JP5504013B2 - Laser light source calibration device - Google Patents

Description

  The present invention relates to a laser light source calibration apparatus.

Conventionally, a reference laser light source that emits a laser beam that is a reference for calibration, a target laser light source that emits a laser beam that is a calibration target, a reference laser light source, and an optical axis of the laser light emitted from the target laser light source An optical system that outputs the same and a frequency counter that measures the frequency by converting the laser light output from the optical system into an electrical signal, and the measurement result by the frequency counter, that is, the reference laser light source and the target laser light source A laser light source calibration device that calibrates the frequency of a target laser light source based on a frequency difference (beat frequency) is known (see, for example, Patent Document 1).
In the calibration method of a laser device (laser light source) described in Patent Document 1, a reference laser (reference laser light source), a calibration target laser (target laser light source), two mirrors (optical system), and a detector as a frequency counter. And a counter, and calibrates the frequency of the laser to be calibrated.

FIG. 8 is a schematic block diagram showing a conventional laser light source calibration apparatus 100.
As shown in FIG. 8, the laser light source calibration apparatus 100 includes a reference laser light source 110, a target laser light source 120, an optical system 130, and a frequency counter 140, and calibrates the frequency of the target laser light source 120. is there.
The optical system 130 reflects the laser beam L1 emitted from the reference laser light source 110, reflects a part of the laser light L1, and transmits a part of the laser light L2 emitted from the target laser light source 120. And a half mirror 132 that outputs the laser beams L1 and L2 with the same optical axis. In FIG. 8, the optical path of the laser beam is indicated by a solid line.

The frequency counter 140 includes a conversion unit 141 that converts laser light L3 (hereinafter referred to as a beat signal) output from the optical system 130 into an electrical signal, and a counter unit 142 that measures the frequency (beat frequency) of the beat signal. Prepare.
The counter unit 142 measures the beat frequency by counting the number of pulses of the beat signal within the gate time corresponding to the input gate signal (arrow G in FIG. 8).
Therefore, if the center frequency of the laser beam L1 is known, the center frequency of the laser beam L2 can be calibrated based on the beat frequency measured by the frequency counter 140.

Specifically, the frequency counter 140 repeatedly measures the beat frequency, and the calibration apparatus 100 determines the center frequency of the laser light L2 based on the center frequency of the laser light L1 and the average value of the measurement results by the frequency counter 140. The frequency of the target laser light source 120 is calibrated by calculating. In addition, the calibration apparatus 100 evaluates the frequency stability of the laser light L2 based on the variation in the measurement result by the frequency counter 140.
Here, since it is necessary to use a laser light source with high frequency stability as the reference laser light source 110, for example, an iodine stabilized laser light source that modulates and emits laser light having a predetermined center frequency with a predetermined modulation signal. Is used.

FIG. 9 is a graph showing the laser light L1 emitted from the reference laser light source 110 and the modulation signal M1 of the reference laser light source 110. 9A is a graph showing the center frequency of the laser light L1, FIG. 9B is a graph showing the modulation signal M1, and FIG. 9C is a graph in which the modulation signal M1 is superimposed. 5 is a graph showing the laser beam L1. In FIG. 9, the vertical axis represents the size of the laser beam L1 or the modulation width of the modulation signal M1, and the horizontal axis represents time.
As shown in FIG. 9, the reference laser light source 110 composed of an iodine stabilized laser light source detects the saturated absorption line of iodine by modulating the laser light with the modulation signal M1, and sets the center frequency of the laser light L1. Since the light is stabilized and emitted, the modulation signal M1 is superimposed on the laser light L1 (see FIG. 9C). In FIG. 9, the center frequency of the laser beam L1 is f1, the modulation width of the modulation signal M1 is Mw1, and the modulation frequency of the modulation signal M1 is Mf1.

  In such a laser light source calibration apparatus 100, if the target laser light source 120 is an iodine stabilized laser light source similar to the reference laser light source 110, the beat frequency may not be constant. In this case, the target laser light source 120 There is a problem that the frequency cannot be properly calibrated.

  FIG. 10 is a diagram illustrating a modulation signal and a beat signal in a state where the modulation width, the modulation frequency, and the phase of the modulation signals of the reference laser light source 110 and the target laser light source 120 are the same. FIG. 11 is a diagram illustrating a modulation signal and a beat signal in a state where the modulation width, modulation frequency, and phase of the modulation signals of the reference laser light source 110 and the target laser light source 120 do not match. FIGS. 10A and 11A are diagrams illustrating modulated signals, and FIGS. 10B and 11B are diagrams illustrating beat signals.

FIGS. 10 and 11 are an upper diagram in which the axis in the horizontal direction of the paper is the modulation width of the modulation signal, the axis in the depth direction of the paper is time, and the axis in the horizontal direction of the paper is the frequency. The figure below is a gain.
10 and 11, the center frequency of the laser beam L1 is f1, the center frequency of the laser beam L2 is f2, the modulation signal M1 is represented by the following equation (1), and the modulation signal M2 is represented by the following equation ( 2).

M1 = Mw1 · sin (2πMf1 + Mθ1) (1)
M2 = Mw2 · sin (2πMf2 + Mθ2) (2)

Specifically, when the modulation widths Mw1 and Mw2, the modulation frequencies Mf1 and Mf2, and the phases Mθ1 and Mθ2 of the modulation signals M1 and M2 match, the beat frequency is constant as shown in FIG. Therefore, the frequency of the target laser light source 120 can be appropriately calibrated. In FIGS. 10 and 11, the phases Mθ1 and Mθ2 are not shown.
However, when the modulation widths Mw1 and Mw2 of the modulation signals M1 and M2, the modulation frequencies Mf1 and Mf2, and the phases Mθ1 and Mθ2 do not match, the beat frequency varies and is constant as shown in FIG. Therefore, there is a problem that the measurement result by the frequency counter 140 varies and the frequency of the target laser light source 120 cannot be calibrated appropriately.

On the other hand, in the calibration method of the laser device described in Patent Document 1, variation in the measurement result by the counter is suppressed by synchronizing the modulation signals of the reference laser and the calibration target laser.
As another method, it is conceivable to suppress variation in measurement results by the frequency counter 140 by sufficiently increasing the gate time of the frequency counter 140.

Japanese Patent Laid-Open No. 2001-274483

  However, in the laser device calibration method described in Patent Document 1, the modulation signal of the reference laser is used as the modulation signal of the calibration target laser by using the modulation signal of the reference laser as the modulation signal of the calibration target laser. The modulation signal of the calibration target laser may not be optimal due to the influence of individual differences between the laser and the calibration target laser. In such a case, since the calibration target laser cannot exhibit sufficient performance, there is a problem that the frequency of the calibration target laser cannot be appropriately calibrated. Further, the laser device calibration method described in Patent Document 1 has a problem that the configuration of the calibration device becomes complicated in order to synchronize the modulation signals of the reference laser and the calibration target laser.

  Further, in the method of sufficiently increasing the gate time of the frequency counter 140, the frequency counter 140 performs measurement for a long time. For example, the measurement result varies depending on other factors such as the influence of temperature change. In such a case, there is a problem that the frequency of the target laser light source 120 cannot be properly calibrated.

  An object of the present invention is to provide a laser light source calibration apparatus capable of appropriately calibrating the frequency of a target laser light source that emits laser light to be calibrated.

The laser light source calibration apparatus according to the present invention includes a reference laser light source that emits a laser beam that is a calibration reference, a target laser light source that emits a laser light that is a calibration target, the reference laser light source, and the target laser light source. An optical system that outputs the laser light emitted from the optical system with the same optical axis, a conversion unit that converts the laser light output from the optical system into an electrical signal, and a frequency that is measured based on the electrical signal from the conversion unit and a frequency counter consists of counter unit which, based on a measurement result by the frequency counter, a calibration device for a laser light source for calibrating the frequency of the target laser light source, the reference laser light source, and the target laser The light source modulates and emits laser light having a predetermined center frequency with a predetermined modulation signal, and the modulation frequency of the modulation signal in the reference laser light source, A period detection unit for detecting a period corresponding to a difference between the modulation frequency of the modulation signal in the target laser light source and a signal generation unit for generating a gate signal of the frequency counter synchronized with the period detected by the period detection unit And the period detection unit is based on a carrier wave signal having a frequency corresponding to a difference between a center frequency of the laser light emitted from the reference laser light source and a center frequency of the laser light emitted from the target laser light source. An FM demodulator that demodulates the electrical signal from the converter by a frequency modulation method, a modulation frequency of the modulation signal in the reference laser light source, and a modulation frequency of the modulation signal in the target laser light source, whichever is higher An AM demodulator that demodulates a demodulated signal demodulated by the FM demodulator using an amplitude modulation method based on a carrier signal having a higher frequency, No. generation unit, based on the demodulated signal demodulated by the AM demodulator, characterized that you generate a gate signal of the frequency counter.

Here, since the reference laser light source and the target laser light source modulate and emit laser light having a predetermined center frequency with a predetermined modulation signal, the beat frequency corresponds to the modulation frequency of the modulation signal in the reference laser light source and the target It fluctuates at a period corresponding to the difference from the modulation frequency of the modulation signal in the laser light source. Therefore, the beat frequency can be measured in synchronization with the fluctuation of the beat frequency by generating the gate signal of the frequency counter synchronized with this cycle.
According to the present invention, since the calibration apparatus includes the period detection unit and the signal generation unit, the frequency of the target laser light source can be obtained with a simple configuration without using the modulation signal of the reference laser light source as the modulation signal of the target laser light source. Can be calibrated appropriately. The gate signal is synchronized with the period detected by the period detection unit, that is, the period corresponding to the difference between the modulation frequency of the modulation signal in the reference laser light source and the modulation frequency of the modulation signal in the target laser light source. The calibration device can measure the beat frequency in synchronization with the fluctuation of the beat frequency. Therefore, the calibration apparatus can suppress variation in the measurement result by the frequency counter, and can set an appropriate gate time as compared with the above-described method of sufficiently increasing the gate time of the frequency counter.

Further , according to the present invention, the period detection unit includes an FM (Frequency Modulation) demodulator and an AM (Amplitude Modulation) demodulator, and the signal generation unit is based on the demodulated signal demodulated by the AM demodulator. Thus, since the gate signal of the frequency counter is generated, the calibration device can appropriately calibrate the frequency of the target laser light source without using the modulation signal in the reference laser light source and the modulation signal in the target laser light source. Therefore, the calibration apparatus can appropriately calibrate the frequency of the target laser light source even when the modulation signal in the target laser light source is unknown.

The block schematic diagram which shows the calibration apparatus of the laser light source which concerns on one Embodiment of this invention. The graph which shows the fluctuation | variation of the beat frequency in the said embodiment. A graph in which a part of the graph showing fluctuations in beat frequency is rewritten with the vertical axis representing intensity and the horizontal axis representing time. The graph which shows the state which is demodulating the beat signal in the said embodiment with FM demodulator. The graph which shows the state which is demodulating with the AM demodulator the demodulated signal demodulated with the FM demodulator in the said embodiment. The graph which shows the gate signal of the frequency counter produced | generated in the signal production | generation part in the said embodiment. The graph which shows an example of the gate signal of the frequency counter produced | generated in a signal production | generation part. The block schematic diagram which shows the calibration apparatus of the conventional laser light source. The graph which shows the laser beam radiate | emitted from a reference | standard laser light source, and the modulation signal of a reference | standard laser light source. The figure which shows the modulation signal and beat signal of the state which the modulation | alteration width | variety, modulation frequency, and phase of the modulation | alteration signal of a reference | standard laser light source and an object laser light source correspond. The figure which shows the modulation signal and the beat signal of the state where the modulation | alteration width | variety, modulation frequency, and phase of the modulation | alteration signal of a reference | standard laser light source and a target laser light source do not correspond.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram showing a laser light source calibration apparatus 1 according to an embodiment of the present invention.
As shown in FIG. 1, a laser light source calibration apparatus 1 includes a reference laser light source 2 that emits laser light that serves as a calibration reference, a target laser light source 3 that emits laser light that is a calibration target, and a reference laser light source. 2 and an optical system 4 that outputs the laser light emitted from the target laser light source 3 with the same optical axis, and a frequency counter 5 that measures the frequency by converting the laser light output from the optical system 4 into an electrical signal. And gate signal generating means 6 for generating a gate signal of the frequency counter 5. The calibration device 1 calibrates the frequency of the target laser light source 3 based on the measurement result by the frequency counter 5, that is, based on the frequency difference (beat frequency) between the reference laser light source 2 and the target laser light source 3.

The reference laser light source 2 and the target laser light source 3 are configured by an iodine stabilized laser light source that modulates and emits laser light having a predetermined center frequency with a predetermined modulation signal.
The optical system 4 reflects the laser beam L1 emitted from the reference laser light source 2, reflects a part of the laser light L1, and transmits a part of the laser light L2 emitted from the target laser light source 3. And a half mirror 42 that outputs the laser beams L1 and L2 with the same optical axis. In FIG. 1, the optical path of the laser beam is indicated by a solid line.
The frequency counter 5 includes a conversion unit 51 that converts laser light L3 (beat signal) output from the optical system 4 into an electrical signal, and a counter unit 52 that measures the frequency (beat frequency) of the beat signal.
The counter unit 52 measures the beat frequency by counting the number of beat signal pulses within the gate time corresponding to the gate signal generated by the gate signal generating means 6.

FIG. 2 is a graph showing fluctuations in beat frequency. In FIG. 2, the vertical axis is the fluctuation of the beat frequency from the center frequency, and the horizontal axis is time. Here, the center frequency of the beat frequency is a difference (| f1-f2 |) between the center frequency f1 of the laser beam L1 and the center frequency f2 of the laser beam L2. In FIG. 2, the modulation width Mw1 of the modulation signal M1 of the reference laser light source 2 is 6.5 MHz, the modulation frequency Mf1 is 1000 Hz, the modulation width Mw2 of the modulation signal M2 of the target laser light source 3 is 7 MHz, and the modulation frequency Mf2 Is simulated at 1005 Hz.
2A is a diagram in which the horizontal axis is 0 to 0.45 s, and FIG. 2B is a diagram in which the horizontal axis is 0 to 0.02 s. That is, FIG. 2B is an enlarged view of part of FIG.
As shown in FIG. 2A, the beat frequency is obtained by changing a long cycle fluctuation of 0.2 s (1 / | Mf1-Mf2 |) from ± 0.5 MHz (± | Mw1-Mw2 |) to ± 13. It is repeated in the range of 5 MHz (± | Mw1 + Mw2 |).
Further, as shown in FIG. 2B, the beat frequency repeats fluctuations with a short period of 1 / Mf2.

FIG. 3 is a graph obtained by rewriting a part of the graph showing the beat frequency variation with the vertical axis representing intensity and the horizontal axis representing time. 3A is a graph in which the region R1 in FIG. 2A is rewritten, and FIG. 3B is a graph in which the region R2 in FIG. 2A is rewritten.
In the region R1, as shown in FIG. 3A, the beat frequency repeats the fluctuation of the cycle of 1 / Mf2 in the range of ± | Mw1-Mw2 | with respect to the center frequency | f1-f2 |. In the region R2, as shown in FIG. 3B, the beat frequency repeats a fluctuation of 1 / Mf2 in a range of ± | Mw1 + Mw2 | with respect to the center frequency | f1-f2 |.

As shown in FIG. 1, the gate signal generation means 6 detects a period corresponding to the difference between the modulation frequency Mf1 of the modulation signal M1 in the reference laser light source 2 and the modulation frequency Mf2 of the modulation signal M2 in the target laser light source 3. A period detection unit 61 and a signal generation unit 62 that generates a gate signal of the frequency counter 5 synchronized with the period detected by the period detection unit 61 are provided.
The period detector 61 demodulates an electric signal based on the beat signal by a frequency modulation method based on a carrier wave signal having a frequency corresponding to the difference between the center frequency f1 of the laser light L1 and the center frequency f2 of the laser light L2. An FM demodulator based on a carrier signal having a higher frequency among the demodulator 611, the modulation frequency Mf1 of the modulation signal M1 in the reference laser light source 2, and the modulation frequency Mf2 of the modulation signal M2 in the target laser light source 3. And an AM demodulator 612 that demodulates the demodulated signal demodulated at 611 using an amplitude modulation method.

FIG. 4 is a graph showing a state where the beat signal is demodulated by the FM demodulator 611. 4A shows beat frequency fluctuation, FIG. 4B shows a carrier wave signal, and FIG. 4C shows a demodulated signal demodulated by the FM demodulator 611.
As described above, the fluctuation of the beat frequency (see FIG. 4A) is obtained by changing the signal of frequency (| f1-f2 |) (see FIG. 4B) to a long cycle of 1 / | Mf1-Mf2 | It can be considered that the signal is frequency-modulated with a signal (see FIG. 4C) that has a short period of 1 / Mf2 and fluctuates in a range of ± | Mw1-Mw2 | to ± | Mw1 + Mw2 |. In other words, the electric signal based on the beat signal is frequency-modulated based on a carrier wave signal having a frequency corresponding to the difference between the center frequency f1 of the laser beam L1 and the center frequency f2 of the laser beam L2 (see FIG. 4B). By demodulating using the method, it is possible to demodulate a signal (see FIG. 4C) having the same period (1 / | Mf1-Mf2 |) as the period of large fluctuation of the beat frequency.

FIG. 5 is a graph showing a state in which the demodulated signal demodulated by the FM demodulator 611 is demodulated by the AM demodulator 612. 5A shows a demodulated signal demodulated by the FM demodulator 611, FIG. 5B shows a carrier wave signal, and FIG. 5C is demodulated by the AM demodulator 612. Demodulated signal.
The demodulated signal demodulated by the FM demodulator 611 (see FIG. 5A) repeats a fluctuation of a period of 1 / Mf2 in the range of amplitudes A1 to A2. Therefore, a signal having the same frequency as the modulation frequency Mf2 and an amplitude A1 (see FIG. 5B), that is, a signal having a higher frequency of the modulation frequency Mf1 and the modulation frequency Mf2 is a predetermined modulation signal (see FIG. 5). 5 (see (C)). In other words, the demodulated signal demodulated by the FM demodulator 611 is demodulated by the amplitude modulation method based on the carrier wave signal having the same frequency as the modulation frequency Mf2 and the amplitude A1 (see FIG. 5B). A signal (see FIG. 5C) having the same period (1 / | Mf1−Mf2 |) and having an amplitude of A2 can be demodulated. The amplitudes A1 and A2 can be expressed by the following equations (3) and (4).

A1 = (| Mw1 + Mw2 | + | Mw1-Mw2 |) / 2 (3)
A2 = (| Mw1 + Mw2 |-| Mw1-Mw2 |) / 2 (4)

  The signal generator 62 generates a gate signal for the frequency counter 5 based on the demodulated signal demodulated by the AM demodulator 612. Specifically, the signal generation unit 62 converts the demodulated signal demodulated by the AM demodulator 612 into a square wave signal using a comparator (not shown), and the square wave signal using a frequency divider (not shown). The frequency counter 5 gate signal is generated by dividing the frequency by two.

FIG. 6 is a graph showing the gate signal of the frequency counter 5 generated by the signal generator 62. In FIG. 6, the vertical axis represents voltage and the horizontal axis represents time. 6A is a demodulated signal demodulated by the AM demodulator 612, FIG. 6B is a square wave signal output from the comparator, and FIG. This is a gate signal output from the frequency divider.
As shown in FIG. 6, the signal generation unit 62 is a gate signal having the same period (1 / | Mf1-Mf2 |) as the period of the demodulated signal demodulated by the AM demodulator 612 (see FIG. 6A). (See FIG. 6C). That is, the signal generation unit 62 generates a gate signal of the frequency counter 5 that is synchronized with the period detected by the period detection unit 61.
Then, the frequency counter 5 repeatedly measures the beat frequency, and the calibration device 1 calculates the center frequency of the laser beam L2 based on the center frequency of the laser beam L1 and the average value of the measurement results by the frequency counter 5. Thus, the frequency of the target laser light source 3 is calibrated. Further, the calibration device 1 evaluates the frequency stability of the laser light L2 based on the variation in the measurement result by the frequency counter 5.

According to this embodiment, there are the following effects.
(1) Since the calibration apparatus 1 includes the period detection unit 61 and the signal generation unit 62, the target laser light source can be configured with a simple configuration without using the modulation signal of the reference laser light source 2 as the modulation signal of the target laser light source 3. The frequency of 3 can be calibrated appropriately. The gate signal is synchronized with the period detected by the period detection unit 61, that is, the period corresponding to the difference between the modulation frequency of the modulation signal in the reference laser light source 2 and the modulation frequency of the modulation signal in the target laser light source 3. Therefore, the calibration apparatus 1 can measure the beat frequency in synchronization with the fluctuation of the beat frequency. Therefore, the calibration apparatus 1 can suppress variation in the measurement result by the frequency counter 5 and can set an appropriate gate time as compared with the above-described method of sufficiently increasing the gate time of the frequency counter. .

(2) The period detector 61 includes an FM demodulator 611 and an AM demodulator 612, and the signal generator 62 is a gate signal of the frequency counter 5 based on the demodulated signal demodulated by the AM demodulator 612. Therefore, the calibration apparatus 1 can appropriately calibrate the frequency of the target laser light source 3 without using the modulation signal M1 in the reference laser light source 2 and the modulation signal M2 in the target laser light source 3. Therefore, the calibration apparatus 1 can appropriately calibrate the frequency of the target laser light source 3 even when the modulation signal M2 in the target laser light source 3 is unknown.

[Modification of Embodiment]
It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the embodiment, the period detection unit 61 includes an FM demodulator 611 and an AM demodulator 612, and demodulates an electric signal based on the beat signal, thereby modulating the modulation frequency of the modulation signal in the reference laser light source 2. The period corresponding to the difference from the modulation frequency of the modulation signal in the target laser light source 3 was detected. On the other hand, for example, the modulation signal may be directly acquired from the reference laser light source and the target laser light source, and the period corresponding to the difference in the modulation frequency of each modulation signal may be detected. In short, the period detection unit only needs to be able to detect a period corresponding to the difference between the modulation frequency of the modulation signal in the reference laser light source and the modulation frequency of the modulation signal in the target laser light source.

  In the embodiment, the signal generation unit 62 converts the demodulated signal demodulated by the AM demodulator 612 into a square wave signal by the comparator, and divides the square wave signal by two by the frequency divider. Although the gate signal of the counter 5 is generated, the gate signal of the frequency counter 5 may be generated by another configuration. In short, the signal generator may generate the gate signal of the frequency counter that is synchronized with the period detected by the period detector.

FIG. 7 is a graph illustrating an example of the gate signal of the frequency counter generated by the signal generation unit. In FIG. 7, the vertical axis represents voltage and the horizontal axis represents time. 7A is a demodulated signal demodulated by the AM demodulator, FIG. 7B is a square wave signal output from the comparator, and FIG. 7C is an arbitrary signal. This is a signal having a period T, and FIG. 7D is a gate signal.
For example, as shown in FIG. 7, the signal generation unit converts the demodulated signal demodulated by the AM demodulator into a square wave signal by a comparator, and based on the square wave signal and a signal having an arbitrary period T. Thus, the gate signal of the frequency counter 5 may be generated with a gate time of T / 2 in the same cycle (1 / | Mf1-Mf2 |) as the cycle of the demodulated signal demodulated by the AM demodulator. Note that such a signal generation unit can be configured using a flip-flop or the like.

  The present invention can be suitably used for a laser light source calibration device, particularly a reference laser light source and a laser light source calibration device using a target laser light source as an iodine stabilized laser light source.

DESCRIPTION OF SYMBOLS 1 ... Calibration apparatus 2 ... Reference laser light source 3 ... Target laser light source 4 ... Optical system 5 ... Frequency counter 6 ... Gate signal generation means 61 ... Period detection part 62 ... Signal generation part 611 ... FM demodulator 612 ... AM demodulator

Claims (1)

A reference laser light source that emits laser light that is a reference for calibration, a target laser light source that emits laser light that is a calibration target, the reference laser light source, and an optical axis of the laser light emitted from the target laser light source A frequency counter configured by an optical system that outputs the same, a conversion unit that converts laser light output from the optical system into an electrical signal, and a counter unit that measures a frequency based on the electrical signal from the conversion unit ; A laser light source calibration device that calibrates the frequency of the target laser light source based on the measurement result of the frequency counter,
The reference laser light source and the target laser light source modulate laser light having a predetermined center frequency with a predetermined modulation signal, and emit the laser light.
A period detector for detecting a period corresponding to a difference between a modulation frequency of the modulation signal in the reference laser light source and a modulation frequency of the modulation signal in the target laser light source;
A signal generation unit that generates a gate signal of the frequency counter synchronized with a cycle detected by the cycle detection unit ;
The period detection unit performs the conversion based on a carrier wave signal having a frequency corresponding to a difference between a center frequency of laser light emitted from the reference laser light source and a center frequency of laser light emitted from the target laser light source. An FM demodulator that demodulates an electric signal from the unit by a frequency modulation method;
A demodulated signal demodulated by the FM demodulator based on a carrier signal having a higher frequency of the modulation frequency of the modulation signal of the reference laser light source and the modulation frequency of the modulation signal of the target laser light source An AM demodulator that demodulates
The signal generating unit on the basis of the demodulated signal demodulated by the AM demodulator, the calibration device of the laser light source, characterized that you generate a gate signal of the frequency counter.

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