CN114006256B

CN114006256B - Artificial PDH laser frequency stabilization device and method

Info

Publication number: CN114006256B
Application number: CN202111288267.1A
Authority: CN
Inventors: 王汉睦; 周健; 黄荣
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2023-03-14
Anticipated expiration: 2041-11-02
Also published as: CN114006256A

Abstract

The invention discloses an artificial PDH laser frequency stabilization device and method. According to the invention, under the conditions that the laser frequency is not required to be modulated and an ultra-stable optical cavity is used as a frequency reference, an error locking signal is obtained and the laser frequency is locked, the laser frequency drift is inhibited, the corresponding locking frequency grabbing range is enlarged while the high precision of the laser frequency locking is ensured, the unlocking is not easy, the existing PDH laser frequency stabilization method is expanded, the modulation technology is not required, the circuit is simplified, and the cost is saved. The high-precision laser frequency locking is ensured, the corresponding grabbing range of the laser locking frequency is enlarged, and the anti-interference capability is strong. The invention can be widely applied to the fields of precision measurement, atomic clocks, quantum information and the like which need high-precision and high-stability locking of laser frequency.

Description

Artificial PDH laser frequency stabilization device and method

Technical Field

The invention relates to the technical field of laser frequency stabilization, in particular to an artificial PDH frequency stabilization device and method for realizing high-precision and high-stability locking of laser frequency of a laser, and particularly relates to an atomic polarization spectrum-based non-modulation artificial PDH laser frequency stabilization device and method, which are suitable for the fields of precision measurement, atomic clocks, quantum information and the like requiring high-precision laser frequency stabilization.

Background

With the development of laser technology, lasers have been widely used in many fields, especially in the field of interaction between light and atoms. In many experiments of interaction between light and atoms, such as slow light speed, optical magnetometer, atomic clock and the like, laser with high-precision frequency locking is needed, so that atoms, molecules and ions are cooled and quantum state operation is realized, and the experiment requires that long-term drift of the laser frequency needs to be lower than 1MHz/h. In general, the frequency stabilization reference for the laser frequency can be divided into two categories, atomic line and optical cavity length. For example, the laser frequency can be locked to the energy level transition of the atom by techniques such as Saturated Absorption Spectroscopy (SAS), electromagnetic induced transparent spectroscopy (EIT), and Polarization Spectroscopy (PS). Alternatively, the laser frequency can be stabilized to the resonance peak of the fabry-perot optical cavity using a Pound-Drever-Hall (PDH) frequency stabilization method.

The PDH laser frequency stabilization method is a widely adopted technique in a narrow-linewidth ultrastable laser, and is also considered to be an important component of a future narrow-linewidth ultrastable laser. However, in the conventional PDH laser frequency stabilization method, a phase modulation crystal such as an electro-optical modulator (EOM) is required to modulate the laser frequency. The phase modulation crystal is driven by a local oscillator to produce the corresponding phase modulation sidebands and an analog or digital phase shifter is also required to compensate for the phase difference between the local oscillator signal and the output signal of the photo-detector, all of which add correspondingly to the complexity and expense of the laser frequency stabilization system.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides an artificial PDH laser frequency stabilization device and method, which are used for developing and supplementing the conventional PDH laser frequency stabilization technology, transplanting the idea of wide bandwidth in the conventional PDH frequency stabilization method into laser frequency stabilization based on atomic transition, obtaining an error locking signal and locking the laser frequency under the conditions of not modulating the laser frequency and using an ultra-stable optical cavity as a frequency reference, inhibiting the laser frequency drift, increasing the corresponding locking frequency grabbing range while ensuring the high precision of laser frequency locking, being not easy to unlock and expanding the conventional PDH laser frequency stabilization method. The method can provide natural differential error signal feedback without modulation technology, thereby simplifying the circuit and saving the cost. The grabbing range of the corresponding laser locking frequency is enlarged while the high accuracy of laser frequency locking is ensured, the function similar to PDH frequency locking is achieved, and the anti-interference capability is high. The method can be widely applied to the fields of precision measurement, atomic clocks, quantum information and the like which need high-precision and high-stability locking of laser frequency.

The invention provides an atomic polarization spectrum based non-modulation artificial PDH laser frequency stabilization device and a method thereof, and the principle is as follows: on the basis of the existing polarization spectrum laser frequency locking technology, a magnetic field is applied to a corresponding atomic gas chamber to obtain a polarization spectrum under the magnetic field, and a corresponding polarization spectrum signal is similar to a differential error signal of PDH (PDH), so that the high-precision and high-stability locking of the laser frequency is realized.

In order to achieve the above object, the present invention provides an artificial PDH laser frequency stabilization device, including:

a laser for generating an initial laser beam;

a first beam splitting mechanism located on the pipeline of the initial laser beam to split the initial laser beam into a first split beam and a second split beam;

an atom gas chamber, located on the optical path of the first splitting light beam and the second splitting light beam, where the first splitting light beam passes through the atom gas chamber along a first direction, and the second splitting light beam passes through the atom gas chamber along a second direction, where the first direction is opposite to the second direction, and the first splitting light beam and the second splitting light beam are coincident;

the second beam splitting mechanism is positioned behind the atom gas chamber in the first direction and used for splitting the second splitting beam into a first laser beam and a second laser beam with phase difference;

the first photoelectric detector is positioned on the light path of the first laser beam to acquire a first spectrum signal corresponding to the first laser beam;

the second photoelectric detector is positioned on the light path of the second laser beam to acquire a second spectrum signal corresponding to the second laser beam;

an adder electrically connected to the first photodetector and the second photodetector to synthesize respective error signals based on the first spectral signal and the second spectral signal;

and the PID servo controller is electrically connected with the adder and the laser to perform proportional integral calculation on the error signal to obtain a corresponding feedback voltage signal and inject the feedback voltage signal into the laser.

In one embodiment, the artificial PDH laser frequency stabilization apparatus further includes:

and the magnetic field generating mechanism is used for generating a magnetic field, and the magnetic field covers the atom gas chamber so as to regulate and control the energy level of atoms in the atom gas chamber and expand the spectrum range.

In one embodiment, the coincidence ratio of the first split beam and the second split beam is 90% to 100%.

and the light barrier is positioned behind the atom gas chamber in the second direction and used for blocking the first split light beam.

a first reflective arrangement is located in the optical path of the first cleaved beam such that the first cleaved beam passes through the atom gas cell in the first direction.

and the second reflection assembly is positioned on the optical path of the second splitting light beam so that the second splitting light beam passes through the atom gas chamber along the second direction.

In one embodiment, the second beam splitting mechanism comprises a half wave plate and a polarization beam splitting prism, wherein the half wave plate is located between the polarization beam splitting prism and the atomic gas chamber.

In order to achieve the above object, the present invention further provides an artificial PDH laser frequency stabilization method, which includes the following steps:

splitting an initial laser beam generated by a laser into a first split beam and a second split beam;

enabling the first splitting light beam and the second splitting light beam to penetrate through the atom gas chamber in opposite directions, and enabling the first splitting light beam and the second splitting light beam to be superposed in the atom gas chamber;

splitting the second split beam into a first laser beam and a second laser beam with a phase difference after the second split beam passes through the atomic gas chamber;

respectively acquiring a first spectrum signal corresponding to a first laser beam and a second spectrum signal corresponding to a second laser beam, and synthesizing corresponding error signals based on the first spectrum signal and the second spectrum signal;

and carrying out proportional integral calculation on the error signal to obtain a corresponding feedback voltage signal and injecting the feedback voltage signal into the laser, thereby realizing laser frequency locking of the laser.

Compared with the prior art, the invention has the following advantages:

1. the laser frequency locking is based on the energy level transition of atoms, is not influenced by factors such as environmental temperature and the like, and can provide absolute frequency reference in long-time operation;

2. natural differential shape feedback can be provided without modules such as modulation and demodulation;

3. the laser frequency locking device can provide a larger frequency capture range under the high-precision condition of laser frequency locking, and has strong anti-interference capability;

4. the frequency locking scheme has the advantages of reduced cost and convenient use, and can be widely applied to the fields of precision measurement, atomic clocks, quantum information and the like which need high-precision and high-stability frequency locking lasers.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a schematic diagram of an embodiment of an artificial PDH laser frequency stabilizer;

FIG. 2 is a schematic diagram of an error signal for frequency locking of a laser, i.e., an artificial PDH error signal, according to an embodiment of the present invention;

fig. 3 is a schematic diagram of the stability of the laser frequency after locking by the artificial PDH frequency stabilizer and the stability of the laser frequency in the free working state in the embodiment of the present invention.

Reference numerals:

1-a laser to be frequency stabilized;

2-a beam splitter;

3 a-a first reflector, 3 b-a second reflector, 3 c-a third reflector, 3 d-a fourth reflector;

4-a light barrier;

5-atomic gas cell;

6-half wave plate;

7-polarization beam splitting prism;

8 a-a first photodetector, 8 b-a second photodetector;

9-an adder;

10-PID servo controller.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

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 noted that all the directional indicators (such as upper, lower, left, right, front, and rear … …) in the embodiment of the present invention are only used to explain the relative position relationship between the components, the motion situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indicator is changed accordingly.

In addition, the descriptions related to "first", "second", etc. in the present invention are only for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "connected," "secured," and the like are to be construed broadly, and for example, "secured" may be a fixed connection, a removable connection, or an integral part; the connection can be mechanical connection, electrical connection, physical connection or wireless communication connection; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood according to specific situations by those of ordinary skill in the art.

In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of the technical solutions by those skilled in the art, and when the technical solutions are contradictory to each other or cannot be realized, such a combination of the technical solutions should not be considered to exist, and is not within the protection scope of the present invention.

Fig. 1 shows an artificial PDH laser frequency stabilization apparatus disclosed in this embodiment, which includes a laser 1 to be frequency stabilized, a first beam splitting mechanism 2, an atomic gas chamber 5, a second beam splitting mechanism, a first photodetector 8a, a second photodetector 8b, an adder 9, a PID servo controller 10, and a magnetic field generating mechanism.

The laser 1 is used to generate an initial laser beam.

The first beam splitting mechanism 2 is located on the conduit for the initial laser beam to split the initial laser beam into a first split beam and a second split beam. In the present embodiment, the first beam splitting mechanism 2 is a beam splitter.

The atomic gas chamber 5 is located on a light path of the first splitting light beam and the second splitting light beam, the first splitting light beam penetrates through the atomic gas chamber 5 along a first direction, the second splitting light beam penetrates through the atomic gas chamber 5 along a second direction, the first direction is opposite to the second direction, the first splitting light beam and the second splitting light beam are overlapped, and the overlapping proportion of the first splitting light beam and the second splitting light beam is 90% -100%. Specifically, a first reflection assembly is further arranged on the optical path of the first split light beam, so that the first split light beam passes through the atom gas chamber 5 along a first direction; a second reflective arrangement is also provided in the optical path of the second cleaved beam to cause the second cleaved beam to pass through the atom gas cell 5 in a second direction. In this embodiment, the first reflecting member is composed of a first reflecting mirror 3a and a second reflecting mirror 3b, and the second reflecting member is composed of a third reflecting mirror 3 c.

The magnetic field generating mechanism is used for generating a magnetic field, and the magnetic field covers the atom gas chamber 5 so as to regulate and control the energy level of atoms in the atom gas chamber 5 and expand the spectrum range.

The second beam splitting mechanism is located behind the atom gas cell 5 in the first direction and is used for splitting the second split beam emitted from the atom gas cell 5 into a first laser beam and a second laser beam with a phase difference, and specifically, the second beam splitting mechanism comprises a half-wave plate 6 and a polarization beam splitter prism 7, wherein the half-wave plate 6 is located between the polarization beam splitter prism 7 and the atom gas cell 5.

The atom gas chamber 5 is provided with a light barrier 4 behind the second direction for blocking the first split light beam emitted from the atom gas chamber 5. Of course, in the specific implementation process, the light barrier 4 may not be provided, and the frequency-stabilized first split beam may be used for other laser tests.

The first photoelectric detector 8a is located on a light path of the first laser beam, and the first laser beam is captured by a probe of the first photoelectric detector 8a, so as to obtain a first spectrum signal corresponding to the first laser beam. The second photoelectric detector 8b is located on a light path of the second laser beam, and the second laser beam is captured by a probe of the second photoelectric detector 8b after being reflected by the fourth reflecting mirror 3d, so that a second spectrum signal corresponding to the second laser beam is obtained.

The adder 9 is electrically connected to the first photodetector 8a and the second photodetector 8b, respectively, and further synthesizes corresponding error signals based on the first spectral signal and the second spectral signal. And the PID servo controller 10 is respectively electrically connected with the adder 9 and the laser 1 to perform proportional integral calculation on the error signal to obtain a corresponding feedback voltage signal and inject the feedback voltage signal into the laser 1, so that the laser frequency locking of the laser 1 is realized.

The working process of the artificial PDH laser frequency stabilizing device comprises the following steps: an initial laser beam emitted by the frequency stabilized laser 1 is split into two beams through the first beam splitting mechanism 2, wherein the two beams are a first split beam and a second split beam respectively. The first split beam sequentially passes through the atom air chamber 5 in the first direction after being reflected by the first reflector 3a and the second reflector 3b, and is finally blocked by the light blocking plate 4. The second cleaved beam is reflected by the third mirror 3c and passes through the atomic cell 5 in a second direction, opposite to the propagation direction of the first cleaved beam. In the atom gas chamber 5, the coincidence proportion of the first splitting beam and the second splitting beam of the frequency stabilized laser 1 is about 90%, and a magnetic field is applied to the atom gas chamber 5 to regulate and control the energy level of atoms. The second split beam passes through the atom air chamber 5, and then passes through the half-wave plate 6 and the polarization beam splitter prism 7 to be changed into two beams of laser, namely a first laser beam and a second laser beam. And the first laser beam and the second laser beam are detected by the first photodetector 8a and the second photodetector 8b, respectively. The signals detected by the first photodetector 8a and the second photodetector 8b are combined into a corresponding error signal by an adder 9. And performing Proportional Integral (PI) calculation on the corresponding error signal through the PID servo controller 10 to obtain a corresponding feedback voltage signal and injecting the feedback voltage signal into the laser 1 to be frequency stabilized, so as to realize laser frequency locking of the laser 1.

The error signal to achieve frequency locking of the laser 1 to be frequency stabilized is shown in fig. 2. The artificial PDH error signal in fig. 2 has a similar dispersion profile as a conventional PDH error signal, and can be referred to as an artificial unmodulated PDH error signal. Similar to the locking effect of the conventional PDH error signal, the steep dispersion curve near the central zero detuning of the artificial PDH error signal maps the laser locking frequency after the laser 1 to be stabilized is locked, and provides a fast response of the absolute frequency deviation. The gain profiles on adjacent sides help to pull the laser frequency back from large deviations even if the laser's locking frequency is far from the center of resonance due to large disturbances such as electrical or mechanical pulses. Therefore, the laser 1 locked by the artificial PDH method has high stability and strong resistance to environmental interference.

In order to evaluate the stability of the laser frequency of the laser 1 after being locked by the artificial PDH frequency stabilization method, the laser wavelength of the laser 1 to be frequency stabilized is directly recorded using a commercial wavelength meter in this embodiment. Fig. 3 shows the deviation of the laser frequency of the laser 1 to be frequency stabilized over time in free-running and after locking by the artificial PDH frequency stabilization method. In the free-running case, the frequency of the laser 1 can drift widely over time. And after the system is locked by the artificial PDH frequency stabilization method, the laser frequency fluctuation of the laser 1 to be frequency stabilized is strongly inhibited, and the change of the corresponding laser frequency along with time is less than 1MHz, which shows that the laser frequency stabilization system adopting the artificial PDH frequency stabilization method is very effective for the accurate frequency locking of the laser 1.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. An artificial PDH laser frequency stabilization device, comprising:

a laser for generating an initial laser beam;

the first beam splitting mechanism is positioned on the pipeline of the initial laser beam to split the initial laser beam into a first split beam and a second split beam;

an atom gas chamber, located on an optical path of the first split light beam and the second split light beam, where the first split light beam passes through the atom gas chamber in a first direction, and the second split light beam passes through the atom gas chamber in a second direction, where the first direction is opposite to the second direction, and the first split light beam and the second split light beam coincide;

the PID servo controller is electrically connected with the adder and the laser to perform proportional-integral calculation on the error signal to obtain a corresponding feedback voltage signal and inject the feedback voltage signal into the laser;

2. The artificial PDH laser frequency stabilization device of claim 1, wherein the coincidence ratio of the first split beam and the second split beam is 90% to 100%.

3. The artificial PDH laser frequency stabilization device of claim 1, further comprising:

4. The artificial PDH laser frequency stabilization device of claim 1, further comprising:

5. The artificial PDH laser frequency stabilization device of claim 1, further comprising:

6. The artificial PDH laser frequency stabilization device of claim 1, wherein the second beam splitting mechanism comprises a half-wave plate and a polarization splitting prism, wherein the half-wave plate is located between the polarization splitting prism and the atomic gas chamber.

7. An artificial PDH laser frequency stabilization method, which is characterized in that the artificial PDH laser frequency stabilization device of any one of claims 1-6 is adopted, and the method specifically comprises the following steps: