JP5136775B2 - Solid state laser oscillator - Google Patents

Description

  The present invention relates to a solid-state laser oscillation device, and more particularly to a solid-state laser oscillation device configured to suppress parasitic oscillation in a laser medium.

2. Description of the Related Art Conventionally, in a solid-state laser oscillation device, excitation light is incident from a pumping unit toward a laser medium, and laser light is output in a predetermined direction.
In such a conventional solid-state laser oscillation device, when the excitation light is incident on the laser medium, parasitic oscillation different from the laser light in the direction desired to be extracted without passing through the resonator mirror occurs in the laser medium. When parasitic oscillation occurs in this way, the output of the original laser beam output from the laser medium via the resonator mirror is reduced, so that conventionally, proposals for preventing parasitic oscillation have been made (for example, Patent Documents). 1, Patent Document 2).
In the apparatus of Patent Document 1, the dimensional ratio between the width of the flat surface at the outer periphery of the laser medium and the inner diameter of the core of the laser medium is set to a predetermined ratio.
In Patent Document 2, an absorber capable of absorbing parasitic oscillation light is provided on either the upper or lower surface of the laser medium.
JP 2007-134560 A JP 2007-188980 A

  However, the above-described conventional laser oscillation device has a drawback that parasitic oscillation cannot be efficiently suppressed. Moreover, since the apparatus of Patent Document 2 includes an absorber that absorbs parasitic oscillations, the drawback of heating the absorber has been pointed out.

In view of the circumstances described above, the present invention described in claim 1 includes a doped portion that contains an active element and oscillates laser light when irradiated with excitation light, and an undoped portion that surrounds the doped portion and does not oscillate laser light. A thin plate-like laser medium having a laser beam and pumping means for making pumping light incident on the laser medium from the side of the laser medium so that the laser beam is output in a predetermined direction from the laser medium. In the solid state laser oscillation device,
In the undoped portion of the laser medium deviated from the optical path of the excitation light, a through hole for suppressing parasitic generation in the laser medium is formed.

  According to the configuration described above, the parasitic oscillation in the laser medium can be efficiently suppressed by the through hole provided in the undoped portion of the laser medium.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIGS. 1 and 2, reference numeral 1 denotes a solid-state laser oscillation device, which is directed vertically upward through an output mirror 2. Laser light L (output light) can be oscillated.
The solid-state laser oscillation device 1 includes a thin plate-like laser medium 3 having a substantially square shape, and first excitation means 11 to 1 that are arranged at four locations so as to surround the laser medium 3 and generate excitation lights L1 to L4. 4 excitation means 14, an AOM 4 for Qsw oscillation arranged above the laser medium 3, the output mirror 2 arranged near the upper side of the AOM 4, and the laser medium 3 are supported horizontally. And a heat sink 5 for cooling the laser medium 3.

  Flat surfaces 3 </ b> A to 3 </ b> D are respectively formed on the side surfaces of the portion corresponding to the four sides of the approximately square of the laser medium 3. The bottom surface of the laser medium 3 on the heat sink 5 side is provided with a total reflection film (not shown) made of a dielectric multilayer film, and the total reflection film and the output mirror 2 constitute a resonator. A surface of the laser medium 3 on the output mirror 2 side is provided with an antireflection film (not shown) so as not to reflect the output light L. On the other hand, each excitation means 11-14 is arrange | positioned at the side orthogonal to each flat surface 3A-3D of the said laser medium 3, and excitation light toward the center part of the laser medium 3 from each excitation means 11-14. L1 to L4 can be made incident.

Since the 1st excitation means 11-the 4th excitation means 14 have the same structure, the structure of the said 1st excitation means 11 is demonstrated on behalf of them. That is, the first pumping means 11 is sequentially arranged between the pumping LD (laser diode) 6 disposed toward the flat surface 3 A of the laser medium 3 and the pumping LD 6 and the flat surface 3 A of the laser medium 3. A first cylindrical lens 7 and a second cylindrical lens 8 are provided. The first cylindrical lens 7 and the second cylindrical lens 8 constitute a condensing unit, and when the excitation light L1 is oscillated from the excitation LD 6, the excitation light L1 is converted into the two cylindrical lenses 7, 8 is focused on the laser medium 3.
The second excitation means 12 to the fourth excitation means 14 are also configured in the same manner as the first excitation means 11, and when the excitation lights L1 to L4 are oscillated from the excitation means 11 to 14, the respective excitation lights L1. ˜L4 is irradiated from the side of the laser medium 3 to the dope portion 3E located in the center through the flat surfaces 3B to 3D on the outer periphery of the laser medium 3.

Next, as shown in an enlarged view in FIG. 3, the laser medium 3 includes a doped portion 3E in which an active element such as Yb is added to a base material made of YAG, and the doped portion 3E. And an undoped portion 3F made of YAG which is a remaining portion to be enclosed. The undoped portion 3F is formed with a plurality of through holes 3G penetrating in the thickness direction and having a circular cross section.
The doped portion 3E has a cylindrical shape, and the doped portion 3E is provided so as to be optically bonded to the center of an undoped portion 3F having a substantially square shape. The undoped portion 3F has a shape in which four flat surfaces 3A to 3D are provided at substantially equal intervals by cutting the outer peripheral surface from a disk shape that is short in the axial direction (thickness direction). It becomes the entrance surface of ~ L4. In this embodiment, the two pairs of flat surfaces (3A and 3C, 3B and 3D) which are opposed positions in the undoped portion 3F are not completely parallel, and one surface is the other so that parasitic oscillation is not amplified. It is inclined about 1 to 2 degrees with respect to the surface.

Further, in the present embodiment, the through holes 3G in the thickness direction are formed in the vicinity of positions corresponding to the four corners of the approximately square of the undoped portion 3F. The inner diameters of these four through holes 3G are the same, and each through hole 3G is formed at the same distance from the dope portion 3E. In addition, the inner diameter of each through hole 3G is set to a size of about 2/3 of the outer diameter of the dope portion 3E. The four through holes 3G are provided at positions deviating from the optical paths of the excitation lights L1 to L4 oscillated from the respective excitation means 11 to 14.
As described above, in the present embodiment, the four through holes 3G are formed in the undoped portion 3F of the laser medium 3 so as to surround the doped portion 3E, whereby the parasitic oscillation in the laser medium 3 is achieved. Can be suppressed.

Here, a manufacturing process of the laser medium 3 configured as described above will be described. First, ceramic powdery YAG fine crystals are put into a mold and pressed to form a cylindrical shape that is short in the axial direction (thickness direction). Next, an axial through hole is formed with a drill in a central portion that is a dope portion of the cylindrical member and a portion where the four through holes 3G are provided. Thereafter, the active element-containing YAG that is pressed into a cylindrical shape by pressing the fine crystals is inserted into the central through hole of the member and sintered so as to be integrated. The laser medium 3 having a substantially cylindrical shape is formed through this sintering process. In addition, by sintering the laser medium 3 in a substantially columnar shape in this way, the doped portion and the undoped portion are optically joined and stress is prevented from accumulating therein. Further, minute irregularities are formed on the outer surface of the laser medium 3.
Thereafter, the four portions of the side surface that becomes the outer peripheral portion of the laser medium 3 are optically polished to form flat surfaces 3A to 3D, and the front and back surfaces (upper and lower surfaces) of the laser medium 3 are optically polished. Note that the surfaces other than the flat surfaces 3A to 3D and the front and back surfaces of the laser medium 3 subjected to optical polishing are not polished so as to leave minute irregularities. In the present embodiment, the laser medium 3 is manufactured in this way.

  Next, as shown in FIG. 2, the heat sink 5 supports the laser medium 3 from the bottom (lower surface) side and has a generally cup shape. Cooling water is supplied from the supply pipe 15 into the heat sink 5 when necessary. As a result, the laser medium 3 can be cooled via the heat sink 5.

The operation of the solid-state laser oscillation device 1 based on the above configuration will be described. First, the excitation lights L1 to L4 are oscillated synchronously from the first excitation means 11 to the fourth excitation means 14 and made incident on the laser medium 3. As a result, the excitation lights L1 to L4 pass through the undoped portion 3F of the laser medium 3 from the flat surfaces 3A to 3D of the laser medium 3 and are irradiated to the doped portion 3E.
As a result, laser light L (output light) is oscillated in the doped portion 3E, and the laser light L is emitted upward through the AOM 4 and the output mirror 2.
At that time, the four through holes 3G are formed at four locations of the undoped portion 3F of the laser medium 3, and these function to suppress amplification of parasitic oscillation. For example, the light K1 generated in the doped portion 3E shown in FIG. 3 is directed from the doped portion 3E to the undoped portion 3F, and the through hole 3G formation surface provided in the undoped portion 3F acts as a convex mirror, and the reflected light is doped. Reflected in a direction away from the portion 3E. The light K2 generated in the doped portion 3E and traveling in a direction different from the light K1 is transmitted from the doped portion 3E through the undoped portion 3F and reflected by the flat surface 3B (outer surface), and then the through hole 3G formation surface. Reflected by. In this way, the reflected light of the light K2 is also reflected in the direction away from the doped portion 3E.
As described above, in this embodiment, the through hole 3G is provided in the undoped portion 3F, so that the light emitted from the doped portion 3E can be prevented from returning to the doped portion 3E again. Parasitic oscillation can be suppressed.

On the other hand, FIG. 5 shows the parasitic oscillation when the laser medium 3 is irradiated with the pumping lights L1 to L4 from the surrounding four pumping means in the conventional laser medium 3 having no through hole in the undoped portion 3F. This shows the state of occurrence. An optical path in which light K3 emitted from the same position as the light K1 in FIG. 3 is repeatedly transmitted through the undoped portion 3F and reflected on the outer surface, and then reflected on the outer surface on the opposite side after passing through the doped portion 3E. It becomes. Also, the light K4 emitted from the same position as the light K2 in FIG. 3 passes through the undoped portion 3F and is reflected by the outer surface thereof, and then passes through the undoped portion 3F again to pass the outer surface (3A) at the adjacent position. Reflected by. Thereafter, the light K4 further passes through the undoped portion 3F, is reflected by the outer surface (3D) at the adjacent position, and then sequentially passes through the undoped portion 3F and the doped portion 3E. Thus, it can be understood that in the conventional laser medium 3, the parasitic oscillation is easily amplified.
As can be easily understood from the comparison of the parasitic oscillation occurrence states shown in FIGS. 3 and 5, in this embodiment, the parasitic oscillation in the laser medium 3 is efficiently suppressed as compared with the conventional case. Obviously we can do it.

  According to the above-described embodiment, the laser medium 3 is irradiated with the excitation lights L1 to L4 from the respective excitation means 11 to 14 by forming the four through holes 3G in the undoped portion 3F of the laser medium 3. At this time, the occurrence of parasitic oscillation in the laser medium 3 can be efficiently suppressed. Therefore, it is possible to provide the solid-state laser oscillation device 1 having better energy efficiency when outputting the laser light L as compared with the conventional case.

  Next, FIG. 4 shows a laser medium 3 as a second embodiment of the present invention. In the first embodiment of FIG. 3, the single large through hole 3G is formed near the square of the laser medium 3. However, in the second embodiment, the undoped portion 3F of the laser medium 3 is formed. Are each formed with a plurality of small through holes 3G. The plurality of through-holes 3G at each corner are formed in the vicinity of the square of the undoped portion 3F so as to be positioned on a substantially semicircular circle that swells toward the doped portion 3E and has an equal pitch. Even in the second embodiment, it is possible to obtain the same operation and effect as the first embodiment described above.

  In the above embodiment, the reflection direction of the parasitic oscillation light incident on the through hole 3G forming surface is changed by forming minute irregularities over the entire through hole 3G forming surface provided in the laser medium 3. By forming such minute irregularities, the light is emitted to the outside of the laser medium 3 depending on the incident angle to the through hole forming surface, and parasitic oscillation is suppressed. Also, if a thin film-like plating with high thermal conductivity is applied over the entire surface where the through hole 3G is formed and cooled by a heat sink, much of the parasitic oscillation light incident on the boundary between the laser medium 3 and the plating can be absorbed. it can. As a plating material in this case, tin, gold tin, or copper can be used.

The top view which shows one Example of this invention. Sectional drawing which follows the II-II line | wire of FIG. The enlarged view of the principal part of FIG. The top view which shows 2nd Example of this invention. The top view of the conventional laser medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fixed laser oscillation apparatus 3 ... Laser medium 3F ... Undoped part 3G ... Through-hole 11 ... 1st excitation means 12 ... 2nd excitation means 13 ... 3rd excitation means 14 ... 4th excitation means L1-L4 ... Excitation light L ... Laser light (output light)

Claims (4)

A thin-plate-shaped laser medium having an active element and a doped portion that oscillates laser light when irradiated with excitation light and an undoped portion that surrounds it and does not oscillate laser light, and from the side of the laser medium A solid-state laser oscillating device comprising excitation means for making excitation light incident on the laser medium and outputting laser light in a predetermined direction from the laser medium;
A solid-state laser oscillation device, wherein a through-hole that suppresses parasitic generation in the laser medium is formed in an undoped portion of the laser medium that is off the optical path of the excitation light.   2. The solid-state laser oscillation device according to claim 1, wherein a number of irregularities are formed on the inner surface of the through hole.   2. The solid-state laser oscillation device according to claim 1, wherein an absorber that absorbs laser light is provided on the inner surface of the through hole, and the absorber is cooled. The laser medium has four sides consisting of flat surfaces on the outer periphery thereof, and a total of four excitation means are arranged to face the four sides of the laser medium,
Further, the through-holes are respectively formed at square positions in the undoped part of the laser medium outside the optical path of the excitation light emitted from the excitation means. 4. The solid-state laser oscillation device according to any one of 3.

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