JPH11202110A - Variable-shape reflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the spherical or aspherical variable-shape reflector which is optionally variable in focal length with high precision. SOLUTION: The variable-shape reflector is provided with a transmission window 18 at its front end part, and a casing 11 wherein a pressure chamber 15 made open toward the transmission window 13 is formed and the transmission window 13 and pressure chamber 15 are screened from each other. This mirror is equipped with a plastic circular reflecting plate 41 and a pressure governing device 51 which adjusts the pressure of fluid filling the pressure chamber 15 and the circumferential part of the reflecting plate 41 is simply supported on the casing 11 through an annular gasket 18. The liquid pressure operates uniformly on the reverse surface of the reflecting plate 41 and the circumferential part is simply supported, so the reflecting surface becomes spherical. As the liquid pressure increases, the reflecting surface becomes larger in curvature and the fluid pressure is adjusted to obtain arbitrary curvature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deformable reflecting mirror whose focal length can be arbitrarily changed. The reflecting mirror of the present invention can be used as a reflecting mirror of a laser oscillator, an optical instrument, or the like.

[0002]

2. Description of the Related Art Recently, semiconductor-pumped high-power solid-state lasers capable of outputting kW-class power have been developed. Higher laser efficiency and higher quality laser light are expected compared to conventional lamp excitation, and are being applied to fields that have been the dominant field of gas lasers such as processing and welding. However, although it became semiconductor laser excitation,
As for the quantum efficiency, the excitation energy is always converted to heat, and k
In the case of a laser having an output of W or more, a large thermal lens effect becomes dominant as in the case of lamp excitation. Therefore,
It has been practiced to optimize the curvature of the resonator mirror to compensate for the thermal lens effect. However, even if the thermal lens effect is compensated in this way, the curvature of the mirror is constant,
It can only handle a certain laser output.

As a technique for changing the curvature of a mirror (reflection mirror), a deformable mirror of a laser beam processing apparatus is known (see Japanese Patent Application Laid-Open No. 8-39282). In this technique, the periphery of the mirror plate is supported by the housing 12 and the cap nut 38, and the central portion of the mirror plate 13 is pushed by an electromechanical actuator 23.
Therefore, a highly accurate spherical surface cannot be obtained, and a paraboloid or an ellipsoid cannot be obtained. For this reason, it cannot be used as a resonator mirror of a high-power solid-state laser in which the thermal lens effect changes depending on the output.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spherical or aspherical deformable reflecting mirror capable of arbitrarily changing the focal length with high accuracy.

[0005]

The deformable reflector according to the present invention has a transmission window provided at a front end thereof, and a casing in which a pressure chamber opened toward the transmission window is formed.
A gasket comprising: a flexible circular reflector for shutting off between the transmission window and the pressure chamber; and a pressure regulator for adjusting the pressure of a fluid filled in the pressure chamber, wherein the periphery of the reflector is an annular gasket. It is simply supported by the casing via.

In the deformable reflecting mirror according to the present invention, since the fluid pressure acts uniformly on the back surface of the reflecting plate and the peripheral portion is simply supported, the reflecting surface is spherical. When the fluid pressure is increased, the curvature of the reflecting surface increases, and by adjusting the fluid pressure, an arbitrary curvature, that is, a focal length can be obtained.

In the deformable reflector, a plurality of concentric grooves centered on the mirror axis may be provided on the back surface of the reflector. Since the groove part deforms more than the other parts,
By properly selecting the number, depth and spacing of the grooves, a parabolic or elliptical mirror surface can be obtained.

In the deformable reflector, an annular gasket retainer is fixed in the pressure chamber adjacent to the back of the reflector.
An annular gasket may be inserted between the reflector and the gasket retainer. When the pressure inside the pressure chamber is negative,
The reflecting plate projects toward the pressure chamber, and the reflecting mirror becomes a concave mirror.

The above-mentioned deformable reflecting mirror may be used as a resonance mirror of a solid-state laser oscillator. In this reflector, a spherical, parabolic or elliptical mirror surface having a required curvature can be formed. Therefore, even if the output of the solid-state laser oscillator changes, it is possible to follow the change in the thermal lens effect, thereby preventing the output from lowering.

[0010]

FIG. 1 shows a deformable reflecting mirror according to the present invention. The variable reflector is mainly composed of the casing 1
1, a reflection plate 41 and a pressure adjusting device 51. The casing 11 includes a holder 12 and a lid 30. The holder 12 has an annular shape, and a transmission window 13 is provided at the front end. Immediately after the transmission window 13 is a pressure chamber 15. An O-ring groove 17 is provided on the outer peripheral side of the transmission window 13, and a reflecting surface-side O-ring 18 is inserted therein. Screw 2 cut on the inner peripheral surface of holder 12
0, an annular O-ring presser 21 is screwed. The back side O-ring 23 is inserted between the O-ring retainer 21 and a reflection plate 41 described later. The O-ring presser 21 supports the back-side O-ring 23 from behind. Also, the holder 12
An O-ring groove 25 is provided on the rear surface of the O-ring, into which an O-ring 26 is inserted.

The lid 30 has a disk shape, and has a piston hole 31, a fluid supply hole 33 and a fluid discharge hole 34 penetrating therethrough. A supply pipe 38 and a discharge pipe 39 are connected to the fluid supply hole 33 and the fluid discharge hole 34, respectively. The reflection plate 41 is inserted into the holder 12 and the lid 30 is
Is attached to the rear surface of the holder 12 with bolts 36. Airtightness is maintained between the holder 12 and the lid 30 by the O-ring 26. The gap between the transmission window 13 and the pressure chamber 15 is sealed by the reflecting surface side O-ring 18 or the back side O-ring 23, and the pressure chamber 15 is formed between the lid 30 and the reflecting plate 41.
The pressure chamber 15 is filled with a fluid from the supply pipe 38. As the fluid, an incompressible fluid such as water or hydraulic oil is used. Instead of each of the O-rings, other annular gaskets can be used.

The reflector 41 has flexibility and is circular. The thickness is constant over the entire surface. Reflector 4
Silicon, glass, or the like is used as the first material.
In particular, silicon has much higher thermal conductivity than conventional glass materials, and polishing with good productivity such as chemical etching,
Processing means can be provided. In addition, since the silicon wafer is a single crystal, its mechanical properties are uniform over the entire surface, deform uniformly, and are suitable as a reflector material. When using a silicon wafer, the surface is plated with gold. The plating thickness is about 0.1 to 10 μm. Reflector 41
Has a diameter of 10 to 300 mm and a thickness of 0.1 to 2.0 mm
It is about. The reflection plate 41 is provided between the transmission window 13 and the pressure chamber 1.
5 is inserted into the holder 12 so as to block the gap between the holder 5 and the holder 5. The reflection plate 41 may be exposed to the atmosphere, and a protective glass may be attached to the transmission window 13 to protect the reflection plate 41.

The pressure adjusting device 51 has a fine feed device 52 and a piston 55. A block-shaped mounting bracket 61 is fixed to the rear side of the lid 30 with a bolt 62. The fine movement feeding device 52 is attached to the lid 30 via a mounting bracket 61. As the fine movement feeder 52, a stepping motor, a combination of a servomotor and a feed screw, a combination of a piezoelectric element and a displacement magnifying mechanism, a linear motor, or the like is used. The piston 55 is provided with an O-ring groove 56 at the tip, and the piston O
A ring 57 is inserted. Piston O-ring 57
However, it is fitted in the piston hole 31. Piston 5
5 is connected to the tip of the drive shaft 53 of the fine movement feeder 52 by a pin 59. Instead of the piston O-ring, another annular packing can be used.

When the liquid in the pressure chamber 15 is pressurized by driving the fine movement feeding device 52 of the pressure adjusting device 51 in the deformable reflecting mirror configured as described above, the peripheral portion of the reflecting plate 41 becomes a reflecting surface. It is simply supported by the side O-ring 18 and projects forward. Since the liquid pressure acts uniformly on the back surface of the reflecting plate 41 and the peripheral portion is simply supported, the reflecting surface is spherical. When the liquid pressure is increased, the curvature of the reflection surface 41 increases, and an arbitrary curvature can be obtained by adjusting the liquid pressure. The liquid pressure is, for example, a reflector having a diameter of 30 mm, a thickness of 0.5 mm and a radius of curvature of 300 m.
In the case of m, it is about 0.38 MPa.

In the above case, since the pressure in the pressure chamber 15 is positive, the reflecting mirror is a convex mirror. To make a reflecting mirror concave,
The O-ring retainer 21 is slightly screwed in, and the back-side O-ring 23 is lightly pressed against the reflector 41 so as not to hinder the deformation of the reflector 41. The piston 55 is retracted, and the pressure inside the pressure chamber 15 is reduced to a negative pressure. The reflecting plate 41 is pressed by the atmospheric pressure, and presses the back side O-ring 23 against the O-ring presser 21. The pressure chamber 15 includes a reflection surface side O-ring 18 and a back surface side O-ring 2.
3 sealed. The peripheral portion of the reflecting plate 41 is simply supported by the back-side O-ring 23 and projects toward the inside of the pressure chamber 15 by the atmospheric pressure, so that the reflecting mirror is a concave mirror.

When a reflecting mirror is used for a high-power laser beam, a liquid such as water flows in the pressure chamber 15 at a constant flow rate in order to prevent the reflecting plate 41 from overheating. For this purpose, for example, a constant-pressure water supply source is provided in the fluid supply pipe 38, and a flow control valve (both not shown) is provided in the fluid discharge pipe 39. The flow rate is 10
Since it is as small as about 50 ml / min, the pressure fluctuation in the pressure chamber 15 due to the flow of water is small. A water thermometer may be provided in the pressure chamber 15 to adjust the flow rate according to the temperature.

FIG. 2 shows another embodiment of the gasket for sealing the pressure chamber. Gasket 65 shown in FIG.
Provided a groove 66 on the inner peripheral side of the O-ring,
Insert the peripheral part of 1. The peripheral portion is held shallow by a groove 66 so as not to hinder free deformation of the peripheral portion of the reflection plate 41.
A gasket 67 shown in FIG. 2B has a grip portion 68 protruding from the inner peripheral side of the O-ring, and a peripheral portion of the reflector 41 is inserted into a groove 69 provided in the grip portion 68. Since the protruded grip portion 68 of the gasket 67 is deformed, free deformation of the peripheral portion of the reflection plate 41 is not hindered.

FIG. 3 shows a reflecting plate 71 used for an aspherical reflecting mirror. A plurality of concentric grooves 72 centered on the mirror axis are provided on the back surface of the reflection plate 71. The number and spacing of the concentric grooves 72 are determined according to the shape of the aspheric surface (parabolic surface or elliptical surface), the size of the reflecting mirror, and the required accuracy of the mirror surface. For example, when the diameter of the reflector is 30 mm, the number of the concentric grooves 72 is five. The depth and width of the concentric groove 72 are each about 10% of the thickness of the reflection plate 71. Regardless of the parabolic surface or the elliptical surface, the interval between the concentric grooves 72 is larger on the inner diameter side and smaller on the outer diameter side. Since the portion of the concentric groove 72 is more deformed than the other portions, a parabolic or elliptical mirror surface can be obtained by appropriately selecting the number, depth and spacing of the concentric grooves 72.

As the pressure adjusting device 52, a pressure adjusting valve can be used in place of the combination of the fine moving device and the piston.

[0020]

EXAMPLE A reflecting plate of a deformable reflecting mirror was made of a silicon wafer. The thickness of the reflector was set to 500 μm so as to follow the thermal lens of 1 m or less expected by a kW class laser. The design was such that the stress was 1/10 or less of the plastic deformation strength even when deformed to a radius of curvature of 1 m.

The actual deformed state was measured by the Hartmann method, and the results are shown in FIG. From this experiment, it was proved that the reflection plate was deformed as a perfect spherical surface with little deviation in directivity, and its reproducibility and stability were high. Further, it can be seen from FIG. 4 that the curvature of the reflecting mirror changes smoothly and in a wide range as the piston moves, that is, the fluid pressure increases. By using the deformable reflecting mirror of the present invention, the focal length of the reflecting mirror can be arbitrarily changed with high accuracy by adjusting the fluid pressure.

In order to demonstrate that a deformable mirror having only a curvature can be applied to the correction of a thermal lens, the deformable reflecting mirror of the present invention is applied to a resonator of an arc lamp pumped solid-state laser in which a thermal lens of 1 m or less is generated. The built-in output power was measured. The result is shown in FIG. Since there is a peak of the condensed power near the curvature required for correcting the thermal lens, it has been found that only the curvature can be corrected. It is also possible to give feedback so as to always take a peak value.

[0023]

According to the deformable reflecting mirror of the present invention, the focal length can be arbitrarily changed with high accuracy, and the mirror surface can be spherical or aspherical. For this reason, it is possible to improve energy efficiency in laser processing or accuracy in optical measurement. The variable reflecting mirror of the present invention can be used not only for the above-mentioned resonance mirror but also for a wide range such as a condensing mirror of a laser processing device, a condensing or magnifying optical system of another optical device, and an illumination device.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a deformable reflecting mirror according to the present invention.

FIG. 2 is a sectional view showing another embodiment of a gasket for sealing a pressure chamber.

FIG. 3 is a rear view showing another embodiment of the reflector.

FIG. 4 is a graph showing a relationship between a movement amount of a piston and a radius of curvature of a reflecting mirror.

FIG. 5 is a graph showing a focusing power characteristic with respect to a change in curvature of an Nd: YAG laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Casing 12 Holder 13 Transmission window 15 Pressure chamber 18 O-ring 30 Lid 31 Piston hole 33 Fluid supply hole 34 Fluid discharge hole 41 Reflection plate 51 Pressure adjustment device 52 Fine feed unit 55 Piston 61 Mounting bracket 65 Gasket 67 Gasket 71 Reflection plate 72 Concentric grooves

Claims (4)

[Claims] A flexible window is provided at a front end of the casing. The casing has a pressure chamber opened toward the window and has a casing formed therein. And a pressure adjusting device for adjusting the pressure of the fluid filled in the pressure chamber, and a peripheral portion of the reflector is simply supported by a casing via an annular gasket. Deformable mirror. 2. The deformable reflecting mirror according to claim 1, wherein a plurality of concentric grooves centered on a mirror axis are provided on a back surface of said reflecting plate. 3. An annular gasket retainer is fixed in the pressure chamber adjacent to the back of the reflector, and an annular gasket is inserted between the reflector and the gasket retainer. Deformation mirror. 4. The deformable reflecting mirror according to claim 1, wherein said reflecting mirror is a resonance mirror of a solid-state laser oscillator.