JP6208475B2 - Laser frequency measuring apparatus and laser stabilization determination method - Google Patents

Description

  The present invention relates to a laser frequency measurement device and a laser stabilization determination method.

An optical frequency comb (also referred to as an optical comb) is a laser in which light of a plurality of frequencies oscillates in phase synchronization at equal frequency intervals (Patent Document 1, Non-Patent Document 1). Hereinafter, it is assumed that the frequency interval of the longitudinal mode of the optical frequency comb is f _rep and the offset frequency that is an offset component remaining when the frequency of the oscillation spectrum is virtually extended to zero is f _CEO . The oscillation frequency f _comb of the optical frequency _comb is expressed by the following equation (1) using the frequency interval f _rep and the offset frequency f _CEO . Note that n is an integer of 0 or more indicating the mode order of the optical frequency comb.

  The optical frequency comb can be used as a means for providing a reference frequency when obtaining an absolute frequency of laser light output from an external laser device. Hereinafter, frequency measurement using an optical frequency comb will be briefly described. FIG. 8 is a spectrum diagram showing the relationship between the optical frequency comb and the absolute frequency of the laser light to be measured.

When the beat frequency f _beat is measured by causing the optical frequency comb to interfere with the laser light to be measured, the frequency interval f _rep and the offset frequency f _CEO are in the relationship shown in FIG. In FIG. 8, the k-th order frequency component (k is an integer) is represented as ν _k . Therefore, the absolute frequency ν _laser of the laser light to be measured is expressed by the following formula (2).

Here, a specific procedure for measuring the laser frequency will be described. First, the laser light to be measured and the output light of the optical frequency comb are caused to interfere, and the interference light is received by a photodetector to obtain a beat signal. In this case, the beat signal includes not only a component of the beat frequency f _beat but also a frequency component such as a frequency interval f _rep and a frequency f _con conjugate with the beat frequency f _beat . Therefore, a frequency signal other than the frequency interval f _rep is cut off with a bandpass filter of an appropriate band, and a frequency spectrum is obtained with a frequency counter. At this time, the beat frequency f _beat changes each time according to the value of the absolute frequency of the laser light to be measured and the frequency interval f _rep of the optical frequency comb. Therefore, when measuring the actual beat frequency f _beat, while the beat frequency f _beat of optical frequency comb and the laser beam was observed by such a spectrum analyzer, a frequency interval as the beat frequency f _beat enters the bandpass passband f Adjust _rep . The beat frequency f _beat is acquired as numerical data by the frequency counter. Then, after specifying the order n, the absolute frequency ν _laser of the laser beam can be obtained by substituting the beat frequency f _beat into the equation (2).

Japanese Patent Laid-Open No. 10-332431

Hajime Inaba et al., “Long-term measurement of optical frequencies using a simple, robust and low-noise fiber based frequency comb”, Optics Express, 12 June 2006, Vol. 14, Issue 12, pp.5223-5231

  However, the inventor has found that the above-described method has the following problems. Usually, when measuring the absolute frequency of laser light, data for a period of several thousand seconds or more is acquired to obtain frequency stability, or the absolute frequency is calculated using an average value. However, there may be a case where the laser light output from the laser device is not properly stabilized at a predetermined frequency due to an operation error of the laser device, a malfunction of the device, or a disturbance such as vibration. If the measurement of the absolute frequency is performed in a state where the laser to be measured is not correctly stabilized at a predetermined frequency, the laser apparatus must be re-stabilized and data for a period of several thousand seconds must be acquired again. That is, in the above-described method, depending on the state of the laser device, it may take a long time to measure the absolute frequency of the laser.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to easily determine whether a laser to be measured is stabilized within a desired frequency range using an optical frequency comb. The determination is made in a short time and reliably.

  The laser frequency measurement device according to the first aspect of the present invention is an optical frequency comb that is output at a predetermined frequency interval and a predetermined offset frequency, the light that is output from the optical frequency comb, and the laser device that is output. A light receiving unit that outputs a signal obtained by photoelectrically converting the interference light of the laser beam, and a beat frequency is detected according to the signal from the light receiving unit, and the laser beam is in a desired frequency range based on the beat frequency. And an arithmetic unit that determines whether the operation is stabilized. Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measurement device according to a second aspect of the present invention is the laser frequency measurement device described above, wherein the arithmetic unit is configured to output the laser beam at a desired frequency when the beat frequency is within a predetermined range. It is determined that the range is stabilized. Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measurement device according to a third aspect of the present invention is the laser frequency measurement device described above, wherein the laser device stabilizes the laser light with reference to one of iodine absorption lines. . Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measurement device according to a fourth aspect of the present invention is the laser frequency measurement device described above, wherein the predetermined range is a range of a predetermined value from an absorption line serving as a reference for stabilizing the laser light. Is. Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measurement device according to a fifth aspect of the present invention is the above laser frequency measurement device, wherein the predetermined value is a beat frequency corresponding to the absorption line that is a reference for stabilization of the laser light, It is smaller than the frequency difference between the beat frequencies corresponding to the other absorption lines. Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measuring device according to a sixth aspect of the present invention is the above-described laser frequency measuring device, wherein the calculation unit detects the beat frequency based on the signal from the light receiving unit. And a determination unit that determines whether the beat frequency is within the predetermined range. Thus, the absolute frequency of the laser beam can be confirmed by simply confirming the beat frequency without specifying the order of the optical comb and calculating using the formula (2), and the laser device can be obtained in a short time. Can be reliably measured.

  A laser frequency measurement device according to a seventh aspect of the present invention is the laser frequency measurement device described above, wherein the calculation unit calculates the frequency of the laser light based on the predetermined frequency interval and the offset frequency. And a frequency calculation unit for performing the above operation. Thereby, the absolute frequency of the laser beam can be calculated after confirming the absolute frequency of the laser beam easily and in a short time.

  A laser frequency measurement device according to an eighth aspect of the present invention is the above laser frequency measurement device, wherein the predetermined frequency interval and the predetermined offset frequency are set in the optical frequency comb and the frequency calculation unit, The apparatus further includes a control unit that sets the order of the optical frequency comb for calculating the frequency of the laser light in the frequency calculation unit. Thereby, it is possible to calculate the absolute frequency of the laser beam after confirming whether the laser is stabilized within a predetermined frequency range in a short time and simply.

  A laser frequency measurement device according to a ninth aspect of the present invention is the laser frequency measurement device described above, wherein the calculation unit adds the predetermined offset frequency to a value obtained by multiplying the order by the predetermined frequency interval. Thus, the frequency of the laser beam is calculated. Thereby, it is possible to calculate the absolute frequency of the laser beam after confirming whether the laser is stabilized within a predetermined frequency range in a short time and simply.

  In the laser stabilization determination method according to the tenth aspect of the present invention, light including a plurality of longitudinal modes at a predetermined frequency interval and a predetermined offset frequency is output to the optical frequency comb and output from the optical frequency comb. Generating a signal obtained by photoelectrically converting interference light between the light and the laser light output from the laser device, detecting a beat frequency according to the signal, and determining whether the laser light is desired based on the beat frequency. It is determined whether the frequency range is stabilized. Thereby, it is possible to calculate the absolute frequency of the laser beam after confirming whether the laser is stabilized within a predetermined frequency range in a short time and simply.

  According to the present invention, it is possible to easily and reliably determine whether or not the laser device is stabilized within a desired frequency range in a short time using the optical frequency comb.

  The above and other objects, features and advantages of the present invention will be more fully understood from the following detailed description and the accompanying drawings. The accompanying drawings are presented for purposes of illustration only and are not intended to limit the present invention.

1 is a configuration diagram schematically showing a configuration of a laser frequency measurement device 100 according to a first exemplary embodiment. 1 is a configuration diagram showing in more detail the configuration of a laser frequency measurement device 100 according to a first exemplary embodiment. 3 is a flowchart showing laser frequency measurement of the laser frequency measurement device 100. An example of a beat frequency generated when an iodine stabilized He-Ne laser and an optical frequency comb are interfered with each of iodine d-line, e-line, f-line, g-line, and h-line absorption line is shown. FIG. It is a figure which shows typically a mode that the frequency shown in FIG. 4 is observed as a spectrum figure with a spectrum analyzer. It is a figure which shows the beat frequency of the laser stabilized to the a8 line near the a10 line which is an absorption line of iodine, a9 line, a10 line, a11 line, a12 line, and an optical frequency comb. It is the figure which represented the beat frequency of FIG. 6 with the frequency spectrum. It is a spectrum figure which shows the relationship between an optical frequency comb and the absolute frequency of the laser used as a measuring object.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

Embodiment 1
First, the laser frequency measuring apparatus 100 according to the first embodiment will be described. FIG. 1 is a configuration diagram schematically illustrating a configuration of a laser frequency measurement device 100 according to the first embodiment. The laser frequency measuring apparatus 100 includes an optical frequency comb 1, a light receiving unit 5, and a calculation unit 6. The optical frequency comb 1 outputs light whose n-th order frequency is represented by the above-described formula (1). Here, the output light of the optical frequency comb 1 including a plurality of longitudinal modes is referred to as light L1.

The laser device 2 outputs a laser beam L2 that is an object of frequency measurement. The laser light L2 interferes with the light L1 and enters the light receiving unit 5 as light L3. The light receiving unit 5 photoelectrically converts the received light and outputs an electric signal SIG. The calculation unit 6 measures the beat frequency f _beat based on the electric signal SIG from the light receiving unit 5. Then, the calculation unit 6 determines whether the beat frequency f _beat is within a predetermined range, and calculates the absolute frequency ν _laser of the laser light L2 according to the determination result.

  Subsequently, the configuration of the laser frequency measuring apparatus 100 will be described in more detail. FIG. 2 is a configuration diagram illustrating the configuration of the laser frequency measurement device 100 according to the first embodiment in more detail. The laser frequency measuring apparatus 100 includes an optical frequency comb 1, a mirror 3, a beam splitter 4, a light receiving unit 5, a calculation unit 6, and a control unit 7.

  The beam splitter 4 is disposed between the optical frequency comb 1 and the light receiving unit 5. A part of the light L1 passes through the beam splitter 4 and propagates toward the light receiving unit 5. The laser beam L 2 is reflected by the mirror 3 and enters the beam splitter 4. A part of the laser beam L2 is reflected by the beam splitter 4 and propagates toward the light receiving unit 5. Thereby, between the beam splitter 4 and the light-receiving part 5, the light L1 and the laser beam L2 interfere, and become the light L3.

The calculation unit 6 includes a beat frequency measurement unit 61, a determination unit 62, and a frequency calculation unit 63. The beat frequency measuring unit 61 measures the beat frequency based on the electric signal SIG from the light receiving unit 5. The beat frequency measuring unit 61 may include a frequency filter f _beat and a level adjusting unit, and may be configured to remove harmonics unnecessary for beat frequency measurement and to measure the beat frequency f _beat with high accuracy. The beat frequency measurement unit 61 outputs the beat frequency f _beat to the determination unit 62. The determination unit 62 determines whether or not the temporary beat frequency f _{beat_r} input from the beat frequency measurement unit 61 is within a predetermined range. The determination unit 62 notifies the determination result to the beat frequency measurement unit 61 by the control signal CON1 and notifies the frequency calculation unit 63 by the control signal CON2. The frequency calculation unit 63 calculates the absolute frequency ν _laser of the laser light L2 output from the laser device 2 in accordance with the control signal CON2 indicating the determination result in the determination unit 62.

  The computing unit 6 can be configured using hardware resources such as a computer. In this case, the calculation unit 6 can be realized by causing the computer to execute a program that defines the operations performed by the beat frequency measurement unit 61, the determination unit 62, and the frequency calculation unit 63.

  The control unit 7 outputs necessary parameters to the optical frequency comb 1 and the frequency calculation unit 63. The control unit 7 can be configured using hardware resources such as a computer. In this case, the control unit 7 can be realized by causing the computer to execute a program that defines the operation performed by the control unit 7.

  Subsequently, laser frequency measurement of the laser frequency measuring apparatus 100 will be described. FIG. 3 is a flowchart showing laser frequency measurement of the laser frequency measuring apparatus 100.

Step S1
The control unit 7 activates the optical frequency comb 1. Then, the control unit 7 sets the beat frequency f _beat and the offset frequency f _CEO in the optical frequency comb 1, and stabilizes the output of the light L1. Further, the control unit 7 outputs the order n used for calculating the beat frequency f _{beat, the} offset frequency f _CEO and the absolute frequency νlaser to the frequency calculation unit 63 of the calculation unit 6.

Step S2
The control unit 7 activates the laser device 2 and stabilizes the output of the laser light L2.

Step S3
The beat frequency measuring unit 61 of the calculation unit 6 confirms the beat frequency using the electric signal SIG from the light receiving unit 5. The beat frequency measuring unit 61 acquires a temporary beat frequency f _{beat_r} from the spectrum indicated by the electric signal SIG. In this case, the accuracy of obtaining the beat frequency _{f Beat_r} may the degree can check the beat frequency _{f Beat_r} is within a range of about ± 100 [kHz].

Step S4
The determination unit 62 of the calculation unit 6 determines _{whether the} temporary beat frequency f _{beat_r} is in the range from the minimum value f _min to the maximum value f _max (f _min ≦ f _{beat_r} ≦ f _max ). When f _min > f _{beat_r} or f _{beat_r} > f _max , as NG determination, it is confirmed whether the laser device 2 is oscillating correctly within the assumed frequency range, and step S3 is retried. Determination unit 62 uses the control signal CON1, it can be acquired to the beat frequency measurement unit 61 tentative beat frequency _{f Beat_r} again.

Step S5
When f _min ≦ f _{beat — r} ≦ f _max , the determination unit 62 assumes that the laser device 2 is oscillating correctly within the frequency range assumed, and uses the control signal CON1 to send the beat frequency measurement unit 61 to the beat frequency. f _beat is calculated. The beat frequency measurement unit 61 acquires a plurality of values in a period of several thousand seconds or more in order to perform high-accuracy measurement, and calculates a beat frequency f _beat using an average value of the acquired values.

Step S6
The frequency calculation unit 63 of the calculation unit 6 receives the control signal CON2 and calculates the absolute frequency ν _laser of the laser beam output from the laser device 2 using Expression (2). Then, the frequency calculating unit 63 outputs the calculated absolute frequency ν _laser to an external display device (not shown).

As described above, in the laser frequency measurement device 100, the frequency at which the laser device 2 is assumed is determined by determining whether or not the temporary beat frequency f _{beat_r} is in the range from the minimum value f _min to f _max in step S4. It is judged whether or not it is oscillating within the range. Hereinafter, the principle of this determination will be described.

  As a laser for measuring the frequency with an optical frequency comb, a laser stabilized with a molecular absorption line having a relatively small oscillation frequency uncertainty is generally used. Specifically, when focusing on the laser for length standard, as is recommended by the Comite International des Poids et Mesures (CIPM), He stabilized by f-line which is an absorption line of iodine. -Ne laser etc. are mentioned. Therefore, the case where the laser apparatus 2 is an iodine stabilized He—Ne laser will be described here.

  According to the CIPM 1997 recommendation, the frequency of the f-line, which is an absorption line used for stabilizing an iodine stabilized He—Ne laser, is 473,612,353,597 [kHz]. The frequency of the laser stabilized to f-line may deviate from the recommended frequency depending on temperature, laser output, adjustment, etc., but the amount is at most about several hundred kHz.

FIG. 4 shows the beat frequency generated when an iodine stabilized He-Ne laser and an optical frequency comb are interfered with each of iodine d-line, e-line, f-line, g-line, and h-line absorption line. It is a figure which shows the example of. FIG. 5 is a diagram schematically showing how the frequency shown in FIG. 4 is observed as a spectrum diagram by a spectrum analyzer. 4 and 5 show examples in which the frequency interval f _rep is set to 98,399,985 [Hz] and the offset frequency f _CEO is set to 10,194,010 [Hz].

  As described above, the error that occurs when the absorption line is stabilized is at most several hundred kHz. Therefore, by looking at the numerical value obtained by inputting the beat frequency signal to the frequency counter and the spectrum observed by the spectrum analyzer, it is possible to identify which absorption line is stabilized and oscillated.

As shown in FIGS. 4 and 5, the beat frequency f _beat corresponding to the laser beam stabilized in the f line is 30,000,000 [Hz]. When measuring a laser that is correctly stabilized at the f-line, a beat frequency within a range of about ± 100 [kHz] with 30 [MHz] as the center is measured.

  On the other hand, there are a plurality of other absorption lines near the f line. For example, the frequency of the e-line that is an absorption line adjacent to the f-line is 473,612,366,960 [kHz], and the frequency of the g-line is 473,612,400,399 [kHz]. When the laser apparatus 2 is erroneously stabilized to any of d-line, e-line, g-line, and h-line, the beat frequencies corresponding to d-line, e-line, g-line, and h-line are 42,175,985 [ Hz], 43,363,000 [Hz], 16,802,000 [Hz], 11,446,985 [Hz]. These are all outside the range of 30,000,000 ± 100,000 [Hz]. Therefore, even if it is erroneously stabilized by another absorption line, it can be easily detected from the value of the beat frequency.

Therefore, in step S4, it can be understood that whether or not the laser device 2 is stabilized by the f-line of iodine can be determined by determining whether or not the temporary beat frequency f _beat is within 30,000,000 ± 100,000 [Hz]. .

Similar to the laser frequency measurement that is generally performed, the beat frequency f _beat is also measured in the time of several thousand seconds in step S5 of the present embodiment. However, since the laser stabilization state is determined in the previous step S4, it is possible to prevent a situation in which the beat frequency f _beat requiring a long time is calculated in an unstable laser state.

  As described above, in the general absolute frequency measurement of laser light, the order of the initial optical frequency comb is unknown. Therefore, the order of the optical frequency comb is determined by performing the calculation of Expression (2) using the temporary absolute frequency value and the measured beat frequency value, and it is confirmed whether the laser is stabilized to a desired absorption line. There was a need. On the other hand, according to this configuration, the laser device to be frequency-measured is stabilized in a desired frequency region without determining the order of the optical comb using the temporary absolute frequency value and the measured beat frequency value. Can be determined. That is, since it is only necessary to confirm the value of the beat frequency, the laser stabilization state can be determined in a short time.

Embodiment 2
Next, a second embodiment will be described. In the first embodiment, an example in which the laser device 2 is an iodine stabilized He—Ne laser has been described. In the present embodiment, a case in which the laser device 2 is an iodine stabilized Nd; YAG laser will be described. In this case, the iodine stabilized Nd: YAG laser is stabilized with respect to the a10 line which is an absorption line of iodine, and outputs a laser beam having a wavelength of 532 nm or its fundamental wave of 1064 nm.

FIG. 6 is a diagram illustrating the beat frequency of the laser and the optical frequency comb stabilized to the a8 line, a9 line, a10 line, a11 line, and a12 line near the a10 line, which is an iodine absorption line. FIG. 7 is a diagram showing the beat frequency of FIG. 6 as a frequency spectrum. 6 and 7 show an example in which the frequency interval f _rep is set to 98,399,980 [Hz] and the offset frequency f _CEO is set to 11,996,800 [Hz].

As shown in FIGS. 6 and 7, the beat frequency f _beat corresponding to the a10 line is ideally 30,000,000 [Hz]. The order n of the optical frequency comb at this time is 5,724,190. The frequency of the laser stabilized to the a10 line is shifted by the error factor of the apparatus itself, but the amount is about ± 100 [kHz] at most.

  Therefore, when measuring the frequency of the Nd: YAG laser stabilized to the a10 line, whether the beat frequency obtained at that time is 30 MHz or not is checked to see if the laser is stabilized to the correct absorption line. It is possible to judge instantly. If the beat frequency is not 30 MHz, there is a high possibility that the other absorption line is erroneously stabilized, so that the laser stabilization state is confirmed again.

In this embodiment, iodine stabilized Nd; YAG has been described. However, even if the iodine stabilized Nd; YVO ₄ laser is stabilized by the a10 line of iodine, it is stabilized to a predetermined absorption line. Can be identified as well.

Other Embodiments The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. The origin signal generation circuit described above is merely an example. For example, in the above-described embodiment, the calculation unit 6 and the control unit 7 have been described as separate configurations, but may be configured as a single piece of hardware.

  Moreover, although the example which stabilizes the laser beam which the laser apparatus 2 outputs to the f line | wire or the a10 line | wire was demonstrated above, stabilizing to another absorption line is not prevented.

In the above description, the iodine stabilized He—Ne laser, the iodine stabilized Nd; YAG, and the iodine stabilized Nd; YVO ₄ laser are described as the laser device 2, but this is merely an example. Other laser devices can be used as long as they have a plurality of discrete absorption lines that are targets for stabilization of the laser frequency.

DESCRIPTION OF SYMBOLS 100 Laser frequency measuring device 1 Optical frequency comb 2 Laser apparatus 3 Mirror 4 Beam splitter 5 Light receiving part 6 Measuring part 7 Control part 61 Beat frequency measuring part 62 Judgment part 63 Frequency calculating part

Claims (11)

An optical frequency comb that outputs light including a plurality of longitudinal modes at a predetermined frequency interval and a predetermined offset frequency;
A light receiving unit that outputs a signal obtained by photoelectrically converting interference light between the light output from the optical frequency comb and the laser light output from a laser device;
Detecting a beat frequency of the provisional in response to the signal from the light receiving unit, e Bei and a computing unit for determining whether the laser beam is stabilized in a desired frequency range on the basis of the beat frequency of the temporary ,
In the laser device, the laser beam is stabilized with respect to any of the absorption lines,
The arithmetic unit determines that the laser beam is stabilized in a desired frequency range when the temporary beat frequency is in a predetermined value range, and determines the beat frequency according to the signal from the light receiving unit. Measuring,
Laser frequency measurement device. In the laser device, the laser beam is stabilized with reference to any of the iodine absorption lines,
The laser frequency measuring device according to claim 1. The computing unit is
If the temporary beat frequency is not in the range of the predetermined value, obtain the temporary beat frequency again,
When the provisional beat frequency acquired again is within the predetermined value range, it is determined that the laser beam is stabilized in a desired frequency range, and the beat frequency is determined according to the signal from the light receiving unit. taking measurement,
The laser frequency measuring device according to claim 1 or 2. The calculation unit acquires a plurality of values of the beat frequency in a predetermined period, and calculates an average value of the acquired values as the beat frequency.
The laser frequency measuring device according to any one of claims 1 to 3. The calculation unit detects the temporary beat frequency in a time shorter than the time required for measuring the beat frequency.
The laser frequency measuring device according to any one of claims 1 to 4. The predetermined value is smaller than a frequency difference between a beat frequency corresponding to the absorption line serving as a reference for stabilization of the laser light and a beat frequency corresponding to another absorption line,
The laser frequency measuring device according to any one of claims 1 to 5 . The computing unit is
A beat frequency detection unit for detecting the temporary beat frequency and the beat frequency based on the signal from the light receiving unit;
A determination unit that determines whether the temporary beat frequency is within the predetermined range,
The laser frequency measuring device according to any one of claims 1 to 6 . The calculation unit further includes a frequency calculation unit that calculates a frequency of the laser light based on the predetermined frequency interval and the predetermined offset frequency.
The laser frequency measuring device according to claim 7 . Control for setting the predetermined frequency interval and the predetermined offset frequency in the optical frequency comb and the frequency calculation unit, and setting the order of the optical frequency comb for calculating the frequency of the laser light in the frequency calculation unit Further comprising
The laser frequency measuring device according to claim 8 . The calculation unit calculates the frequency of the laser light by adding the predetermined offset frequency to a value obtained by multiplying the order by the predetermined frequency interval.
The laser frequency measuring device according to claim 9 . Output light including a plurality of longitudinal modes at a predetermined frequency interval and a predetermined offset frequency to the optical frequency comb,
A signal obtained by photoelectrically converting interference light between the light output from the optical frequency comb and the laser light output from the laser device;
A temporary beat frequency is detected according to the signal,
In the laser device, the laser beam is stabilized with respect to any of the absorption lines,
When the temporary beat frequency is within a predetermined value range from an absorption line that serves as a reference for stabilizing the laser beam, it is determined that the laser beam is stabilized in a desired frequency range;
Measuring the beat frequency according to the signal,
Laser stabilization determination method.

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