JPH05165072A - Laser beam wave-length changing device - Google Patents

Abstract

PURPOSE:To provide certain and quick adjustability for dislocation of the optimum tuning angle of nonlinear optical crystal to vary the wavelength of laser beam. CONSTITUTION:A laser beam wavelength converting device is equipped with a laser oscillator 11, nonlinear optical crystal 17 converting the wavelength of laser beam generated by the laser oscillator 11, a laser oscillator for measuring 23 for putting the first measuring light and second measuring light incident to the nonlinear optical crystal 17 at angles approx symmetrical about the optical axis of the laser beam, a first sensor 29 and second sensor 31 to sense the outputs of the first and second measuring lights emitted by the nonlinear optical crystal 17, and a computer 20 which sets the nonlinear optical crystal to the optimum phase tuning angle relative to the optical axis of the laser beam in compliance with the difference in the outputs sensed by these sensors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength converter for converting the wavelength of laser light output from a laser oscillator into different wavelengths.

[0002]

2. Description of the Related Art In recent years, laser light has been used in various fields, for example, laser processing and writing / reading of an optical disk. In these applications, laser light having a short wavelength is required in order to improve the processing accuracy and the performance of the optical disc.

When a YAG laser or a semiconductor laser is used as the laser oscillator, a nonlinear optical crystal is known as a means for shortening the wavelength of the laser light output from these laser oscillators. .. FIG. 5 shows the structure of a conventional wavelength conversion device using a nonlinear optical crystal. In the figure, 1 is a laser oscillator. The first laser light L ₁ having a wavelength of ω ₁ output from the laser oscillator ₁ is condensed by the lens 2 and enters the nonlinear optical crystal 3. In this nonlinear optical crystal 3, a part of the _first laser light L ₁ is converted into a _second laser light L ₂ having a half wavelength ω ₂ . Then, from this nonlinear optical crystal 3, the _first laser light L ₁ whose wavelength is not converted is emitted together with the _second laser light L ₂ . The beam splitter 4 is provided in the outgoing optical path of the _first and _second laser lights L ₁ and L _2.
Are arranged. The beam splitter 4 reflects the _first laser light L ₁ and transmits the _second laser light L ₂ .
Therefore, the beam splitter 3 separates the _first laser light L ₁ and the second laser light L ₂ .

By the way, in the wavelength conversion device having such a structure, in order to keep the conversion efficiency of the _first laser light L ₁ by the nonlinear optical crystal 3 always in the highest state, the nonlinear optical crystal 3 is used. Must be rotated about a certain axis so that the refractive indices for the _first laser beam L ₁ and the second laser beam L ₂ are equal. The angle formed by the crystal axis T of the nonlinear optical crystal 3 and the optical axis O of the laser light in such a state is called the optimum phase tuning angle θ.

By the way, since the above-mentioned nonlinear optical crystal 3 has a high temperature dissimilarity, the room temperature is changed or the first laser light L is changed.
The value of the optimum phase tuning angle θ changes when the temperature changes such as when ₁ is incident. Furthermore, the nonlinear optical crystal 3 is also sensitive to mechanical stability and frequency stability of laser light, and the value of the optimum phase tuning angle .theta.

Therefore, conventionally, the output of a part of the _second laser light L ₂ converted by the nonlinear optical crystal 3 is monitored, and the nonlinear optical crystal 3 is adjusted to the optimum phase tuning angle θ according to the output. It was done to adjust to. However, by simply monitoring the output, it is not possible to determine whether the optimum phase tuning angle θ of the nonlinear optical crystal 3 has deviated to the + direction or the-direction of the arrow shown in FIG. Therefore, when the output of the _second laser light L ₂ is reduced, it is difficult to set the nonlinear optical crystal 3 to the optimum phase tuning angle θ reliably and quickly.

The decrease in the output of the _second laser light L ₂ wavelength-converted by the nonlinear optical crystal 3 is not limited to the case where the optimum phase tuning angle θ of the nonlinear optical crystal 3 is deviated. It is also caused by the displacement of the optical resonator in the oscillator 1 and the stain of the mirror. However, in the conventional method of only monitoring the output, it is necessary to determine whether the cause of the decrease in the output is due to the change in the optimum phase tuning angle θ of the nonlinear optical crystal 3 or due to other causes. Sometimes it was not possible.

[0008]

Thus, when the output of the wavelength-converted laser light output from the nonlinear optical crystal is simply monitored, when the output is lowered,
In some cases, it is not possible to determine the shift direction of the optimum phase tuning angle of the nonlinear optical crystal, and it is also impossible to determine whether the cause of the output reduction is due to the shift of the optimum phase tuning angle.

The present invention has been made in view of the above circumstances. An object of the present invention is to optimize the phase tuning of the nonlinear optical crystal when the output of laser light wavelength-converted by the nonlinear optical crystal is lowered. (EN) Provided is a laser light wavelength conversion device capable of not only knowing the angular deviation direction but also determining whether the output decrease is due to the deviation of the optimum phase tuning angle of the nonlinear optical crystal. Especially.

[0010]

In order to solve the above problems, the present invention provides a laser oscillator and a wavelength of the laser light provided in the optical path of the laser light generated by the laser oscillator. And a first non-linear optical crystal for converting the non-linear optical crystal into the non-linear optical crystal at a substantially symmetric angle about the optical axis of the laser light after passing through the non-linear optical crystal. Measuring means for making them enter so as to intersect with each other, a first detector and a second detector for detecting outputs of the first measuring light and the second measuring light emitted from the nonlinear optical crystal, and these detectors. And a control means for rotating the non-linear optical crystal in accordance with the difference in the output detected by the optical axis and setting the angle formed by the crystal axis and the optical axis of the laser light to the optimum phase tuning angle. And

[0011]

According to the above construction, when the optimum phase tuning angle of the nonlinear optical crystal changes, one of the first detector and the second detector detects it according to the direction of deviation of the angle. Since the output of the measurement light decreases and the output of the measurement light detected by the other detector increases, the deviation direction of the nonlinear optical crystal can be known by the difference between the outputs and each detector detects it. When the output of the wavelength-converted laser light decreases without causing a difference in the output of the measurement light, it can be determined that the cause is not the change in the optimum phase tuning angle.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The wavelength conversion device shown in FIG.
A laser oscillator 11 such as an AG laser is provided. The laser oscillator 11 includes a laser rod 12, a pump lamp 13 for optically pumping the laser rod 12, and a high-reflection mirror forming an optical resonator arranged opposite to both end faces of the laser rod 12. 14 and a partial reflection mirror-15.
When the laser rod 12 is optically excited by the excitation lamp 13, the partial reflection mirror 15 outputs the _first laser light L ₁ having the wavelength ω ₁ .

The first laser light L ₁ is condensed by the first lens 16 and enters the nonlinear optical crystal 17. The nonlinear optical crystal 17, the first record - generating a - second harmonic of laser light L ₁ (laser light L ₂ second Les wavelengths omega _2). The nonlinear optical crystal 17 is mounted and fixed on a rotary mounting table 19 which is rotationally driven by a drive source 18 composed of a stepping motor. The drive source 18 is rotationally driven by a drive signal from the computer 20 as described later.

A part of the _second laser light L ₂ generated by the nonlinear optical crystal 17 is split by the beam splitter 21. The output of the _second laser light L ₂ split by the beam splitter 21 is detected by the monitor 22. The detection signal from the monitor 22 is input to the computer 20 and compared with the set value set in the computer 20.

On the other hand, the nonlinear optical crystal 17 has an angle at which the first measuring light S ₁ and the second measuring light S ₂ are substantially symmetrical with respect to the optical axis O of the _first laser light L _1. Is incident at. Laser light S generated by the measurement laser oscillator 23 is split into these measurement lights S ₁ and S ₂ . That is, the measuring laser oscillator 23 has a laser light S having the same wavelength as that of the _first laser light L _1.
To occur. The laser light S is reflected by the first reflection mirror 24, and is divided by the half mirror 25 into the first measurement light S ₁ and the second measurement light S ₂ . The first measuring light S ₁ reflected by the half mirror 25 is condensed by the second lens 26, and the nonlinear optical crystal is formed at an angle α ₁ with respect to the optical axis O of the _first laser light L _1. It is incident on 17. The second measurement light S ₂ transmitted through the half mirror 25 is reflected by the second reflection mirror 27, is condensed by the third lens 28, and is incident on the nonlinear optical crystal 17. This second measurement light S ₂ is emitted from the first measurement light S ₂ .
Les - The light L of the first with respect to the optical axis O of the _first measuring beam S ₂
It is incident at an angle of α ₂ which is almost symmetrical with. In addition,
The first measurement light S ₁ and the second measurement light S ₂ are set in a twisted relationship such that they do not overlap with the optical axis O in the nonlinear optical crystal 17.

The output of the first measuring light S ₁ which has been wavelength-converted by the nonlinear optical crystal 17 and is emitted is detected by the first detector 29. The output of the second measurement light S ₂ is detected by the second detector 31. These detectors 2
The outputs from 9 and 31 are input to an amplifier 32, where they are amplified and sent to the computer 19. In this computer 19, the first detector 29 and the second detector 3 are
The difference between the detected value and 1 is detected, and the drive source 18 is operated according to the detected difference to rotate the rotary mounting table 19. As a result, the angle formed by the crystal axis T of the nonlinear optical crystal 17 and the optical axis O is controlled to be the optimum phase tuning angle θ as described later.

Next, the operation of outputting the _second laser light L ₂ whose wavelength has been converted to ½ by the wavelength conversion device having the above-described configuration with the highest conversion efficiency will be described. First,
The laser oscillator 11 is operated to output the _first laser light L ₁ and the measuring laser oscillator 23 is operated to generate the measuring laser light S. When the first laser light L ₁ is incident on the nonlinear optical crystal 17, the wavelength ω of the _first laser light L ₁ is emitted from the nonlinear optical crystal 17.
The second laser light L ₂ having a wavelength ω _{2 which} is half the wavelength of ₁ is generated and output. Further, the measurement laser light S output from the measurement laser oscillator 23 is split by the half mirror 25, and has an angle symmetric with respect to the optical axis O of the _first laser light L _1. The light enters the nonlinear optical crystal 17 at α ₁ and α ₂ .

Here, if the angle formed by the crystal axis T of the nonlinear optical crystal 17 and the optical axis O is set to the optimum phase tuning angle θ, they are arranged at an angle symmetrical with respect to the optical axis O. The outputs of the _second laser light L ₂ detected by the first detector 29 and the second detector 31 are the same. This state is shown in FIG. That is, X in the figure is the nonlinear optical crystal 1.
7, the intensity distribution of the _second laser light L ₂ wavelength-converted into the second harmonic by the nonlinear optical crystal 17 is symmetrical about the optimum phase tuning angle θ. It has a normal distribution curve. Therefore, if there is no deviation in the optimum phase tuning angle θ of the nonlinear optical crystal 17, the output P detected by the pair of detectors 29 and 31 arranged at the angles α ₁ and α ₂ symmetrical with respect to the optical axis O is It becomes the same value. If the outputs detected by the pair of detectors 29 and 31 are the same, there is no difference. Therefore, the drive signal is not output from the computer 20 to the drive source 18.

When the optimum phase tuning angle of the nonlinear optical crystal 17 deviates from θ to θm due to temperature change or mechanical change, the angle characteristic curve X formed by the nonlinear optical crystal 17 is also as shown in FIG. 2 (b). Therefore, the center shifts from θ to θm. If the angle characteristic curve X deviates, the output detected by the first detector 29 decreases from P to P ₁ according to the direction of the deviation, and the output detected by the second detector 31 decreases by P.
Increases to ₂ . This causes a difference in the outputs detected by the detectors 29 and 31, and a drive signal corresponding to the difference is output from the computer 19 to the drive source 18. The drive source 18 rotationally drives the rotary mounting table 19 at an angle and a direction according to the difference between the output signals until there is no difference in the outputs detected by the first detector 29 and the second detector 31. That is,
In this case, the non-linear optical crystal 17 is rotationally driven until the angle formed by the crystal axis T and the optical axis O changes from θ to θm. Thereby, the nonlinear optical optical crystal 17
Since the crystal axis T is set to the optimum phase tuning angle θm with respect to the optical axis O, the wavelength conversion efficiency by the nonlinear optical crystal 17 can be maintained at the maximum state.

The output P ₁ detected by the first detector 29 increases and the output P ₂ detected by the second detector 31 increases.
In the case where is decreased, the nonlinear optical crystal 17 can be maintained at the optimum phase tuning angle by rotationally driving the nonlinear optical crystal 17 in the opposite direction to the above.

That is, the pair of detectors 2 with respect to the optical axis O
By arranging 9 and 31 symmetrically, the nonlinear optical crystal 17
Can be quickly and reliably controlled to the optimum phase tuning angle, so that the second harmonic can always be generated with high conversion efficiency.

If the decrease in the output of the _second laser light L ₂ is caused by the laser oscillator 11 side, not by the fluctuation of the optimum phase tuning angle of the nonlinear optical crystal 17, a pair of detectors is used. First and second measurement light beams S ₁ and S ₂ detected by 29 and 31
There is no difference in output. Therefore, the monitor 22
When the output of the _second laser light L ₂ detected by the detector decreases, it depends on whether or not there is a difference between the outputs of the measurement lights S ₁ and S ₂ detected by the pair of detectors 29 and 31. The cause of output reduction can be determined.

FIG. 3 shows another embodiment of the present invention. In this embodiment, the nonlinear optical crystal 17 is incorporated in the optical resonator of the laser oscillator 11a. In other words, the laser oscillator 11a of this embodiment has a laser rod 51 excited by the excitation lamp 50 and a first high-reflection mirror arranged opposite to one end face of the laser rod 51.
52, a dichroic mirror 53 arranged on the other end surface at an angle of 45 degrees with respect to the optical axis O of the _first laser light L ₁ output from the laser rod 51, and this dichroic First laser light L ₁ reflected by the mirror 53
And a second high-reflecting mirror 54 arranged on the optical axis O.

The dichroic mirror 53 is configured to reflect the _first laser light L ₁ and transmit the _second laser light L ₂ which is its second harmonic. Then, the dichroic mirror 53 and the second high-reflection mirror-5 described above.
4, the nonlinear optical crystal 17 mounted and fixed on the rotary mounting table 19 is arranged. Thereby, while the first laser light L ₁ generated by the laser rod 51 is repeatedly reflected and amplified by the first high reflection mirror 52 and the second high reflection mirror 54, By passing through the nonlinear optical crystal 17, the wavelength is converted into the _second laser light L ₂ having a half wavelength. The wavelength-converted _second laser light L ₂ is transmitted through the dichroic mirror 53 and output.

On the other hand, a measuring laser oscillator 2 is provided between the second high reflection mirror 54 and the dichroic mirror 53.
3 are arranged. The measuring laser light S output from the measuring laser oscillator 23 is split by the half mirror 55. First measurement light S ₁ reflected by the harf mirror 55
Is a predetermined angle α _{1 with} respect to the optical axis O of the _first laser light L _1.
The second measuring light S _{2 which} is incident on the nonlinear optical crystal 17 at and is transmitted through the half mirror 55 is the first measuring light S ₂ about the optical axis O.
Of the measuring light S ₁ and the nonlinear optical crystal 1 in a symmetric angle alpha ₂
It is incident on 7. The first and second measurement lights S ₁ and S ₂ are set in a twisted state in the nonlinear optical crystal 17 so as not to overlap the optical axis O.

Then, the first and second measurement lights S ₁ and S _{2 which} are incident on the nonlinear optical crystal 17 and whose wavelengths have been converted are respectively emitted from the dichroic mirror 53 to the first detector 29 and the first detector 29. The output is detected by the second detector 31.

Even with such a configuration, as in the case of the above-described embodiment, the outputs of the outputs detected by the first and second detectors 29 and 31 indicating that the optimum phase tuning angle of the nonlinear optical crystal 17 has deviated. The difference can be determined, and the angle of the nonlinear optical crystal 17 can be adjusted according to the amount of deviation.

FIG. 4 shows still another embodiment of the present invention. In this embodiment, the measuring light S is obtained without using the measuring laser oscillator. That is, the first laser light L ₁ generated by the laser oscillator 11 is firstly placed on the optical path.
The Haafu Mira 61 is placed at an angle of 45 degrees. The first laser light L ₁ reflected by the first half mirror 61 is reflected by the first reflection mirror 62 to become the first measuring light S ₁ , and the first laser light is obtained. The light enters the nonlinear optical crystal 17 at a predetermined angle α ₁ with respect to the optical axis O of L ₁ .

In the optical path of the _first laser beam L ₁ which has passed through the first half mirror 61, the second half mirror 63 has a symmetry 45 with the first half mirror 61. It is arranged at an angle of degrees. The first laser light L ₁ reflected by the second half mirror 63 is reflected by the second reflection mirror 64 to become the second measurement light S ₂ , and the first laser light is generated. An angle α symmetrical to the _first measurement light S ₁ about the optical axis O of the light L _1
The light enters the nonlinear optical crystal 17 at ₂ .

Therefore, the first measuring light S ₁ and the second measuring light S ₂ wavelength-converted by the nonlinear optical crystal 17 are detected by the first detector 29 and the second detector 31, respectively. As a result, as in the case of the first embodiment, the crystal axis T of the nonlinear optical crystal 17 can always be adjusted to the optimum phase tuning angle with respect to the optical axis O.

[0031]

As described above, the present invention provides a nonlinear optical crystal for converting the wavelength of laser light, in which the first measuring light and the second measuring light are arranged substantially symmetrically with respect to the optical axis of the laser light. The measuring light of (1) is made incident, and the nonlinear optical crystal is set to the optimum phase tuning angle according to the difference of the measuring light emitted from the nonlinear optical crystal.

Therefore, it is possible to know the shift amount and the direction of the optimum phase tuning angle of the nonlinear optical crystal from the difference between the pair of measurement lights, so that the control can be performed surely and quickly. Moreover, it is possible to know whether or not the cause of the output decrease of the laser light wavelength-converted is due to the shift of the optimum phase tuning of the nonlinear optical crystal depending on whether or not there is a difference between the outputs of the pair of measurement lights. Also, it is possible to reliably handle when the output is reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2A is an angle characteristic curve diagram when there is no deviation in the optimum phase tuning angle of the nonlinear optical crystal, and FIG. 2B is an angle characteristic curve diagram when there is also a deviation.

FIG. 3 is a configuration diagram of a laser oscillator showing another embodiment of the present invention.

FIG. 4 is a configuration diagram of a laser oscillator showing still another embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional wavelength conversion device.

[Explanation of symbols]

11 ... Laser oscillator, 17 ... Nonlinear optical crystal, 18 ... Driving source, 19 ... Rotary mounting table, 20 ... Computer, 23 ...
Measurement laser oscillator, 29 ... First detector, 31 ... Second
Detector.

Claims (1)

[Claims] 1. A laser oscillator, a nonlinear optical crystal for converting the wavelength of the laser light provided in the optical path of the laser light generated by the laser oscillator, and the nonlinear optical crystal having the above-mentioned nonlinear optical crystal. Measuring means for injecting the first measuring light and the second measuring light so as to intersect each other after passing through the nonlinear optical crystal at an angle substantially symmetrical with respect to the optical axis of the laser light; A first detector and a second detector for detecting outputs of the first measurement light and the second measurement light emitted from the crystal;
Control means for rotating the non-linear optical crystal according to the difference in output detected by these detectors and setting the angle formed by the crystal axis and the optical axis of the laser light to the optimum phase tuning angle. A wavelength conversion device for laser light.