JP2015076578A - Laser frequency stabilizing method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser frequency stabilizing method and a device thereof which are capable of stabilizing a frequency of a laser beam for a long period of time with less influence of disturbance like vibration and sound and of a temperature.SOLUTION: The laser frequency stabilizing device includes an optical system including a gas cell 20 and an optical system including an etalon 28. In a previous operation (initialization or the like) before an actual operation, a frequency of a laser beam emitted from a laser beam source is controlled on the basis of the light intensity of the laser beam transmitted through the optical system including the gas cell 20 to match the frequency of the laser beam with a center frequency of a saturation absorption line of the gas cell 20. A temperature of the etalon 28 is controlled on the basis of the light intensity of the laser beam transmitted through the etalon 28, and the temperature of the etalon at the time when a resonance frequency of the etalon 28 matches the frequency of the laser beam, namely the center frequency of the saturation absorption line, is detected as a calibration temperature. In the actual operation, the etalon 28 is kept at the calibration temperature, and the frequency of the laser beam emitted from the laser beam source is controlled on the basis of the light intensity of the laser beam transmitted through the optical system including the etalon 28.

Description

  The present invention relates to a laser frequency stabilization method and apparatus, and more particularly to a laser frequency stabilization method and apparatus for stabilizing the frequency (wavelength) of laser light using a semiconductor laser as a light source.

  The iodine-stabilized HeNe laser is known as one in which the oscillation frequency of the HeNe laser is locked to a specific saturated absorption line of iodine having a high accuracy frequency to stabilize the oscillation frequency (for example, Patent Documents 1 and 2). reference).

  It is also known to use a solid-state resonator (solid etalon) that transmits only a specific frequency of laser light emitted from a laser light source as a technique for stabilizing and narrowing the frequency of laser light (for example, patent literature) 3).

JP 2001-274497 A JP 2003-224319 A Japanese Patent Laid-Open No. 08-018145

  By the way, the conventional iodine-stabilized HeNe laser has a problem that the frequency (wavelength) of the laser beam is unlocked by vibration and sound because the resonator is in the atmosphere. The lockable frequency range is as small as several MHz.

  The solid etalon (solid resonator) has few problems described above and has a wide range of lockable frequencies. However, solid etalon is susceptible to temperature because its refractive index and thickness change with temperature. In addition, in order to control the temperature of the solid etalon, there is a problem that the frequency stability and accuracy are not good because the accuracy of the thermometer used for the control is not sufficient.

  The present invention has been made in view of such circumstances, and is less affected by disturbances such as vibration and sound and temperature, and can stabilize the frequency of laser light over a long period of time. An object of the present invention is to provide a method and an apparatus therefor.

  In order to achieve the above object, a laser frequency stabilizing device according to the present invention includes a light source that emits laser light, and a light splitting unit that splits the laser light emitted from the light source into a first laser light and a second laser light. A first optical system including a gas cell through which the first laser light split by the light splitting unit passes, and a first detection signal indicating a light intensity of the first laser light passed through the first optical system. Based on one light detection means and a first detection signal detected by the first light detection means, the frequency of the laser light emitted from the light source is matched with the center frequency of the saturated absorption line of the gas cell. The first control means for controlling the frequency of the laser light emitted from the light source, the second optical system including an etalon through which the second laser light divided by the light splitting means passes, and the second optical system passed Second laser beam Based on the second detection signal that detects the second detection signal indicating the light intensity, and the second detection signal detected by the second detection unit, the frequency of the laser beam emitted from the light source is the etalon. The second control means for controlling the frequency of the laser light emitted from the light source so as to match the resonance frequency, and the control of the frequency of the laser light emitted from the light source are controlled by the first control means and the first control means. 2 is a control switching unit that is set to be switchable to any one of the control by the control unit, and controls the frequency of the laser beam emitted from the light source when the previous operation is performed before the main operation. Control switching means for setting the control by the first control means, and setting the control of the frequency of the laser light emitted from the light source to the control by the second control means at the time of carrying out the main operation; Temperature control means for controlling the temperature of the talon, wherein the temperature control means detects the second detection detected by the second light detection means while changing the temperature of the etalon when the pre-operation is performed. Etalon calibration temperature detection that acquires a signal and detects the temperature of the etalon when the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell as a calibration temperature based on the acquired second detection signal And etalon temperature maintaining means for maintaining the temperature of the etalon at the calibration temperature detected by the etalon calibration temperature detecting means when the operation is performed.

  According to the present invention, when this operation is performed, the frequency of the laser light is controlled to be locked to the center frequency of the saturated absorption line of the gas cell by the frequency lock control of the laser light using the etalon. Therefore, it is difficult to be affected by disturbances such as vibration and sound, and laser light having a stable frequency over a long time can be provided to the outside.

  Also, the etalon is easily affected by temperature, and the resonance frequency of the etalon fluctuates depending on the temperature, and the frequency at which the laser beam is locked fluctuates. However, in the present invention, the temperature of the etalon when the resonance frequency coincides with the center frequency of the saturated absorption line of the gas cell is detected as the calibration temperature at the time of performing the previous operation before the main operation. Controls the temperature of the etalon to maintain its calibration temperature. Therefore, a laser beam having a stable frequency can be provided without the frequency of the laser beam changing due to the influence of temperature.

  Further, in the present invention, the temperature control means is configured such that the resonance frequency of the etalon is a saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means when the main operation is performed. An etalon temperature correcting means for correcting the temperature of the etalon so as to match the center frequency of the etalon may be provided.

  According to this aspect, when this operation is performed, the error between the temperature of the etalon controlled by the temperature control means or the temperature of the etalon detected by the temperature sensor and the actual temperature of the etalon changes, and the resonance frequency of the etalon However, even when a situation occurs that deviates from the center frequency of the saturated absorption line of the gas cell, the deviation is based on the first detection signal detected by the laser beam that has passed through the optical system including the gas cell. It is corrected. Accordingly, it is possible to provide laser light having a stable frequency over a long period of time.

  Further, in the present invention, the first control means is configured to detect the frequency of the laser light emitted from the light source and the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means. First deviation signal detecting means for detecting a first deviation signal indicating a deviation from the center frequency is emitted from the light source so that the first deviation signal becomes zero or smaller than the current value. It is possible to control the frequency of the laser light.

  Also, in the present invention, the second control means is configured to calculate a frequency of the laser light emitted from the light source and a resonance frequency of the etalon based on the second detection signal detected by the second light detection means. A second deviation signal detecting means for detecting a second deviation signal indicating a deviation; the laser beam emitted from the light source so that the second deviation signal becomes 0 or smaller than a current value; It can be set as the aspect which controls a frequency.

  In the present invention, the laser beam emitted from the light source is a laser beam that is frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0, and the first deviation signal detecting means includes the first light. The first deviation signal may be detected based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the first detection signal detected by the detection unit.

  The second deviation signal detecting means detects the second deviation signal based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the second detection signal detected by the second light detecting means. It can be.

  The laser frequency stabilization method according to the present invention includes a light source that emits laser light, a light splitting unit that splits the laser light emitted from the light source into a first laser beam and a second laser beam, and the light splitting unit. A first optical system including a gas cell through which the first laser light divided by the first light passes, and a first light detection means for detecting a first detection signal indicating a light intensity of the first laser light that has passed through the first optical system; Based on the first detection signal detected by the first light detection means, the frequency of the laser light emitted from the light source is emitted from the light source so as to coincide with the center frequency of the saturated absorption line of the gas cell. First control means for controlling the frequency of the laser light, a second optical system including an etalon through which the second laser light split by the light splitting means passes, and second laser light that has passed through the second optical system. Second indicating light intensity Based on the second light detection means for detecting the outgoing signal and the second detection signal detected by the second light detection means, the frequency of the laser light emitted from the light source matches the resonance frequency of the etalon. The second control means for controlling the frequency of the laser light emitted from the light source and the control of the frequency of the laser light emitted from the light source are controlled by the first control means and the control by the second control means. A laser frequency stabilization method in a laser frequency stabilization device, comprising: a control switching unit that is set to be switchable to any one of the above; and a temperature control unit that controls the temperature of the etalon, wherein the control switching unit includes: At the time of performing the previous operation before the main operation, the control of the frequency of the laser light emitted from the light source is set to the control by the first control means, and at the time of performing the main operation The control of the frequency of the laser light emitted from the light source is set to control by the second control means, and the temperature control means changes the temperature of the etalon when the pre-operation is performed, The second detection signal detected by the second light detection means is acquired, and the etalon when the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell based on the acquired second detection signal Is detected as a calibration temperature, and the temperature of the etalon is maintained at the calibration temperature when the operation is performed.

  According to the present invention, when this operation is performed, the frequency of the laser light is controlled to be locked to the center frequency of the saturated absorption line of the gas cell by the frequency lock control of the laser light using the etalon. Therefore, it is difficult to be affected by disturbances such as vibration and sound, and laser light having a stable frequency over a long time can be provided to the outside.

  Also, the etalon is easily affected by temperature, and the resonance frequency of the etalon fluctuates depending on the temperature, and the frequency at which the laser beam is locked fluctuates. However, in the present invention, the temperature of the etalon when the resonance frequency coincides with the center frequency of the saturated absorption line of the gas cell is detected as the calibration temperature at the time of performing the previous operation before the main operation. Controls the temperature of the etalon to maintain its calibration temperature. Therefore, a laser beam having a stable frequency can be provided without the frequency of the laser beam changing due to the influence of temperature.

  Further, in the present invention, the temperature control means is configured such that the resonance frequency of the etalon is a saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means when the main operation is performed. The temperature of the etalon can be corrected so as to match the center frequency.

  According to this aspect, when this operation is performed, the error between the temperature of the etalon controlled by the temperature control means or the temperature of the etalon detected by the temperature sensor and the actual temperature of the etalon changes, and the resonance frequency of the etalon However, even when a situation occurs that deviates from the center frequency of the saturated absorption line of the gas cell, the deviation is based on the first detection signal detected by the laser beam that has passed through the optical system including the gas cell. It is corrected. Accordingly, it is possible to provide laser light having a stable frequency over a long period of time.

  Further, in the present invention, the first control means is configured to detect the frequency of the laser light emitted from the light source and the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means. First deviation signal detecting means for detecting a first deviation signal indicating a deviation from the center frequency is emitted from the light source so that the first deviation signal becomes zero or smaller than the current value. It is possible to control the frequency of the laser light.

  Also, in the present invention, the second control means is configured to calculate a frequency of the laser light emitted from the light source and a resonance frequency of the etalon based on the second detection signal detected by the second light detection means. A second deviation signal detecting means for detecting a second deviation signal indicating a deviation; the laser beam emitted from the light source so that the second deviation signal becomes 0 or smaller than a current value; It can be set as the aspect which controls a frequency.

  In the present invention, the laser beam emitted from the light source is a laser beam that is frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0, and the first deviation signal detecting means includes the first light. The first deviation signal may be detected based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the first detection signal detected by the detection unit.

  The second deviation signal detecting means detects the second deviation signal based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the second detection signal detected by the second light detecting means. It can be.

  According to the present invention, the influence of disturbance such as vibration and sound and the influence of temperature are small, and the frequency of the laser beam can be stabilized for a long time.

The block diagram which showed the structure of the laser frequency stabilization apparatus based on this invention The figure which illustrated the frequency characteristic of the transmittance of a gas cell Diagram showing signal value indicated by deviation signal Diagram illustrating frequency characteristics of etalon transmittance Flow chart showing operation procedure in laser frequency stabilization device The figure which showed the modification of the laser frequency stabilization apparatus of FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a configuration of a laser frequency stabilization device according to the present invention.

  A laser frequency stabilizing device 1 shown in FIG. 1 is a device that can be used as a source of laser light used in a measuring instrument that uses laser light such as a laser interferometer, and is a laser having a predetermined frequency (wavelength). The light is output to the outside as reflected light from a beam splitter 12 described later. In the following description, the frequency f of the laser beam and the signal is expressed using an angular frequency ω obtained by multiplying the frequency f by a value of 2 · π, and the angular frequency ω is simply referred to as a frequency ω.

  In the laser frequency stabilizing device 1 shown in FIG. 1, a laser light source 10 is, for example, a semiconductor laser, and oscillates by a driving current supplied from a current driver 80 to emit laser light having a predetermined frequency.

  In addition, a sinusoidal modulation current having a frequency ωm output from the oscillator 60 is superimposed on the drive current. As a result, the frequency of the laser light emitted from the laser light source 10 is frequency-modulated by a signal of β · sin (ωm · t). Laser light emitted from the laser light source 10 enters the beam splitter 12.

  The beam splitter 12 splits the laser light incident from the laser light source 10 into reflected light and transmitted light. The reflected light is emitted from the apparatus 1 to the outside as laser light used outside. The transmitted light is incident on the polarization beam splitter 14.

  The polarization beam splitter 14 reflects S-polarized (S-polarized component) laser light out of the laser light incident from the beam splitter 12 and transmits P-polarized (P-polarized component) laser light. P-polarized laser light is incident on the polarization beam splitter 16 as laser light that passes through an optical system (optical path) including the gas cell 20, and S-polarized laser light is laser light that passes through an optical system (optical path) including the etalon 28. The light enters the polarization beam splitter 24.

  First, the optical system including the gas cell 20 will be described. The polarization beam splitter 16 transmits the P-polarized laser light incident from the polarization beam splitter 14. The transmitted P-polarized laser light is incident on the quarter-wave plate 18.

  The polarization beam splitter 16 reflects S-polarized laser light incident from the quarter-wave plate 18 as will be described later. The reflected S-polarized laser light is incident on the photodetector 40.

  The quarter wavelength plate 18 converts the P-polarized laser light incident from the polarization beam splitter 16 from P-polarized light to circularly-polarized light. The laser light converted into circularly polarized light enters the gas cell 20.

  The quarter-wave plate 18 converts circularly polarized laser light incident from the gas cell 20 from circularly polarized light to S-polarized light as will be described later. The laser beam converted to S-polarized light enters the polarization beam splitter 16 as described above.

  The gas cell 20 is a light absorption cell in which a gas such as iodine is sealed, and transmits the laser light incident from the quarter wavelength plate 18 with a transmittance according to the frequency. The transmitted laser light is reflected by the mirror 22 and enters the gas cell 20 again. The gas cell 20 transmits laser light incident from the mirror 22 with a transmittance corresponding to the frequency.

  In this way, the laser light incident on the gas cell 20 is turned back by the mirror 22, and the laser light transmitted through the gas cell 20 again enters the quarter-wave plate 18 as described above. Then, after being converted from circularly polarized light to S polarized light by the ¼ wavelength plate 18, it is reflected by the polarization beam splitter 16 and enters the photodetector 40.

  The photodetector 40 photoelectrically converts the laser beam incident from the polarization beam splitter 16 and outputs a voltage signal having a magnitude corresponding to the light intensity of the incident laser beam as a detection signal. The detection signal output from the photodetector 40 is input to the detector 42.

  Here, the detection signal IG (t) output from the photodetector 40 can be expressed by a function F (ω) of the frequency ω of the laser light that varies with time t.

  On the other hand, the function F (ω) corresponds to the frequency characteristic of the transmittance of the gas cell 20. FIG. 2 is a diagram illustrating the frequency characteristics of the transmittance of the gas cell 20. As shown in the figure, the gas cell 20 has a saturated absorption line with a bandwidth of several MHz in which the light transmittance increases in a mountain shape. The saturated absorption line exhibits a maximum transmittance at a substantially central frequency (center frequency ωa) of the band.

  By using the saturated absorption line, it is possible to detect a shift in the frequency of the laser light with respect to the center frequency ωa of the saturated absorption line, based on the detection signal IG (t) obtained by the photodetector 40. Then, by controlling the frequency of the laser light emitted from the laser light source 10 so as to eliminate the deviation, it is possible to lock the laser light frequency to be in a state substantially matching the center frequency ωa of the saturated absorption line. .

  Along with the principle of the frequency lock control, the processing of the related processing unit will be described.

  First, the laser light emitted from the laser light source 10 has a spectral line width of sub MHz, and has a frequency ω obtained by modulating a frequency (for example, a center frequency) ω0 indicating the spectral line with a sine wave having a frequency ωm. That is, the frequency ω of the laser beam is expressed by the following equation (1).

ω = ω0 + β · sin (ωm · t) (1)
Since β is extremely small compared to ω0, the frequency of the laser beam can be regarded as ω0 except for the arithmetic processing using the formula (1). Hereinafter, ω0 is referred to as a reference frequency of laser light.

  On the other hand, the detection signal IG (t) output from the photodetector 40 can be expressed by the function F (ω) corresponding to the frequency characteristic of the transmittance of the gas cell 20 as described above. When Taylor expansion is performed around ω = ω0, the following expression (2) is obtained.

F (ω) = F (ω0) + (ω−ω0) · F ⁽¹⁾ (ω0) + (1/2!) · (Ω−ω0) ² · F ⁽²⁾ (ω0) + (1/3 !) ・ (Ω−ω0) ³・ F ⁽³⁾ (ω0) + ... + (1 / n!) ・ (Ω−ω0) ⁿ · F ⁽ⁿ⁾ (ω0) + ... (2)
However, F ⁽ⁿ⁾ (ω0) indicates the nth derivative of F at ω = ω0.

  Substituting ω0 + β · sin (ωm · t) shown in Equation (1) into ω in Equation (2) and deforming the detection signal IG (t) is expressed by the following Equation (3).

IG (t) = F (ω0 + β · sin (ωm · t))
= F (ω0) + ...
+ Sin (ωm · t) · {β · F ⁽¹⁾ (ω0) + (3/24) · β ³ · F ⁽³⁾ (ω0) + ...}
+ Cos (2 · ωm · t) · {(− 1/4) · β ² · F ⁽²⁾ (ω0) + (− 1/48) · β ⁴ · F ⁽⁴⁾ (ω0) +.
+ Sin (3 · ωm · t) · {(− 1/24) · β ³ · F ⁽³⁾ (ω0) + (− 5/1920) · β ⁵ · F ⁽⁵⁾ (ω0) +.
≒ F (ω0) + ...
+ Sin (ωm · t) · β · F ⁽¹⁾ (ω0)
+ Cos (2 · ωm · t) · (−1/4) · β ² · F ⁽²⁾ (ω0)
+ Sin (3 · ωm · t) · (−1/24) · β ³ · F ⁽³⁾ (ω0) (3)
According to this, a signal of sin (n · ωm · t) is mixed (mixed) and detected (locked in) with respect to the detection signal IG (t) detected by the laser beam that has passed through the gas cell 20. The signal component of the frequency n · ωm can be extracted, and an nth-order differential signal (a voltage signal having a magnitude corresponding to the value of the nth-order differentiation) at ω = ω0 of F (ω) is obtained. In the present embodiment, a third-order differential signal of F (ω) at ω = ω0 is obtained by the detector 42 as follows.

  That is, in FIG. 1, the detection signal IG (t) (F (ω)) output from the photodetector 40 is input to the detector 42, and the reference signal βsin (3 · ωm · t) is supplied from the amplifier 62. A signal having a value multiplied by a predetermined value is input.

  The amplifier 62 generates a sine wave signal having a frequency 3 · ωm that is three times as a modulation signal based on the sine wave signal having the frequency ωm output from the oscillator 60, amplifies the amplitude, and outputs the amplified signal to the detector 42.

  The detector 42 mixes the reference signal βsin (3 · ωm · t) input from the amplifier 62 with the detection signal IG (t) input from the photodetector 40 to obtain a signal of frequency 3 · ωm. (Signal component) is detected (locked in). As a result, a third derivative signal having a magnitude corresponding to the value of the third derivative of F (ω) at ω = ω0 is obtained.

  The third-order differential signal obtained by the detector 42 is output from the detector 42 as a deviation signal DG indicating the deviation amount (deviation) of the laser light frequency (reference frequency ω0) with respect to the center frequency ωa of the saturated absorption line. The deviation signal DG is input to the signal processor 44 and also input to the signal processor 70 via the switch 76.

  FIG. 3 shows the third-order differential signal (deviation signal DG) of ω = ω0 of F (ω) when the value of the reference frequency ω0 of the laser beam is changed around the center frequency ωa of the saturated absorption line. It is the figure which showed the signal value shown simply.

  As shown in the figure, when the reference frequency ω0 of the laser beam is equal to the center frequency ωa of the saturated absorption line, the signal value DG0 indicated by the point Pa is obtained. The signal value DG0 ideally shows a 0 value. In the following, it is assumed that the signal value DG0 is a zero value.

  As the value of the reference frequency ω0 is decreased from the frequency ωa of the saturated absorption line, the signal value gradually decreases and becomes a minimum value indicated by a point Pb at a predetermined frequency ωb. As the value of the reference frequency ω0 is further decreased, the signal value gradually increases and finally shows a 0 value.

  On the other hand, when the value of the reference frequency ω0 is increased from the frequency ωa of the saturated absorption line, the signal value gradually increases and becomes the maximum value indicated by the point Pc at the predetermined frequency ωc. As the value of the reference frequency ω0 is further increased, the signal value gradually decreases and finally shows a 0 value.

  According to this, if the control range of the reference frequency ω0 of the laser light emitted from the laser light source 10 is limited to the range from the frequency ωb to the frequency ωc, the third-order differential signal (deviation signal DG) obtained by the detector 42 is reduced. The signal value indicates the amount of deviation of the reference frequency ω0 from the center frequency ωa of the saturated absorption line.

  Note that the signal value DG0 when the reference frequency ω0 matches the center frequency ωa of the saturated absorption line is not necessarily zero, and in this case, the deviation signal DG subtracts the signal value DG0. The value may be set as follows.

  Further, in this embodiment, among the n-order differential signals of F (ω) at ω = ω0, the third-order differential signal when n = 3 is the deviation signal DG, but n when n is an odd number other than 3. The second derivative signal can be the deviation signal DG. That is, the signal value of the nth-order differential signal when n is an odd number increases or decreases around the center frequency ωa of the saturated absorption line when the reference frequency ω0 is increased. Therefore, if the control range of the reference frequency ω0 is limited to a range in which the signal value of the n-th order differential signal increases or decreases, the signal value of the n-th order differential signal, like the third-order differential signal, becomes the center frequency ωa of the saturated absorption line. The amount of deviation of the reference frequency ω0 with respect to is shown, and can be used as the deviation signal DG.

  The signal processor 44 in FIG. 1 performs feedback control based on the deviation signal DG input from the detector 42 so that the reference frequency ω0 of the laser light emitted from the laser light source 10 matches the center frequency ωa of the saturated absorption line. I do.

  That is, when the deviation signal DG input from the detector 42 is not a zero value (DG0), the signal processor 44 is a control signal that changes the reference frequency ω0 of the laser light source 10 in a direction in which the deviation signal DG becomes a zero value. Is output to the current driver 80 via the switch 74.

  The current driver 80 controls the drive current injected into the laser light source 10 according to the control signal input from the signal processor 44 to change the reference frequency ω 0 of the laser light emitted from the laser light source 10.

  As a result, when the reference frequency ω 0 of the laser light changes, the deviation signal DG at the changed reference frequency ω 0 is input from the detector 42 to the signal processor 44. If the deviation signal DG is not a zero value, the signal processor 44 provides the current driver 80 with a control signal for changing the reference frequency ω0 in a direction in which the deviation signal DG becomes a zero value.

  By repeating such processing, the signal processor 44 performs feedback control on the reference frequency ω0, and fixes (locks) the reference frequency ω0 to a state in which the reference frequency ω0 matches the center frequency ωa of the saturated absorption line.

  In this embodiment, regarding the feedback control with respect to the reference frequency ω0, the reference frequency ω0 is controlled so that the deviation signal DG has a zero value. However, the present invention is not limited to this, and the deviation signal DG is smaller than the current value. The reference frequency ω0 may be controlled as described above, or the reference frequency ω0 may be controlled so that the deviation signal DG becomes smaller than a predetermined threshold other than the zero value.

  Here, such feedback control (frequency lock control of the laser beam using the gas cell 20) is a frequency in the control range from the frequency ωb to the frequency ωc, as shown in FIG. In this case, the reference frequency ω0 can be appropriately converged and locked to the center frequency ωa of the saturated absorption line.

  However, once the reference frequency ω0 is set to a value outside the control range for some reason, the reference frequency ω0 can be converged again to the center frequency ωa of the saturated absorption line only by continuing the above feedback control. A phenomenon occurs in which the lock cannot be released.

  On the other hand, the gas cell 20 is easily affected by disturbances such as vibration and sound, and an error due to the disturbances is likely to occur in the deviation signal DG obtained by the detector 42.

  As shown in FIG. 3, the control range of the reference frequency ω0 from the frequency ωb to the frequency ωc is narrower than the bandwidth of the saturated absorption line and is extremely narrow, about several MHz, so that when an error occurs in the deviation signal DG, When the reference frequency ω0 is changed accordingly, the reference frequency ω0 is likely to be out of the control range.

  Therefore, in the laser light frequency lock control using the gas cell 20, it is difficult to lock the laser light frequency to the center frequency ωa of the saturated absorption line for a long time.

  Therefore, in the present apparatus 1, the frequency lock control of the laser beam is directly performed using the etalon 28.

  The etalon 28 is less susceptible to disturbances such as vibration and sound, and can lock the frequency of the laser light to the resonance frequency ωs of the etalon 28 for a long time.

  On the other hand, as is well known, the etalon 28 easily changes its refractive index and thickness due to temperature changes, and is easily affected by temperature. Therefore, when the temperature fluctuates, the resonance frequency ωs of the etalon 28 fluctuates, and the frequency (lock frequency) for locking the laser light also fluctuates. Further, the relationship among the etalon 28, the temperature, and the resonance frequency ωs (lock frequency) is not accurately determined.

  Therefore, at the time of initial setting when the apparatus 1 is activated, that is, at the time of the previous operation before the main operation, the laser cell frequency lock control using the gas cell 20 is performed to set the reference frequency ω0 of the laser beam to the gas cell 20. The temperature of the etalon 28 is calibrated so that the resonance frequency ωs of the etalon 28 matches the center frequency ωa of the saturated absorption line of the gas cell 20.

  In this operation, the etalon 28 is used to control the frequency lock of the laser light, and the etalon 28 is maintained at the calibrated temperature, and the resonance frequency ωs of the etalon 28 is stabilized to stabilize the frequency of the laser light. Turn into.

  Further, during the frequency lock control using the etalon 28, the temperature of the etalon 28 is corrected using the deviation signal DG from the detector 42 detected by the laser light that has passed through the optical system including the gas cell 20, and the laser The frequency of light is further stabilized.

  The optical system including the etalon 28 will be described. The polarization beam splitter 24 in FIG. 1 reflects the S-polarized laser light incident from the polarization beam splitter 14 as described above. The reflected laser light is incident on the quarter-wave plate 26.

  Further, the polarization beam splitter 24 transmits the P-polarized laser light incident from the quarter-wave plate 26 as will be described later. The transmitted P-polarized laser light is incident on the photodetector 50.

  The quarter wavelength plate 26 converts the S-polarized laser light incident from the polarization beam splitter 24 into circularly polarized light. The laser light converted into circularly polarized light enters the etalon 28.

  The quarter-wave plate 26 converts circularly polarized laser light incident from the etalon 28 from circularly polarized light to P-polarized light as will be described later. The laser beam converted to P-polarized light enters the polarization beam splitter 24 as described above.

  The etalon 28 transmits the laser light incident from the quarter-wave plate 26 with a transmittance according to the frequency and reciprocates to return to the quarter-wave plate 26.

  The laser light transmitted through the etalon 28 and returned to the quarter-wave plate 26 is converted from circularly polarized light to P-polarized light by the quarter-wave plate 26 and then transmitted through the polarization beam splitter 24 to be light. The light enters the detector 50.

  The etalon 28 also includes a temperature controller 30 that controls the temperature of the etalon 28 (ambient temperature or the temperature of a specific component of the etalon 28).

  The photodetector 50 photoelectrically converts the laser beam incident from the polarization beam splitter 24, and outputs a voltage signal having a magnitude corresponding to the light intensity of the incident laser beam as a detection signal. The detection signal output from the photodetector 50 is input to the detector 52 and the signal processor 70.

  The temperature controller 30 controls the temperature of the etalon 28 (ambient temperature or the temperature of a specific component of the etalon 28) according to a temperature control signal provided from a signal processor 70 described later.

  Further, the temperature controller 30 outputs temperature information indicating the current temperature of the etalon 28 detected by a temperature sensor (not shown) to the signal processor 70.

  First, the processing of the processing unit related to the laser light frequency lock control using the etalon 28 will be described. The principle is the same as that in the case of the frequency lock control of the laser beam using the gas cell 20 described above, and the details are omitted.

  Similar to the detection signal IG (t) output from the photodetector 40, the detection signal IE (t) output from the photodetector 50 is a function G (ω) of the frequency ω of the laser beam that varies with time t. Can be expressed as The function G (ω) corresponds to the frequency characteristic of the transmittance of the etalon 28.

  The etalon 28 has a configuration of a solid etalon in which reflection surfaces (reflection films) are formed on both surfaces of a substrate such as quartz, and has a frequency characteristic of transmittance as shown in FIG. The etalon 28 may be an air gap etalon instead of a solid etalon.

  As shown in the figure, the etalon 28 has a pass band in which the light transmittance increases around the resonance frequency for each free spectral region (FSR).

  FSR is expressed by the following equation (4).

FSR = c / (2 · n · d · cos θ) (4)
However, c is the speed of light, n is the refractive index, d is the thickness of the substrate, and θ is the incident angle of the laser beam.

  The full width at half maximum (FWHM) of each pass band is expressed by the following equation (5).

FWHM = (1-R) · FSR / (π · R ^0.5 ) (5)
Finesse indicating the sharpness of the peak is expressed by the following equation (6).

Finese = FSR / FWHM = π · R ^0.5 / (1-R) (6)
In the present apparatus 1, an etalon 28 having a sufficiently large Finesse (FWHM is sufficiently small) and a passband whose resonance frequency ωs substantially coincides with the center frequency ωa of the saturated absorption line of the gas cell 20 is used.

  Then, by using the pass band, the laser light frequency lock control using the etalon 28 is performed in the same manner as the laser light frequency lock control using the gas cell 20 described above.

  That is, the detection signal IE (t) obtained by the photodetector 50 is expressed by the following equation (7), similarly to the above equation (3).

IE (t) ≈G (ω0) +
+ Sin (ωm · t) · β · G ⁽¹⁾ (ω0)
+ Cos (2 · ωm · t) · (−1/4) · β ² · G ⁽²⁾ (ω0)
+ Sin (3 · ωm · t) · (−1/24) · β ³ · G ⁽³⁾ (ω0) (7)
In FIG. 1, the detector 52 receives the detection signal IE (t) (G (ω)) output from the photodetector 50 and receives a reference signal βsin (3 · ωm · t) from the amplifier 64 as a predetermined value. A doubled signal is input.

  The amplifier 64 generates a sine wave signal having a frequency 3 · ωm that is three times as a modulation signal based on the sine wave signal having the frequency ωm output from the oscillator 60, amplifies the amplitude, and outputs the modulated signal to the detector 52.

  The detector 52 mixes the reference signal βsin (3 · ωm · t) input from the amplifier 64 with the detection signal IE (t) input from the photodetector 50 to obtain a signal having a frequency of 3 · ωm. Is detected (locked in). As a result, a third derivative signal having a magnitude corresponding to the value of the third derivative of G (ω) at ω = ω0 is obtained. The third-order differential signal obtained by the detector 52 is output as a deviation signal DE indicating a deviation amount (deviation) of the laser light frequency (reference frequency ω0) with respect to the resonance frequency ωs of the etalon 28. This deviation signal DE is input to the signal processor 54.

  In this embodiment, among the n-order differential signals of G (ω) at ω = ω0, the third-order differential signal when n = 3 is the deviation signal DE, but n when n is an odd number other than 3 is used. The second derivative signal can be the deviation signal DE.

  Based on the deviation signal DE input from the detector 52, the signal processor 54 performs feedback control so that the reference frequency ω0 of the laser light emitted from the laser light source 10 matches the resonance frequency ωs of the etalon 28.

  That is, the signal processor 54 switches a control signal for changing the reference frequency ω0 of the laser light source 10 in a direction in which the deviation signal DE becomes zero when the deviation signal DE input from the detector 52 is not zero. The current is output to the current driver 80 via 74.

  The switch 74 switches the connection to either the signal processor 44 or the signal processor 54 in accordance with a switching signal given from the signal processor 70.

  Further, in the present embodiment, regarding the feedback control with respect to the reference frequency ω0, the reference frequency ω0 is controlled so that the deviation signal DE becomes 0 value. However, the present invention is not limited to this, and the deviation signal DE becomes smaller than the current value. The reference frequency ω0 may be controlled as described above, or the reference frequency ω0 may be controlled so that the deviation signal DE becomes smaller than a predetermined threshold other than the zero value.

  In this operation, the signal processor 70 connects the switch 74 to the signal processor 54 and inputs the control signal output from the signal processor 54 to the current driver 80. Thereby, the frequency lock control of the laser beam using the etalon 28 is performed. During the pre-operation before this operation, the switch 74 is connected to the signal processor 44 and the control signal output from the signal processor 44 is input to the current driver 80. Thereby, the frequency lock control of the laser beam using the gas cell 20 is implemented.

  The current driver 80 controls the drive current injected into the laser light source 10 according to the control signal input from the signal processor 54 to change the reference frequency ω 0 of the laser light emitted from the laser light source 10.

  Thus, when the reference frequency ω 0 of the laser light changes, the deviation signal DE at the changed reference frequency ω 0 is input from the detector 52 to the signal processor 54. If the deviation signal DE is not 0 value, the signal processor 54 gives the current driver 80 a control signal for changing the reference frequency ω 0 in a direction in which the deviation signal DE becomes 0 value.

  The signal processor 44 performs feedback control on the reference frequency ω0 by repeating such processing, and locks the reference frequency ω0 to a state in which the reference frequency ω0 matches the resonance frequency ωs of the etalon 28.

  Next, processing of the processing unit related to the calibration of the temperature of the etalon 28 during the previous operation will be described.

  During a pre-operation such as when the apparatus 1 is turned on, the signal processor 70 connects the switch 74 to the signal processor 44 and inputs the control signal output from the signal processor 44 to the current driver 80. Thus, the frequency lock control of the laser light using the gas cell 20 is performed, and the reference frequency ω 0 of the laser light emitted from the laser light source 10 is locked to the center frequency ωa of the saturated absorption line of the gas cell 20.

  During the previous operation, the signal processor 70 outputs a temperature control signal for setting the temperature of the etalon 28 to a predetermined initial temperature to the temperature controller 30. The temperature controller 30 controls the temperature of the etalon 28 according to the temperature control signal input from the signal processor 70, and the signal processor 70 uses the current temperature (current temperature) of the etalon 28 detected by the temperature sensor as temperature information. Output to.

  The signal processor 70 confirms that the temperature of the etalon 28 is stable based on the temperature information input from the temperature controller 30, and then sets the temperature of the etalon 28 to one cycle of the modulation signal of the laser light with respect to the initial temperature. A temperature control signal that is modulated with a sufficiently large period (sufficiently small frequency) as compared with the minute time 2 · π / ωm is output to the temperature controller 30.

  That is, assuming that the signal value of the temperature control signal is a value corresponding to the temperature to be set by the etalon 28, a temperature obtained by adding a sine wave modulation signal having a sufficiently large period to the signal value corresponding to the initial temperature. A control signal is output to the temperature controller 30.

  Accordingly, when the temperature of the etalon 28 changes at a predetermined period, the resonance frequency ωs of the etalon 28 changes according to the temperature, and the magnitude of the detection signal IE (t) output from the photodetector 50 also changes.

  The signal processor 70 averages the detection signal IE (t) input from the photodetector 50 every time 2 · π / ωm of one period of the modulation signal of the laser light, and calculates the detection signal IE (t). The average value for every time 2 · π / ωm is obtained sequentially. Then, the temperature of the etalon 28 when the average value of the detection signal IE (t) shows the maximum value is detected as the calibration temperature.

  As the detection of the calibration temperature of the etalon 28, for example, the temperature of the temperature information given from the temperature controller 30 when the average value of the detection signal IE (t) indicates the maximum value, that is, the temperature indicated by the temperature sensor. Or the signal value of the temperature control signal output to the temperature controller 30 when the average value of the detection signal IE (t) indicates the maximum value, that is, for setting the etalon 28 to the calibration temperature. The signal value of the temperature control signal may be detected. In this embodiment, the latter is adopted, and the detected signal value of the temperature control signal is stored in the internal storage means as the calibration temperature value.

  Here, the resonance frequency ωs of the etalon 28 when the average value of the detection signal IE (t) shows the maximum value matches the reference frequency ω0 of the laser beam, and the gas cell 20 is used as the reference frequency ω0. By performing the frequency lock control of the laser light, it matches the center frequency ωa of the saturated absorption line of the gas cell 20.

  Therefore, the calibration temperature of the etalon 28 is a temperature at which the resonance frequency ωs of the etalon 28 matches the center frequency ωa of the saturated absorption line of the gas cell 20, and the calibration temperature value of the temperature control signal is the etalon 28 at the calibration temperature. The signal value of the temperature control signal for setting is shown.

  When the above processing is completed, the signal processor 70 outputs the temperature control signal of the calibration temperature value stored in the storage means to the temperature controller 30 and sets the etalon 28 to the calibration temperature.

  Then, the calibration of the temperature of the etalon 28 during the previous operation is finished.

  When detecting the temperature of the temperature information given from the temperature controller 30 when detecting the calibration temperature of the etalon 28 when the average value of the detection signal IE (t) shows the maximum value, the signal processor 70 Then, the temperature of the etalon 28 is set by outputting a temperature control signal to the temperature controller 30 so that the temperature of the etalon 28 indicated by the temperature information from the temperature controller 30 becomes the calibration temperature.

  Next, temperature control of the etalon 28 during this operation will be described. When the temperature calibration of the etalon 28 in the previous operation is completed as described above, the signal processor 70 switches the connection of the switch 74 from the signal processor 44 to the signal processor 54, and the control signal output from the signal processor 54 Is input to the current driver 80.

  As a result, the frequency lock control of the laser beam using the etalon 28 is started, and the reference frequency ω 0 of the laser beam emitted from the laser light source 10 is locked to the resonance frequency ωs of the etalon 28.

  Further, during this operation, the signal processor 70 maintains the temperature of the etalon 28 at the calibration temperature detected during the previous operation. That is, the temperature control signal of the calibration temperature value stored in the storage means is continuously output to the temperature controller 30 to maintain the temperature of the etalon 28 at the calibration temperature.

  According to this, since the temperature of the etalon 28 is controlled so as to become the calibration temperature, the resonance frequency ωs of the etalon 28 is maintained in a state where it matches the center frequency ωa of the saturated absorption line of the gas cell 20. Is locked to a state in which the reference frequency ω 0 of the laser beam emitted from the laser beam coincides with the center frequency ωa of the saturated absorption line of the gas cell 20.

  Further, the temperature fluctuation of the etalon 28 is reduced by the temperature control by the temperature controller 30, and a laser beam with high frequency stability and high accuracy can be obtained.

  Further, in the frequency lock control of the laser beam using the etalon 28, the frequency control range (frequency range where the lock cannot be released) is several hundred MHz, which is larger than that in the case of the gas cell 20. Therefore, it is difficult for the situation that the lock is released when the frequency of the laser beam fluctuates due to disturbance or the like, and the frequency of the laser beam can be stabilized for a long time.

  On the other hand, when the etalon 28 is controlled to be maintained at the calibration temperature by the temperature controller 30, the actual temperature of the etalon 28 is caused to resonate due to temperature measurement error (uncertainty). The frequency ωs may fluctuate from the calibration temperature that matches the center frequency ωa of the saturated absorption line of the gas cell 20.

  At this time, the resonance frequency ωs of the etalon 28 is shifted from the center frequency ωa of the saturated absorption line of the gas cell 20, and the reference frequency ω 0 of the laser beam is shifted from the center frequency ωa of the saturated absorption line of the gas cell 20.

  Therefore, it is preferable to correct the temperature of the etalon 28 as follows, and the apparatus 1 is configured to perform the temperature correction.

  During this operation, the signal processor 70 sets the switch 76 to the connected state (conducting state) and acquires the deviation signal DG output from the detector 42.

  If the deviation signal DG acquired from the detector 42 is not zero, the signal value of the temperature control signal output to the temperature controller 30 is corrected from the calibration temperature value based on the value of the deviation signal DG.

  That is, when the deviation signal DG is different from 0 value, it means that the resonance frequency ωs of the etalon 28 is shifted from the center frequency ωa of the saturated absorption line of the gas cell 20. Therefore, by correcting the calibration temperature value of the temperature control signal, the temperature of the etalon 28 is corrected so that the deviation signal DG becomes zero.

  By correcting the temperature of the etalon 28 based on the deviation signal DG, the reference frequency ω0 of the laser beam is more stable over a long time to the center frequency ωa of the saturated absorption line in the frequency lock control of the laser beam using the etalon 28. Therefore, a laser beam with higher frequency stability and accuracy can be obtained.

  Further, even if an instantaneous error occurs in the deviation signal DG output from the detector 42 due to disturbance such as vibration or sound, even if the temperature of the etalon 28 is corrected accordingly, the etalon 28 Therefore, if the deviation signal DG returns to a normal value, the temperature of the etalon 28 also returns to a normal value.

  The operation procedure in the laser frequency stabilizing device 1 will be described with reference to the flowchart of FIG.

  When the power is turned on, first, a pre-operation (warming up) process is performed.

  That is, in step S <b> 10, the signal processor 70 connects the switch 76 to the signal processor 44 and performs frequency lock control of laser light using the gas cell 20. Thereby, the reference frequency ω 0 of the laser light emitted from the laser light source 10 is locked to the center frequency ωa of the saturated absorption line of the gas cell 20.

  Subsequently, in step S12, the signal processor 70 stabilizes the temperature of the etalon 28 to a predetermined initial temperature by a temperature control signal output to the temperature controller 30, and then changes the temperature of the etalon 28 to detect light. Based on the detection signal output from the vessel 50, the temperature of the etalon 28 when the resonance frequency ωs of the etalon 28 matches the center frequency ωa of the saturated absorption line of the gas cell 20 is detected as the calibration temperature. Information relating to the detected calibration temperature (the signal value of the temperature control signal or the temperature value indicated by the temperature information from the temperature controller 30) is stored in the storage means.

  Next, in step S14, the signal processor 70 sets the temperature of the etalon 28 to the calibration temperature detected in step S12 by the temperature control signal output to the temperature controller 30.

  When the above pre-processing is completed, the process proceeds to the main processing.

  In step S <b> 16, the signal processor 70 connects the switch 74 to the signal processor 54, and performs the laser light frequency lock control using the etalon 28. As a result, the reference frequency ω0 of the laser light emitted from the laser light source 10 is locked to the resonance frequency ωs of the etalon 28 that matches the center frequency ωa of the saturated absorption line of the gas cell.

  Subsequently, in step 18, the signal processor 70 puts the switch 76 into a connected state (conductive state). Thereby, the deviation signal DG output from the detector 42 is acquired.

  Next, in step S20, the signal processor 70 determines whether or not the deviation signal DG acquired from the detector 42 is zero. That is, it is determined whether or not the reference frequency ω0 of the laser beam matches the center frequency ωa of the saturated absorption line of the gas cell. When it determines with NO, it transfers to step S22, and when it determines with YES, the process of step S20 is repeated.

  When the process proceeds to step S22, the signal processor 70 adjusts the temperature controller so that the deviation signal DG becomes 0, that is, the resonance frequency ωs of the etalon 28 matches the center frequency ωa of the saturated absorption line of the gas cell. The temperature of the etalon 28 is corrected by the temperature control signal output to 30. When the process of step S24 ends, the process returns to step S20, and the processes of step S20 and step S22 are repeated until the apparatus 1 is turned off.

  As described above, as the laser light source 10 in the above embodiment, a DBR-LD (Distributed Bragg Reflection Laser Diode) having a resonator in a semiconductor chip and capable of changing the resonator length by modulating the refractive index by current or It is preferable to use DFB-LD (Distributed FeedBack Laser Diode). However, the laser light source 10 is not limited to this. Moreover, it is not necessarily limited to a semiconductor laser.

  In addition, the frequency modulation of the laser light may be performed by a modulator disposed outside the laser light source 10. For example, as shown in FIG. 6, a modulator 90 is disposed between the beam splitter 12 and the polarization beam splitter 14 in FIG. 1, and the laser light having the reference frequency ω 0 from the laser light source 10 that has passed through the beam splitter 12 is modulated. 90 can be configured to modulate with a sine wave of frequency ωm. The modulation signal in the modulator 90 is given from the oscillator 60, for example.

  DESCRIPTION OF SYMBOLS 1 ... Laser frequency stabilization apparatus, 10 ... Laser light source, 12 ... Beam splitter, 14, 16, 24 ... Polarizing beam splitter, 18, 26 ... 1/4 wavelength plate, 20 ... Gas cell, 22 ... Mirror, 28 ... Etalon, DESCRIPTION OF SYMBOLS 30 ... Temperature controller, 40, 50 ... Photo detector, 42, 52 ... Detector, 44, 54, 70 ... Signal processor, 60 ... Oscillator, 62, 64 ... Amplifier, 74, 76 ... Switch, 80 ... Current Driver, 90 ... modulator

Claims (12)

A light source that emits laser light;
A light splitting means for splitting the laser light emitted from the light source into a first laser light and a second laser light;
A first optical system including a gas cell through which the first laser beam split by the light splitting unit passes;
First light detection means for detecting a first detection signal indicating the light intensity of the first laser light that has passed through the first optical system;
Based on the first detection signal detected by the first light detection means, the laser emitted from the light source so that the frequency of the laser light emitted from the light source matches the center frequency of the saturated absorption line of the gas cell. First control means for controlling the frequency of light;
A second optical system including an etalon through which the second laser light split by the light splitting means passes;
Second light detection means for detecting a second detection signal indicating the light intensity of the second laser light that has passed through the second optical system;
Based on the second detection signal detected by the second light detection means, the frequency of the laser light emitted from the light source is adjusted so that the frequency of the laser light emitted from the light source matches the resonance frequency of the etalon. Second control means for controlling;
Control switching means for setting the control of the frequency of the laser light emitted from the light source so as to be switchable between control by the first control means and control by the second control means. At the time of performing the previous pre-operation, the control of the frequency of the laser light emitted from the light source is set to control by the first control means, and at the time of carrying out the main operation, the laser light emitted from the light source Control switching means for setting frequency control to control by the second control means;
Temperature control means for controlling the temperature of the etalon;
With
The temperature control means acquires a second detection signal detected by the second light detection means while changing the temperature of the etalon when the pre-operation is performed, and based on the acquired second detection signal Etalon calibration temperature detection means for detecting the temperature of the etalon when the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell as a calibration temperature;
Etalon temperature maintaining means for maintaining the temperature of the etalon at the calibration temperature detected by the etalon calibration temperature detecting means during the implementation of the main operation;
A laser frequency stabilization device.   In the temperature control means, the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means when the operation is performed. The laser frequency stabilizing device according to claim 1, further comprising etalon temperature correcting means for correcting the temperature of the etalon.   The first control means calculates a deviation between the frequency of the laser light emitted from the light source and the center frequency of the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means. First deviation signal detecting means for detecting the first deviation signal, and the frequency of the laser beam emitted from the light source is set so that the first deviation signal becomes 0 or smaller than the current value. The laser frequency stabilization device according to claim 1 or 2 to be controlled.   The second control means has a second deviation indicating a deviation between the frequency of the laser light emitted from the light source and the resonance frequency of the etalon based on the second detection signal detected by the second light detection means. A second deviation signal detecting means for detecting a signal is provided, and the frequency of the laser beam emitted from the light source is controlled so that the second deviation signal becomes zero or smaller than a current value. The laser frequency stabilizing device according to 1, 2, or 3. The laser beam emitted from the light source is a laser beam frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0.
The said 1st deviation signal detection means detects the said 1st deviation signal based on the signal component of the frequency of the odd multiple of frequency (omega) m contained in the 1st detection signal detected by the said 1st optical detection means. A laser frequency stabilizing device as described in 1. above. The laser beam emitted from the light source is a laser beam frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0.
5. The second deviation signal detection unit detects the second deviation signal based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the second detection signal detected by the second light detection unit. A laser frequency stabilizing device as described in 1. above. A light source that emits laser light;
A light splitting means for splitting the laser light emitted from the light source into a first laser light and a second laser light;
A first optical system including a gas cell through which the first laser beam split by the light splitting unit passes;
First light detection means for detecting a first detection signal indicating the light intensity of the first laser light that has passed through the first optical system;
Based on the first detection signal detected by the first light detection means, the laser emitted from the light source so that the frequency of the laser light emitted from the light source matches the center frequency of the saturated absorption line of the gas cell. First control means for controlling the frequency of light;
A second optical system including an etalon through which the second laser light split by the light splitting means passes;
Second light detection means for detecting a second detection signal indicating the light intensity of the second laser light that has passed through the second optical system;
Based on the second detection signal detected by the second light detection means, the frequency of the laser light emitted from the light source is adjusted so that the frequency of the laser light emitted from the light source matches the resonance frequency of the etalon. Second control means for controlling;
Control switching means for setting the control of the frequency of the laser light emitted from the light source to be switchable between one of the control by the first control means and the control by the second control means;
Temperature control means for controlling the temperature of the etalon;
A laser frequency stabilization method in a laser frequency stabilization device comprising:
The control switching means sets the control of the frequency of the laser light emitted from the light source to the control by the first control means at the time of execution of the previous operation before the main operation, and at the time of execution of the main operation, Set the control of the frequency of the laser light emitted from the light source to the control by the second control means,
The temperature control means acquires a second detection signal detected by the second light detection means while changing the temperature of the etalon when the pre-operation is performed, and based on the acquired second detection signal Then, the temperature of the etalon when the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell is detected as a calibration temperature. maintain,
Laser frequency stabilization method.   In the temperature control means, the resonance frequency of the etalon coincides with the center frequency of the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means when the operation is performed. The laser frequency stabilization method according to claim 7, wherein the temperature of the etalon is corrected as described above.   The first control means calculates a deviation between the frequency of the laser light emitted from the light source and the center frequency of the saturated absorption line of the gas cell based on the first detection signal detected by the first light detection means. First deviation signal detecting means for detecting the first deviation signal, and the frequency of the laser beam emitted from the light source is set so that the first deviation signal becomes 0 or smaller than the current value. The laser frequency stabilization method according to claim 7 or 8, wherein the laser frequency stabilization method is controlled.   The second control means has a second deviation indicating a deviation between the frequency of the laser light emitted from the light source and the resonance frequency of the etalon based on the second detection signal detected by the second light detection means. A second deviation signal detecting means for detecting a signal is provided, and the frequency of the laser beam emitted from the light source is controlled so that the second deviation signal becomes zero or smaller than a current value. The laser frequency stabilization method according to 7, 8, or 9. The laser beam emitted from the light source is a laser beam frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0.
The first deviation signal detecting means detects the first deviation signal based on a signal component having a frequency that is an odd multiple of the frequency ωm included in the first detection signal detected by the first light detecting means. The laser frequency stabilization method described in 1. The laser beam emitted from the light source is a laser beam frequency-modulated by a sine wave having a frequency ωm with respect to a reference frequency ω0.
The said 2nd deviation signal detection means detects the said 2nd deviation signal based on the signal component of the frequency of the odd multiple of frequency (omega) m contained in the 2nd detection signal detected by the said 2nd light detection means. The laser frequency stabilization method described in 1.

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