JP3234052B2 - Laser wavelength converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In a laser oscillation apparatus, a laser beam is transmitted through a nonlinear optical crystal to generate a harmonic, thereby converting the wavelength. 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, a laser beam incident on the nonlinear optical crystal is condensed by a lens or the like to increase the power density and increase the conversion efficiency.

As described above, the nonlinear optical crystal used for wavelength conversion has a laser beam incident / exit end face which is optically polished.
An anti-reflective coating is applied thereon. The optically polished input / output end face, anti-reflection coating, and even the crystal itself are damaged by the irradiation of the high power density laser beam, and it is difficult to maintain stable wavelength conversion for a long time. Has become.

Attempts have been made to convert an infrared laser beam to an ultraviolet region by wavelength conversion and to use the laser beam in the ultraviolet region for processing or the like. Due to the deterioration of the nonlinear optical crystal due to the irradiation of the laser beam with a high density, stable processing cannot be performed.

As described above, the wavelength conversion cannot be stably continued 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 has been improved or the surface coating has been improved.However, as described above, the higher the power density of the irradiated laser beam, the higher the wavelength conversion efficiency. In many cases, the power density of the laser beam is increased to the level just before damage to the nonlinear optical crystal. Therefore, the reliability of the laser wavelength converter is
This is a factor that is reduced by the nonlinear optical crystal.

[0006] As a technique for improving the wavelength conversion efficiency based on the above, there is Japanese Patent Application Laid-Open No. 4-39975.
In this technique, a parallel plate is provided with a member that is rotatably mounted 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. Thus, the temperature distribution is made uniform.

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

For this reason, the laser beam passing through the nonlinear optical crystal constantly undergoes wavelength conversion by passing through a place where the temperature gradient direction changes, and depending on the direction of the rotation angle, the phase matching condition is determined by the temperature gradient of the crystal. Deviates from the optimal angle due to the presence of the refractive index gradient based on For this reason,
In a nonlinear optical crystal with a small allowable range of the phase matching angle,
The wavelength conversion efficiency decreases.

Accordingly, in the wavelength conversion of the continuous laser output which performs the wavelength conversion at any position during the rotation of the parallel plate, the wavelength conversion efficiency deviates from the center position of the phase matching angle depending on the rotation angle azimuth, and the output stability is reduced. Degree of decline.

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

[0011]

As described above, when the power density of the laser beam is increased to continuously convert the wavelength of the laser beam, the temperature of the crystal rises and the antireflection coating is damaged, so that high reliability is obtained. I can't.

In order to solve this problem, in the method of rotating the nonlinear optical crystal, there may be cases where the relationship between the polarization direction in which phase matching can be achieved and the crystal orientation is not satisfied. Therefore, the present invention provides a laser wavelength conversion device capable of dispersing heat generated by a laser beam in an amorphous optical crystal, and maintaining a polarization direction and a crystal orientation of the laser beam necessary for phase matching and performing stable wavelength conversion. The purpose is to:

[0013]

According to the first aspect of the present invention, a non-linear
The fourth harmonic is emitted by transmitting a laser beam through a shaped optical crystal.
Beam splitter in the laser wavelength converter
A pair of resonator mirrors that are arranged to face each other
One of the resonator mirrors and the beam
A laser rod placed between the laser
A first flat plate disposed between the rod and the beam splitter;
Line plate transmission plate, parallel plate transmission plate and the other resonator mirror
Nonlinear optical crystal for second harmonic generation disposed between
And a fourth height arranged on the output optical path of the beam splitter.
A nonlinear optical crystal for generating harmonics, and
A second parallel plate transmission plate disposed on the transmission light path;
And the second parallel plate transmission plate
Respectively transmitting the first and second parallel plate transmission plates.
Laser beam shifts are 180 degrees opposite each other
A vibration mechanism that vibrates by reciprocating rotation within a predetermined angle range
And a second harmonic generation and a fourth harmonic generation.
Each nonlinear optical crystal has an angle of the phase matching condition of harmonic generation.
Reciprocating between the first and second parallel plate transmission plates with sensitive crystal orientation
Same as the direction of vibration of the laser beam oscillating by rotation
This is a laser wavelength converter that is arranged so as to be in the same direction to achieve the above object.

[0014]

[0015]

[0016]

According to the first aspect, the laser rod and the beam spout
The first parallel flat transmission plate disposed between the first and second liters vibrates.
Through the nonlinear optical crystal for second harmonic generation.
The optical path of the passing laser beam spreads over its oscillation range.
This laser beam passes through the nonlinear optical crystal and
Converted into two harmonics and emitted from the beam splitter,
Subsequently, the light enters the nonlinear optical crystal for generating the fourth harmonic, and
Here, it is converted to the fourth harmonic. This nonlinear optical crystal is transmitted through
The laser beam, which has been converted to the fourth harmonic,
The light enters the parallel plate transmission plate and returns to the original optical path position.
Is output. In this case, the polarization direction of the laser beam is
For each of the second harmonic generation and the fourth harmonic generation
The crystal direction of the optical crystal is set to an orientation that allows phase matching.
In this state, the first parallel plate transmission plate vibrates and the laser
Even if the optical path of the beam is shifted, the lasing polarization direction and the
The relationship between the first and second nonlinear optical crystals does not change,
Continue to maintain the phase matching condition of occurrence.

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a laser wavelength converter. The laser resonator mirrors 1 and 2 have high reflectance at the frequency f (wavelength λ) and spectral characteristics with high transmittance at the 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 having a frequency f. A laser excitation lamp 4 is provided in parallel with 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. Note that the Q switch element 5 is operated by the driver 7.

Between the laser rod 3 and the mirror 2 in the laser resonator, there are disposed 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. ing.

The parallel plate transmission plate 10 is connected to a vibration mechanism 11, and the rotation axis thereof reciprocates, that is, vibrates. Specifically, it is a mechanism similar to a scanner mechanism used for a galvanometer mirror scanner or the like.

Next, the operation of the above-configured device 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, aperture 8, laser rod 3, laser resonator mirrors 1, 2, etc.

If the normal direction of the parallel plate transmission plate 10 coincides with the optical axis of the laser beam, the laser beam axis of the parallel plate transmission plate 10 is placed on the center axis of the aperture 8. No optical axis shift occurs.

However, if the parallel plate transmission plate 10 is tilted at an angle a as shown in FIG. 2 by the vibration drive of the vibration mechanism 11, the oscillation optical axis shifts from the center axis position A of the aperture 7 in the horizontal direction. The optical axis position is A1.

When the parallel plate transmission plate 10 is inclined at the angle b, the oscillation optical axis shifts in the horizontal direction from the central axis position A of the aperture 8 and the optical axis position becomes A2. When the parallel plate transmission plate 10 reciprocates at a high speed in the range of the angles a to b, that is, vibrates in this manner, the optical path of the laser beam transmitted 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 direction is also set to an orientation that allows phase matching,
In this state, even if the parallel plate transmission plate 10 vibrates as described above and shifts the optical path of the laser beam, the relationship between the laser oscillation polarization direction and the nonlinear optical crystal 9 does not change, and the phase matching condition for harmonic generation is changed. You can keep holding.

Accordingly, the laser beam is converted into a higher harmonic by the nonlinear 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 to generate harmonics and wavelength conversion is performed, a parallel plate transmission plate 10 disposed on the laser beam incident side of the nonlinear optical crystal 9 is vibrated by a vibration mechanism 11 so that Since the optical path of the beam is shifted, the portion of the nonlinear optical crystal 9 where the spot of the laser beam passes is shifted, which is equivalent to an enlargement of the area irradiated with the laser beam. It can be less than the fixed beam condition.

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 surface coat can be reduced.

Further, the rise in the temperature inside the nonlinear optical crystal 9 helps to reduce the induction of the phase mismatch condition between the crystal and the passing laser beam. That is, when scanning is performed by oscillating the laser beam in one direction, the temperature distribution in the laser beam irradiated 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,
By arranging the crystal orientation with a wider angle tolerance in the direction perpendicular to the direction, it is possible to realize a condition of high wavelength conversion efficiency. As a result, the angle matching becomes even closer to the ideal, and the conversion efficiency to harmonics can be increased.

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

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

A laser rod 23, a Q switch element 24 and a second
A nonlinear optical crystal 25 for harmonic generation is arranged.
Of these, the laser rod 23 is used for a laser excitation lamp 2.
6 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. A parallel plate transmission plate 31 is disposed between the condenser lens 28 and the nonlinear optical crystal 29 on the optical path, and a parallel plate transmission plate 31 is provided between the nonlinear optical crystal 29 and the collimator lens 30. 32 are arranged.

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

Next, the operation of the device 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 applied to the nonlinear optical crystal 25.
Is converted to a harmonic of frequency 2f by passing through
This is emitted from the dichroic mirror 22. The laser beam converted to the frequency 2f is applied to the condenser lens 2
The light is condensed 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 vibrated by the vibration drive of the vibration mechanism 33, the optical path of the laser beam transmitted through the nonlinear optical crystal 29 is the same as in the first embodiment. Spread over the vibration range.

The laser beam transmitted through the nonlinear optical crystal 29 and converted into a harmonic having a frequency of 4f enters the parallel 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 in which phase matching can be achieved. In this state, the parallel plate transmission plates 31 and 32 vibrate as described above, and the optical path of the laser beam Is shifted, the relationship between the laser oscillation polarization direction and the crystal orientation of the nonlinear optical crystal 29 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 each of the nonlinear optical crystals 25 and 29, and is output as a laser beam 36 whose wavelength has been converted. As described above, according to the second embodiment, the present invention can be applied to shift a laser beam to a nonlinear optical crystal 29 disposed outside a laser resonator. In this case, frequency 2
Damage is more likely to occur in the non-linear optical crystal 29 that converts to a frequency 4f having a shorter wavelength than in the non-linear optical crystal 25 that converts to f, so that damage to the crystal 29 can be reduced.

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

In the prior art, a large output was obtained using an excimer laser and used for large-scale material processing and the like. However, some of these uses can be applied to a solid-state laser as in this embodiment. .

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

FIG. 4 is a block diagram of the laser wavelength converter. This laser wavelength converter shows an application example in which a parallel plate transmission plate is arranged inside a 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 interposed therebetween. A laser rod 4 is provided between the laser resonator mirrors 40 and 41.
3. A parallel plate transmission plate 44 and a nonlinear optical crystal 45 for generating the second harmonic are arranged. A laser excitation lamp 46 is provided in parallel with the laser rod 43.

On the output optical path of the beam splitter 42,
A nonlinear optical crystal 47 for generating the fourth harmonic and a parallel plate transmission plate 48 are arranged. Each parallel plate transmission plate 44, 4
Numeral 8 indicates that the rotating shaft is reciprocated 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 apparatus 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 plate transmission plate 44 is vibrating, the optical path of the laser beam transmitted through the nonlinear optical crystal 45 spreads in the vibration range. This laser beam
The light passes through the nonlinear optical crystal 45 and is converted into a harmonic 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, where it is converted to a harmonic having the frequency 4f. The laser beam incident on the nonlinear optical crystal 47 spreads over the vibration range of the parallel plate transmission plate 44.

The laser beam transmitted through the nonlinear optical crystal 47 and converted into a harmonic having a frequency of 4f is incident on a parallel 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 nonlinear optical crystals 45 and 47 are set to directions that can achieve phase matching. In this state, the parallel plate transmission plate 44 vibrates as described above and the optical path of the laser beam Is shifted, the relationship 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.

Accordingly, the laser beam is converted into a harmonic having a frequency of 4f by the nonlinear 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 disposed outside the laser resonator. As a result, the temperature of the nonlinear optical crystal 47 can be prevented from rising. Also, the laser oscillation polarization direction and the nonlinear optical crystal 4
The relationship with 5, 47 does not change, and the phase matching condition of harmonic generation can be maintained. Also generates the fourth harmonic
A laser resonator configuration for causing
Optical element 45 for generating a second harmonic within
By arranging, high efficiency can be achieved. And bee
The laser rod 4
A parallel plate transmission plate 44 is provided between the beam splitter 3 and the beam splitter 42.
By arranging, the vibration is caused by the parallel plate transmission plate 44.
Then, the laser light wavelength-converted to the second harmonic is used as it is.
After passing through the beam splitter 42,
The light enters the linear optical element 47. On the other hand, no wavelength conversion
The laser beam reflected by the beam splitter 42
When the light passes through the plate transmission plate 44, it returns to the original optical path.
Therefore, wavelength conversion can be performed efficiently with a simple configuration
And also suppresses damage to both nonlinear optical elements.
Can be

As described in the above embodiments, a parallel plate transmission plate is arranged on the incident side of the nonlinear optical crystal, and the parallel plate transmission plate is reciprocally oscillated to reciprocate the laser beam. Scanning by enlarging in one direction on the incident surface to reduce the average incident power per unit area, flatten the temperature distribution of the nonlinear optical crystal in one direction, and allow the phase matching angle of the crystal in that direction. By arranging the crystal in a direction with a narrow angle, it is possible to prevent damage to the crystal and the surface and improve the wavelength conversion efficiency by the incident focused laser beam.

The present invention is not limited to the above embodiment, but 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]

According to the present invention as described above in detail, according to the present invention, the non
Transmit the laser beam through the linear optical crystal to generate the fourth harmonic
Efficient and simple
A laser wavelength converter capable of performing wavelength conversion with a simple configuration can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a laser beam shifting operation by 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 the 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 ... nonlinear optical crystal, 10, 31, 32, 44, 48 ... parallel plate transmission plate, 11, 33, 34 ... vibration mechanism, 22 ... dichroic mirror, 35 ... vibration control device.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-39975 (JP, A) JP-A-1-233785 (JP, A) JP-A-3-208387 (JP, A) JP-A-4- 82284 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/00-3/30 G02F 1/35 JICST file (JOIS)

Claims (1)

(57) [Claims] A laser beam is transmitted through a nonlinear optical crystal.
In a laser wavelength converter that outputs a fourth harmonic by using a pair of resonators that are opposed to each other via a beam splitter.
A mirror and one of the resonator mirrors,
Laser rod disposed between the beam splitter and the beam splitter
And placed between this laser rod and the beam splitter
A first parallel plate transmission plate, and between the parallel plate transmission plate and the other resonator mirror
A non-linear optical crystal for generating a second harmonic, and a fourth optical crystal disposed on an output optical path of the beam splitter.
A nonlinear optical crystal for generating harmonics, and a second plane disposed on a transmission optical path of the nonlinear optical crystal.
Row plate transmission plate, the first parallel plate transmission plate, and the second parallel plate transmission plate
And the first and second parallel plate transmission plates, respectively.
The shift of the laser beam passing through each
Shake by reciprocating rotation within a predetermined angle range so that it is
Comprising a vibrating mechanism for moving, and a second harmonic generating each of said non-linear between the fourth harmonic for generating
The optical crystal has an angle-sensitive coupling of the phase matching conditions for harmonic generation.
The crystal orientation is reciprocating rotation between the first and second parallel plate transmission plates.
Same direction to the direction of vibration of the laser beam vibrating due to
A laser wavelength conversion device, wherein the laser wavelength conversion device is disposed so as to face up.