JPH0722686A - Laser wavelength conversion device - Google Patents

Abstract

PURPOSE:To perform stable wavelength conversion by diffusing heat due to a laser beam in amorphous optical crystallization besides holding the direction of the laser beam polarization and crystal orientation required for phase matching. CONSTITUTION:At the time of transmitting a laser beam through a nonlinear optical crystal 9 inside the laser resonators 1, 2 so as to generate high harmonic for converting wavelength, a transmission plate 10 arranged on the incident side of the laser beam of the nonlinear optical crystal 9 is made to oscillate by an oscillation mechanism 11 so as to shift an optical path of the laser beam. This shifting expands the pass part of the laser beam in the nonlinear optical crystal in the nonlinear optical crystal 9 so as to ease a temperature rise. Further, since an optical path of the laser beam is oscillatingly shifted, the relation of the laser beam to the polarization direction and the crystal orientation is not changed so as to allow it to continuously fill a phase matching condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser wavelength conversion device for converting a wavelength by transmitting an oscillated laser beam through a nonlinear optical crystal.

[0002]

2. Description of the Related Art In a laser oscillating device, the oscillation wavelength of a laser beam is transmitted through a nonlinear optical crystal to generate a harmonic wave, which causes wavelength conversion. In such wavelength conversion, the higher the power density of the laser beam in the nonlinear optical crystal, the higher the wavelength conversion efficiency. Therefore, the laser beam incident on the nonlinear optical crystal is focused by a lens or the like to increase the power density and increase the conversion efficiency.

As described above, in the nonlinear optical crystal used for wavelength conversion, the input and output end faces of the laser beam are optically polished,
An antireflection coating is applied on it. Thus, the optically polished input / output end faces, the antireflection coating, and the crystal itself are damaged by the irradiation of the laser beam having a high power density, and it is difficult to stably maintain the wavelength conversion for a long time. Has become.

Attempts have been made to convert the wavelength of an infrared laser beam into the ultraviolet region by wavelength conversion and utilize this laser beam in the ultraviolet region for processing and the like. Due to the deterioration of the non-linear optical crystal due to the irradiation of the high density laser beam, stable processing cannot be performed.

As described above, the wavelength conversion cannot be stably maintained for a long time due to the deterioration of the nonlinear optical crystal.
In order to solve this, the material of the nonlinear optical crystal itself is improved, and the surface coating is improved. However, the higher the power density of the laser beam irradiated as described above, the higher the wavelength conversion efficiency becomes. In many cases, the power density of the laser beam is increased up to the point where the nonlinear optical crystal is almost damaged. Therefore, the reliability of the laser wavelength converter is
This is a factor causing the deterioration due to the nonlinear optical crystal.

As a technique for improving the wavelength conversion efficiency from the above, there is JP-A-4-39975.
In this technique, a parallel plate is provided with a member that is rotatably attached so that the direction inclined with respect to the normal line is the direction of the rotation axis, and the position where the laser beam passes through the nonlinear crystal is scanned in a circular shape. The temperature distribution is made uniform.

However, although this technique has an apparent effect in making the temperature distribution uniform, the temperature distribution has a high temperature at the center position of the circular scan and a low temperature distribution at the circumferential position.

For this reason, the laser beam passing through the nonlinear optical crystal constantly passes through a portion where the temperature gradient direction changes to perform wavelength conversion. Depending on the direction of the rotation angle, the phase matching condition may be the temperature gradient of the crystal. Due to the existence of the refractive index gradient due to For this reason,
For a nonlinear optical crystal with a small phase matching angle tolerance,
The wavelength conversion efficiency is reduced.

Therefore, in the wavelength conversion of the continuous laser output that performs the wavelength conversion function at any position during the rotation of the parallel plate, the phase conversion angle deviates from the center position due to the rotation angle azimuth, the wavelength conversion efficiency decreases, and the output is stabilized. Cause a decrease in degree.

Another technique is disclosed in Japanese Patent Laid-Open No. 4-82284.
In the publication, a non-linear optical crystal is rotatably attached, and the non-linear optical crystal is rotated to diffuse the temperature and prevent the temperature from rising. However, in this technique, the crystal orientation is not fixed by being rotated with respect to the polarization direction of the laser beam as in the above, and the wavelength conversion efficiency is reduced.

[0011]

As described above, when the power density of the laser beam is increased and the wavelength of the laser beam is continuously converted, the temperature rise of the crystal and the antireflection coating are damaged, and high reliability is obtained. I can't.

In the method of rotating the non-linear optical crystal in order to solve this, there are cases in which the relationship between the polarization direction and the crystal orientation that can achieve phase matching is not satisfied. Therefore, the present invention provides a laser wavelength conversion device that disperses heat generated by a laser beam in an amorphous optical crystal and that can maintain stable polarization direction and crystal orientation of the laser beam necessary for phase matching for stable wavelength conversion. The purpose is to

[0013]

According to a first aspect of the present invention, there is provided a laser wavelength conversion device for converting a wavelength of a laser beam by transmitting a laser beam in a laser resonator into a nonlinear optical crystal to generate a harmonic. , A laser wavelength for achieving the above object, comprising a transmission plate for shifting a laser beam optical path, which is arranged on the laser beam incident side of the nonlinear optical crystal in the laser resonator, and a vibrating means for vibrating the transmission plate. It is a conversion device.

According to a second aspect of the present invention, there is provided a laser wavelength converter for converting a wavelength of a laser beam by transmitting a laser beam oscillated by a laser resonator into a nonlinear optical crystal to generate a harmonic wave. A first transmitting plate for shifting the laser beam optical path, which is arranged on the laser beam incident side, and a first transmitting plate which vibrates the first transmitting plate.
Vibrating means, a second transmission plate for shifting the optical path of the laser beam arranged on the emission side of the laser beam in the nonlinear optical crystal, and the second transmission plate vibrates in response to the vibration of the first transmission plate. And a second vibrating means for achieving the above object.

According to a third aspect of the present invention, the laser beam oscillated by the laser resonator is transmitted through a nonlinear optical crystal arranged outside the laser oscillator to generate a harmonic wave, and a laser wavelength for wavelength conversion of the laser beam is generated. A laser wavelength conversion device for achieving the above object, which is provided with a transmissive plate for shifting a laser beam optical path arranged in a laser oscillator and a vibrating means for vibrating the transmissive plate.

[0016]

According to the first aspect of the present invention, when the laser beam is transmitted through the nonlinear optical crystal in the laser resonator to generate higher harmonics and wavelength conversion is performed, the nonlinear optical crystal is arranged on the incident side of the laser beam. The optical path of the laser beam is shifted by vibrating the transparent plate by vibrating means. Due to this shift, the portion of the nonlinear optical crystal through which the laser beam passes is enlarged and the temperature rise is moderated. or,
Since the optical path of the laser beam is oscillatingly shifted, the relationship between the polarization direction of the laser beam and the crystal orientation does not change, and the phase matching condition can be continuously satisfied.

According to a second aspect of the present invention, when the laser beam is transmitted through the nonlinear optical crystal to generate harmonics and the wavelength is converted, the transmission plate disposed on the incident side of the laser beam of the nonlinear optical crystal is vibrated. Then, the optical path of the laser beam is shifted, and the transmitting plate is vibrated again on the emission side of the nonlinear optical crystal to shift the optical path of the laser beam back to the original state. Claim 3
According to the method, a transmission plate is arranged in the laser oscillator, and the transmission plate is vibrated to shift the optical path of the laser beam.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a laser wavelength converter. The laser resonator mirrors 1 and 2 have a high reflectance at a frequency f (wavelength λ) and a spectral characteristic of a high transmittance at a frequency 2f, and are arranged to face each other.

A laser rod 3 is arranged between the laser resonator mirrors 1 and 2. This laser rod 3 has an oscillation gain with light of frequency f. A lamp 4 for laser excitation is arranged in parallel on the laser rod 3.

A Q switch element 5 and a polarizing plate 6 are arranged between the laser rod 3 and the mirror 1 in the laser resonator. The Q switch element 5 is operated by the driver 7.

Further, between the laser rod 3 and the mirror 2 in the laser resonator, an aperture 8 for mode control, a nonlinear optical crystal 9 and a parallel plate transmission plate 10 for shifting the optical path of the laser beam are arranged. ing.

Of these, the parallel plate transmission plate 10 is connected to a vibrating mechanism 11, and its rotary shaft reciprocally rotates, that is, vibrates. Specifically, it has the same mechanism as the scanner mechanism used in a galvanometer mirror scanner or the like.

Next, the operation of the apparatus configured as described above will be described. When the laser excitation lamp 4 is turned on to excite the laser rod 3 and a laser oscillation gain is obtained by this excitation, laser oscillation occurs at the laser transition wavelength λ. At this time, the laser oscillation optical path is parallel plate transmission plate 1
0, the aperture 8, the laser rod 3, the laser resonator mirrors 1, 2, etc.

Here, if the normal line direction of the parallel flat plate transmission plate 10 coincides with the optical axis of the laser beam, the laser beam axis of the parallel flat plate transmission plate 10 lies on the central axis of the aperture 8. No optical axis shift occurs.

However, when the parallel flat plate transmission plate 10 is tilted at an angle a as shown in FIG. 2 by vibrating the vibrating mechanism 11, the oscillation optical axis is shifted from the central axis position A of the aperture 7 in the horizontal direction. , Its optical axis position is A1.

When the parallel plate transmission plate 10 is tilted at the angle b, the oscillation optical axis shifts from the central axis position A of the aperture 8 in the horizontal direction, and the optical axis position becomes A2. In this way, when the parallel flat plate transmission plate 10 reciprocally rotates at a high speed in the range of the angles a to b, that is, vibrates, the optical path of the laser beam passing through the nonlinear optical crystal 9 spreads in the vibration range.

On the other hand, the polarization direction of the laser beam is defined by the polarizing plate 6. In addition, the nonlinear optical crystal 9
The crystal orientation of is also set to an orientation that allows phase matching,
Even if the plane-parallel plate 10 vibrates as described above and shifts the optical path of the laser beam in this state, the relationship between the polarization direction of the laser oscillation and the nonlinear optical crystal 9 does not change, and the phase matching condition for harmonic generation is set. You can keep holding.

Therefore, the laser beam is converted into a harmonic by the non-linear optical crystal 9 and output as a wavelength-converted laser beam 12. As described above, in the first embodiment, the nonlinear optical crystal 9 in the laser resonator is used.
When a laser beam is transmitted through the inside to generate a higher harmonic wave and the wavelength is converted, the parallel flat plate transmission plate 10 arranged on the laser beam incident side of the nonlinear optical crystal 9 is vibrated by a vibrating mechanism 11 to generate a laser beam. Since the optical path of the beam is shifted, the passing portion of the spot of the laser beam in the non-linear optical crystal 9 is shifted, which is equivalent to expanding the area irradiated with the laser beam, thereby increasing the temperature in the non-linear optical crystal 9. More relaxed than fixed beam conditions.

This means that not only the crystal surface of the nonlinear optical crystal 9 but also the average light energy density inside the crystal can be reduced, and the deterioration rate of the crystal base material and the deterioration rate of the surface coat can be slowed down.

Further, the rise in temperature inside the nonlinear optical crystal 9 also serves to alleviate the induction of the phase mismatch condition between the crystal and the passing laser beam. That is, when the laser beam is oscillated and scanned in one direction, the temperature distribution in the laser beam irradiation portion can be made uniform except for the scanning end portion within the range of the vibration scanning direction of the parallel plate transmission plate 10. it can.

Therefore, if the angle-sensitive crystal orientation of the phase matching condition of the nonlinear optical crystal 9 is oriented in this direction,
A condition with high wavelength conversion efficiency can be realized by arranging the crystal orientation having a wider angle permissible range in the direction perpendicular thereto. As a result, the angle matching becomes even closer to the ideal, and the conversion efficiency into harmonics can be increased.

Further, inconsistency with the angle allowable range of the nonlinear optical crystal when the scanning direction is circularly scanned can be avoided. Next, a second embodiment of the present invention will be described.

FIG. 3 is a block diagram of a laser wavelength converter. This laser wavelength conversion device shows an application example in which a nonlinear optical crystal is arranged outside the laser resonator. The laser resonator mirrors 20 and 21 are the dichroic mirror 2.
The two are opposed to each other.

Between the laser resonator mirrors 20 and 21, a laser rod 23, a Q switch element 24, and a second switch are provided.
A nonlinear optical crystal 25 for generating harmonics is arranged.
Of these, the laser rod 23 has a lamp 2 for exciting the laser.
6 are arranged side by side, and the Q switch element 24 has its driver 27
It is connected to the.

On the output optical path of the dichroic mirror 22, a condenser lens 28, a nonlinear optical crystal 29 and a collimator lens 30 are arranged. Further, a parallel plate transmission plate 31 is arranged between the condenser lens 28 and the nonlinear optical crystal 29 on this optical path, and a parallel plate transmission plate is provided between the nonlinear optical crystal 29 and the collimator lens 30. 32 are arranged.

These parallel flat plate transmission plates 31 and 32 have their rotation axes reciprocally rotated by vibrating mechanisms 33 and 34, respectively.
That is, it vibrates. These vibrating mechanism 3
The vibration control device 35 controls the movement of the laser beams 3, 34, and the shift of the laser beam by the parallel flat plate transmission plate 32 is 180 degrees opposite to the shift by the parallel flat plate transmission plate 31.

Next, the operation of the apparatus configured as described above will be described. When the laser excitation lamp 26 is turned on to excite the laser rod 23 and a laser oscillation gain is obtained by this excitation, laser oscillation occurs at the laser transition wavelength λ.

This laser beam is used by the nonlinear optical crystal 25.
Is converted to a harmonic with a frequency of 2f by passing through
This is emitted from the dichroic mirror 22. The laser beam converted to the frequency 2f is collected by the condenser lens 2
The light is focused by 8 and enters the nonlinear optical crystal 29, where it is converted into a harmonic having a frequency of 4f.

Since the parallel plate transmission plate 31 is vibrating by vibrating the vibrating mechanism 33, the optical path of the laser beam passing through the nonlinear optical crystal 29 is the same as in the first embodiment. Spread in the vibration range.

Then, the laser beam transmitted through the non-linear optical crystal 29 and converted into the harmonic of the frequency 4f is incident on the parallel flat plate transmission plate 32, where it returns to the original optical path position. On the other hand, with respect to the polarization direction of the laser beam, the crystal direction of the non-linear optical crystal 29 is also set to an orientation capable of achieving phase matching. In this state, the parallel flat plate transmission plates 31 and 32 vibrate as described above and the optical path of the laser beam. Even if is shifted, the laser oscillation polarization direction and the crystal orientation relationship of the nonlinear optical crystal 29 do not change, and the phase matching condition for harmonic generation can be maintained.

Therefore, the laser beam is converted into a harmonic having a frequency of 4f by each of the nonlinear optical crystals 25 and 29, and is output as a wavelength-converted laser beam 36. As described above, according to the second embodiment, it can be applied to shift the laser beam with respect to the nonlinear optical crystal 29 arranged outside the laser resonator. In this case, frequency 2
Since the nonlinear optical crystal 29 converting to the frequency 4f having a shorter wavelength than the nonlinear optical crystal 25 converting to f is more likely to be damaged, the damage to the crystal 29 can be reduced.

An oscillating parallel plate transmission plate may be arranged for the nonlinear optical crystal 25 to shift the incident laser beam. The technique of shortening the wavelength up to the frequency 4f is effective in generating an ultraviolet laser.
For example, a wavelength of 1.06 μm such as Nd: YAG laser
When the oscillation wavelength of is shortened to the frequency 4f by generation of harmonics, ultraviolet light of 266 nm is obtained.

Conventionally, an excimer laser was used to obtain a large output, and it was used for processing a large-scale material. However, some of these applications can be applied to a solid-state laser as in this embodiment. .

Therefore, the same laser oscillator can be used to generate wavelengths in the range from infrared rays to ultraviolet rays, and fine processing can be performed using wavelengths depending on the material to be processed. Next, a third embodiment of the present invention will be described.

FIG. 4 is a block diagram of a laser wavelength converter. This laser wavelength conversion device shows an application example in which a parallel plate transmission plate is arranged inside the laser resonator and a nonlinear optical crystal is arranged outside the laser resonator.

The laser resonator mirrors 40 and 41 are arranged to face each other with a beam splitter 42 in between. The laser rod 4 is provided between the laser resonator mirrors 40 and 41.
3, the parallel plate transmission plate 44 and the nonlinear optical crystal 45 for generating the second harmonic are arranged. Of these, a laser excitation lamp 46 is arranged in parallel on the laser rod 43.

On the output optical path of the beam splitter 42,
A nonlinear optical crystal 47 for generating a fourth harmonic and a parallel plate transmission plate 48 are arranged. Parallel plate transmission plates 44, 4
8, the rotation axis of each of them is reciprocally rotated by a vibration mechanism,
That is, it vibrates. The shift of the laser beam by the parallel plate transmission plate 48 is 180 degrees opposite to the shift by the parallel plate transmission plate 44.

Next, the operation of the device configured as described above will be described. When the laser excitation lamp 46 is turned on to excite the laser rod 43 and a laser oscillation gain is obtained, laser oscillation occurs at the laser transition wavelength λ.

Here, since the parallel flat plate transmission plate 44 is vibrating, the optical path of the laser beam passing through the nonlinear optical crystal 45 spreads in the vibration range. This laser beam
By passing through the nonlinear optical crystal 45, it is converted into a harmonic wave having a frequency of 2f, which is emitted from the beam splitter 42.

The laser beam converted to the frequency 2f subsequently enters the nonlinear optical crystal 47 and is converted into a harmonic of the frequency 4f here. The laser beam incident on the nonlinear optical crystal 47 spreads in the vibration range of the parallel plate transmission plate 44.

Then, the laser beam transmitted through the nonlinear optical crystal 47 and converted into the harmonic of the frequency 4f is incident on the parallel flat plate transmission plate 48, where it returns to the original optical path position. On the other hand, with respect to the polarization direction of the laser beam, the crystal directions of the non-linear optical crystals 45 and 47 are set so as to achieve phase matching. In this state, the parallel flat plate transmission plate 44 vibrates as described above and the optical path of the laser beam. Even if is shifted, the relation between the laser oscillation polarization direction and the nonlinear optical crystals 45 and 47 does not change, and the phase matching condition for harmonic generation can be maintained.

Therefore, the laser beam is converted into a harmonic having a frequency of 4f by the non-linear optical crystals 45 and 47 and output as a wavelength-converted laser beam 49. As described above, according to the third embodiment, it is possible to dispose the parallel plate transmission plate 44 inside the laser resonator and expand the transmission portion of the laser beam with respect to the nonlinear optical crystal 47 arranged outside the laser resonator. Therefore, the temperature rise of the nonlinear optical crystal 47 can be prevented. Also, the laser oscillation polarization direction and the nonlinear optical crystal 4
The relationship with Nos. 5 and 47 does not change, and the phase matching condition for harmonic generation can be maintained.

As described above with reference to the above embodiments, the parallel plate transmission plate is arranged on the incident side of the nonlinear optical crystal, and the parallel plate transmission plate is oscillated in a reciprocating rotary manner, whereby the laser beam of the nonlinear optical crystal is changed. The incident surface is enlarged and scanned in one direction to reduce the average incident power per unit area, the temperature distribution of the nonlinear optical crystal is flattened in one direction, and the phase matching angle of the crystal is allowed in that direction. By arranging the crystal in a direction with a narrow angle, it is possible to prevent the crystal and the surface from being damaged by the incident condensed laser beam and improve the wavelength conversion efficiency.

The present invention is not limited to the above-mentioned one embodiment, and may be modified within the scope of the invention. For example, a parallel plate transmission plate may be arranged between the nonlinear optical crystal 8 and the mirror 2 shown in the first embodiment, and the laser beam shifted by the parallel plate transmission plate 9 may be returned to the original optical axis position. Good.

[0055]

As described in detail above, according to the present invention, the heat generated by the laser beam in the amorphous optical crystal is dispersed, and the polarization direction and crystal orientation of the laser beam necessary for phase matching are maintained and stable. It is possible to provide a laser wavelength converter that can perform various wavelength conversions.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a laser wavelength conversion device according to the present invention.

FIG. 2 is a diagram showing a laser beam shifting action of the apparatus.

FIG. 3 is a configuration diagram showing a second embodiment of the laser wavelength conversion device according to the present invention.

FIG. 4 is a configuration diagram showing a third embodiment of a laser wavelength conversion device according to the present invention.

[Explanation of symbols]

1, 2, 20, 21, 40, 41 ... Laser resonator mirror, 3, 23, 43 ... Laser rod, 4, 26 ... Lamp, 5, 24 ... Q switch element, 6 ... Polarizing plate, 8 ... Aperture, 9 , 29, 45, 47 ... Non-linear optical crystal, 10, 31, 32, 44, 48 ... Parallel plate transmission plate, 11, 33, 34 ... Vibration mechanism, 22 ... Dichroic mirror, 35 ... Vibration control device.

Claims (3)

[Claims] 1. A laser wavelength converter for converting a wavelength of the laser beam by transmitting a laser beam in the laser resonator through a nonlinear optical crystal to generate harmonics, the nonlinear optical device in the laser resonator. A laser wavelength conversion device comprising: a transmission plate for shifting a laser beam optical path, which is disposed on a laser beam incident side of a crystal; and vibrating means for vibrating the transmission plate. 2. A laser beam oscillated by a laser resonator is transmitted through a nonlinear optical crystal to generate a harmonic wave,
In a laser wavelength conversion device that performs wavelength conversion of the laser beam, a first transmission plate for shifting a laser beam optical path, which is arranged on the incident side of the laser beam in the nonlinear optical crystal,
The first vibrating means for vibrating the first transmission plate, the second transmission plate for shifting the laser beam optical path disposed on the emission side of the laser beam in the nonlinear optical crystal, and the second transmission plate And a second vibrating unit that vibrates in response to the vibration of the first transmission plate. 3. A laser wavelength converter for converting a wavelength of the laser beam by transmitting a laser beam oscillated by a laser resonator to a nonlinear optical crystal arranged outside the laser oscillator to generate a harmonic. A laser wavelength conversion device comprising: a transmission plate for shifting the optical path of a laser beam arranged in the laser oscillator; and a vibrating means for vibrating the transmission plate.