阅读说明：本技术 基于脉冲调制宽谱梳齿型激光的碘分子光钟及其控制方法 (Iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser and control method thereof ) 是由 陈景标 商浩森 关笑蕾 何进 李春来 潘俊 胡国庆 于 2020-04-27 设计创作，主要内容包括：本发明涉及基于脉冲调制宽谱梳齿型激光的碘分子光钟及控制方法。该碘分子光钟的电源控制系统生成脉冲调制信号传至激光系统生成脉冲信号,经隔离器对后方光路的光反馈隔离,隔离器之后依次连接第一半波片和第一偏振分光棱镜；激光稳频光路为依次连接的第二半波片和第二偏振分光棱镜；第二偏振分光棱镜之后分两束：光强较强一束作为泵浦激光依次经格兰泰勒棱镜、第三半波片和电光相位调制器,被第三偏振分光棱镜反射至光路倍增系统；光强较弱一束作为探测激光光路倍增系统和第三偏振分光棱镜,被高速光电探测器接收后输入至激光鉴相及高速伺服反馈控制电路,产生电源控制系统的伺服信号。(The invention relates to an iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser and a control method. The power supply control system of the iodine molecule optical clock generates a pulse modulation signal, transmits the pulse modulation signal to the laser system to generate a pulse signal, and isolates the optical feedback of a rear optical path through an isolator, and a first half-wave plate and a first polarization beam splitter prism are sequentially connected behind the isolator; the laser frequency stabilizing light path comprises a second half-wave plate and a second polarization beam splitter prism which are connected in sequence; the second polarization beam splitter prism is divided into two beams: one beam with stronger light intensity is used as pump laser, passes through the Glan Taylor prism, the third half-wave plate and the electro-optic phase modulator in sequence, and is reflected to the light path multiplication system by the third polarization beam splitting prism; and one beam with weaker light intensity is used as a detection laser light path multiplication system and a third polarization beam splitter prism, is received by the high-speed photoelectric detector and then is input into the laser phase discrimination and high-speed servo feedback control circuit, and generates a servo signal of the power supply control system.)

1. An iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth-shaped laser is characterized by comprising a 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system, an isolator, a first half-wave plate, a second half-wave plate, a third half-wave plate, a fourth half-wave plate, a first polarization beam splitter prism, a second polarization beam splitter prism, a third polarization beam splitter prism, a Glan Taylor prism, an electro-optic phase modulator, an iodine molecule absorption cell optical path multiplication system, a high-speed photoelectric detector, a laser phase discrimination and high-speed servo control circuit and a power supply control system, wherein the Glan Taylor prism is used for changing the polarization direction of laser and further inhibiting the residual amplitude modulation; the power supply control system generates a pulse modulation signal, transmits the pulse modulation signal to 532nm laser and sends the pulse modulation signal to a laser system, and the laser system generates a comb-tooth-shaped 532nm laser pulse signal under the action of the pulse modulation signal, wherein the frequency spectrum interval between any two adjacent comb teeth of the comb-tooth-shaped 532nm laser pulse signal is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400-50 GHz and is matched with Doppler broadening of a molecular spectrum in a corresponding temperature absorption cell, and the line width of a single comb tooth is smaller than the line width of a transition energy level; the isolator is connected behind the laser system and used for isolating the optical feedback of the rear optical path; the first half-wave plate and the first polarization beam splitter prism are sequentially connected behind the isolator; the first polarization beam splitter prism is divided into two paths: a laser frequency stabilization light path and a frequency stabilization laser emitting light path; the laser frequency stabilizing light path comprises a second half-wave plate and a second polarization beam splitter prism which are connected in sequence; the second polarization beam splitter prism is divided into two beams: one beam with stronger light intensity is used as pump laser, and is reflected to the light path multiplication system of the iodine molecule absorption cell by the third polarization beam splitter prism after sequentially passing through the Glan Taylor prism, the third half-wave plate and the electro-optic phase modulator; one beam with weaker light intensity is used as detection laser, passes through an iodine molecule absorption cell light path multiplication system and a third polarization beam splitter prism, and is received by a high-speed photoelectric detector; the signal of the high-speed photoelectric detector is input to a laser phase discrimination and high-speed servo feedback control circuit and is sequentially connected with a power supply control system and a photoelectric phase modulator; the generated servo signal is used for controlling a power supply control system, so that laser output with high frequency stability is realized.

2. The pulse-modulated wide-spectrum comb-tooth laser-based iodine molecule optical clock according to claim 1, wherein the laser system is composed of a narrow linewidth laser and a frequency doubling system; the narrow linewidth laser adopts an Nd-YAG solid laser, the laser is obtained by frequency multiplication of Nd-YAG laser, and the narrow linewidth laser has the tuning characteristics of open loop frequency, power stability, narrow linewidth and precise frequency; or semiconductor 532nm laser is used, and the 532nm laser is obtained by frequency doubling Nd-YAG laser.

3. The iodine molecule optical clock based on the pulse modulation wide-spectrum comb-tooth laser as claimed in claim 1, wherein the iodine molecule absorption cell optical path multiplication system comprises a first reflection prism, a second reflection prism, a third reflection prism, an iodine molecule absorption cell and a temperature control module; wherein, the iodine molecule absorption pool is a cylinder formed by sealing and burning quartz glass and is divided into an iodine bubble and a cold finger; the temperature control module consists of a temperature control circuit, a semiconductor refrigeration piece, a thermistor and a heat insulation material, wherein the semiconductor refrigeration piece and the heat insulation material are sequentially wrapped outside the iodine molecule absorption pool; the temperature control module provides enough saturated vapor pressure for the refrigeration iodine molecule absorption pool and reduces the influence of external temperature fluctuation on the quantum reference spectral line; the pumping laser and the detection laser reversely and coaxially pass through the light path multiplication system and pass through the triple folded light path, so that the actual absorption length of the four times of the length of the iodine molecule absorption pool is realized.

4. The iodine molecule optical clock based on the pulse modulation wide-spectrum comb-tooth laser as claimed in claim 3, wherein the iodine molecule absorption cell optical path multiplication system further comprises a first four-hole diaphragm and a second four-hole diaphragm respectively disposed at the front and rear ends of the iodine molecule absorption cell for solving the problem of stray light caused by multiple transmission on the window sheets at the two ends of the iodine molecule absorption cell and multiple reflection by the reflecting prism.

5. The pulse-modulated wide-spectrum comb-tooth-type laser-based iodine molecule optical clock according to claim 1, wherein the laser phase discrimination and high-speed servo control circuit comprises a signal source for generating a radio frequency modulation signal, a mixer for performing mixing demodulation on a high-speed photoelectric detector signal, and a high-speed servo feedback circuit for generating a servo signal; a radio frequency modulation signal generated by a signal source is divided into two paths, one path is input into an electro-optic phase modulator to carry out phase modulation on pump laser, and the other path is input into a mixer to carry out frequency mixing demodulation with a high-speed photoelectric detector signal to obtain an error signal; after the error signal passes through the high-speed servo feedback circuit, the generated servo signal is fed back to a fast feedback port and a slow feedback port of the power control system, and high-speed full-bandwidth locking is realized.

6. The pulse-modulated wide-spectrum comb-tooth-type laser-based iodine molecule optical clock according to claim 1, wherein the adjustable spectral interval between any two adjacent comb teeth is 1-5MHz, and further comprising: the iodine molecule saturation spectral line width is 400kHz, and the frequency interval between the comb teeth is more than twice the spectral line width.

7. An iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth type laser is characterized by comprising a 532nm pulse modulation wide-spectrum comb-tooth type laser system, an isolator, a first half wave plate, a second half wave plate, a third half wave plate, a fourth half wave plate, a first polarization beam splitter prism, a second polarization beam splitter prism, a third polarization beam splitter prism, an electro-optic phase modulator, an iodine molecule absorption cell optical path multiplying system, a high-speed photoelectric detector, a laser phase discrimination and high-speed servo control circuit, a power supply control system and an external laser modulator, wherein the power supply control system generates pulse modulation signals, divides the pulse modulation signals into two paths, respectively applies the two paths to the external laser modulator and transmits 532nm laser to a laser system, the laser system generates comb-tooth type 532nm laser pulse signals with a plurality of frequency components under the action of the pulse modulation signals, the split power is adjusted through the matching of the first half-wave plate and the first polarization beam splitter prism, and the laser is split into two beams, one beam is used for a laser frequency stabilization light path, and the other beam is used as a frequency stabilization laser emergent light path; the frequency spectrum interval between any two adjacent comb teeth of a comb-shaped 532nm laser pulse signal is adjustable from 1 MHz to 5MHz, the total frequency spectrum width is adjustable from 400MHz to 50GHz, the total frequency spectrum width is matched with Doppler broadening of molecular spectrums in corresponding temperature absorption cells, and the line width of a single comb tooth is smaller than the transition energy level line width; the laser used for the laser frequency stabilization light path is sequentially connected with a second half-wave plate and a second polarization beam splitter prism, and is divided into two beams with different light intensities by the second half-wave plate and the second polarization beam splitter prism, wherein one beam with stronger light intensity is used as pump laser, one beam with weaker light intensity is used as detection laser, and the two beams of the pump laser and the detection laser are reversely coincided; the high-speed photoelectric detector receives signals input into a laser phase discrimination and high-speed servo control circuit and is sequentially connected with a power supply control system and an electro-optical phase modulator, and the generated servo signals are used for controlling the power supply control system, so that laser output with high frequency stability is realized.

8. A control method based on a pulse modulation wide-spectrum comb-tooth type laser iodine molecule optical clock is characterized by comprising the following steps:

the ⑴ power control system transmits the generated pulse modulation signal to a 532nm pulse modulation wide-spectrum laser system, the 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system generates a comb-tooth-shaped 532nm laser signal, the frequency spectrum interval between any two adjacent comb teeth is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400-50 GHz, and the line width of a single comb tooth is smaller than the line width of a transition energy level;

⑵ comb-tooth-shaped 532nm laser with multiple frequency components passes through an isolator, and then is sequentially matched by a first half-wave plate and a first polarization beam splitter prism to adjust the beam splitting power and divide the laser into two beams, wherein one beam is used for a laser frequency stabilizing light path, and the other beam is used as a frequency stabilizing laser emitting light path;

⑶ dividing the beam into two beams with different light intensity by a second half-wave plate and a second polarization beam splitter prism, wherein the beam with stronger light intensity is used as pump laser, the beam with weaker light intensity is used as detection laser, the two beams of laser are reversely superposed, interact with almost all the iodine molecules in the speed group in the iodine molecule absorption cell light path multiplication system, and the detection laser is received by a high-speed photoelectric detector;

⑷ in the light path multiplication system of the iodine molecule absorption cell, the pump laser and the detection laser are reversely and coaxially incident, and the actual absorption length of 4 times of the iodine molecule absorption cell length is realized through the triple folding light path of the first reflection prism, the second reflection prism and the third reflection prism;

⑸ laser phase discrimination and high speed servo feedback control circuit comprises a signal source for generating radio frequency modulation signal, a mixer for mixing and demodulating high speed photoelectric detector signal, a high speed servo feedback circuit for generating servo signal, an electro-optic phase modulator driven by the signal source to modulate the phase of the pump laser, and a mixer for mixing and demodulating the high speed photoelectric detector signal to obtain error signal, which is fed back to the fast feedback port and the slow feedback port of the power control system via the high speed servo feedback circuit to realize high speed full bandwidth locking of laser frequency, thereby realizing iodine molecule optical clock based on pulse modulation wide spectrum comb tooth type laser.

9. The method for controlling the pulse-modulated wide-spectrum comb-tooth-shaped laser iodine molecule optical clock according to claim 8, wherein the pulse-modulated wide-spectrum comb-tooth-shaped laser system in step ⑴ is composed of a narrow-line-width laser and a frequency doubling system, the narrow-line-width laser is a Nd-YAG solid laser, the laser is obtained by frequency doubling of Nd-YAG laser, and the narrow-line-width laser has tuning characteristics of open-loop frequency and power stability and narrow line width and precision frequency, or the semiconductor 532nm laser is used, and the 532nm laser is obtained by frequency doubling of Nd-YAG laser.

10. The control method of the pulse modulation wide-spectrum comb-tooth-type laser iodine molecule optical clock according to claim 8, wherein the temperature control module in the step ⑶ comprises a temperature control circuit, a semiconductor refrigeration piece, a thermistor and a heat insulation material, the temperature control module is used for achieving high-precision temperature control of the iodine molecule absorption pool, the semiconductor refrigeration piece and the heat insulation material are sequentially wrapped outside the iodine molecule absorption pool, the thermistor is arranged below the semiconductor refrigeration piece and close to the wide center of the piece, the thermistor and the semiconductor refrigeration piece are connected into the temperature control circuit through conducting wires and used for measuring temperature and refrigerating the iodine molecule absorption pool, and the laser frequency stabilization optical path in the step ⑶ adopts a modulation-transfer spectrum frequency stabilization technology of rapid phase modulation.

Technical Field

The invention relates to the technical field of optical frequency atomic clocks and optical frequency quantum frequency standards, in particular to an iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser and a control method thereof.

Background

The 532nm iodine absorption transition is ground state absorption, and compared with other adjacent wave bands, the absorption coefficient is larger, and the line width is narrower, so that the 532nm iodine molecule frequency standard has excellent frequency stability in the visible light wave band, and the frequency stability Allan deviation of 5 × 10-14 in 1s sampling time can reach, and the iodine molecule is one of the recommended standards defined by recurring meters.

In the prior art [ e.g. "532 nm iodine molecule optical frequency standard", zang-di army, et al, vol. 32, 2 nd, p. 203-208 of the Chinese laser ], a 532nm solid laser frequency standard device for iodine molecule frequency stabilization is disclosed, which aims to provide a molecular frequency standard realized by using hyperfine components in the oscillation transition of iodine molecules as natural references. Compared with an atomic or ionic frequency standard, the technical scheme has the advantages of relatively simple structure, less cost, easy realization and excellent short-term frequency stability. But has the following disadvantages: by utilizing single-frequency laser output, only a few iodine molecules with transverse speed close to zero speed contribute to a frequency stabilization signal of a transition spectral line, the effective utilization rate of the iodine molecules is very low, and the further improvement of the frequency stability index of an optical clock of the iodine molecules is limited. In addition, because the molecular transition absorption is weak, in order to improve the effective utilization rate of the iodine molecules, the length of an iodine molecule absorption pool is usually designed to be dozens of centimeters or even meters, the temperature control difficulty is high when the iodine molecule absorption pool is applied, and the system volume is large. If the absorption length of the interaction between the laser beam and the iodine molecule is short, an error control signal with a high signal-to-noise ratio cannot be obtained, which is very unfavorable for further improving the frequency stability of the iodine molecule optical clock.

Disclosure of Invention

The first technical problem to be solved by the present invention is to provide a pulse modulation wide-spectrum comb-tooth type 532nm laser system comprising a plurality of frequency components, which is generated by applying a pulse modulation signal to the 532nm pulse modulation wide-spectrum laser system, so that the pulse modulation wide-spectrum comb-tooth type 532nm laser system interacts with almost all iodine molecules of different transverse velocity groups, more iodine molecules in an iodine molecule absorption pool can participate in contribution to a transition spectral line frequency stabilization signal, the effective utilization rate of the iodine molecules can be increased by hundreds of times, and further, the extremely high signal-to-noise ratio is realized, thereby increasing the laser frequency stability by approaching magnitude and being based on the pulse modulation wide-spectrum comb-tooth type laser, and a control method thereof. The second technical problem solved by the invention is to provide an iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser and a control method thereof, wherein the iodine molecule optical clock is capable of improving the laser frequency stability close to magnitude level, greatly shortening the length of the iodine molecule absorption pool on the basis of improving the signal to noise ratio of the hyperfine spectral line of the iodine molecule optical clock and realizing a miniaturized iodine molecule optical clock, aiming at the problems that the length of an iodine molecule absorption pool is designed to be dozens of centimeters or even meters in order to improve the effective utilization rate of iodine molecules in the prior art, so that the difficulty in controlling the temperature is high and the system size is large. The third technical problem solved by the invention is to provide a thought and a development direction for improving the effective utilization rate of molecules and further improving the signal-to-noise ratio of hyperfine spectral lines for other molecular frequency standards with weak absorption, and the iodine molecular optical clock based on pulse modulation wide-spectrum comb-tooth laser and the control method thereof have wider application prospects in the field of future molecular frequency standards. The fourth technical problem solved by the invention is to provide a iodine molecule optical clock and a control method thereof based on pulse modulation broad-spectrum comb-tooth type laser, wherein a first four-hole diaphragm and a second four-hole diaphragm are respectively arranged at the front end and the rear end of an iodine molecule absorption cell, so that the stray light problem caused by multiple transmission on window sheets at two ends of the iodine molecule absorption cell and multiple reflection of a reflecting prism can be effectively solved, and the problem of stray light caused by multiple transmission on the window sheets at two ends of the iodine molecule absorption cell and the multiple reflection of the reflecting prism can be effectively solved The method is carried out.

The technical scheme of the invention is that the iodine molecule optical clock based on the pulse modulation wide-spectrum comb-tooth-shaped laser is characterized by comprising a 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system, an isolator, a first half wave plate, a second half wave plate, a third half wave plate, a fourth half wave plate, a first polarization beam splitter prism, a second polarization beam splitter prism, a third polarization beam splitter prism, a Glan Taylor prism for changing the polarization direction of the laser and further inhibiting the residual amplitude modulation, an electro-optic phase modulator, an iodine molecule absorption cell light path multiplication system, a high-speed photoelectric detector, a laser phase discrimination and high-speed servo control circuit and a power supply control system, wherein the laser phase discrimination and high-speed servo control circuit are used for generating radio frequency modulation signals, demodulating, filtering and phase discrimination error signals and controlling high-speed servo feedback; the power supply control system generates a pulse modulation signal, transmits the pulse modulation signal to 532nm laser and sends the pulse modulation signal to a laser system, and the laser system generates a comb-tooth-shaped 532nm laser pulse signal under the action of the pulse modulation signal, wherein the frequency spectrum interval between any two adjacent comb teeth of the comb-tooth-shaped 532nm laser pulse signal is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400-50 GHz and is matched with Doppler broadening of a molecular spectrum in a corresponding temperature absorption cell, and the line width of a single comb tooth is smaller than the line width of a transition energy level; the isolator is connected behind the laser system and used for isolating the optical feedback of the rear optical path; the first half-wave plate and the first polarization beam splitter prism are sequentially connected behind the isolator; the first polarization beam splitter prism is divided into two paths: a laser frequency stabilization light path and a frequency stabilization laser emitting light path; the laser frequency stabilizing light path comprises a second half-wave plate and a second polarization beam splitter prism which are connected in sequence; the second polarization beam splitter prism is divided into two beams: one beam with stronger light intensity is used as pump laser, and is reflected to the light path multiplication system of the iodine molecule absorption cell by the third polarization beam splitter prism after sequentially passing through the Glan Taylor prism, the third half-wave plate and the electro-optic phase modulator; one beam with weaker light intensity is used as detection laser, passes through an iodine molecule absorption cell light path multiplication system and a third polarization beam splitter prism, and is received by a high-speed photoelectric detector; the signal of the high-speed photoelectric detector is input to a laser phase discrimination and high-speed servo feedback control circuit and is sequentially connected with a power supply control system and a photoelectric phase modulator; the generated servo signal is used for controlling a power supply control system, so that laser output with high frequency stability is realized.

Furthermore, the laser system consists of a narrow linewidth laser and a frequency doubling system; the narrow linewidth laser adopts an Nd-YAG solid laser, the laser is obtained by frequency multiplication of Nd-YAG laser, and the narrow linewidth laser has the tuning characteristics of open loop frequency, power stability, narrow linewidth and precise frequency; or semiconductor 532nm laser is used, and the 532nm laser is obtained by frequency doubling Nd-YAG laser.

Further, the iodine molecule absorption cell optical path multiplication system comprises a first reflecting prism, a second reflecting prism, a third reflecting prism, an iodine molecule absorption cell and a temperature control module; wherein, the iodine molecule absorption pool is a cylinder formed by sealing and burning quartz glass and is divided into an iodine bubble and a cold finger; the temperature control module consists of a temperature control circuit, a semiconductor refrigeration piece, a thermistor and a heat insulation material, wherein the semiconductor refrigeration piece and the heat insulation material are sequentially wrapped outside the iodine molecule absorption pool; the temperature control module provides enough saturated vapor pressure for the refrigeration iodine molecule absorption pool and reduces the influence of external temperature fluctuation on the quantum reference spectral line; the pumping laser and the detection laser reversely and coaxially pass through the light path multiplication system and pass through the triple folded light path, so that the actual absorption length of the four times of the length of the iodine molecule absorption pool is realized.

Furthermore, the optical path multiplication system of the iodine molecule absorption pool also comprises a first four-hole diaphragm and a second four-hole diaphragm which are respectively arranged at the front end and the rear end of the iodine molecule absorption pool and used for solving the problem of stray light caused by multiple transmission on window sheets at two ends of the iodine molecule absorption pool and multiple reflection of a reflecting prism.

Furthermore, the laser phase discrimination and high-speed servo control circuit comprises a signal source for generating a radio frequency modulation signal, a mixer for performing mixing demodulation on a high-speed photoelectric detector signal, and a high-speed servo feedback circuit for generating a servo signal; a radio frequency modulation signal generated by a signal source is divided into two paths, one path is input into an electro-optic phase modulator to carry out phase modulation on pump laser, and the other path is input into a mixer to carry out frequency mixing demodulation with a high-speed photoelectric detector signal to obtain an error signal; after the error signal passes through the high-speed servo feedback circuit, the generated servo signal is fed back to a fast feedback port and a slow feedback port of the power control system, and high-speed full-bandwidth locking is realized.

Further, the adjustable frequency spectrum interval between any two adjacent comb teeth of 1-5MHz further comprises: the iodine molecule saturation spectral line width is 400kHz, and the frequency interval between the comb teeth is more than twice the spectral line width.

The iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser is characterized by comprising a 532nm pulse modulation wide-spectrum comb-tooth laser system, an isolator, a first half wave plate, a second half wave plate, a third half wave plate, a fourth half wave plate, a first polarization beam splitter prism, a second polarization beam splitter prism, a third polarization beam splitter prism, an electro-optic phase modulator, an iodine molecule absorption cell optical path multiplication system, a high-speed photoelectric detector, a laser phase discrimination and high-speed servo control circuit, a power supply control system and an external laser modulator, wherein the power supply control system generates pulse modulation signals, divides the pulse modulation signals into two paths, respectively applies the two paths to the external laser modulator and transmits 532nm laser to the laser system, the laser system generates comb-tooth 532nm laser pulse signals with a plurality of frequency components under the action of the pulse modulation signals, the split power is adjusted through the matching of the first half-wave plate and the first polarization beam splitter prism, and the laser is split into two beams, one beam is used for a laser frequency stabilization light path, and the other beam is used as a frequency stabilization laser emergent light path; the frequency spectrum interval between any two adjacent comb teeth of a comb-shaped 532nm laser pulse signal is adjustable from 1 MHz to 5MHz, the total frequency spectrum width is adjustable from 400MHz to 50GHz, the total frequency spectrum width is matched with Doppler broadening of molecular spectrums in corresponding temperature absorption cells, and the line width of a single comb tooth is smaller than the transition energy level line width; the laser used for the laser frequency stabilization light path is sequentially connected with a second half-wave plate and a second polarization beam splitter prism, and is divided into two beams with different light intensities by the second half-wave plate and the second polarization beam splitter prism, wherein one beam with stronger light intensity is used as pump laser, one beam with weaker light intensity is used as detection laser, and the two beams of the pump laser and the detection laser are reversely coincided; the high-speed photoelectric detector receives signals input into a laser phase discrimination and high-speed servo control circuit and is sequentially connected with a power supply control system and an electro-optical phase modulator, and the generated servo signals are used for controlling the power supply control system, so that laser output with high frequency stability is realized.

The invention also provides a technical scheme of the control method of the pulse modulation wide-spectrum comb-tooth-shaped laser iodine molecule optical clock, which is characterized by comprising the following steps of:

the ⑴ power control system transmits the generated pulse modulation signal to a 532nm pulse modulation wide-spectrum laser system, the 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system generates a comb-tooth-shaped 532nm laser signal, the frequency spectrum interval between any two adjacent comb teeth is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400-50 GHz, and the line width of a single comb tooth is smaller than the line width of a transition energy level;

⑵ comb-tooth-shaped 532nm laser with multiple frequency components passes through an isolator, and then is sequentially matched by a first half-wave plate and a first polarization beam splitter prism to adjust the beam splitting power and divide the laser into two beams, wherein one beam is used for a laser frequency stabilizing light path, and the other beam is used as a frequency stabilizing laser emitting light path;

⑶ dividing the beam into two beams with different light intensity by a second half-wave plate and a second polarization beam splitter prism, wherein the beam with stronger light intensity is used as pump laser, the beam with weaker light intensity is used as detection laser, the two beams of laser are reversely superposed, interact with almost all the iodine molecules in the speed group in the iodine molecule absorption cell light path multiplication system, and the detection laser is received by a high-speed photoelectric detector;

⑷ optical path multiplication system of iodine molecule absorption cell, pump laser and detection laser are incident reversely and coaxially, and the actual absorption length of 4 times iodine molecule absorption cell length is realized by three times folding optical path through the first reflection prism, the second reflection prism and the third reflection prism;

⑸ the laser phase discrimination and high speed servo control circuit generates the modulation signal to drive the electro-optic phase modulator to modulate the phase of the pump laser, and the high speed photoelectric detector signal is input to the laser phase discrimination and high speed servo control circuit to demodulate, filter and discriminate the phase, to obtain the error signal, which is fed back to the fast feedback port and the slow feedback port of the power control system through the high speed servo feedback circuit, to realize the high speed full bandwidth locking of the laser frequency, and further realize the iodine molecule optical clock based on the pulse modulation wide spectrum comb tooth type laser.

The invention also provides a technical scheme of the control method of the pulse modulation wide-spectrum comb-tooth-shaped laser iodine molecule optical clock, which is characterized by comprising the following steps of:

the ⑴ power control system transmits the generated pulse modulation signal to a 532nm pulse modulation wide-spectrum laser system, the 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system generates a comb-tooth-shaped 532nm laser signal, the frequency spectrum interval between any two adjacent comb teeth is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400-50 GHz, and the line width of a single comb tooth is smaller than the line width of a transition energy level;

⑵ comb-tooth-shaped 532nm laser with multiple frequency components passes through an isolator, and then is sequentially matched by a first half-wave plate and a first polarization beam splitter prism to adjust the beam splitting power and divide the laser into two beams, wherein one beam is used for a laser frequency stabilizing light path, and the other beam is used as a frequency stabilizing laser emitting light path;

⑶ dividing the beam into two beams with different light intensity by a second half-wave plate and a second polarization beam splitter prism, wherein the beam with stronger light intensity is used as pump laser, the beam with weaker light intensity is used as detection laser, the two beams of laser are reversely superposed, interact with almost all the iodine molecules in the speed group in the iodine molecule absorption cell light path multiplication system, and the detection laser is received by a high-speed photoelectric detector;

⑷ in the light path multiplication system of the iodine molecule absorption cell, the pump laser and the detection laser are reversely and coaxially incident, and the actual absorption length of 4 times of the iodine molecule absorption cell length is realized through the triple folding light path of the first reflection prism, the second reflection prism and the third reflection prism;

⑸ laser phase discrimination and high speed servo feedback control circuit comprises a signal source for generating radio frequency modulation signal, a mixer for mixing and demodulating high speed photoelectric detector signal, a high speed servo feedback circuit for generating servo signal, an electro-optic phase modulator driven by the signal source to modulate the phase of the pump laser, and a mixer for mixing and demodulating the high speed photoelectric detector signal to obtain error signal, which is fed back to the fast feedback port and the slow feedback port of the power control system via the high speed servo feedback circuit to realize high speed full bandwidth locking of laser frequency, thereby realizing iodine molecule optical clock based on pulse modulation wide spectrum comb tooth type laser.

The pulse modulation wide-spectrum comb-tooth type laser system is further composed of a narrow-line-width laser and a frequency doubling system, wherein the narrow-line-width laser adopts a Nd-YAG solid laser, the laser is obtained by frequency doubling of Nd-YAG laser, and the narrow-line-width laser has the tuning characteristics of open loop frequency and power stability and narrow line width and precision frequency, or semiconductor 532nm laser is used, and the 532nm laser is obtained by frequency doubling of the Nd-YAG laser.

Furthermore, the temperature control module in step ⑶ includes a temperature control circuit, a semiconductor refrigeration chip, a thermistor and a thermal insulation material for realizing high-precision temperature control of the iodine molecule absorption cell, the semiconductor refrigeration chip and the thermal insulation material are sequentially wrapped outside the iodine molecule absorption cell, the thermistor is arranged below the semiconductor refrigeration chip and close to the wide center of the chip, the thermistor and the semiconductor refrigeration chip are connected to the temperature control circuit through wires for measuring temperature and refrigerating the iodine molecule absorption cell, and the laser frequency stabilization optical path in step ⑶ adopts a modulation transfer spectrum frequency stabilization technology of rapid phase modulation.

Compared with the prior art, the invention has the beneficial effects that:

⑴ the invention relates to an iodine molecule optical clock based on pulse modulation wide-spectrum comb tooth type laser, which generates comb tooth type 532nm laser signal by applying pulse modulation signal to 532nm pulse modulation wide-spectrum laser system, the comb tooth type 532nm laser signal contains multiple frequency components, and interacts with almost all iodine molecules with different transverse velocity groups, so that more iodine molecules in an iodine molecule absorption pool can participate in the contribution to the transition spectral line frequency stabilization signal, the effective utilization rate of the iodine molecules is increased by hundreds of times, the signal-to-noise ratio of the hyperfine spectral line of the iodine molecule optical clock is increased by orders of magnitude, and the laser frequency stability is increased by approaching to orders of magnitude.

⑵ the length of the iodine molecule absorption cell is designed to dozens of centimeters or even meters in order to improve the effective utilization rate of iodine molecules in the prior art, which leads to the problems of high difficulty in temperature control and large system volume during application.

⑶ the invention not only realizes the further improvement of the frequency stability index of iodine molecule optical clock, but also provides a thought and development direction for improving the effective utilization rate of molecules for other molecular frequency standards (such as methane, carbon dioxide, etc.) with weak absorption, thereby improving the signal-to-noise ratio of hyperfine spectral lines, and the future molecular frequency standard field will have wider application prospect.

⑷ the pump laser and the detection laser of the invention are reversely coaxial and pass through the optical path multiplication system, and the actual absorption length of four times of the iodine molecule absorption pool length is realized by three times of folding optical paths.

Drawings

FIG. 1 is a schematic structural diagram of an embodiment of an iodine molecule optical clock (internal modulation) based on a pulse modulation wide-spectrum comb-tooth type laser of the invention;

FIG. 2 is a schematic structural diagram of an embodiment of an iodine molecule optical clock (external modulation) based on a pulse modulation wide-spectrum comb-tooth type laser of the invention;

FIG. 3 is a schematic structural diagram of an optical path multiplication system of an iodine molecule absorption cell in an iodine molecule optical clock embodiment based on pulse modulation wide-spectrum comb-tooth laser.

Description of the main component symbols:

laser system 1 isolator 2 first half-wave plate 3

First polarization beam splitter 4, second half-wave plate 5 and second polarization beam splitter 6

The third half-wave plate 8 electro-optical phase modulator 9 of the Glan Taylor prism 7

Fourth half-wave plate 11 and third polarization beam splitter prism 12 of optical path multiplying system 10

High-speed photoelectric detector 13 laser phase discrimination and high-speed servo control circuit 14 power supply control system 15

External laser modulator 16 first reflecting prism 301 and second reflecting prism 302

Third reflecting prism 303 iodine molecule absorption cell 304 first four-hole diaphragm 305

Second four-aperture stop 306 temperature control module 307

Detailed Description

The invention will be described in more detail below with reference to the accompanying drawings:

fig. 1 and 3 show a first embodiment of the present invention.

Referring to fig. 1, an internal modulation method is adopted for a 532nm pulse modulation wide-spectrum comb-tooth laser system 1, and an iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser includes: the 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system for applying pulse modulation signals comprises a 532nm pulse modulation wide-spectrum comb-tooth-shaped laser system 1, an isolator 2, a first half-wave plate 3, a second half-wave plate 5, a third half-wave plate 8, a fourth half-wave plate 11, a first polarization splitting prism 4, a second polarization splitting prism 6, a third polarization splitting prism 12, a Glan Taylor prism 7, an electro-optic phase modulator 9, an iodine molecule absorption cell optical path multiplication system 10, a high-speed photoelectric detector 13, a laser phase discrimination and high-speed servo control circuit 14 and a power supply control system 15. The power control system 15 generates a pulse modulation signal and transmits the pulse modulation signal to the 532nm pulse modulation wide-spectrum comb-tooth type laser system 1; the 532nm pulse modulation wide-spectrum comb tooth type laser system 1 generates a comb tooth type 532nm laser signal, the frequency spectrum interval between any two adjacent comb teeth is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400MHz-50GHz, and the line width of a single comb tooth is smaller than the line width of a transition energy level;

the 532nm comb-tooth-shaped laser with a plurality of frequency components passes through the isolator 2, the splitting power of the 532nm comb-tooth-shaped laser is adjusted by matching the first half wave plate 3 and the first polarization splitting prism 4 in sequence, the 532nm comb-tooth-shaped laser divides the laser into two beams, one beam is used for a laser frequency stabilizing light path, and the other beam is used as a frequency stabilizing laser emitting light path;

a laser beam used for a laser frequency stabilization light path is divided into two beams with weak light intensity and strong light intensity by a second half-wave plate 5 and a second polarization beam splitter prism 6. One beam with a plurality of frequency components and strong light intensity is subjected to phase modulation by the electro-optic phase modulator 9 and then is reversely coincided with one beam of laser with weak light intensity, and interacts with iodine molecules of all velocity groups in the iodine molecule absorption cell light path multiplication system 10. The driving signal of the electro-optic phase modulator 9 is generated by a laser phase discrimination and high-speed servo control circuit 14, after the driving signal is acted, a beam of laser with weaker light intensity is received by a high-speed photoelectric detector 13, the photoelectric detection signal is input into the laser phase discrimination and high-speed servo control circuit 14 to be demodulated, filtered and discriminated to obtain an error signal, and the laser phase discrimination and high-speed servo control circuit 14 controls a power supply control system 15 to obtain laser output with high frequency stability.

Referring to fig. 3, an optical path multiplication system 10 of an iodine molecule absorption cell in an iodine molecule optical clock based on pulse modulation wide-spectrum comb-tooth laser includes: a first reflecting prism 301, a second reflecting prism 302, a third reflecting prism 303, an iodine molecule absorption cell 304, a first 4-hole diaphragm 305, a second 4-hole diaphragm 306 and a temperature control module 307. The laser beam with strong light intensity split by the second polarization beam splitter prism 6 and the laser beam with weak light intensity are reversely and coaxially incident, and the light path is folded for three times through the first reflecting prism 301, the second reflecting prism 302 and the third reflecting prism 303, so that the actual absorption length of 4 times of the length of the iodine molecule absorption cell is realized. In order to avoid the influence of stray light, a first four-aperture diaphragm 305 and a second four-aperture diaphragm 306 are respectively disposed at the front end and the rear end of the iodine molecule absorption cell 304. The temperature control module 307 is used for performing high-precision temperature control on the iodine molecule absorption cell 304.

In this embodiment, the temperature control module in the optical path multiplication system of the iodine molecule absorption cell is composed of a temperature control circuit, a semiconductor refrigeration chip, a thermistor and a thermal insulation material, and is used for refrigerating the iodine molecule absorption cell, providing sufficient saturated vapor pressure and reducing the influence of external temperature fluctuation on the quantum reference spectral line.

The laser phase discrimination and high-speed servo control circuit 14 comprises a signal source for generating a radio frequency modulation signal, a mixer for performing mixing demodulation on a high-speed photoelectric detector signal, and a high-speed servo feedback circuit for generating a servo signal; a radio frequency modulation signal generated by a signal source is divided into two paths, one path is input into an electro-optic phase modulator to carry out phase modulation on pump laser, and the other path is input into a mixer to carry out frequency mixing demodulation with a high-speed photoelectric detector signal to obtain an error signal; after the error signal passes through the high-speed servo feedback circuit, the generated servo signal is fed back to a fast feedback port and a slow feedback port of the power control system, and high-speed full-bandwidth locking is realized.

Referring to fig. 1 and fig. 3, the method for controlling a pulse modulation wide-spectrum comb-tooth type laser iodine molecule optical clock includes the following steps:

the ⑴ power control system 15 transmits the generated pulse modulation signal to the 532nm pulse modulation wide spectrum laser system 1, the 532nm pulse modulation wide spectrum comb-tooth type laser system 1 generates a comb-tooth shape 532nm laser signal, the frequency spectrum interval between any two adjacent comb teeth is adjustable within 1-5MHz, the total frequency spectrum width is adjustable within 400MHz-50GHz, and the line width of a single comb tooth is smaller than the line width of a transition energy level;

⑵ comb-tooth-shaped 532nm laser with multiple frequency components passes through the isolator 2, the split power is adjusted by matching the first half-wave plate 3 and the first polarization beam splitter prism 4 in sequence, and the laser is divided into two beams, one beam is used for a laser frequency stabilizing light path, and the other beam is used as a frequency stabilizing laser emitting light path;

⑶, dividing the laser beam in the frequency-stabilized optical path into two beams with different light intensities by a second half-wave plate 5 and a second polarization beam splitter prism 6 in sequence, wherein one beam with stronger light intensity is used as a pump laser, the other beam with weaker light intensity is used as a detection laser, the two beams of the pump laser and the detection laser are reversely superposed, interact with almost all the iodine molecules in the iodine molecule absorption cell optical path multiplication system 10 with the temperature control module 307, and the detection laser is received by a high-speed photoelectric detector 13;

⑷ the optical path multiplication system 10 of the iodine molecule absorption pool with the temperature control module 307, the pump laser and the detection laser are reversely and coaxially incident, and the optical path is folded three times through the first reflection prism 301, the second reflection prism 302 and the third reflection prism 303, so that the actual absorption length of four times the length of the iodine molecule absorption pool is realized;

⑸ the laser phase discrimination and high speed servo feedback control circuit 14 comprises a signal source for generating radio frequency modulation signal, a mixer for mixing and demodulating the high speed photoelectric detector signal, a high speed servo feedback circuit for generating servo signal, the signal source generates modulation signal to drive the electro-optic phase modulator 9, phase modulates the pump laser, inputs the high speed photoelectric detector 13 signal into the mixer for mixing and demodulating to obtain error signal, the error signal is fed back to the fast feedback port and the slow feedback port of the power control system 15 by the high speed servo feedback circuit to realize the high speed full bandwidth locking of laser frequency, and further realize the iodine molecule optical clock based on pulse modulation wide spectrum comb tooth type laser.

In this embodiment, the pulse-modulated wide-spectrum comb-tooth laser system 1 described in step ⑴ is composed of a narrow-line-width laser and a frequency doubling system, the narrow-line-width laser is a Nd: YAG solid-state laser, and the laser is obtained by frequency doubling of Nd: YAG laser, and has tuning characteristics of open-loop frequency and power stability, and narrow line width and precision frequency, or is obtained by frequency doubling of Nd: YAG laser using semiconductor 532nm laser, and 532nm laser.

In this embodiment, the temperature control module 307 in step ⑶ includes a temperature control circuit, a semiconductor chilling plate, a thermistor and a thermal insulation material for realizing high-precision temperature control of the iodine molecule absorption cell, the semiconductor chilling plate and the thermal insulation material are sequentially wrapped outside the iodine molecule absorption cell, the thermistor is placed below the semiconductor chilling plate and near the center of the plate width, the thermistor and the semiconductor chilling plate are connected to the temperature control circuit through wires for measuring temperature and refrigerating the iodine molecule absorption cell, and the laser frequency stabilization optical path in step ⑶ adopts a modulation transfer spectrum frequency stabilization technology of fast phase modulation.

Fig. 2 and 3 show a second embodiment of the present invention.

Referring to fig. 2 and 3, an external modulation method is adopted for the 532nm pulse modulation wide-spectrum comb-tooth type laser system 1, and a pulse modulation signal generated by the power control system 15 is applied to an external laser modulator 16, such as an electro-optical modulator, and other processes are the same as the internal modulation method shown in fig. 1 of the first embodiment, and are not described herein again.

The above-mentioned embodiments are only preferred embodiments of the present invention, and all equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.