be significantly suppressed. Further, in the laser element having the core-clad structure of the present invention, since the laser medium is not contained in the clad, the pumping light is not absorbed in the clad and the energy of the incident pumping light reaches the core as it is.

FIG. 2 shows the second feature of the present invention for suppressing the temperature rise of the laser element used in the present invention and obtaining stable high-power single fundamental mode laser oscillation. This is for explaining the effect when a fluoride glass is used, and is a typical oxide optical glass BK-
7 shows the wavelength dependence of the transmittance of fluoride glass containing ZrF ₄ as a main component and water. As can be seen from this figure, cooling water absorbs radiant energy in the wavelength range of 2.3 μm to 3.5 μm, but transmits radiant energy in the wavelength range of 2.3 μm or less. On the other hand, oxide glass is 1.
The transmittance starts to decrease from around 5 μm, and the radiant energy near the wavelength of 2 μm is absorbed. That is, when the oxide glass is used as the laser base material, even if the periphery of the laser element is cooled with water, the temperature of the laser element rises due to the radiant energy transmitted through the water. In contrast, the fluoride glass containing ZrF ₄ as a main component has a transmittance of 99% or more for wavelengths of 4 μm or less, and particularly has an absorption coefficient of 2.3 × 10 ⁻⁸ cm ^{−1 for} wavelengths of 2.5 μm or less. Since it is below, the temperature rise of the laser element due to the radiant energy transmitted through the cooling water can be completely ignored. Therefore, when fluoride glass is used as the base material of the laser element and the laser element is composed of the core containing the laser medium and the clad not containing the laser medium, the temperature rise of the laser element depends on the laser medium contained in the core. Only the temperature rise due to absorption is lower than in the case of using an oxide glass as a laser base material, and more stable high power single fundamental mode laser oscillation can be obtained. Furthermore, when fluoride glass is used as the laser base material, as shown in FIG. 2, since fluoride glass transmits infrared light having a longer wavelength than oxide glass, infrared laser oscillation is possible. Become.

[0008]

Embodiment 1 FIG. 3 shows an embodiment of a solid-state laser according to the present invention. FIG. 3A is a cross-sectional view taken in a direction perpendicular to the optical axis of the laser beam, in which 9 is a laser element, 2 is a lamp of an excitation light source, and 3 is an elliptic cylinder reflecting mirror for concentrating the excitation light on the laser element. ,
Reference numeral 4 is a pipe for flowing cooling water, and 5 is cooling water. In the laser element 9, the core 7 has a neodymium glass (LiN) containing neodymium as a laser medium having a diameter of 1 mm.
dP ₄ O ₁₂ refractive index = 1.60), and the cladding 8 is a light crown glass (refractive index = 1.515) having an outer diameter of 5 mm and having good transmittance in the near infrared region to the visible light region. It is called optical glass. FIG. 3B is a sectional view in a direction parallel to the optical axis of the laser light, and 10 is a wavelength of 1.06.
It is a concave reflecting mirror with a radius of curvature of 2 m, which has a reflectance of 99% or more for μm, and 11 is 90 for a wavelength of 1.06 μm.
It is a plane reflecting mirror having a reflectance of%, and these two reflecting mirrors 10 and 11 are resonators. Reflector 10,
The distance between 11 is 120 mm, the length of the laser element 9 is 50 m
m. The wavelength of the laser light oscillated by the reflecting mirrors 10 and 11 was 1.06 μm, and the laser beam diameter of the single fundamental mode (the beam diameter at which the intensity becomes 1 / e ² ) was 0.77 mm, which was absorbed by the core. Excitation light energy is almost 100
% Contributes to oscillation of a single fundamental mode. In the solid-state laser of this example, since the temperature rise of the laser element due to absorption of the excitation light is small, the instability of laser oscillation due to the temperature rise of the laser element is extremely small, and high-power single fundamental mode laser oscillation can be obtained. To be

[0009]

[Embodiment 2] This embodiment is a solid-state laser using a fluoride glass based on zirconium as a laser base material. Fluoride glass (53ZrF ₄ -20Ba) in which a part of lanthanum, which is a constituent element of fluoride glass, is replaced with neodymium as a laser medium is used for the core 7 of FIG.
F ₂ -20NaF-2LaF ₃ -2NdF ₃ over 3AlF
₃₎ using a fluoride glass having a refractive index than the core glass was replaced with hafnium part of Jirukonyuumu cladding 8 does not include a laser medium low (33HfF ₄ over 20Z
rF ₄ over 20BaF ₂ over 20NaF over 4LaF ₃ over 3A
The laser element 9 was constructed using 1F ₃ ). A solid-state laser using a fluoride glass for the laser element 9 is a laser element 9
Since there is no temperature rise due to absorption of the laser element, the temperature rise of the laser element 9 is lower than that of the first embodiment, and the laser oscillation of the single fundamental mode with higher stability and higher output than the solid-state laser using the oxide glass as the laser element is obtained. can get.

[0010]

Third Embodiment This embodiment is a solid-state laser using erbium as a laser medium. That is, in the solid-state laser of the second embodiment, erbium is added to the core 7 in place of neodymium as a laser medium. The composition of the core 7 is (53ZrF ₄ -20BaF ₂ -20Na
An F-over 4ErF ₃ over 3AlF _3). The oscillation wavelength of the present embodiment is 2.7 μm, and it is possible to oscillate in the infrared region, which was impossible with a solid-state laser using an oxide glass as a laser element.

[0011]

As described above, since the laser element has the dual structure of the core containing the laser medium and the clad not containing the laser medium, the temperature rise of the laser element due to the absorption of the laser medium is significantly suppressed. At the same time, the pumping efficiency is more than doubled, the pumping energy for obtaining the same laser output as the conventional one is reduced, and the temperature rise due to the absorption of the laser element is also reduced to 1/10 or less. A laser element with a core diameter of 1 mm, a clad diameter of 5 mm, and a laser medium absorption coefficient of 4 cm-1 has a beam diameter of 1 mm. When comparing the energy of the excitation light required to oscillate a laser of the same output with the laser element, the energy of the excitation light required for the oscillation of the laser element of the present invention may be about 45% of that of the conventional rod. The temperature rise of the laser element due to the absorption of the base material is also reduced. That is, in the solid-state laser of the present invention, the temperature rise of the laser element due to the radiant energy from the excitation light source is significantly suppressed, so that the instability of laser oscillation in a single fundamental mode such as the lens effect accompanying the temperature rise of the laser element. Factor is reduced,
High power single fundamental mode laser oscillation becomes possible, and the effect is great in fields requiring high power single fundamental mode laser light such as ultra-precision processing. Furthermore, by using fluoride glass as the laser base material, the wavelength range of laser oscillation is expanded to the infrared region, and medical equipment such as a laser knife,
The application of new laser light such as a light source for spectral analysis in the infrared region becomes possible, and the effect of the present invention is extremely large.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a laser device used in the present invention.

FIG. 2 is a characteristic diagram for explaining wavelength dependency of transmittance in a laser element used in the present invention.

FIG. 3 is a horizontal sectional view (a) and a vertical sectional view (b) of a solid-state laser according to the present invention.

FIG. 4 is a cross-sectional view showing the structure of a conventional solid-state laser.

FIG. 5 is a cross-sectional view of a laser element used in a conventional solid-state laser.

[Explanation of symbols]

 1 Lamp of Excitation Light Source 2 Laser Element Used for Conventional Solid-State Laser 3 Elliptic Cylinder Reflector for Focusing Excitation Light 4 Cooling Pipe 5 Cooling Water 6 Laser Beam Outer Diameter 7 Core 8 Cladding 9 Laser Element Used in the Present Invention 10 Reflector 11 Reflector

Front Page Continuation (72) Inventor Tetsuya Nakai International Telegraph and Telephone Corporation, 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo

Claims (2)

[Claims] 1. A laser device comprising a core to which an element which becomes a laser medium is added and a clad which does not contain an element which becomes a laser medium, and an excitation light source for inducing laser oscillation,
A cooling means for cooling the laser element, a resonator attached to the laser element for performing laser oscillation, and a columnar reflecting mirror for converging the light of the excitation light source on the laser element were provided. Solid-state laser. 2. The solid-state laser according to claim 1, wherein the laser element is made of fluoride glass.