JPH0214587A - Solid laser equipment - Google Patents

Abstract

PURPOSE:To obtain a soled laser equipment of high efficiency which is superior in beam quality and output stability by making the end face of a laser medium a vertical rectangular parallelepiped to an optical smooth surface and arranging a plurality of all the reflecting parts and partial reflecting parts at the end part thereof. CONSTITUTION:A slab 1 in which the whole area is nearly unifomly excited by a lamp 5 and a substage condenser 7 is taken out as a laser beam 11d a by resonator in which part of energy is composed of a partial reflecting mirror 10a, wholly reflecting mirror 10b and return mirrors 9a, 9b and the greater part of the other energy is cleared by indirect cooling from a slab surface 12. At this time a square temperature distribution of high temperature in the center part is generated in the slab, but, since whole the area is nearly uniformly excited and nearly uniformly cooled from the whole surface of the slab, a temperature gradient nearly produces in the thickness direction alone, a refraction factor distribution does not only produce in the width direction because it produces nearly in the thickness direction, but also that refraction factor by the temperature distribution does not produce longitudinally. Therefore, an inexpensive device of high efficiency which is superior in beam quality and output stability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to laser beam transport, excitation, and cooling of a slab-type solid-state laser device.

[Conventional technology]

8 and 9 respectively show a conventional solid-state laser device as shown in Japanese Patent Application Laid-Open No. 61-40073, and FIG.
The figure is a side view schematically showing the configuration of the main parts, Figure 9 is a sectional view taken along line 11-11 in Figure 8, and Figure 10 (a).
, (b) shows the temperature distribution generated when the laser device d of FIG. 8 is operated, in a cross section and a longitudinal section, respectively.

(1), (shown for 2υ).

In Figures 8 and 9, (1) is a solid-state laser cable formed into a rectangular plate shape with a vertical dimension a and a horizontal dimension b (b≧2a) and a dimension t in a cross section perpendicular to the optical axis. On both sides of this solid-state laser element (1), excitation surfaces @, (6) are irradiated with excitation light emitted from an excitation lamp (not shown).These excitation surfaces (2) , @ are optically polished to allow for efficient total reflection internally.Furthermore, both ends of this solid-state laser element (1) are provided with grooves that correspond to the traveling direction of the laser beam output from the solid-state laser element (1). Each pair of inclined surfaces (13 & ) + (
13b), (14a), and (14b) are formed by optical polishing, respectively, and each pair of inclined surfaces (lJa)j(13b) + (14a)
-(14b), laser beam input/output ends αη and Q barrels each having a substantially chevron shape (apex angle σW) with substantially central portions protruding outward are formed. In addition, a solid-state laser element (1
) at both ends of the laser beam input/output end 07), (7) has a high reflection part (9) that completely reflects the laser beam, and the other end can transmit a part of the laser beam and reflect the remainder. The laser light emitting parts QO are arranged opposite to each other H1'g f''. This high reflection part (9) is formed by a right angle prism reflector.

Furthermore, the laser beam emitting section (10 includes a solid-state laser element (10)
) at one inclined surface (14a) of the laser beam input/output end (G).
) and an output mirror (l) whose upper half is partially transparent.
oa) and the other #XX field '14b), a total reflection mirror (1ob) is disposed in the lower half thereof, respectively.

Next, the operation will be explained. The excitation light emitted from the excitation lamp is irradiated onto the excitation surface (6) of the solid-state laser element (1), as indicated by the arrow αQ in FIG.

The laser beam excited inside the solid-state laser element (1) is transmitted to the laser beam input/output end α7 of the solid-state laser element (1).
), each pair of inclined surfaces (13a), (13b), (
14a), (14b), it is refracted and proceeds while repeating total reflection on each excitation surface @, (6) of the solid-state laser probe (1), and oscillates.

In this case, since the high reflection part (9) is formed by a right-angle prism reflector, the laser beam component emitted from one inclined surface (ISa) (or (13b)) side of the laser beam input/output end αη is the bifocal plane of the right-angle prism reflector (
9a), (9b) (or (9b), (9h)), respectively, and enter the other inclined surface (13b) (or (1:5a)) side of the laser beam input end. It has become. Furthermore, the laser beam emitting part (G) includes an output mirror (LOA) on the upper half side that is partially transparent, and one inclined surface (14a) of the laser beam input/output end (G) of the solid-state laser element (1). ) and total reflection on the lower half side [(10b
), the laser beam component emitted from one inclined surface (14b) side of the laser beam input/output end (to) is totally reflected a (10b) at the laser beam output section 01.
The laser beam component is totally reflected and enters again from the same inclined surface (14b) side, and a part of the laser beam component is emitted from the other inclined surface (14a) side of the laser beam input/output end (toward). It is totally reflected by the output mirror (10a) and enters the same inclined surface (14a) itIII again, and the rest is taken out to the outside via this output mirror (LOA).

Thus, upper SE Ffi! (1) can form a laser optical path so as to fill the entire interior of the solid-state laser device (1). A rhombic solid-state laser element whose entire interior can contribute to laser oscillation,
In other words, the laser square root efficiency can be improved compared to a rhombic slab. Roughly speaking, since the entire interior of the solid-state laser device (1) can be used as a laser optical path, it is possible to form approximately twice as many laser optical paths inside the solid-state laser device (1) as compared to a rhombic slab. A solid-state laser device (
1) The overall long awn size can be shortened.

Note that the solid-state laser element (1
), part of it is taken out to the outside as laser output as described above, but most of the rest is thermal energy and is removed from the excitation surface, that is, the slab surface, by the coolant (3). .

[Issues that Kanmei tries to solve]

A conventional solid-state laser device is configured as described above.
As shown in FIG. 10, the solid-state laser device (1) has a uniform distribution A (61) approximately in the thickness direction of the solid-state laser device (1).
iu degree/! as shown in (6z), (6'a) : J distribution occurs, but the approximately chevron-shaped end αη, α barrel is not directly cooled,
A temperature gradient also occurs in the longitudinal direction of the slab, resulting in a two-dimensional temperature gradient. Therefore, the chevron-shaped portions of the ends αη, H are not directly excited and cooled, and there is leakage of excitation light from the excitation portion, so a temperature gradient also occurs in the longitudinal direction of the laser element (1). The resulting refractive index gradient and optical distortion caused by thermal deformation cause the so-called end φ effect (Reference [Engineering EEL" J, Quart
, Electron-QE22J' (1986) 2
099], the end portion α of the laser element that is not excited is not effectively used as a laser medium;
Further, there are problems such as increased costs due to an increase in the number of optically polished surfaces in the substantially angular portion.

The present invention was made to solve the above-mentioned problems, and has excellent beam quality and output stability by reducing optical distortion at the end of the slab (i.e., laser cable), and also enables laser beams to cover the entire slab area. By effectively using it as a medium, the purpose is to obtain a solid-state laser device WL with high efficiency, and to reduce costs by making a single line with a lake surface shape.

[Means to solve the problem]

In the solid-state laser device according to the present invention, the laser medium is a rectangular parallelepiped whose ends are perpendicular to the optically smooth surface of the laser medium, and the laser beam propagates through different optical paths within the laser medium. A plurality of total reflection parts and partial reflection parts are disposed at the end of the laser medium so as to complementarily fill the laser medium.

In addition, the entire @ region of the laser medium is excited, and
It is preferable that the side and end surfaces of the laser medium be thermally insulated, and that the entire optically smooth surface be cooled.

Further, one end face of the laser medium may be coated with a total reflection film, and the beam ffM within the laser medium may be reflected by the total reflection film.

[Effect]

In the solid-state laser device according to the present invention, the temperature gradient in the longitudinal direction at the end of the slab, the resulting refractive index gradient, and the optical distortion caused by thermal deformation are reduced, and the entire area of the slab is effectively utilized as a laser medium. The shape of the end becomes simple.

In addition, it is possible to further reduce optical distortion due to the heat insulation of the side and end faces of the laser medium. Further, by coating one end face of the laser medium with a total reflection film, a beam optical path that fills the laser medium in a complementary manner can be easily obtained.

〔Example〕

The invention will now be explained with reference to the figures. FIG. 1 is a side configuration diagram showing a beam propagation path of a solid-state laser device according to an embodiment of the present invention, and FIGS. FIG. 3(a) is a horizontal cross-sectional configuration diagram and a vertical cross-sectional configuration diagram.

(b) is a temperature distribution diagram within a laser medium according to an embodiment of the present invention. In FIG. 1, (1) is a slag, that is, a laser medium, and its surface (2) is optically smooth so that the laser beam is totally internally reflected.

Q4 is an optically smooth end face perpendicular to this surface, which is the exit surface of the laser beam, and the slab (1) is a rectangular parallelepiped tube. (
lla) and (llb) are laser beams that propagate in a zigzag manner through different optical paths within the slab, and each beam (1ua) and (1ub) is directed to the central plane (1c) of the slab in the stacking direction. It is symmetrical with respect to, and fills the slab in a complementary manner. (9a) and (9b) are folding mirrors that direct one beam (for example, 01a)) to the optical path of the other by -1° (
0 (loa) is a partially reflecting mirror, (l
ob) is a total reflection mirror and constitutes a resonator. (lie
) is the non-travel part of the laser beam, but it is not necessary to fill the laser beam up to the edge parts (13c, l, (14c) of the slab end face. Basically, the entire head M of the slab is covered with the laser beam. It is possible to run with

In addition, in Fig. 2, (2) is an indirect cooling support material that is transparent to the excitation light and has a lower refractive index than the slab, and the slab is cooled by the coolant (3) through the indirect cooling support material (2). Cooled type. (5) is an excitation lamp cooled by a refrigerant (6), and (4) is a partition plate between the slab refrigerant (3) and the lamp refrigerant, which is transparent to effective excitation light. (7)
is the excitation light concentrator in the width direction of the slab: '//.

Longitudinal direction: To uniformly excite all @Vi of t If#
has been completed. (8) is the casing, and (80) is its spacer. αQ is the side surface of the slab, and the peaks near the outside thereof are filled with a non-dissolvable, damaged substance, such as gas, and is true 2. Slab end face (to), external vicinity of α fathom (b), -g is also 2
Like surface 111, it is in an insulated state.

In addition, cooling of the slab is also performed in the same direction as excitation.

Longitudinal direction: is performed uniformly over the entire @ area.

Next, the operation of the above embodiment will be explained.

The slab (1), which has all its components excited almost uniformly by the rung (5) and the condenser (7), sends a -part of the energy to the partial reflection mirror (1OA), total reflection mirror (LOB), and reflection. The light is extracted as a laser beam (lld) by a resonator formed by mirrors (9a) and (9b).

Most of the other energy is removed by direct cooling across the slab surface. At this time, as shown in FIG. 3, the slab has a two-bundle degree distribution where the temperature is high in the center.

In the figure, (61) is a high temperature section, (62) is a medium temperature section, (
63) is a low temperature part, and σe indicates excitation light.

In the above embodiment, the entire slab f@* is excited almost uniformly and cooled almost uniformly from the entire surface of the slab, so the temperature gradient remains only in the thickness direction, as shown in Figure 3. Therefore, the refractive index distribution occurs almost only in the thickness direction. The important point here is that a refractive index distribution due to temperature distribution does not occur not only in the width direction near the side surfaces of the slab but also in the longitudinal direction near the end surfaces of the slab. On the other hand, in the conventional example in which substantially chevron-shaped portions Q'7) and (g) are present on the slab end surface, these substantially chevron-shaped portions are not directly cooled, as shown in FIG. When excitation occurs, a temperature gradient as shown in the figure occurs also in the longitudinal direction of the slab, and it is inevitable that a corresponding refractive index distribution will occur.

Under such circumstances, the laser optical paths 0s, (1), ■υ at different positions in the thickness direction experience different optical paths at the chevron edges aη, (g) due to the refractive index distribution associated with the temperature distribution. In particular, laser beams are distorted.

Further, the thermal deformation of the slab becomes complicated as it also reflects the shape of the end portion.

The above phenomenon is what is called an end effect.

In contrast, in the present invention, since the end face of the slab has a simple shape perpendicular to the surface, thermal deformation is simple and distortion of the laser beam is reduced.

Furthermore, in the conventional example, the slag end was only partially excited, and the other part became a laser beam absorption part, whereas in the present invention, the entire slab head is almost uniformly excited up to the end. Since there is no absorption part present, the oscillation efficiency can be expected to be improved, and the effect is significant from the standpoint of effective use of expensive laser media. In the present invention, the shape of the slab is a rectangular parallelepiped, and the number of optically polished surfaces at the end is reduced compared to the conventional example.
Cost reduction can also be expected. Furthermore, it is clear that the rectangular parallelepiped slab is easier to manufacture than the other conventional rhombic slab.

Next, we will discuss the laser beam input/output method and polarization.

FIG. 4 is an explanatory diagram showing the optical path, beam propagation angle, and polarization according to an embodiment of the present invention.

θi is the angle of incidence on the end face of the slab, 00 is the angle of refraction at the end face,
θrfd' is the total reflection angle within the slab. As a method for emitting a laser beam, there is a method in which θ1 is set to a Prüther angle of 20 B and the propagating beam is made into P-polarized light. When the slab is Nd:YAG, the refractive index n=1.82, and when incident from the atmosphere, θi2θB=61.2°, θ0=27.
5゜θr = 62.5°, indirect cooling support material is glass: n = 1.5, fl is critical angle 200 = 65.5°, υ, θr〉θC, total reflection condition is satisfied.

In the case of Brewster incidence, if the material of the slab that is the laser medium is determined, θ0. θr is uniquely determined, but
It is also possible to increase the degree of freedom in designing the beam propagation angle by applying anti-reflection coatings (13d) and (14d) to the end faces for θ1 where θr satisfies total internal reflection. In particular, as shown in FIG. 5, it is also possible to apply anti-reflection coatings (13f) and (14f) for S-polarized light so that the total internal reflection becomes S-polarized light.

In the above embodiment, a case has been described in which the folding mirror is divided into two parts, but it can also be replaced with one corner mirror (9c) as shown in FIG.

In addition, in the series of embodiments described above, the laser beam was reflected by an external optical element, but as shown in FIG. 7, a thin metal film, a dielectric multilayer film, etc. The beam may be reflected inside the slab by coating with a total reflection film (9d). In this case, an external optical element is not required, which simplifies the apparatus, and is also highly effective in terms of cost reduction.

〔Effect of the invention〕

As described above, according to the present invention, the laser medium is formed into a rectangular parallelepiped whose end face is perpendicular to the optically smooth surface of the laser medium, and the laser beam propagates in the laser medium through different optical paths, thereby causing the laser beam to emit light. Since the solid-state laser device is constructed by arranging a plurality of total reflection parts and partial reflection parts at the end of the laser medium so as to fill the medium in a complementary manner, beam quality and output stability can be improved. This has the effect of providing a highly efficient and inexpensive device.

In addition, the entire head of the laser medium is excited, the side and end surfaces of the laser medium are insulated, and the entire optically smooth surface is cooled, thereby further suppressing optical distortion and beam A solid-state laser device of good quality and excellent stability can be obtained.

Furthermore, one end face of the laser medium is coated with a total reflection film, and if the beam optical path within the laser medium is turned back by the total reflection film, the device can be simplified and costs can be reduced.

[Brief explanation of the drawing]

Figure i1 is a side configuration diagram showing a beam propagation path of a solid-state laser device according to an embodiment of the present invention, and Figure 2(a). 3(b) is a cross-sectional configuration diagram and a vertical sectional configuration diagram showing a solid-state laser device according to an embodiment of the present invention, and FIG. 3(a). (b) is a distribution diagram showing the temperature distribution in the laser medium according to an embodiment of the present invention, and Figure 4 is an explanatory diagram showing the beam propagation angle, polarization state, and information according to an embodiment of the present invention. FIG. 5 is an explanatory diagram showing a beam propagation angle and polarization state according to another embodiment of the present invention, and FIGS. 6 and 7 are side configuration diagrams showing a solid-state laser device according to another embodiment of the present invention, respectively. Figure 8 is a side configuration diagram showing a conventional solid-state laser device, and Figure 9 is a diagram of Figures 8 - ■.
The line sectional view and FIGS. 1O (a) and 1(b) are a cross-sectional configuration diagram and a 11@-plane configuration diagram showing the temperature distribution and beam path during operation of a conventional solid-state laser device, respectively. (1)... Laser medium, (3)... Refrigerant, (5)...
...Excitation lamp, (9a), (9b)...Folding mirror (9c)...Corner mirror (9d)...Total reflection film, (10a)...Partial reflection mirror, (10b)... Total reflection mirror, (1Ua), (11b), (lld)...
Laser beam, (b) ... surface, α, i, (14
1... End, C10... Side, (1, (9...
Excitation light Note that the same reference numerals in the drawings indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A solid-state laser in which a laser beam propagates in a zigzag pattern in a laser medium that has two optically smooth surfaces and two side surfaces facing each other along the optical axis, and whose cross section perpendicular to the optical axis is approximately rectangular. In the apparatus, the laser medium has a rectangular parallelepiped whose end face is perpendicular to the optically smooth surface, and
A plurality of total reflection parts and partial reflection parts are arranged at an end of the laser medium so that the laser beam propagates in the laser medium on different optical paths and complementarily fills the laser medium. solid-state laser device. (2) The solid-state laser device according to claim 1, wherein the entire region of the laser medium is excited, the side and end faces of the laser medium are insulated, and the optically smooth surface is entirely cooled. . (3) A solid-state laser device according to claim 1, wherein one end face of the laser medium is coated with a total reflection film, and the beam optical path within the laser medium is folded by the total reflection film.