JPH0322069B2 - - Google Patents

Description

Detailed Description of the Invention "Industrial Application Field" The present invention is an optical parametric oscillator in which phase matching is performed by rotating the orientation of a crystal, in which the incident beam does not deviate from the incident plane of the crystal when the crystal is rotated. This invention relates to a wavelength tunable laser device that is movable in this manner.

"Prior Art" Generally, wavelength tunable laser systems include a dye laser system, a temperature tuning system, an optical parametric oscillation system, and an alexandrite laser system.
Among these, the wavelength tunable laser device using the optical parametric oscillation method is as shown in FIG. The optical parametric oscillator 6 is constructed by the following.

In such a configuration, for example, the excitation light is
When a 355 nm pulsed laser is input, light of a wavelength different from the original wavelength (355 nm) is generated from the nonlinear optical crystal 5. The rotation angle (θ) is 90 as shown in Figure 4 a.
degree, two lights of 500nm and 1230nm are generated. When the rotation angle (θ) of the crystal 5 is changed as shown in FIG. 4b, the wavelengths of the two lights approach each other with characteristic curves o and e as shown in FIG. Since these lights are weak, they are caused to resonate between the two input/output reflection mirrors 2 and 3, amplified, and output.

"Problems to be Solved by the Invention" When the rotation angle (θ) of the crystal 5 is changed, as shown in FIG. 5, the output wavelength also changes continuously. However, as shown in FIG. 4a, there is a limit to the incident surface dimension a of the crystal 5, and the incident laser beam 7 also has an effective diameter b, so as shown in FIG. 4b, the crystal 5 is When the rotation exceeds the allowable limit, a part of the incident laser beam 7 comes off the incident surface of the crystal 5, and the matching condition is no longer satisfied, causing a problem that this part becomes a loss. Furthermore, if there is a permissible limit on the rotation angle (θ) of the crystal 5, there is also a limit on the oscillation wavelength.

"Means for Solving the Problems" The present invention has been made to solve the above problems, and provides an optical parametric oscillator that performs phase matching by rotating the orientation of a nonlinear optical crystal using a crystal orientation rotation device. , further comprising a moving device for moving the nonlinear optical crystal in a direction intersecting the incident light within a plane rotated by the crystal orientation rotating device.

"Operation" When a pulsed laser beam of a certain wavelength is incident on the incidence surface of a nonlinear optical crystal, laser beams of two wavelengths different from the wavelength of the incident laser beam are generated and output. When phase matching is performed by rotating the orientation of the crystal using an orientation rotation device, a laser beam whose two wavelengths are changed to approach each other is obtained. If the azimuth rotation of the crystal exceeds the allowable limit and the incident laser beam deviates from the incident plane of the crystal,
Detect it and move the crystal. Therefore, the incident laser beam is incident on the same incident surface of the crystal without being deviated.

“Example” An example of the present invention will be described below based on the drawings.

In FIG. 1, reference numeral 6 denotes an optical parametric oscillation section, and this optical parametric oscillation section 6 is composed of a collimator lens 1, reflection mirrors 2 and 3 on the input side and output side, and a nonlinear optical crystal 5.
These are the same as in FIG. 3 and are given the same reference numerals. Further, when a urea crystal is used as the crystal 5, since the urea crystal 5 has deliquescent property, it is sealed in a container 8 made of aluminum or the like together with matching oil 9.
0 and 11 are provided.

As shown in FIG.
is installed on top. This azimuth rotation device 12 is placed on a rotation stage 13, and this rotation stage 13 is connected to a stepping motor 14.
The azimuth rotation angle (θ) is controlled by a command from the rotation angle control unit 15 in the figure.

The rotary stage 13 is also placed on a linear drive table 17 of a moving device 16, and is slidably provided on two linear guides 19, 19 perpendicular to the optical axis 7 by a linear pulse motor 18. There is. The moving device 16 moves the nonlinear optical crystal 5 together with the azimuth rotating device 12 in a direction perpendicular to the incident optical axis 7 in response to a signal from the pulse generator 20 shown in FIG. On the output side of the optical parametric oscillator 6, there is a half mirror 21 for detecting the deviation of the incident light;
Detect deviations from part of the output extracted by
CCD (solid-state image sensor), photodiode, PSD
a photo sensor 22 consisting of a photo sensor 22, a comparator circuit 24 that compares the output of the photo sensor 22 with a signal with no deviation stored in the memory 23 in advance and outputs a deviation amount h, and a pulse number calculated from the output of the comparator circuit 24. It consists of a calculation section 25 that produces a corresponding output, and the pulse generator 20 that outputs a pulse signal based on the output of the calculation section 25, and the output from the pulse generator 20 is sent to the moving device 16. Note that 26 is an encoder and 27 is a filter.

The operation of the above configuration will be explained.

Using a urea crystal as the nonlinear optical crystal 5,
It is assumed that this crystal 5 is excited with a laser beam of 355 nm. When the rotation angle (θ) of the crystal 5 is 90 degrees, that is, when the incident optical axis 7 and the incident plane of the crystal 5 are perpendicular, the excitation light 7 is transmitted through the incident window 10, the matching oil 9, the crystal 5, and the output. Go straight through window 11 and pass through. At this time, two lights of 500 nm and 1230 nm, which are different from the 355 nm laser light, are generated by the crystal 5, and a straight laser light 7a is output as shown by the dotted line in FIG.

Here, the stepping motor 14 of the azimuth rotation device 12 is rotated by a signal from the rotation angle control section 15,
When the crystal 5 is azimuthally rotated to a rotation angle (θ) smaller than 90 degrees, the excitation light 7 is reflected by the solid line in FIG. The laser beam 7b is refracted as shown in FIG.
It outputs as a laser beam 7c parallel to . At this time, in response to continuous changes in the rotation angle (θ) of the crystal 5, the wavelengths of the two lights change continuously as shown by characteristic lines e and o in FIG. 5.

Here, a part of the output from the optical parametric oscillator 6 is sent to the photo sensor 22 by the half mirror 21, the position of the optical axis is detected, and the detected value is sent to the comparison circuit 24. The comparison circuit 24 receives data when there is no optical axis deviation from the memory 23, compares it with the output of the optical axis deviation caused by the rotation of the crystal 5, and outputs a signal corresponding to the amount of deviation h. When this shift amount h becomes large enough to cause the incident light to deviate from the incident surface of the crystal 5, a corresponding number of pulses is output from the calculation unit 25 and further sent to the linear pulse motor 18 of the moving device 16 via the pulse generator 20. . Then, the linear drive table 17 is moved on the linear guides 19, 19 by the linear pulse motor 18 to correct the deviation of the incident light.

In the embodiment described above, the amount of deviation h is obtained by comparing the detected value of the deviation of the optical axis on the output side by the photo sensor 22 with the data stored in the memory 23, and the amount of deviation h is
When the value exceeds a certain value, the moving device 16 is driven to correct it. However, since there is a predetermined relationship between the rotation angle control signal from the rotation angle control section 15 and the deviation of the incident light from the crystal 5, it can be known in advance.
A signal from the rotation angle control section 15 may be sent to the calculation section 25, and when the rotation angle (θ) reaches a predetermined value, the moving device 16 may be driven to perform correction.

In the embodiment described above, the direction of movement by the moving device 16 is perpendicular to the optical axis 7, but the direction is not limited to the direction perpendicular to the optical axis 7 as long as it intersects with the optical axis 7.

"Effects of the Invention" Since the present invention is configured as described above, even if the incident light deviates from the incident surface of the crystal, the crystal is moved by the moving device to correct the deviation, and the matching conditions of the incident light are adjusted. It is possible to obtain stable output light without loss of power density.

In addition, since the correction is performed automatically, the entire device can be reliably protected from dust and dust, and burn-in and damage to mirrors, lenses, crystals, etc., and reduction in oscillation efficiency can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of a wavelength tunable laser device according to the present invention, FIG. 2 is a cross-sectional view of the interior of the optical parametric oscillation unit, FIG. 3 is an explanatory diagram of a conventional device, and FIG. 4 5 is an explanatory diagram showing the relationship between the nonlinear optical crystal and the incident light, and FIG. 5 is a characteristic diagram showing the relationship between the azimuth rotation angle (θ) and the wavelength of the output light. DESCRIPTION OF SYMBOLS 1... Collimator lens, 2, 3... Reflection mirror, 4... Rotating table, 5... Nonlinear optical crystal, 6... Optical parametric oscillation unit, 7... Incident light, 8... Container, 9... Matching oil, 10
... Entrance window, 11 ... Output window, 12 ... Azimuth rotation device, 14 ... Stepping motor, 15 ... Rotation angle control section, 16 ... Movement device, 17 ... Linear drive table, 18 ... Linear Pulse motor, 1
9...Linear guide, 20...Pulse generator, 2
1...Half mirror, 22...Photo sensor, 2
3...Memory, 24...Comparison circuit, 25...Arithmetic unit, 26...Encoder, 27...Filter.

Claims (1)

[Scope of Claims] 1. In an optical parametric oscillator that performs phase matching by rotating the orientation of a nonlinear optical crystal using a crystal orientation rotation device, the nonlinear optical crystal is rotated within a plane rotated by the crystal orientation rotation device. A wavelength tunable laser device comprising a moving device for moving in a direction intersecting incident light. 2. The moving device is provided in claim 1, in which a linear drive table is movably provided on a linear guide provided in a direction intersecting the optical axis, and a crystal orientation rotation device is placed on the linear drive table. wavelength tunable laser device.