JP2013069931A - Laser device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser device with improved light intensity and a control method thereof.SOLUTION: There is provided a laser device which comprises a first laser, a second laser, an external resonator, and a control unit. The first laser emits a first laser beam. The second laser emits a second laser beam. The first laser beam and the second laser beam are made incident to the external resonator. The control unit controls a resonant wavelength of the external resonator to resonate the external resonator to the first laser beam and controls the second laser to resonate the second laser beam to the external resonator.

Description

  Embodiments described herein relate generally to a laser device and a control method thereof.

Since laser light is excellent in monochromaticity and interference, it is used as inspection light for sensors. Laser light is excellent in directivity and convergence, can concentrate light energy in a narrow area, and is used as a light source for processing materials or chemically reacting or decomposing substances.
For example, laser light in the mid-infrared region can be emitted by, for example, a quantum cascade laser (QCL) using subband transition. However, since QCL has a small oscillation output, when used as a light source for inspection light or chemical reaction, the light intensity may not be sufficient.

JP 2007-212212 A

  Embodiments of the present invention provide a laser device with improved light intensity and a control method thereof.

  According to the embodiment, a laser device including a first laser, a second laser, an external resonator, and a control unit is provided. The first laser emits a first laser beam. The second laser emits a second laser beam. The first laser beam and the second laser beam are incident on the external resonator. The control unit controls the resonance frequency of the external resonator to resonate with the first laser beam, and controls the second laser to resonate the second laser beam with the external resonator.

1 is a schematic view illustrating a laser device according to a first embodiment. It is a schematic diagram which illustrates the laser apparatus which concerns on 2nd Embodiment. It is a schematic diagram which illustrates the laser apparatus which concerns on 3rd Embodiment. 9 is a flowchart illustrating a laser device control method according to a fourth embodiment. 12 is a flowchart illustrating a laser device control method according to a fifth embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings. The drawings are schematic or conceptual, and the shape of each part, the relationship between vertical and horizontal dimensions, the size ratio between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings. Further, in the present specification and each drawing, the same reference numerals are given to the same elements as those described above with reference to the previous drawings, and detailed description thereof will be omitted as appropriate.

First, the first embodiment will be described.
FIG. 1 is a schematic view illustrating a laser device according to the first embodiment.
The laser device 1 receives a first laser 2 that emits a first laser beam IL1, a second laser 3 that emits a second laser beam IL2, and first and second laser beams IL1 and IL2. And an external resonator 4, and a control unit 5 that controls the second laser 3 and the external resonator 4. The laser device 1 also includes a mirror 6 and a polarizing prism 7 that cause the first laser beam IL1 and the second laser beam IL2 to enter the external resonator 4. The laser device 1 illustrated in FIG. 1 is an external resonator type laser device.

  The first laser 2 is, for example, QCL, and emits first laser light in the mid-infrared region of, for example, a wavelength of 10 μm. The first laser light is linearly polarized light, and is applied to the polarization beam splitter 7 through the mirror M1 so as to be P-polarized light. The first laser beam IL1 passes through the polarization beam splitter PBS1 and enters the external resonator 4.

  The second laser 3 is, for example, QCL, and emits second laser light in the mid-infrared region of, for example, a wavelength of 10 μm. The second laser light is linearly polarized light and is applied to the polarization beam splitter 7 so as to be S-polarized light. The second laser light is reflected by the polarization beam splitter 7 and enters the external resonator 4. Thus, the first laser beam and the second laser beam are linearly polarized in directions orthogonal to each other. Further, the wavelength of the first laser beam and the wavelength of the second laser beam are substantially the same.

  The external resonator 4 includes a pair of mirrors 8 and 9 and a piezoelectric element 10 provided on the mirror 9. The pair of mirrors 8 and 9 is constituted by, for example, a concave mirror having a reflectance of 99% or more. The output-side mirror 9 can be moved with respect to the input-side mirror 8 by controlling the voltage V10 supplied to the piezoelectric element 10. As described above, the external resonator 4 can change the resonance wavelength by controlling the voltage V <b> 10 supplied to the piezoelectric element 10.

The control unit 5 includes a polarization beam splitter 11, a first photodetector 12, a second optical transformer 13, a first controller 14, and a second controller 15. Yes.
The polarization beam splitter 11 makes the first laser beam IL1 and the second laser beam IL2 transmitted through the external resonator 4 enter. The first laser beam IL1 irradiated to the polarization beam splitter 11 with P-polarized light is transmitted through the polarization beam splitter 11, and is incident on the first photodetector 12 as transmitted light OL1. The second laser light IL2 irradiated with S-polarized light to the polarizing beam splitter 11 is reflected by the polarizing beam splitter 11, and is incident on the second photodetector 13 as reflected light OL2.

  The first photodetector 12 and the second photodetector 13 are, for example, photodetectors using a photoconductor whose electrical resistance changes according to incident light OL1 and OL2, or, for example, photo It is a diode. The first photodetector 12 converts the transmitted light OL1 transmitted through the polarization beam splitter 11 into an electric signal V1. The second photodetector 13 converts the reflected light OL2 reflected by the polarization beam splitter 11 into an electric signal V2.

  The first controller 14 is, for example, a PID (Proportional Integral Derivative) controller, and controls the resonance wavelength of the external resonator 4. The first controller 14 receives the electrical signal V1 output from the first photodetector 12, controls the voltage V10 supplied to the piezoelectric element 10 of the external resonator 4, and causes the external resonator 4 to The first laser beam IL1 is resonated. The intensity of the transmitted light OL1 transmitted through the external resonator 4 is maximized when the external resonator 4 resonates with the first laser light. Therefore, the external resonator 4 can be made to resonate with the first laser light by controlling the external resonator 4 so that the electric signal output from the first photodetector 12 is maximized.

  The second controller 15 is a PID controller, for example, and controls the oscillation wavelength of the second laser 3. The second controller 15 receives the electric signal V2 output from the second photodetector 13, and controls at least one of the current supplied to the second laser 3 and the temperature of the second laser 3. Thus, the wavelength of the second laser beam IL2 is caused to resonate with the external resonator 4. Similar to the first controller 14, the second controller 15 controls the second laser IL2 so that the electrical signal V2 output from the second photodetector 13 is maximized. As a result, the wavelength of the first laser beam IL1 and the wavelength of the second laser beam IL2 are substantially equal.

  In addition, compared with the wavelength of 1st laser beam IL1 and 2nd laser beam IL2, the mechanical space | interval of the mirrors 8 and 9 in the external resonator 4 is very long. Therefore, the optical distance between the mirrors 8 and 9 of the external resonator 4 is n times the transmitted light OL1 and m times the reflected light OL2. Here, n and m are sufficiently large integers, and m is not necessarily n. As a result, the wavelength of the first laser beam IL1 and the wavelength of the second laser beam IL2 may be slightly different. However, the wavelength difference is small with respect to the wavelengths of the first and second laser beams IL1 and IL2, and the first laser beam IL1 and the second laser beam IL2 have substantially the same wavelength.

  Moreover, the 1st controller 14 and the 2nd controller 15 can operate | move independently, for example, can operate | move simultaneously. Further, for example, the first controller 14 can be operated first, and the second controller 15 can be operated later. Furthermore, for example, the gain of the first controller 14 may be set larger than the gain of the second controller 15 and operated simultaneously.

  In the present embodiment, since the first laser beam and the second laser beam having substantially the same wavelength are incident on the external resonator 4, the first laser beam or the second laser beam is incident. In comparison, the effective light intensity in the external resonator 4 can be increased.

For example, when the irradiated object 16 introduced into the external resonator 4 is a gas that reacts or decomposes when irradiated with laser light, the irradiated object 16 can be irradiated with stronger light. 16 reaction and decomposition | disassembly can be accelerated | stimulated conventionally.
Further, when the irradiated object 16 is a substance to be inspected, it is possible to inspect with higher sensitivity than before by increasing the light intensity of the laser beam to be irradiated. Specifically, for example, when the irradiated object 16 is a gas having an absorption peak with respect to light in the mid-infrared region, the irradiated object 16 can be inspected with higher detection sensitivity than before.
The irradiated body 16 may be allowed to flow into and pass through the external resonator 4 or may be confined in the external resonator 4.

FIG. 2 is a schematic view illustrating a laser device according to the second embodiment.
As shown in FIG. 2, the laser device 1a is different from the laser device 1 according to the first embodiment in that a measuring instrument 17 is added. The other configuration is the same as that shown in FIG.

  The measuring instrument 17 is an oscilloscope, for example, and is a voltmeter, for example. The measuring instrument 17 measures at least one of the electrical signal V1 output from the first photodetector 12 and the electrical signal V2 output from the second photodetector 13.

  For example, when the irradiated object 16 as the inspection object is introduced into the external resonator 4, the measuring instrument 17 emits light at the wavelengths of the first and second laser beams IL <b> 1 and IL <b> 2 of the irradiated object 16. Absorption can be measured. As a result, the composition and molecular structure of the irradiated object 16 can be specified with high sensitivity. In addition, the to-be-irradiated body 16 in this case is, for example, a gas having an absorption spectrum peak in the middle infrared region.

  Also in the present embodiment, since the first laser light and the second laser light having substantially the same wavelength are incident on the external resonator 4, the first laser light or the second laser light is incident. Compared with the case, the effective light intensity in the external resonator 4 can be increased.

FIG. 3 is a schematic view illustrating a laser device according to the third embodiment.
As shown in FIG. 3, the laser device 1 b is different from the laser device 1 a according to the second embodiment in the configuration of the control unit 5. That is, in the present embodiment, a control unit 5a is provided instead of the control unit 5 in the second embodiment. The configuration other than the control unit of the laser apparatus according to the present embodiment is the same as the configuration illustrated in FIG.

The control unit 5a is different from the control unit 5 in the first and second embodiments in that a wavelength control unit 18 is added.
The wavelength control unit 18 controls the oscillation wavelength of the first laser 2 by controlling at least one of the current supplied to the first laser 2 and the temperature of the first laser 2, so that the first laser 2 is controlled within a certain range. The wavelength of one laser beam IL1 is changed continuously or intermittently.

  For example, the wavelength control unit 18 can generate a triangular wave and continuously increase the current supplied to the first laser 2. The wavelength control unit 18 may be a computer, for example, and may control the oscillation wavelength of the first laser 2 to a predetermined value according to a stored program. The wavelength controller 18 can also control the first controller 14, the second controller 15, and the measuring instrument 17. In this case, the wavelength controller 18 controls the first controller 14 and the second controller 15, and further continuously changes the oscillation wavelength of the first laser 2, so that the absorption spectrum of the irradiated object 16 is obtained. Can be measured.

  Also in the present embodiment, since the first laser light and the second laser light having substantially the same wavelength are incident on the external resonator 4, the first laser light or the second laser light is incident. Compared with the case, the effective light intensity in the external resonator 4 can be increased.

Next, a fourth embodiment will be described.
FIG. 4 is a flowchart illustrating a laser device control method according to the fourth embodiment.
In FIG. 4, when the first laser 2 emits the first laser beam IL1 having a target wavelength, the external resonator 4 and the second laser 3 are controlled, and the external resonator 4 is controlled. Represents a control method for causing the first and second laser beams IL1 and IL2 to resonate.

As shown in FIG. 4, the external resonator 4 is resonated with the first laser beam IL1 (step S11).
For example, the first laser beam IL1 is incident on the external resonator 4, and the resonance wavelength of the external resonator 4 is controlled so that the intensity of the transmitted light OL1 of the external resonator 4 is maximized. For example, the resonance wavelength of the external resonator 4 is controlled by controlling the voltage V10 supplied to the piezoelectric element 10 and adjusting the mechanical distance between the mirrors 8 and 9 of the external resonator 4.

Further, the second laser beam IL2 is caused to resonate with the external resonator 4 (step S12).
For example, the second laser light IL2 is incident on the external resonator 4 and the current supplied to the second laser 3 and the second laser 3 so that the intensity of the reflected light OL2 of the external resonator 4 is maximized. Control at least one of the temperatures.

  Note that the step of resonating the external resonator 4 with the first laser beam IL1 (step S1) and the step of resonating the second laser beam IL2 with the external resonator 4 (step S2) are independent and at the same time. May be executed. Alternatively, the external resonator 4 may be first resonated with the first laser beam IL1, and then the second laser beam IL2 may be resonated with the external resonator 4.

  In the present embodiment, since the first laser beam and the second laser beam incident on the external resonator 4 are controlled to have substantially the same wavelength, the first laser beam or the second laser beam is incident. Compared with the case where the effective light intensity in the external resonator 4 can be increased.

FIG. 5 is a flowchart illustrating a laser device control method according to the fifth embodiment.
In FIG. 5, a laser that continuously changes the wavelengths of the first laser beam IL1 and the second laser beam IL2 within a certain range while causing the external resonator 4 to resonate with the first and second laser beams IL1 and IL2. The control method of an apparatus is represented.

As shown in FIG. 5, first, the wavelength of the first laser beam IL1 is set to an initial value (step S10).
For example, the current supplied to the first laser 2 and the temperature of the first laser 2 are controlled to the initial values.
Next, the external resonator 4 is resonated with the first laser beam IL1 (step S11). Further, the second laser beam IL2 is caused to resonate with the external resonator 4 (step S12).
Steps S11 and S12 are the same as steps S11 and S12 shown in FIG. 4, respectively, and detailed description thereof is omitted.

  Next, measurement values are recorded at the controlled wavelengths of the first and second laser beams IL1 and IL2 (step S13). For example, a measured value obtained by measuring at least one of the electric signals V1 and V2 output from the first and second photodetectors 12 and 13 via the measuring instrument 17 is stored in the wavelength control unit 18.

Next, it is determined whether the measurement is completed (step S14). For example, it is determined whether the wavelength of the first laser beam IL1 has reached the final value.
When it is determined that the measurement is finished (step S14: YES), the process is finished.
When it is determined that the measurement has not ended (step S14: NO), the wavelength of the first laser beam IL1 is increased by an increment value (step S15), and the process returns to step S11.

  Also in this embodiment, since the first laser beam and the second laser beam incident on the external resonator 4 are controlled to have substantially the same wavelength, the first laser beam or the second laser beam is incident. Compared with the case where the effective light intensity in the external resonator 4 can be increased.

  Moreover, in this embodiment, since the oscillation wavelength of the 1st laser 2 is changed continuously, the absorption spectrum of the to-be-irradiated body 16 can be measured.

  Note that the control methods according to the fourth and fifth embodiments can be implemented as hardware as a control unit, and can also be implemented as software as a computer program. The control method can also be recorded on a computer-readable medium as a computer program.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1, 1a, 1b ... Laser apparatus, 2 ... 1st laser, 3 ... 2nd laser, 4 ... External resonator, 5, 5a ... Control part, 6 ... Mirror, 11, 11 ... Polarizing beam splitter, 8, DESCRIPTION OF SYMBOLS 9 ... Mirror, 10 ... Piezoelectric element, 12 ... 1st photodetector, 13 ... 2nd photodetector, 14 ... 1st controller, 15 ... 2nd controller, 16 ... Subject to be irradiated, 17 ... Measuring instrument, 18 ... Wavelength controller

Claims (5)

A first laser that emits a first laser beam;
A second laser that emits a second laser beam;
An external resonator on which the first laser beam and the second laser beam are incident;
A control unit that controls a resonance wavelength of the external resonator to resonate with the first laser beam, and controls the second laser to resonate the second laser beam with the external resonator;
A laser apparatus comprising: The external resonator is
A pair of mirrors;
A piezoelectric element provided on at least one of the pair of mirrors;
Have
The laser apparatus according to claim 1, wherein the control unit controls the piezoelectric element.   The laser device according to claim 1, wherein the control unit controls at least one of a current supplied to the second laser and a temperature of the second laser.   The laser device according to claim 1, wherein the first laser beam and the second laser beam are linearly polarized light orthogonal to each other. A method of controlling a laser device having a first laser, a second laser, and an external resonator,
Controlling the external resonator to resonate the external resonator with laser light emitted from the first laser;
A method of controlling a laser device, wherein the second laser is controlled to cause the external resonator to resonate the second laser light emitted from the second laser.

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