JPS63184383A - Wavelength calibrating apparatus for wavelength-tunable laser - Google Patents

Abstract

PURPOSE:To facilitate calibrating the wavelength scale of a wavelength reader for an output light and adjusting a light axis by a light axis regulator simultaneously by introducing a calibration light to the position of the light axis regulator in the latter stage of an optical parametric oscillator through a half mirror. CONSTITUTION:A continuous laser beam with a known wavelength, for instance the 2nd harmonic of an Nd-YAG laser device which is a laser beam with a wavelength of 530 nm, is generated and reflected and refracted by a half mirror 10 and transmitted through a light axis regulator 11 to a spectroscope 7. In the spectroscope 7, if there is a difference between a read sc ale value and the real wavelength of an inputted calibration light, the difference is calibrated. After the calibration in the spectroscope 7, a control signal is outputted and the crystal 5 of an optical parametric oscillator 6 is turned to vary the wavelength of the output light of the oscillator 6 so as to make the wavelength 530 nm which is equal to the wavelength of the calibration light in the spectroscope 7. As a discrepancy (d) of the light axis 8 of the output light is produced by the turn of the crystal 5, the calibration light is inputted so as to coincide with the cross point of the light from a wavelength calibration light source generator 18 axis 8 which is moved by the discrepancy (d) and the half mirror 10. Then a control signal is outputted from a light axis adjustment driving circuit 24 and the dielectric 17 of the light axis regulator 11 to adjust the light axis.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to an optical parametric oscillator using a nonlinear optical crystal, in which wavelength scale calibration of a wavelength reading device for output light and optical axis adjustment by an optical axis correction device are performed. The present invention relates to a wavelength calibrating device for a wavelength tunable laser that can be used at the same time.

"Prior Art" Generally, wavelength tunable laser systems include a dye laser system, a temperature tuning system, an optical parametric oscillation system, an alexandrite laser system, and the like. Among these, the wavelength tunable laser device using the optical parametric oscillation method has a collimator lens (1), an input reflection mirror (
2) An optical parametric oscillator (6) is composed of an output reflection mirror (3), a nonlinear optical crystal (5) placed on a rotary table (4), and the like.

In such a configuration, for example, 355n is used as the excitation light.
When a pulsed laser of m is input, a nonlinear optical crystal (5)
Light with a wavelength different from the original wavelength (355 nm) is generated. When the rotation angle (θ) is 90 degrees, 500 nm and 12
Two lights of 30 nm are generated. Rotation angle of crystal (5) (
0), the wavelengths of the two lights change continuously in the direction of approaching each other. Since these lights are weak, they are amplified by resonance between the two input and output reflecting mirrors (2) and (3), and then output.

``Problems to be Solved by the Invention'' In order to calibrate the wavelength of the output light of the optical parametric oscillator to the correct value, as shown in Figure 2, a spectroscope must be calibrated in advance using a known light source as a wavelength reading device. (7) is used to detect and calibrate the difference between the actual reading scale of this spectrometer (7) and the correct wavelength.

However, when the rotation angle (O) of the nonlinear optical crystal (5) is changed, the oscillation wavelength changes, so that the optical axis (8) of the output light from the crystal (5) also shifts (cl). When using this output light for optical system adjustment or various measurements, the optical axis (8
) shifts, the measurement position with respect to the object to be measured changes, which is undesirable. Therefore, in the past, correction of this optical axis deviation was performed separately from wavelength scale calibration of the spectrometer, which required a great deal of time and effort for correction and adjustment. Furthermore, since the output light of the optical parametric oscillator (16) is a low-frequency pulsed laser beam, there is a problem in that it is extremely difficult to adjust the optical system using this low-frequency pulsed laser beam.

``Means for Solving the Problems j'' In view of the above-mentioned points, the present invention enables the wavelength scale calibration of the wavelength reading device and the adjustment of the optical axis correction of the optical system to be performed at the time of wavelength calibration. , an optical parametric oscillator in which a nonlinear optical crystal is excited with a pulsed laser beam, an output light having a wavelength different from that of the input light is obtained from the crystal, and the wavelength of the output light is changed depending on the rotation angle of the crystal. A wavelength calibration light source introduction half mirror, an optical axis correction device, and a wavelength reading device are arranged in this order on the output side of the device.

"Operation" Calibration light consisting of continuous light of different wavelengths is introduced by a half mirror to coincide with the output optical axis of the optical parametric oscillator, and the wavelength scale of the spectrometer as a wavelength reading device is calibrated. The output light from the optical parametric oscillator is read by a calibrated spectrometer, and the rotation angle of the crystal is controlled so that the reading scale value of the spectrometer matches the calibrated −3=wavelength of the light.

Since this rotation of the crystal causes a shift in the optical axis of the output light, continuous calibration light is introduced through a half mirror, and the optical axis is corrected by an optical axis correction device. The rotation angle of the crystal and the optical axis correction value at this time are stored in the memory of the CPU. Next, the same operation is repeated several times using calibration light of different wavelengths, and each time is stored in the memory of the CPU. Using the data calibrated as described above, analogous data for wavelengths other than the calibration light is calculated and stored in the memory of the CPU.

Next, during normal use, the half mirror is removed from the optical axis. When the crystal is rotated to obtain output light of a desired wavelength, the optical axis is automatically corrected in a certain relationship with the rotation angle based on data stored in the memory in advance.

"Example" Hereinafter, one embodiment of the present invention will be described based on the drawings.

(6) is an optical parametric oscillator (hereinafter referred to as OP○)
As shown in Figure 2, this OPO (6) consists of a collimator lens (1), an input reflection mirror (2), and an output reflection mirror (
3), basically consists of a nonlinear optical crystal (5) on a rotary table (4).

on the optical axis (8) on the output side of ○P○ (6) with
- On the Y stage (9), there is a half mirror (10), an optical axis correction device (11), and a spectrometer (as a wavelength reading device).
7) and output light intensity detectors (12) are sequentially provided.

The half mirror (10) is provided with a linear table (14) that is movable on a linear guide (13) perpendicular to the optical axis (8).
4) is configured to be moved by a motor (15).

The optical axis correction device (11) is constructed by attaching a dielectric material (17) such as transparent glass to a rotary table (16). Further, a wavelength calibration light source generator (18) is provided facing the half mirror (10).

Next, (19) is the CPU, and this CPU (19)
is connected to a keyboard (20) as an input device, a ROM (21,) that stores programs, etc., and a RAM (22) that stores data, and further includes an X-Y stage drive circuit (23), an optical axis Correction drive circuit (24), half mirror drive circuit (25), rotation angle control drive circuit (2
6) are combined.

The operation of the above configuration will be explained.

A continuous laser beam whose wavelength is known in advance, for example, a 530 nm laser beam which is the second harmonic of an Nd-YAG laser device, is generated from a wavelength calibration light source generator (18), and is reflected and refracted by a half mirror (10). , optical axis correction device (11
) is transmitted to the spectrometer (7). In the spectrometer (7), if there is a difference between the value read on the scale and the true wavelength of the input calibration light, this is calibrated.

After calibrating the spectrometer (7), a control signal is output from the rotation angle control drive circuit (26) via the CPU (19) in response to an input signal from the keyboard (20), and the O P O (6)
rotate the crystal (5) to change the wavelength of its output light,
The wavelength is set to 530 nm, the same as the calibration light, using a spectrometer (7).

The data of the rotation angle (θ) at this time is RAM (22)
to be memorized. The rotation of the crystal (5) causes a shift (d) in the optical axis (8) of the output light, so the wavelength Calibration light is matched and inputted from the calibration light source generator (18). Then, in response to input signals from the keyboard (20), a control signal is output from the optical axis correction drive circuit (24) via the CPU (19), and the optical axis correction device (11)
) is rotated to correct the optical axis. The optical axis correction data at this time is also stored in RAM (22). In addition, in order to completely match the output light from ○P○ (6) in the half mirror (10) with the calibration light, the keyboard (20), CPU (19), and X-Y stage drive circuit (23 ) through the X-Y stage (9)
, and the position data when the output detected by the detector (12) is maximum is stored in the RAM (22) via the CPU (19).

The above operations complete calibration of the scale and adjustment of the optical axis using the 530 nm calibration light. Next, similar operations are performed using He-Ne laser calibration light of another wavelength, for example, 632.8 nm, to obtain rotation angle data of the crystal (5) and optical axis correction device (11) and the X-Y stage (9). The movement data of 514n is stored in RAM (22), and further, for example, 514n
A similar operation is performed using the argon ion laser calibration light of m, and the data is stored in RAM (22).

As described above, using each data obtained using a plurality of calibration lights having different wavelengths, analogous data for wavelengths other than the calibration light is calculated and stored in the RAM (22).

After the data of the entire range of wavelengths changed by the crystal (5) is calculated and stored in the RAM (22), the CPU (1
9), a signal is output from the half mirror drive circuit (25) to drive the motor (15) and drive the linear table (14).
The half mirror (10) fixed to the lens is removed from the optical axis (8) to enter the normal use state.

In the above examples, continuous wave light was used as the calibration light, but
In order to separate the calibration light from stray light which is external noise, the calibration light may be modulated into high frequency light of approximately IKHz using a chopper or the like. Furthermore, when using spectrum light from a discharge tube such as a hollow cathode lamp as a calibration light source, it may be electrically continuous or amplitude modulated. in this case,
In the light receiving section of the spectrometer (7), only the light tuned to the calibration light is extracted by a filter circuit.

"Effects of the Invention" As described above, the present invention introduces the calibration light through a half mirror to the position of the optical axis correction device after the optical parametric oscillator. Numerical calibration and adjustment of optical axis changes due to wavelength changes can be performed using the same calibration light.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of a wavelength calibrating device for a wavelength tunable laser according to the present invention, and FIG. 2 is an explanatory diagram of a conventional wavelength calibrating device. (4)...rotary table, (5)...○Po crystal,
(6)...Optical parametric oscillator (OP○), (7
)...Wavelength reading device (spectroscope), (8)...Optical axis, (11)...Optical axis correction device, (12)...Detector, (18)...Wavelength calibration Light source generator for (19)...
・CPU, (20)...Keyboard, (21)...
ROM, (22)...RAM. Applicant Hamamatsu Photonics Co., Ltd. Procedural Amendment (Chief) June 9, 1988

Claims (3)

[Claims] (1) Excite a nonlinear optical crystal with pulsed laser light, obtain output light from this crystal with a wavelength different from that of the input light, and
In the optical parametric oscillator in which the wavelength of the output light is changed by the rotation angle of the crystal, a light source introduction half mirror for wavelength calibration, an optical axis correction device, and a wavelength reading device are arranged in sequence on the output side of the crystal. A wavelength calibration device for a wavelength tunable laser, characterized in that: (2) A wavelength calibrating device for a wavelength tunable laser according to claim 1, wherein the wavelength reading device comprises a spectrometer. (3) A wavelength calibrating device for a wavelength tunable laser according to claim 1, wherein the light source introduction half mirror for wavelength calibration is removed from the optical axis after calibration.