JPH03225880A - Solid-state laser oscillator device - Google Patents

Abstract

PURPOSE:To ensure a very small spreading characteristic in the same input range by moving an optical system in accordance with an excitation input axially of a solid state laser medium. CONSTITUTION:A concave lens 16 is combined with a condensing lens presented by a laser rod 6 and provides a laser resonator condition together with resonator mirrors 13, 14, and a focused laser diameter in the resonators is maximum in the laser rod 6 by the action of the concave lens 6 and the laser rod 6. Accordingly, the state of a maximum light flux diameter in the laser rod 6 is fixed, and a positional relationship of the concave lens 16 where lasing is not interrupted in response to an input is stored, and further a control unit 11 for issuing a control signal based upon the stored contents is provided, whereby the concave lens 16 is kept at a proper position in response to the excitation input. Hereby, lowering of a laser output is reduced as well as spreading angle of the laser light is reduced.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a solid-state laser oscillation device.

(Prior Art) Generally, in a solid-state laser oscillation device such as a YAG laser, a thermal lens effect occurs in the laser rod, which is a solid-state laser medium, during laser oscillation. This thermal lens effect is caused by the laser rod receiving optical energy from the outside during the excitation process and cooling the outer circumference of the laser rod, which causes a thermal distribution inside the laser rod, which causes the refractive index to change compared to the surrounding area. This is a phenomenon that causes an effect similar to a convex lens or a concave lens because it is not uniform at the center. This thermal lens effect causes the laser rod to act as a condensing or diverging beam guide, reducing the directivity of the laser beam.
In particular, there was a problem that the divergence angle of the laser beam became large. When this divergence angle becomes large, light convergence deteriorates, leading to a situation where processing ability and processing accuracy are reduced.

Conventionally, in order to reduce such a divergence angle, W
“S solid” by alter K.
-StateLaserEngneerin
g J (2nd edition, 1988), attempts were made to achieve this by providing a mode selector between the resonator mirrors or by adding a telescope.

(Problem to be solved by the invention) In the technique of installing a mode selector, the central part of the laser rod, which is the part that oscillates in the low-order mode, is selected for oscillation, so the active volume in the laser rod is It could not be used effectively, and the output had to be significantly reduced. In fact, when the mode selector was used to reduce the spread angle of the laser beam to 1/10, the laser output was also reduced to 1/10 or less. On the other hand, a technique for installing a telescope devised to eliminate such a reduction in laser output is to enlarge the portion of the laser rod that oscillates in a low-order mode and to correct the thermal lens effect. Therefore, in order to correct this, the distance between two or more lenses constituting the telescope is slightly deviated from the design value for the telescope.

Therefore, the stability of the resonator cannot be maintained unless the removed distance is matched according to the magnitude of the thermal lens effect, which has the fatal drawback that the effect actually only occurs in a narrow input range.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a solid-state laser oscillation device that reduces the reduction in laser output and reduces the spread angle of laser light. .

[Structure of the invention] (Means and effects for solving the problem) Excitation means for exciting a solid-state laser medium, at least one set of resonator mirrors provided with the solid-state laser medium in between, and the resonator mirror. an optical system provided between one of the above and the solid-state laser medium, the optical system being movable in the axial direction of the solid-state laser medium to enlarge the diameter of the light beam incident on the solid-state laser medium; and a movement control means for controlling the position of the optical system accordingly, so that the optical system expands the luminous flux of the low-order mode laser light in the solid laser medium over a wide input range, and also reduces the divergence angle. .

(Example) Hereinafter, the present invention will be explained based on drawings showing embodiments.

In FIG. 1, reference numeral 1 denotes a solid-state laser oscillation device which is an embodiment of the present invention and is constructed as follows. That is, it has a base table 2, and an excitation unit 3 is installed approximately in the center of the table. This excitation unit 3
is equipped with a condensing elliptical cylinder mirror 4 which also serves as a cooling jacket, and a laser rod 6 and an excitation lamp 9 provided at focal positions inside the condensing elliptical mirror 4, respectively. The excitation lamp 9 is connected to a first power supply unit 10 as an external power supply means.
It is connected to the. A control unit 11 is connected to this first power supply unit 10. In addition, the condensing elliptical mirror 4
is connected to a circulation unit 12 that circulates cooling water, and the laser rod 6 and excitation lamp 9 are cooled during laser oscillation by the cooling water supplied into the condensing elliptical cylindrical mirror 4 through the circulation. There is.

Further, an output mirror 13, which is one of the resonator mirrors, is provided at one end of the base table 2, and a high reflection mirror 14, which is one of the resonator mirrors, is provided at the other end. The mirrors face each other on the axis of the laser rod 6. A mode selector 15 is provided between the output mirror 13 and the excitation unit 3, and a concave lens 16 is provided between the high reflection mirror 14 and the excitation unit 3. This concave lens 16, output mirror 13, and high reflection mirror 14 constitute a stable resonator. On the base table 2, the concave lens 16 is fixedly supported by a slider 17 as a support means. This slider 17 is supported by a receiver 18 provided on the base table 2 so as to be movable forward and backward in the axial direction of the laser port/end 6.

19 is a drive unit that drives the receiver 18;
0 is a second power supply unit connected to this drive unit 19, and is controlled by the control unit 11.

Next, the operation of the above configuration will be explained. During laser oscillation, at the initial stage of oscillation, the peripheral portion of the laser rod 6 has a higher heat distribution than the central portion, so the refractive index also increases, thus exhibiting a concave lens effect, but as it cools, the heat distribution gradually reverses. It begins to exhibit a convex lens-like effect. The concave lens 16 corrects the Luns effect affecting the laser light generated by the excitation unit 3, and also expands the luminous flux of the laser light including both high-order and low-order modes returning from the high-reflection mirror 14. This increases the volume included in the resonator within the laser rod 6.

Therefore, by limiting the higher-order modes expanded simultaneously by the expansion of the luminous flux using the mode selector 15, excitation efficiency can be increased and low-order oscillations can be produced. Furthermore, the divergence angle θ when the oscillation mode is TEMoo is expressed as 2λ/πω0. Here, λ is the wavelength of the laser beam, and ω0 is the radius of the beam of the laser beam. As is clear from this, since the divergence angle θ is inversely proportional to the luminous flux, the expansion of the luminous flux described above gives a low divergence angle. Incidentally, in a stable resonator, the δ positional relationship among the output mirror 13, high reflection mirror 14, laser rod 6, and concave lens 16 is important in order to stabilize the resonator. When the laser rod 6 is arranged to maximize the beam diameter, it has been simulated that the input range to the excitation lamp 9 is narrowed from the viewpoint of stabilization, and this has been confirmed as a result of experiments.

If an attempt is made to widen the input range, the beam diameter within the laser rod 6 tends to become smaller. The inventor has discovered that by changing the position of the concave lens 16 in accordance with the input to the excitation lamp 9, the diameter of the light beam within the laser rod 6 can be kept large.

Therefore, in the present invention, the positional relationship of the concave lens 16 that fixes the beam diameter in the laser rod 6 at its maximum and does not stop oscillation in response to an input is stored, and the control unit 11 issues a control signal based on this memory. Since the concave lens 16 is provided, the concave lens 16 is maintained at an appropriate position according to the excitation input.

In the above embodiment, a concave lens was used as the optical system, or a telescope made up of a plurality of lenses, a beam expander made up of a plurality of prisms, etc., could be used as the optical system. It is fine as long as it can be expanded.

[Effects of the Invention] A stable resonator incorporating an optical system that expands the beam diameter of the laser beam toward the solid-state laser medium is provided, and this optical system is moved along the axial direction of the solid-state laser medium according to human power for excitation. Since the movement is controlled, it is possible to realize a high-brightness laser oscillator that can obtain an extremely small spread characteristic (b) in a similar input range compared to the conventional spread characteristic (a), as shown in Figure 2. Now you can. Therefore, the beam spot can be narrowed down to a finer size, and at the same time, the energy density of the beam spot is increased, making it possible to perform high-speed drilling of thick materials in laser processing, for example, and to narrow the cutting width in cutting processing. In machining, high-precision micro-machining was achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between laser output and divergence angle. 1... Solid-state laser oscillation device, 6... Laser rod (
solid state laser medium) 9... excitation lamp (excitation means),
11... Control unit, 13... Output mirror 14...
High reflection mirror 16... Concave lens (optical system), 17.
... Sligg Procedures Kanayama Seisho January 21, 1989 Toshi Uematsu, Director General of the Special JT Agency, 1, Indication of the incident, Japanese Patent Application No. 2-18905, 2, Name of the invention, solid-state laser oscillation device 3, Person making the amendment Relationship to the incident Patent applicant (307) Toshiba Corporation 17-2 Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100 Telephone 03 (3502>3181 (main representative) (5847)
Patent Attorney Takehiko Suzue 7. Contents of the amendment (1) On page 2, line 16 of the specification, the phrase "2nd edition" is amended to read "2nd edition." (2) Similarly, in the second line of page 5, the phrase "approximately the center of this table" is corrected to "a position that is not an edge of this table." (3) Similarly, in the 14th line of the 6th page to the 13th line of the 7th page, the phrase ``Next, the above configuration...'' is replaced with ``Next, the operation of the above configuration will be explained. Laser oscillation In this case, the laser rod 6 absorbs the excitation light and is heated.A heat distribution is generated within the laser rod 6, which gives rise to a refractive index distribution within the inner surface of the laser rod 6.Nd: YAG crystal, etc. In many laser rods, the condensing refraction 1 min (indicates the properties of a +i lens).The concave lens 16 is combined with the condensing lens shown by the resa rod 6, and together with the resonator mirrors 13 and 14, it satisfies the laser resonator conditions. In addition, due to the action of the concave lens 16 and the laser rod 6, the diameter of the laser beam inside the resonator can be changed within the laser lot 6.
become maximum. In this way, since the laser beam east longitude becomes large within the laser rod 6, the laser oscillation fundamental mode (TE
Volume contained in the rod (Mo 0 mode) (mode volume)
can be made larger. Since the laser mode that provides a laser output with the smallest divergence angle is T E M 00, the expansion within the laser rod 6 of the laser mode that makes the low divergence angle smaller provides a high output and a low divergence angle. ” he corrected. (4) Similarly, between lines 11 and 12 on page 8, “
Further, as a result of simulation, the focal length of the concave lens 16 is -100 cm when the backward focal length of the thermal lens effect indicated by the laser rod 6 is between 15 cm and 35 cm.
It was found that the value should be -300. ” he added. (5) Similarly, on page 8, lines 13-14, the word "telescope" is corrected to "magnifying optical system." (6) Correct box 1 and box 2 in the drawing as per the attached sheet. However, there are no correction points in Figure 1.

Claims (1)

[Claims] an excitation means for exciting a solid-state laser medium; at least one set of resonator mirrors provided with the solid-state laser medium in between; provided between either one of the resonator mirrors and the solid-state laser medium; an optical system that is movable in the axial direction of the solid-state laser medium and expands the diameter of the light beam incident on the solid-state laser medium; and a movement control means that controls the position of the optical system in accordance with input to the excitation means. A solid-state laser oscillation device characterized by: