CN114649732A - Saturated absorption spectrum laser frequency locking method and device and frequency-locked laser - Google Patents
Saturated absorption spectrum laser frequency locking method and device and frequency-locked laser Download PDFInfo
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Abstract
The invention provides a saturated absorption spectrum laser frequency locking method, wherein a beam of laser is used as pump light to enter an atomic gas chamber, the part of the pump light emitted from the atomic gas chamber, which is transmitted by a partial reflector, carries Doppler broadening background information and is converted into a first electric signal by a first photoelectric detector; the part of the pump light emitted from the atomic gas chamber, which is reflected by the partial reflector, is detection light carrying Doppler broadening background information and saturated absorption spectrum information, and is converted into a second electric signal by a second photoelectric detector; the differential amplifier receives and processes the first electric signal and the second electric signal and outputs a third electric signal with Doppler broadening background information eliminated; the phase-locked amplifier receives and processes the third electric signal, outputs an error signal, and the error signal is received by the negative feedback controller, converted into a frequency-locked signal and fed back to the laser. The invention can eliminate Doppler broadening background information in saturated absorption spectrum information by only using one laser beam, realizes laser frequency locking and has simple light path design.
Description
Technical Field
The invention relates to the technical field of laser frequency locking, in particular to a saturated absorption spectrum laser frequency locking method and device and a frequency-locked laser.
Background
The ruby laser is used as an artificial light source and has the characteristics of high intensity, good coherence and the like. The laser is widely applied to the fields of military, medical treatment, industrial production, precision measurement and the like, such as laser guidance, laser cosmetology, laser welding, laser marking, optical frequency marking, atomic magnetometer and the like. In the field of precision measurement, lasers are used as pump sources or detection means for polarization of atomic ensembles or for sensing atomic states. The frequency, light intensity and polarization stability of the laser determine the level of precision measurement. In practical applications, the laser frequency may be shifted due to external environmental disturbances, such as vibration and temperature variation. The slow drift of the center frequency of a free running laser within 5 minutes can reach tens of megahertz. For optical precision measurements, the frequency fluctuations of the laser strongly influence the sensitivity of the measurement. Active frequency locking is required in addition to ensuring constant temperature and preventing external vibration.
There are many methods for locking the frequency of a laser, and one of the more common methods is to lock the frequency of the laser to an appropriate atomic transition frequency, thereby obtaining a laser with high spectral purity, narrow line width, and high frequency stability. The saturated absorption spectrum frequency locking technology is one of the commonly used laser frequency locking technologies. The method adopts the transition frequency between atomic energy levels as a reference, obtains a frequency discrimination error signal by comparing the laser frequency with the reference frequency, and then corrects the laser frequency by feedback to lock the laser frequency at the atomic transition reference frequency, thereby stabilizing the laser frequency.
The traditional frequency locking of the saturated absorption spectrum is to divide laser output by a laser into two beams (pump light with strong light intensity and probe light with weak light intensity), and to inject the two beams into an atomic gas chamber simultaneously in opposite incidence directions. When the laser frequency is appropriate, only atoms with zero velocity along the direction of light propagation can interact with both beams of laser light simultaneously. Because the intensity of the pumping light is high, a large number of particles distributed at the lower energy level are pumped to the upper energy level, and the absorption capacity of atoms on the detection light is weakened when weaker detection light passes through, so that a convex transmission peak called a saturated absorption peak is obtained by detection on a light path of a transmission atom gas chamber. The frequency corresponding to the highest point of the saturated absorption peak is the central frequency of the laser. The purpose of laser frequency locking is to lock the center frequency of the laser. Because the velocity distribution of atoms obeys the Boltzmann distribution, the formed Doppler absorption spectrum has a very wide background. The saturated absorption peak is the transmission peak on the large doppler absorption background. The Doppler background affects the signal-to-noise ratio of the signal and the laser frequency locking. In order to eliminate the influence of the doppler background and highlight the information of the saturated absorption spectrum, obtain a higher signal-to-noise ratio and more conveniently lock the highest point of the transmission peak, a method for eliminating the doppler background is usually introduced.
Currently, the doppler background is usually eliminated by introducing a reference optical path. The specific method is to divide the laser emitted by the same light source into three beams. Two beams of weaker light pass through the atomic gas cell in parallel along different spatial locations, one beam is called the reference beam and the other beam is called the probe beam. The other beam of strong light is called as pumping light, and after passing through a proper light path, the pumping light is reversely incident from the atomic gas chamber and is opposite to the detection light, so that a saturated absorption spectrum structure is formed. And the reference light directly passes through the atomic gas chamber and is incident to the photoelectric detector, and carries Doppler broadening background information. And finally, subtracting the saturated absorption spectrum information obtained by the probe light and the Doppler background signal obtained by the reference light to obtain the saturated absorption spectrum information without Doppler broadening of the background.
However, the method of introducing the reference optical path eliminates the doppler background by using a complicated device structure, which is not favorable for applications, and especially under the condition of compact requirement, the multiple beams increase the complexity and volume of the device.
Disclosure of Invention
In order to solve the existing problems, the Doppler broadening background information in the saturated absorption spectrum information can be eliminated by only using one laser beam, the laser frequency locking is realized, and the light path design is simple. Meanwhile, the invention can eliminate the common mode interference of the external boundary to the frequency locking system or the intensity fluctuation of the laser by using the method of differential signal frequency locking, thereby effectively reducing the requirements on the performance of the laser, in particular to the laser with obvious light intensity fluctuation.
One embodiment of the present invention provides a saturated absorption spectrum laser frequency locking method, including:
after incident laser provided by the laser is split by the light splitting device, one laser beam is used as pump light and is incident to the atomic gas chamber;
pump light emitted from the atomic gas cell: the part transmitted by the partial reflector carries Doppler broadening background information, and is detected by a first photoelectric detector and converted into a first electric signal; the part reflected by the partial reflector is detection light, and the detection light carries Doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, is detected by a second photoelectric detector and is converted into a second electric signal;
the first electric signal and the second electric signal are received and processed by a differential amplifier, and a third electric signal is output, wherein the third electric signal contains saturated absorption spectrum information with Doppler spread background information eliminated;
the third electric signal is received and processed by a phase-locked amplifier, an error signal is output, and the error signal is received by a negative feedback controller, converted into a frequency-locked signal and fed back to the laser.
Further, the part transmitted by the partial reflecting mirror carries doppler spread background information, and is detected by the first photodetector and converted into a first electrical signal, specifically:
the part transmitted by the partial reflector carries Doppler broadening background information, is attenuated to a light intensity range capable of being detected by the first photoelectric detector by the optical filter, is focused to the first photoelectric detector by the first lens, is detected by the first photoelectric detector and is converted into a first electric signal.
Further, after the incident laser provided by the laser is split by the splitting device, one of the laser beams is used as a pump beam and is incident to the atomic gas cell, specifically:
incident laser provided by the laser is split by a first assembly consisting of a first 1/2 wave plate and a first prism, wherein one laser beam reflected by the first prism is standby laser, and one laser beam transmitted by the first prism is transmitted by a second assembly consisting of a second 1/2 wave plate and a second prism and then is used as pump light to be incident to an atomic gas cell.
Further, a part reflected by the partial reflector is detection light, and the detection light carries doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, and is detected by a second photodetector and converted into a second electrical signal, specifically:
the part reflected by the partial reflector is detection light, the detection light passes through the atomic gas cell, carries Doppler broadening background information and saturation absorption spectrum information, is completely reflected by a third component consisting of 1/4 wave plates and the second prism, is arranged on either side of the atomic gas cell, is focused to the second photoelectric detector by the second lens, and is detected by the second photoelectric detector and converted into a second electric signal.
Furthermore, the first photoelectric detector and the second photoelectric detector are both phototubes capable of responding to optical signals with light of the central wavelength of the optical device; wherein the optical device includes: the first 1/2 wave plate, the first prism, the second 1/2 wave plate, the second prism, and the partial mirror.
Further, the first prism and the second prism are both polarization splitting prisms.
Further, the atomic gas cell is made of pyrex glass.
Further, the negative feedback controller is a proportional-integral-derivative controller.
An embodiment of the invention provides a saturated absorption spectrum laser frequency locking device, which comprises a laser, an atomic gas chamber, a photoelectric detector, a differential amplifier, a phase-locked amplifier, a proportional-integral-derivative controller and a related optical device, wherein the saturated absorption spectrum laser frequency locking device is used for realizing any one saturated absorption spectrum laser frequency locking method.
One embodiment of the invention provides a frequency-locked laser which is a tunable laser and is used for realizing any one of the saturated absorption spectrum laser frequency locking methods.
Compared with the prior art, the embodiment of the invention has the beneficial effects that:
1. the invention provides a saturated absorption spectrum laser frequency locking method, wherein a beam of laser is used as pump light to enter an atomic gas chamber, the part of the pump light emitted from the atomic gas chamber, which is transmitted by a partial reflector, carries Doppler broadening background information, and the Doppler broadening background information is detected by a first photoelectric detector and converted into a first electric signal; the part of the pump light emitted from the atomic gas chamber, which is reflected by the partial reflector, is detection light, and the detection light carries Doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, is detected by a second photoelectric detector and is converted into a second electric signal; a differential amplifier receives and processes the first electric signal and the second electric signal, and outputs a third electric signal, wherein the third electric signal contains saturated absorption spectrum information with Doppler spread background information eliminated; the phase-locked amplifier receives and processes the third electric signal and outputs an error signal; the error signal is received by a negative feedback controller, converted into a frequency locking signal and fed back to the laser; the invention can eliminate Doppler broadening background information in saturated absorption spectrum information by only using one laser beam, realizes laser frequency locking and has simple light path design.
2. According to the laser frequency locking method for the saturated absorption spectrum, the 1/4 wave plate and the second prism are used for completely reflecting the detection light, so that the detection light is prevented from being emitted into a laser and damaging the laser.
3. According to the laser frequency locking method for the saturated absorption spectrum, the common-mode interference of the external boundary to a frequency locking system or the intensity fluctuation of a laser can be eliminated by using a differential signal frequency locking method.
4. The laser frequency locking device for the saturated absorption spectrum effectively reduces the requirements on the performance of the laser, and particularly relates to the laser with obvious light intensity fluctuation.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a method for frequency locking of a laser with a saturated absorption spectrum according to an embodiment of the present invention;
FIG. 2 is a flowchart of a method for laser frequency locking of a saturable absorption spectrum according to another embodiment of the present invention;
fig. 3 is a structural diagram of a saturated absorption spectrum laser frequency locking device according to an embodiment of the present invention;
fig. 4 is a structural diagram of a saturated absorption spectrum laser frequency locking device according to another embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be understood that the step numbers used herein are for convenience of description only and are not used as limitations on the order in which the steps are performed.
It is to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "comprises" and "comprising" indicate the presence of the described features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items.
In order to solve the technical problems of complex device structure and unfavorable application caused by the fact that Doppler broadening background information in absorption spectrum information is eliminated through multiple beams of light in the prior art, the Doppler broadening background information in saturated absorption spectrum information can be eliminated only through one beam of laser, laser frequency locking is achieved, and the light path design is simple.
A first aspect.
Please refer to fig. 1 and fig. 3. One embodiment of the present invention provides a method for laser frequency locking of a saturated absorption spectrum, including:
s10, after the incident laser light provided by the laser is split by the beam splitter, one of the laser light is incident to the atomic gas cell as pump light.
The laser 10 refers to a device capable of emitting laser light, and is not limited to a fiber laser or a semiconductor laser.
The light splitting device 20 is used for splitting the laser light provided by the laser, and the light splitting device 20 is not limited to an optical device such as a polarization splitting prism.
The atomic gas cell 30 is used to provide a reference frequency required for laser frequency locking. In one embodiment of the present invention, the atomic gas cell 30 may be a cylindrical glass bubble with a bottom diameter of 20mm and a height of 40 mm. In another embodiment of the present invention, the atomic gas cell 30 may be selected from pyrex glass. In another embodiment of the present invention, the atomic chamber is filled with helium (A), (B), (C), (D) and E)4He) atomic gas.
S20, pump light emitted from the atomic gas cell: the part transmitted by the partial reflector carries Doppler broadening background information, and is detected by a first photoelectric detector and converted into a first electric signal; the part reflected by the partial reflector is detection light, and the detection light carries Doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, is detected by a second photoelectric detector and is converted into a second electric signal.
The pumping light is emitted from the atomic gas chamber 30 and carries Doppler broadening background information, and then the pumping light is emitted to the partial reflector 40; the transmitted portion of the partially reflective mirror 40 carries the doppler broadened background information and is detected by the first photodetector 50 and converted into a first electrical signal, i.e. said first electrical signal carries the doppler broadened background information; the part reflected by the partial reflecting mirror 40 is probe light, the probe light carries doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas cell 30 in the opposite direction to the pumping light, and the probe light is detected by the second photodetector 60 and converted into a second electrical signal, that is, the second electrical signal carries the doppler broadening background information and the saturation absorption spectrum information.
It should be noted that, by adjusting the transmittance of the partial mirror 40, most of the light intensity of the pump light is transmitted through the partial mirror 40, and a small part of the light intensity is reflected from the mirror surface of the partial mirror 40, and the reflected light is defined as probe light.
In an embodiment of the present invention, the first photodetector 50 and the second photodetector 60 are both phototubes, and are both used for converting an optical signal into an electrical signal and reading information carried by the optical signal; that is, the first photodetector 50 converts the optical signal of the pump light into a first electrical signal to read doppler spread background information carried by the pump light, and the second photodetector 60 converts the optical signal of the probe light into a second electrical signal to read doppler spread background information and saturated absorption spectrum information carried by the probe light.
S30, receiving and processing the first electric signal and the second electric signal by a differential amplifier, and outputting a third electric signal, wherein the third electric signal contains saturated absorption spectrum information with Doppler spread background information eliminated.
The first electrical signal carrying the doppler broadening background information and the second electrical signal carrying the doppler broadening background information and the saturation absorption spectrum information are subjected to operation processing by the differential amplifier 70 to obtain a third electrical signal, wherein the third electrical signal contains the saturation absorption spectrum information with the doppler broadening background information removed.
And S40, the third electric signal is received and processed by a phase-locked amplifier, an error signal is output, and the error signal is received and converted into a frequency-locked signal by a negative feedback controller and fed back to the laser.
And the lock-in amplifier 80 is used for demodulating the third electric signal to determine the central frequency point of the laser. The negative feedback controller 90 is a proportional-integral-derivative controller (also called PID controller) for closing the frequency locking system to perform laser frequency locking. It should be noted that the lock-in amplifier 80 and the negative feedback controller 90 can also be implemented by software programming.
The invention provides a saturated absorption spectrum laser frequency locking method, wherein a beam of laser is used as pump light to enter an atomic gas chamber, the part of the pump light emitted from the atomic gas chamber, which is transmitted by a partial reflector, carries Doppler broadening background information, and the Doppler broadening background information is detected by a first photoelectric detector and converted into a first electric signal; the part of the pump light emitted from the atomic gas chamber, which is reflected by the partial reflector, is detection light, and the detection light carries Doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, is detected by a second photoelectric detector and is converted into a second electric signal; a differential amplifier receives and processes the first electric signal and the second electric signal, and outputs a third electric signal, wherein the third electric signal contains saturated absorption spectrum information with Doppler spread background information eliminated; the phase-locked amplifier receives and processes the third electric signal and outputs an error signal; the error signal is received by a negative feedback controller, converted into a frequency locking signal and fed back to the laser; the invention can eliminate Doppler broadening background information in saturated absorption spectrum information by only using one laser beam, realizes laser frequency locking and has simple light path design.
Referring to fig. 2 and 4, in one embodiment:
step S10 specifically includes:
s11, splitting the incident laser provided by the laser by a first assembly consisting of a first 1/2 wave plate and a first prism, wherein one laser beam reflected by the first prism is standby laser, and one laser beam transmitted by the first prism is completely transmitted by a second assembly consisting of a second 1/2 wave plate and a second prism and then is used as pump light to be incident to an atom gas cell.
The first 1/2 wave plate 22 and the first prism 23 are used to divide the laser output from the laser 10 into two beams according to a preset light intensity ratio or light splitting ratio, one beam is used for standby or for each specific laser application scenario, which may be called standby laser, and the other beam is emitted into the second module. The preset light intensity proportion or the light splitting proportion can be adjusted according to actual needs, and the specific operation is as follows: rotating the first 1/2 wave plate 22 causes the first prism 23 to split the light beam into two beams according to a predetermined intensity ratio. The first prism 23 is not limited to a polarization splitting prism. It should be noted that the purpose of the first component is to split light, and is not limited to use of the above two components, and if the laser is a fiber output, a fiber splitter may be used to split light.
The second 1/2 wave plate 24 and the second prism 25 are used to control the intensity of the laser, and the specific operations are as follows: the second 1/2 wave plate 24 is rotated so that the laser light is completely transmitted from the second prism 25 without being reflected, and after transmission, is used as pump light.
Step S20 includes:
s21, the part transmitted by the partial reflector carries Doppler broadening background information, is attenuated to a light intensity range capable of being detected by the first photoelectric detector by the optical filter, is focused to the first photoelectric detector by the first lens, and is detected by the first photoelectric detector and converted into a first electric signal.
The pumping light carrying the doppler broadening background information after being emitted from the atomic gas cell 30 is emitted to the partial reflector 40, is emitted to the optical filter 41 through a part of the partial reflector 40, is attenuated to a light intensity range capable of being detected by the first photoelectric detector 50 by the optical filter 41, is emitted to the first lens 42, is focused to the first photoelectric detector 50 by the first lens 42, is detected by the first photoelectric detector 50 and is converted into a first electric signal carrying the doppler broadening background information.
The filter 41 is a neutral density filter, and the absorption rate of the neutral density filter 41 is adjusted to attenuate the intensity of the pump light transmitted from the partial reflecting mirror 40 to a light intensity range capable of being detected by the first photodetector 50. The first lens 42 is a first plano-convex lens, and the distance of the first plano-convex lens 42 is adjusted so that the pump light is focused on the sensing element of the first photodetector 50, and the optical signal of the pump light is converted into a first electrical signal.
S22, the part reflected by the partial reflector is detection light, the detection light passes through the atomic gas cell, carries Doppler broadening background information and saturation absorption spectrum information, is totally reflected by a third component consisting of a 1/4 wave plate and a second prism, is arranged on either side of the atomic gas cell, is focused to a second photoelectric detector by a second lens, and is detected by the second photoelectric detector and converted into a second electric signal.
The pumping light carrying the doppler broadening background information after exiting from the atomic gas cell 30 is then directed to the partial mirror 40, and the portion reflected by the partial mirror 40 is the probe light. In a specific embodiment, after passing through the atomic gas cell 70 in the opposite direction to the pumping light, the detection light carries doppler broadening background information and saturation absorption spectrum information, passes through the third assembly composed of the 1/4 wave plate 26 and the second prism 25, is totally reflected, and then is directed to the second lens 61, focused by the second lens 61 to the second photodetector 60, and detected by the second photodetector 60 and converted into a second electrical signal. In another embodiment, the detection light passes through the atomic gas cell 30 after being emitted to the 1/4 wave plate 26, and carries the doppler broadening background information and the saturation absorption spectrum information, the detection light emitted from the atomic gas cell 30 is emitted to the second prism 35, and under the action of the third assembly composed of the 1/4 wave plate 26 and the second prism 25, the detection light is totally reflected and emitted to the second lens 61, is focused to the second photodetector 60 by the second lens 61, and is detected by the second photodetector 60 and converted into the second electrical signal.
According to the saturated absorption spectrum laser frequency locking method provided by the invention, the 1/4 wave plate and the second prism are used for completely reflecting the detection light so as to prevent the detection light from being emitted into the laser and damaging the laser. The method of using the differential signal frequency locking can eliminate the common mode interference of the external limit to the frequency locking system or the intensity fluctuation of the laser.
A second aspect.
Referring to fig. 4, an embodiment of the invention provides a frequency locking device for a laser with a saturated absorption spectrum, which includes:
the first 1/2 wave plate 22 and the first prism 23 are used for dividing the output laser of the laser 10 into two beams, one beam is specially used for laser frequency locking, and the other beam is used for various specific laser application scenes. The purpose of this structure is to split light, and is not limited to use of the above two devices, and if the laser 10 is an optical fiber output, a fiber splitter may be used to split light, and the splitting ratio may be adjusted according to actual needs.
A second 1/2 wave plate 24, a second prism 25 for controlling the intensity of the pumping light, and the combination of the second prism 25 and the 1/4 wave plate 26 makes the detection light backward propagating from the other end of the optical path totally reflected from the second prism 25, realizes the splitting of the detection light, and prevents the backward propagating detection light from damaging the laser 10.
The atomic gas cell 30 is used for interacting with the pumping light and the probe light to generate the information of the saturated absorption spectrum, it should be noted that the atomic gas cell 30 is placed behind the second prism 25, and the 1/4 wave plate 26 can be placed in front of or behind the atomic gas cell 30 (fig. 4 is: 1/4 wave plate placed in front of the atomic gas cell), so that the final frequency locking effect is not affected.
And the partial reflector 40 is used for reflecting one part of the pumping light back to the atomic gas cell 30, defined as probe light, and transmitting the other part of the pumping light, wherein the pumping light transmitted through the partial reflector carries Doppler broadening background information. The reflection ratio of the partial mirror 40 is adjusted according to the light intensity requirement in order to improve the signal-to-noise ratio.
And a filter 41 for attenuating the intensity of the light beam transmitted from the partial mirror 40, wherein the filter 41 may be a neutral density filter.
A first lens 42 for focusing the light beam on a first photodetector 50, said first lens 42 may be a plano-convex lens.
The first photodetector 50 converts the optical signal of the pump light into a first electrical signal, and reads doppler spread background information carried by the pump light.
The arrangement of the first prism 25 along the direction perpendicular to the exit light of the laser 10 comprises:
a second lens 61 for focusing light onto the second photodetector 60, wherein the second lens 61 may be a plano-convex lens.
The second photodetector 60 converts the optical signal of the detection light into a second electrical signal, and reads the saturation absorption spectrum information and the doppler spread background information carried by the detection light.
The differential amplifier 70 performs a differential operation on the first electrical signal carrying the doppler broadening background information and the second electrical signal carrying the saturation absorption spectrum information and the doppler broadening background information to obtain a third electrical signal, where the third electrical signal includes the saturation absorption spectrum information with the doppler broadening background information removed.
And the lock-in amplifier 80 is configured to demodulate the third electrical signal to obtain an error signal based on the transition frequency of the atom in the atom gas cell, so as to determine the center frequency point of the laser 10.
The negative feedback controller 90 is used to close the system for laser frequency locking, and the negative feedback controller 90 may be a proportional-integral-derivative controller (also called PID controller).
The lock-in amplifier 80 and the negative feedback controller 90 can also be implemented by software programming.
In a specific embodiment, a frequency locking method by the saturated absorption spectrum laser frequency locking device includes:
s001, dividing a laser beam emitted from a laser 10 modulated by a signal generator into two beams by a first 1/2 wave plate 22 and a first prism 23 according to different light intensity ratios, wherein one beam is used for frequency locking of a saturated absorption spectrum, and the other beam is used for various practical applications.
The first prism 23 splits the light beam into two laser beams with different intensity ratios by rotating the first 1/2 wave plate 22.
S002, the pumping light for the frequency locking of the saturated absorption spectrum is adjusted to be completely transmitted by the second 1/2 wave plate 24, enters the second prism 25, is converted into circularly polarized light by the 1/4 wave plate 26, then enters the atom gas chamber 30, pumps atoms and enables atom samples to reach saturated absorption; alternatively, the atoms may be first incident on the atom cell 30, pumped to saturate the atom sample, and then passed through the 1/4 waveplate 26 to achieve polarization conversion.
The second 1/2 wave plate 24 is used to adjust the linear polarization direction of the laser light so that the laser light is completely transmitted through the second prism 25 without being reflected by the second prism 25. The second prism 25 is used to separate out the probe light which is subsequently reflected back, the 1/4 wave plate 26 is used to convert the linearly polarized light into circularly polarized light, and the atom gas cell 30 is used to provide the reference frequency required for laser locking.
The second 1/2 wave plate 24 is rotated so that the laser light is fully transmitted from the second prism 25 without being reflected. The beam that is now completely transmitted through the second prism 25 acts as pump light.
The pump light passes through 1/4 wave plate 26, whose polarization state changes from linear polarization to circular polarization, and then enters atom gas cell 30 to pump the atoms to a saturated absorption state.
And S003, the pump light emitted from the atomic gas cell 30 is incident on the partial reflector 40, wherein a part of the pump light is transmitted through the partial reflector 40 to carry Doppler broadening background information, is attenuated to light intensity which can be detected by the first photoelectric detector 50 by the optical filter 41, and is focused on the first photoelectric detector 50 by the first lens 42 to provide a first electric signal carrying saturated absorption spectrum information and Doppler broadening background information.
The transmittance of the partial mirror 40 is adjusted so that most of the light intensity of the pump light is transmitted through the partial mirror 40 and a small portion of the light intensity is reflected from the mirror surface of the partial mirror 40, which is defined as probe light.
The absorption rate of the filter 41 is adjusted so that the intensity of the pump light transmitted from the partial mirror 40 is attenuated to a range detectable by the first photodetector 50.
The distance of the first lens 42 is adjusted so that the pump light is focused on the sensing element of the first photodetector 50 and the optical signal of the pump light is converted into a first electrical signal.
S004 the pumping light emitted from the atomic gas cell 30 is reflected by the surface of the partial mirror 40, defined as probe light, and enters the atomic gas cell 30 again in the direction opposite to the direction of the pumping light. The probe light entering the atomic gas cell 30 carries the saturation absorption information and the doppler broadening background information through the atomic gas cell 30.
And S005, the detection light carrying the saturated absorption spectrum information and the Doppler broadening background information enters 1/4 wave plate 26 in the direction opposite to the direction of the pumping light, and is converted into linearly polarized light by circularly polarized light, and the polarization direction of the linearly polarized light is perpendicular to the polarization direction of the linearly polarized light which enters along the direction of the pumping light before.
The detection light emitted from the 1/4 wave plate 26 at S006 is incident into the second prism 25, totally reflected by the second prism 25, and focused on the second photodetector 60 through the second lens 61, so as to provide a second electrical signal carrying saturated absorption information and doppler spread background information.
And S007, sending the first electric signal carrying the Doppler broadening background information and the second electric signal carrying the saturation absorption spectrum information and the Doppler broadening background information into a differential amplifier 70, and subtracting the first electric signal carrying the Doppler broadening background information from the second electric signal carrying the saturation absorption spectrum information and the Doppler broadening background information to obtain a third electric signal, wherein the third electric signal comprises pure saturation absorption spectrum information with the Doppler broadening background information eliminated, and common mode interference is eliminated by the third electric signal.
And adjusting the differential proportionality coefficient of the differential amplifier 70 to a proper value, and subtracting the first electric signal from the second electric signal, so as to eliminate the Doppler broadening background information and the common-mode interference in the saturated absorption spectrum frequency locking information.
S008, the third electrical signal from the differential amplifier 70 is sent to the phase-locked amplifier 80 for demodulation, the third electrical signal is converted into an error signal, and the error signal is sent to the negative feedback controller 90 for servo feedback to the laser 10, thereby completing the closed-loop locking of the laser frequency.
The invention provides a saturated absorption spectrum laser frequency locking device which comprises a laser, an atomic gas chamber, a photoelectric detector, a differential amplifier, a phase-locked amplifier, a proportional-differential-integral controller and a related optical device, wherein the saturated absorption spectrum laser frequency locking device is used for realizing any one saturated absorption spectrum laser frequency locking method. The laser frequency locking device for the saturated absorption spectrum effectively reduces the requirements on the performance of the laser, and particularly relates to the laser with obvious light intensity fluctuation.
In the following, based on helium: (4He) atomic single beam Doppler broadening saturated absorption spectrum lock frequency as a specific example, which illustrates the working process and principle of the invention:
1. the specific devices selected for use are as follows:
the center wavelengths of the first 1/2 wave plate and the second 1/2 wave plate are 1083 nm. The first prism and the second prism are polarization beam splitting prisms with the central wavelength of 1083 nm. 1/4 wave plate has a central wavelength of 1083 nm. The atomic gas chamber is a cylindrical glass bubble with a bottom surface diameter of 20mm and a height of 40mm, and the inside of the atomic gas chamber is filled with helium (4He) atomic gas, the gas pressure being 1 Torr. The central wavelength of the partial mirror is 1083 nm. The filter is a neutral density filter with a central wavelength of 1083 nm. The first lens and the second lens are both plano-convex lenses with the central wavelength of 1083nm and the focal length of 10 mm. The first photoelectric detector and the second photoelectric detector are both InGaAs phototubes capable of responding to optical signals with central wavelength of 1083 nm. The differential amplifier is a signal differential circuit board containing a self-made preamplifier.
2. The working process and principle are as follows:
after laser beams generated by any 1083nm laser introduced into small modulation by the signal generator pass through the combination of the first 1/2 wave plate and the first prism, the laser beams are divided into two beams of laser according to a specific light intensity proportion, one beam of laser is supplied to specific laser application for output light, and the other beam of laser is used for saturated absorption spectrum frequency locking. The second 1/2 wave plate is rotated so that the laser light is completely transmitted through the second prism without being reflected, and the laser light transmitted through the second prism acts as pump light. The pump light passes through 1/4 wave plate, and its polarization state is converted from linear polarization state to circular polarization stateThen enters an atom gas chamber which contains helium (helium) excited to a metastable state by an 38.88MHz radio frequency power source4He) atom. Pump light and metastable helium: (4He) atomic interactions, optically pumping the metastable energy levels and achieving saturation absorption. Subsequently, the pump light is incident on the partial mirror, and the transmittance of the partial mirror (70% transmittance is used in this example) is adjusted so that most of the pump light is transmitted through the partial mirror and a small portion of the pump light is reflected from the partial mirror, defined as probe light, whose circular polarization direction is changed to the opposite circular polarization direction of the pump light. The pump light carries the doppler broadened background information, which is attenuated to a suitable intensity and then focused on a first photodetector, in turn through a neutral density filter of suitable optical density (in this example an optical density of 0.5) and a first lens with a focal length of 10mm, generating a first electrical signal. The detection light is reflected from the partial reflector, enters the atomic gas chamber which has reached saturation absorption along the direction opposite to the direction of the pumping light, and forms a transmission peak on the Doppler broadening background, which is a saturation absorption peak and provides a frequency reference required by the frequency locking of the saturation absorption spectrum. The probe light emitted from the atomic gas cell passes through 1/4 wave plate, and its polarization state is converted from circular polarization to linear polarization perpendicular to the linear polarization of the pump light. Thus, the probe light changed to the linear polarization state is completely reflected by the second prism without any transmitted light. Further, the detection light passes through a second lens having a focal length of 10mm, and is focused on a second photodetector, generating a second electrical signal. Inputting two photoelectric detection signals into a differential amplifier internally provided with a preamplifier, adjusting a proper differential proportionality coefficient, and subtracting a first electric signal carrying Doppler broadening background information from a second electric signal carrying the Doppler broadening background information and saturated absorption spectrum information to obtain a third electric signal, wherein the third electric signal comprises the saturated absorption spectrum information for eliminating the Doppler broadening background information and common-mode interference. And the third electric signal output by the differential amplifier is accessed to the phase-locked amplifier for demodulation, then is subjected to servo feedback through the proportional-integral-derivative controller, and finally is accessed to the laser to complete the closed-loop locking of the laser frequency.
In a third aspect.
Another embodiment of the present invention provides a frequency-locked laser, which is a tunable laser, and is configured to implement any one of the above-mentioned methods for laser frequency locking of a saturated absorption spectrum.
It is to be understood that the specific embodiments described herein are merely illustrative of the application and are not limiting of the application. In addition, for convenience of description, only a part of structures related to the present application, not all of the structures, are shown in the drawings. The step numbers used herein are also for convenience of description only and are not intended as limitations on the order in which the steps are performed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The terms "first", "second", etc. in this application are used to distinguish between different objects and not to describe a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
The above description is only for the purpose of illustrating embodiments of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings of the present application or are directly or indirectly applied to other related technical fields, are also included in the scope of the present application.
Claims (10)
1. A saturated absorption spectrum laser frequency locking method is characterized by comprising the following steps:
after incident laser provided by the laser is split by the light splitting device, one laser beam is used as pump light and is incident to the atomic gas chamber;
pump light emitted from the atomic gas cell: the part transmitted by the partial reflector carries Doppler broadening background information, and is detected by a first photoelectric detector and converted into a first electric signal; the part reflected by the partial reflector is detection light, and the detection light carries Doppler broadening background information and saturation absorption spectrum information after passing through the atomic gas chamber, is detected by a second photoelectric detector and is converted into a second electric signal;
the first electric signal and the second electric signal are received and processed by a differential amplifier, and a third electric signal is output, wherein the third electric signal contains saturated absorption spectrum information with Doppler spread background information eliminated;
the third electric signal is received and processed by a phase-locked amplifier, an error signal is output, and the error signal is received by a negative feedback controller, converted into a frequency-locked signal and fed back to the laser.
2. The method according to claim 1, wherein the portion transmitted by the partial mirror carries doppler broadening background information, and is detected by the first photodetector and converted into a first electrical signal, specifically:
the part transmitted by the partial reflector carries Doppler broadening background information, is attenuated to a light intensity range capable of being detected by the first photoelectric detector by the optical filter, is focused to the first photoelectric detector by the first lens, is detected by the first photoelectric detector and is converted into a first electric signal.
3. The method according to claim 1, wherein after the incident laser light provided by the laser is split by the splitting device, one of the laser light is used as the pump light and is incident on the atomic gas cell, specifically:
incident laser provided by the laser is split by a first assembly consisting of a first 1/2 wave plate and a first prism, wherein one laser beam reflected by the first prism is standby laser, and one laser beam transmitted by the first prism is transmitted by a second assembly consisting of a second 1/2 wave plate and a second prism and then is used as pump light to be incident to an atomic gas cell.
4. The method according to claim 3, wherein the portion reflected by the partial reflector is probe light, and the probe light, after passing through the atomic gas cell, carries doppler broadening background information and saturation absorption spectrum information, and is detected by a second photodetector and converted into a second electrical signal, specifically:
the part reflected by the partial reflector is detection light, the detection light passes through the atomic gas cell, carries Doppler broadening background information and saturation absorption spectrum information, is completely reflected by a third component consisting of 1/4 wave plates and the second prism, is arranged on either side of the atomic gas cell, is focused to the second photoelectric detector by the second lens, and is detected by the second photoelectric detector and converted into a second electric signal.
5. The method according to claim 3, wherein the first photodetector and the second photodetector are both photodiodes capable of responding to optical signals of light with a wavelength centered on the optical device; wherein the optical device includes: the first 1/2 wave plate, the first prism, the second 1/2 wave plate, the second prism, and the partial mirror.
6. The method according to claim 3, wherein the first prism and the second prism are polarization splitting prisms.
7. The method according to claim 1, wherein the atomic gas cell is made of pyrex.
8. The method according to claim 1, wherein the negative feedback controller is a pid controller.
9. A saturated absorption spectrum laser frequency locking device, which comprises a laser, an atomic gas chamber, a photoelectric detector, a differential amplifier, a phase-locked amplifier, a proportional-integral-derivative controller and related optical devices, and is characterized in that the saturated absorption spectrum laser frequency locking device is used for realizing the saturated absorption spectrum laser frequency locking method as claimed in any one of claims 1to 8.
10. A frequency-locked laser, wherein the frequency-locked laser is a tunable laser, and is used for implementing the saturated absorption spectrum laser frequency locking method according to any one of claims 1to 8.
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| CN202011520857.8A CN114649732B (en) | 2020-12-21 | Saturated absorption spectrum laser frequency locking method and device and frequency locking laser |
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| CN202011520857.8A CN114649732B (en) | 2020-12-21 | Saturated absorption spectrum laser frequency locking method and device and frequency locking laser |
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