JPH0895102A - Wavelength converter for laser beam - Google Patents

Abstract

PURPOSE: To facilitate the alignment of a basic wave and second harmonic wave by decreasing the number of parts of a device for converting the wavelength of a laser beam, thereby making its constitution compact. CONSTITUTION: An anamorphic prism 4 and BBO (β-BαB2 O4 ) 5 are disposed within a laser resonator composed of a laser tube 1 and a reflection mirror 2 and output mirror 3 arranged on both sides of this laser tube 1. Wavelength conversion efficiency is improved by increasing the power density of the laser beam while the angle phase matching in the direction of the small permissible width for the angle phase matching in this BBO 5 is assured by forming the laser beam made incident on the BBO 5 to elliptic patterns by this anamorphic prism 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for wavelength conversion of laser light, and more particularly to a wavelength conversion device using BBO (β-BaB ₂ O ₄ ).

[0002]

2. Description of the Related Art In recent years, laser wavelengths have been shortened in order to miniaturize laser processing, improve recording density, and increase chemical reactivity. It is being actively promoted. However, in the current development situation, the short wavelength of laser diode is limited to the blue region, and in order to differentiate from the laser diode in response to the demand for shorter wavelength, it is possible to realize in the ultraviolet region. ing.
He-Cd lasers and excimer lasers have been used as lasers of this type, but they have advantages and disadvantages in output, life, and compactness.

For this reason, recently, attempts have been made to obtain a laser reaching the ultraviolet region by converting the wavelength of the generated laser into the short wavelength side. This kind of wavelength converter is
It is composed of a laser and a wavelength conversion element, and the wavelength can be halved by making laser light enter the wavelength conversion element. In such a wavelength conversion device, unlike the shortening of the wavelength based on the improvement of the laser diode, the shortening of the wavelength is relatively easy, and a laser with a proven track record and reliability can be selected. A short wavelength laser can be developed in a short development period by sufficiently grasping or using an appropriate wavelength conversion element.

At present, an Ar laser (wavelength 514.5 nm) is attracting attention because of its simplicity and efficiency.
There is a 257 nm ultraviolet laser wavelength conversion device that wavelength-converts by arranging BBO as a wavelength conversion element in the resonator.
FIG. 7: Applied Physics Vol. 61 No. 931-934 / 19
92. This type of wavelength conversion device (wavelength: 257n) quoted from FIG. 2 of "High efficiency frequency multiplication of continuous oscillation ion laser".
m ultraviolet wavelength converter).

In FIG. 7, the optical resonator comprises an Ar laser tube 21, a reflection mirror 22 and an output mirror 23,
Laser light is generated as a result of the stimulated emission of light. In this optical resonator, a condenser lens 26 and a cylindrical lens 27,
A BBO 25 is arranged together with a lens system 24 composed of 28, and wavelength conversion is performed in this BBO 25.
As a result, the output mirror 23 emits ultraviolet light to obtain an output. Since the wavelength conversion efficiency is proportional to the square of the laser electric field density, the conversion efficiency is increased by the condenser lens 26.

Further, when the angular phase matching allowable width of the BBO 25 (deviation of the incident angle of the laser which halves the wavelength conversion efficiency) is compared with the horizontal direction (Ar laser polarization direction) in FIG. 7, the BBO 25 In the first type phase matching in which the optical axis Y axis is set in the horizontal direction, the horizontal angular phase matching allowable width is smaller than the vertical angular phase matching allowable width, so the laser beam is directed to the cylindrical lens 27. If it is narrowed to an elliptical shape extending in the horizontal direction, the conversion efficiency does not decrease, and the laser electric field density is the same as the cylindrical lens 27.
The conversion efficiency is increased because it is increased by.

However, since the allowable angle width of the BBO 25 is very small at 0.01 degree, if the lens system 24 including many optical components is arranged as shown in FIG. The angle is easily deviated by 0.01 degree or more, and not only the second harmonic UV oscillation (257 nm) is lost, but even the fundamental wave (514.5 nm) easily diverges the laser optical axis and stops oscillation. I had woken up. This is because many optical parts such as the two cylindrical lenses 27 and 28 and the condenser lens 26 have to be inserted.

In view of such a problem, the device shown in FIG. 8 uses a waveguide structure to achieve high efficiency. This is described in JP-A-3-245130. This device has a waveguide structure by forming a path for reflecting light so that the light does not diverge in response to the stoppage of oscillation, which is a problem in the device of FIG. That is, the BSBO thin film 32 is epitaxially grown on the BBO substrate 31, a waveguide type wavelength conversion element is prepared, and the end surface of the BSBO thin film 32 is
The YAG laser light output from the YAG laser device 33 is made incident. The YAG laser light propagates in the waveguide with almost no attenuation of the laser power density. Then, a part of the wavelength is converted to obtain the second harmonic. The BS
The BO thin film 32 is obtained by replacing barium in BBO crystals with strontium which is a divalent metal. 1.0
The ordinary refractive index at 6 microns is 1.7750. BBO
Has an ordinary light refractive index of 1.6570, and is 0.1 between the two.
A difference in refractive index of 180 occurs, and as a result, it becomes possible to form an optical waveguide.

However, in such a waveguide type wavelength conversion device, it is difficult to form a concentric waveguide having a small size on the order of micron, and it is inevitable that the waveguide is a rectangular parallelepiped. Similar to the beam pattern of the laser diode, the beam pattern does not have an elliptical and clean Gaussian mode, and there is a problem that alignment of the second harmonic becomes difficult.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wavelength conversion device which can reduce the number of parts to make the structure compact and can easily align the fundamental wave and the second harmonic.

[0011]

A wavelength converter for laser light of the present invention is a wavelength converter for converting a wavelength of laser light by transmitting it through a BBO, and a beam cross-sectional shape of the laser light incident on the BBO is elliptical. It is characterized by including an anamorphic prism.

For example, a BBO and an anamorphic prism are arranged in a laser resonator composed of a laser tube and a reflection mirror and an output mirror arranged on both sides of the laser tube.

In this case, a plurality of anamorphic prisms are arranged with the same direction. Alternatively, a plurality of anamorphic prisms are opposed to each other in opposite directions and are arranged at positions sandwiching BBO.

[0014]

By making the laser light incident on the BBO into an elliptical pattern by the anamorphic prism, the power density of the laser light is increased while ensuring the angular phase matching in the direction in which the allowable angular phase matching width in the BBO is small, Improves wavelength conversion efficiency.

[0015]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention, in which Ar
An optical resonator is constituted by a laser tube 1, a reflection mirror (resonant mirror) 2 and an output mirror 3 arranged on the optical axis of the Ar laser tube, and stimulated emission is generated based on the gain obtained by the Ar laser tube 1. Then, laser light having a required frequency is generated.
An anamorphic prism 4 and a BBO 5 are arranged in series on the optical axis between the Ar laser tube 1 and the output mirror 3, and the laser light output through the output mirror 3 is anamorphic. Fick prism 4 and BB
After passing through O5, wavelength conversion is performed in this BBO5.

The anamorphic prism 4 is provided in a cylindrical housing 11 as shown in FIG.
The right-angle prisms 12p13 are arranged to face each other in the optical axis direction at a required angle, and the right-angle prisms 12 and 13 refract a laser light flux having a basic pattern with a circular cross-section incident from the right end of the drawing. , The cross-sectional shape of the laser beam emitted from the left end is transformed into an elliptical pattern. In this configuration, of the X and Y directions of the laser light flux, the Y direction remains unchanged and only the X direction is reduced to form an elliptical pattern. Then, the laser beam having the elliptic pattern is transmitted through the BBO 5.

The laser light transmitted through the BBO 5 is BBO.
In this case, the wavelength conversion is performed by 5 so that the wavelength becomes 1/2, and it is converted into ultraviolet light and output through the output mirror 3. Since the wavelength conversion efficiency in the BBO 5 is proportional to the square of the laser electric field density, the wavelength conversion efficiency can be increased by forming the fundamental beam pattern of the laser beam by the anamorphic prism 4 into an elliptical beam pattern.

FIG. 3 is a diagram showing the wavelength conversion efficiency in this BBO 5, and when comparing the horizontal direction (Ar laser polarization direction) with the vertical direction, the first type in which the optical axis Y axis of the BBO 5 is set horizontally In phase matching, the horizontal angular phase matching allowable width (θZX) is smaller than the vertical angular phase matching allowable width (θZY). Therefore, even if the power density of the fundamental wave is increased and the laser beam is uniformly narrowed in order to increase the conversion efficiency, the laser beam spreads in inverse proportion to the beam diameter, so that the angle tolerance such as BBO is small (θZX = (0.01 degree), the laser output component exceeding 0.01 degree is not wavelength-converted. Therefore, to increase the power density, the vertical direction (θZ
Only from Y), the beam is focused and the conversion efficiency is increased.

Therefore, in this embodiment, the laser beam is converted into an elliptical beam pattern which is vertically narrowed by the anamorphic prism 4 to transmit the BBO 5 for wavelength conversion, and as a result, wavelength conversion efficiency can be improved. Therefore, a cylindrical lens and other lenses are not required, and the number of parts can be reduced and a compact and compact wavelength conversion device can be realized. Further, the alignment of the fundamental wave and the second harmonic (angle phase matching) becomes easy.

FIG. 4 is a block diagram of the second embodiment of the present invention, in which parts equivalent to those of the first embodiment are designated by the same reference numerals. In this embodiment, first and second anamorphic prisms 4 are provided between the Ar laser tube 1 and the output mirror 3.
A and 4B are arranged in series with the same direction. By using two anamorphic prisms in series in this way, the laser light is made into an elliptical pattern by the first anamorphic prism 4A, and the minor axis direction is further changed by the second anamorphic prism 4A. It is a reduced elliptical pattern. Therefore, the laser light having the elliptical pattern is transmitted through the BBO 5 and the wavelength is converted, so that the wavelength conversion can be realized with higher efficiency than that in the above-described embodiment.

FIG. 5 is a block diagram of a third embodiment of the present invention, in which parts equivalent to those of the above-mentioned embodiments are designated by the same reference numerals. In this embodiment, the first and second anamorphic prisms 4A and 4B are arranged so as to face each other with the BBO 5 in between. Therefore, the laser light is transformed into an elliptical pattern by the first anamorphic prism 4A and transmitted through the BBO 5, so that the wavelength conversion efficiency is improved as in the first embodiment. Then, the wavelength-converted laser light is transmitted to the second anamorphic prism 4
By transmitting B in the opposite direction, it is returned to the circular basic pattern, and as a result, the laser light is output as a circular beam of the basic pattern, which makes it easier to use the laser light thereafter.

In the first to third embodiments, laser light is generated by using the Ar laser tube, but photons are generated by stimulated emission of light from a YAG laser, dye laser, semiconductor laser or the like. The gain medium for amplification may be used to generate the laser light. Even with this structure, the same effect as described in each of the embodiments can be obtained.

FIG. 6 is a schematic perspective view showing an essential part of the fourth embodiment of the present invention. Here, a pair of multi-reflection cylindrical mirrors 6A and 6B are arranged opposite to each other on both sides of the BBO 5. In this configuration, the laser beam is incident on the BBO 5 through one of the multi-reflection cylindrical mirrors 6A, and when it is transmitted, it is reflected by the other multi-reflection cylindrical mirror 6B, is incident on the BBO 5 from the opposite direction, and is further transmitted through the BBO 5. It is reflected by the multi-reflection cylindrical mirror 6A. After that, while repeating this a plurality of times, the light is transmitted through the BBO 5 and wavelength conversion is performed. As a result, it is possible to directly realize wavelength conversion with an extremely simple configuration.

In the fourth embodiment, the multi-reflection cylindrical mirror is used because the wavelength conversion efficiency is higher when the laser light is formed into an elliptical pattern. However, when the elliptical pattern is not used, the elliptic mirror, You may comprise so that multiple reflection may be performed using a perfect circular mirror, a flat mirror, etc.

[0025]

As described above, the present invention is provided with the anamorphic prism that makes the cross-sectional shape of the light beam of the laser light incident on the BBO for converting the wavelength of the laser light into an elliptical shape. It is possible to increase the power density of the laser light and increase the wavelength conversion efficiency while ensuring the angular phase matching in the direction in which the allowable angular phase matching width is small. As a result, the number of parts constituting the wavelength conversion device can be reduced, and the wavelength conversion device can be made compact and compact. In addition, the alignment of the fundamental wave and the second harmonic can be facilitated.

Further, by disposing a plurality of anamorphic prisms in the same direction, it is possible to make the elliptical shape of the luminous flux of the laser light even more flat and to further improve the wavelength conversion efficiency.

Alternatively, a plurality of anamorphic prisms are opposed to each other in opposite directions, and are arranged at positions sandwiching the BBO so that the luminous flux of the laser light incident on the BBO is made into an ellipse to improve the wavelength conversion efficiency. On the other hand, the luminous flux of the laser light can be returned to a circular shape and output, and the laser light can be easily used.

The anamorphic prism is BB
By arranging so as to form an elliptical pattern along a direction perpendicular to the direction in which the angle tolerance of O is small, the above-mentioned BB is formed.
It is possible to increase the power density of the laser light and increase the wavelength conversion efficiency while ensuring the angular phase matching in the direction in which the allowable angular phase matching width in O is small.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of an anamorphic prism.

FIG. 3 is a diagram for explaining wavelength conversion efficiency in BBO.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of an example of a conventional wavelength conversion device.

FIG. 8 is a configuration diagram of another example of a conventional wavelength conversion device.

[Explanation of symbols]

 1 Ar Laser Tube 2 Reflection Mirror 3 Output Mirror 4, 4A, 4B Anamorphic Prism 5 BBO 6A, 6B Multiple Reflection Cylindrical Mirror

Claims (5)

[Claims] 1. A laser light wavelength conversion device for converting a wavelength of laser light through a BBO, comprising an anamorphic prism for making the cross-sectional shape of the light flux of the laser light incident on the BBO into an elliptical shape. Wavelength converter for laser light. 2. A BBO and an anamorphic prism are arranged in a laser resonator composed of a laser tube and a reflecting mirror and an output mirror arranged on both sides of the laser tube. Laser light wavelength converter. 3. The wavelength conversion device for laser light according to claim 1, wherein a plurality of anamorphic prisms are arranged with the same direction facing each other. 4. The laser light wavelength conversion device according to claim 1, wherein a plurality of anamorphic prisms are opposed to each other in opposite directions and are arranged at positions sandwiching BBO. 5. The wavelength conversion device for laser light according to claim 1, wherein the anamorphic prism is arranged so as to form an elliptical pattern along a direction perpendicular to the direction in which the angle tolerance of BBO is small.