CN110364926A - Atomic Doppler broadened peak laser frequency-locking device and frequency-locked laser including it - Google Patents

Abstract

The present invention provides a kind of atom dopplerbroadening peak laser frequency locking device and including its frequency locking laser, atom dopplerbroadening peak laser frequency locking device includes beam splitting arrangement, is used to the laser that tunable laser projects separating first laser；Atomic air chamber in the optical path of the first laser；Photodetector is used to the first laser transmitted from the atomic air chamber being converted to electric signal；Lock-in amplifier receives the electric signal and output error signal of the photodetector output；And negative feedback control device, it is used to lock the frequency for the laser that the tunable laser projects according to the error signal that the lock-in amplifier exports.Frequency locking device optical path of the invention is relatively easy, and without big power consuming device, stability and operability are greatly improved；Building for optical path is more simple, reduces costs, and provides advantage for industrialization.

Description

Atomic Doppler broadened peak laser frequency-locking device and frequency-locked laser including it

technical field

The invention relates to the field of lasers, in particular to an atomic Doppler broadening peak laser frequency locking device and a frequency locking laser comprising the same.

Background technique

In the experimental research of atomic physics and the development of precision instruments, the key technology is to lock the frequency of the laser on the spectral line of the selected atom.

At present, there are mainly two laser frequency locking schemes, one is a Doppler linewidth saturation absorption frequency locking device, and the other is a Dichroic Atomic Vapor Laser Lock (DAVLL, a dichroic atomic vapor laser frequency locking device).

FIG. 1 is a schematic structural diagram of a Doppler linewidth saturable absorption frequency locking device in the prior art. As shown in Figure 1, the laser light emitted by the external cavity semiconductor laser 11 is incident on the polarization beam splitting prism 12 after passing through the half-wave plate 101, and the polarization beam splitting prism 12 reflects the S polarized laser light 121 for standby, and the P polarized Laser light 122 is transmitted. The P-polarized laser light 122 is incident on the polarization beam splitting prism 13 after passing through the half-wave plate 102 . The polarization beam splitting prism 13 reflects a part of the laser light 1221 of the P-polarized laser light 122 , and transmits another part of the laser light 1222 to the mirror 151 . The laser light 1221 is used as the probe light, which passes through the half-wave plate 103 and then enters the atomic gas chamber 14 filled with rubidium atoms. The laser light 1221 emitted from the atomic gas chamber 14 is transmitted through the polarization beam splitter prism 16 and is incident on the photodetector. device 17. The laser light 1222 is reflected by the mirrors 151 and 152 and is incident on the polarization beam splitting prism 16 through the half-wave plate 104. The optical paths overlap, and finally enter the external cavity semiconductor laser 11 as its pumping light.

As the laser frequency emitted by the external cavity semiconductor laser 11 scans around the transition frequency of the atoms in the atomic gas chamber 14 (that is, the laser frequency changes periodically around the atomic transition frequency), the atoms in the atomic gas chamber 14 detect different frequencies The absorption of laser light 1221 is different. Based on the Doppler frequency shift effect, an atomic Doppler absorption peak (broadened peak) is formed. The photodetector 17 converts the atomic Doppler broadening peak into a corresponding electrical signal, so that the electrical signal output by the photodetector 17 can reflect the atomic absorption intensity.

Figure 2 is a schematic diagram of Doppler broadening peaks and hyperfine structure peaks. The solid line (like a Gaussian curve) is the Doppler broadening peak, and the dotted line depression on it is the hyperfine structure peak. The better the coincidence of the pump light 1222 and the probe light 1221 is, the better the hole-burning effect of the Lamb depression on the Doppler broadening peak is. In order to ensure the high coincidence of the pump light 1222 and the probe light 1221 , very high requirements are placed on the stability of the entire optical path, resulting in a low anti-interference ability of the frequency locking device shown in FIG. 1 . In addition, the intensity of the pump light and probe light needs to be kept in an appropriate range. If the intensity of the probe light is too small, the saturated absorption spectrum will be small; if the probe light is too large, the power of the spectral line will be broadened, which is not good for the saturated absorption spectrum. .

Refer again to FIG. 1 to illustrate the negative feedback control process of laser frequency locking. The high-frequency (several kilohertz) modulation signal output by the lock-in amplifier 18 is applied to the injection current of the external cavity semiconductor laser 11, so that the measured hyperfine structure peak is also superimposed on the modulation signal.

FIG. 3 is a waveform diagram of an input signal and an output signal of a lock-in amplifier in the frequency locking device shown in FIG. 1 . As shown in FIG. 3 , the input signal 181 is a hyperfine structure peak in the Doppler peak, which is superimposed with a high-frequency modulation signal; the output signal 182 is an error signal. The lock-in amplifier 18 performs lock-in amplification on the hyperfine structure peak superimposed with the high-frequency modulation signal, and its output signal 182 is similar to a dispersion line, and is used as an error signal of the proportional-integral-derivative controller 19 .

The proportional-integral-differential controller 19 controls the voltage of the piezoelectric ceramic in the external cavity semiconductor laser 11 based on the error signal it receives, thereby adjusting the length of the external cavity of the laser tube mode selection, and then adjusting the output laser of the external cavity semiconductor laser 11. The frequency is such that the electrical signal output by the photodetector 17 is near the valley of the hyperfine structure peak, that is, the error signal output by the lock-in amplifier 18 is near zero.

Since the full width at half maximum of the hyperfine structure peak is about 10MHz, the laser frequency must be stabilized at the order of 1MHz, which is easily interfered by external mechanical noise, which may easily lead to the drift of the laser frequency. The frequency stability locked on the hyperfine structure peak is not high, and the frequency is easily unlocked by external interference. Therefore, the requirements for the laser optical path and system stability are very high, which reduces the operability of practical applications.

Fig. 4 is a structural schematic diagram of a dichroic atomic vapor laser frequency locking device in the prior art. As shown in Figure 4, the laser light emitted by the external cavity semiconductor laser 21 is incident on the Glan-Taylor prism 22 through the half-wave plate 201, wherein a part of the laser light 221 is transmitted from the Glan-Taylor prism 22 for standby, and the other part of the laser light 222 passes through After being reflected by the Glan-Taylor prism 22 , it is incident on the atomic gas cell 23 , and the laser light 222 emitted from the atomic gas cell 23 is incident on the polarization beam splitter prism 24 through the quarter-wave plate 202 . Part of the laser light 2221 is incident on the photodetector 26 after being transmitted from the polarizing beam splitting prism 24 , and another part of the laser light 2222 reflected by the polarizing beam splitting prism 24 is incident on the photo detector 25 .

DAVLL uses the Zeeman energy level of atoms to absorb linearly polarized light difference, and detects the change of polarization to lock the frequency. The linearly polarized laser light 222 is incident into the atomic gas chamber 23 wound with the conducting wire, and the strong magnetic field generated by the conducting wire causes Zeeman splitting of atomic energy levels. Since the linearly polarized laser light 222 can be decomposed into a superposition state of left-handed and right-handed circularly polarized light, and the transitions between Zeeman energy levels of different magnetic quantum numbers have different absorptions for left-handed light and right-handed light, thus the photodetector 25 , 26 outputting different electrical signals.

The differential amplifier 27 receives the electrical signals output by the photodetectors 25 and 26, and obtains an error signal after a differential amplification operation. Fig. 5 is an error signal output by a differential amplifier in the dichroic atomic vapor laser frequency locking device shown in Fig. 4 . It can be seen from Figure 5 that the curve of the error signal is similar to the dispersion line, where Δ is the laser frequency detuning, and Γ is the laser line width. This error signal is used for laser frequency locking.

The negative feedback controller 28 controls the voltage of the piezoelectric ceramic in the external cavity semiconductor laser 21 based on the error signal, and then adjusts the frequency of the laser light output by the external cavity semiconductor laser 21, so that the error signal output by the differential amplifier 27 is near zero, thereby realizing frequency lock.

Based on the above principles, on the one hand, in order to reflect the difference in absorption of the left-handed light and right-handed light of the linearly polarized light by the Zeeman level, it is necessary to use the Glan-Taylor prism 22 to obtain high-purity linearly polarized light. Glan-Taylor prisms add significantly to cost compared to polarizing beamsplitters. On the other hand, the Zeeman level splitting size of an atom is Among them, m _F is the Zeeman level magnetic quantum number, g is the Lande factor, μ is the Bohr magneton, B is the magnetic field size, is the reduced Planck constant. Since DAVLL needs a strong magnetic field on the order of 100 to 1000 Gauss to generate Zeeman splitting, it puts forward very high requirements for coil winding, heat dissipation and power supply, and requires high-power consumption equipment to realize it, which is not conducive to the system. Miniaturization and integration.

Contents of the invention

Aiming at the above-mentioned technical problems existing in the prior art, the present invention provides an atomic Doppler broadened peak laser frequency locking device for tunable lasers, including:

A beam splitting device, which is used to split the laser light emitted by the tunable laser into the first laser light;

an atomic gas cell located on the optical path of the first laser light;

a photodetector for converting the first laser light transmitted from the atomic gas cell into an electrical signal;

a lock-in amplifier, which receives the electrical signal output by the photodetector and outputs an error signal; and

The negative feedback controller is used for locking the frequency of the laser light emitted by the tunable laser according to the error signal output by the lock-in amplifier.

Preferably, the negative feedback controller adjusts the laser frequency emitted by the tunable laser to be the atomic transition frequency of the atomic gas cell according to the error signal output by the lock-in amplifier.

Preferably, the negative feedback controller makes the error signal output by the lock-in amplifier near zero.

Preferably, the lock-in amplifier also outputs a modulation signal to the injection current of the tunable laser, and the frequency of the modulation signal is higher than the frequency of the error signal.

Preferably, the beam splitting device is a polarizing beam splitting prism.

Preferably, the beam splitting device is a Glan Taylor prism.

Preferably, the negative feedback controller is a proportional-integral-derivative controller.

Preferably, the tunable laser is an external cavity semiconductor laser, and the voltage output by the negative feedback controller is applied to the piezoelectric ceramic of the external cavity semiconductor laser.

Preferably, the piezoelectric ceramic is used to adjust the external cavity length of the laser tube mode selection of the tunable laser.

The present invention also provides a frequency-locked laser, comprising:

Tunable lasers; and

Atomic Doppler broadened peak laser frequency-locking device for tunable lasers as described above.

The frequency locking device of the present invention has the following advantages: the stability and precision of the frequency locking device fully meet the actual application requirements; the optical path of the frequency locking device is relatively simple, without large power consumption equipment, and the stability and operability are greatly improved; the construction of the optical path It is simpler, lowers the cost, and provides favorable conditions for industrialization. It can be used in prospecting, anti-submarine, magnetomagnetic and brain magnetometry systems, etc.

Description of drawings

Embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic structural diagram of a Doppler linewidth saturable absorption frequency locking device in the prior art.

Figure 2 is a schematic diagram of Doppler broadening peaks and hyperfine structure peaks.

FIG. 3 is a waveform diagram of an input signal and an output signal of a lock-in amplifier in the frequency locking device shown in FIG. 1 .

Fig. 4 is a structural schematic diagram of a dichroic atomic vapor laser frequency locking device in the prior art.

Fig. 5 is an error signal output by a differential amplifier in the dichroic atomic vapor laser frequency locking device shown in Fig. 4 .

Fig. 6 is a schematic structural diagram of an atomic Doppler broadened peak laser frequency locking device according to a preferred embodiment of the present invention.

FIG. 7 is a schematic diagram of atomic Doppler broadening peaks of the frequency locking device shown in FIG. 6 .

FIG. 8 is a waveform diagram of an input signal and an output signal of a lock-in amplifier in the frequency locking device shown in FIG. 6 .

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

Fig. 6 is a schematic structural diagram of an atomic Doppler broadened peak laser frequency locking device according to a preferred embodiment of the present invention. As shown in FIG. 6 , the atomic Doppler broadened peak laser frequency locking device 30 includes a polarization beam splitter prism 32 , an atomic gas chamber 33 , a photodetector 34 , a lock-in amplifier 35 , and a proportional-integral-derivative controller 36 .

The laser light emitted by the external cavity semiconductor laser 31 is incident on the polarizing beam splitting prism 32, and the polarizing beam splitting prism 32 transmits the P polarized laser light 321 for standby, and reflects the S polarized laser light (hereinafter referred to as frequency-locked laser light 322) to the atomic gas cell 33 in. The atomic gas chamber 33 is filled with potassium atoms, and the vapor pressure of the potassium atoms in the atomic gas chamber 33 is about 1×10 ⁻⁶ mbar. Laser light emitted from the atomic gas cell 33 enters the photodetector 34 .

The voltage of the piezoelectric ceramic in the external cavity semiconductor laser 31 is scanned at 11.88 Hz (that is, the voltage of the piezoelectric ceramic is periodically adjusted), and the length of the external cavity cavity of the laser tube mode selection is periodically adjusted, so that the laser frequency is in the vicinity of the atomic transition frequency. Sexual changes. The velocity of the vapor movement of potassium atoms in the atomic gas chamber 33 is projected on the one-dimensional propagation direction of the frequency-locked laser 322, forming a Gaussian-like velocity distribution, in which the atoms with a velocity of zero are the most, and the greater the velocity, the fewer atoms are distributed. As the laser frequency is scanned, atomic Doppler broadening peaks are formed based on the atomic Doppler frequency shift effect.

FIG. 7 is a schematic diagram of atomic Doppler broadening peaks of the frequency locking device shown in FIG. 6 , where F is the atomic transition frequency. It can be seen from Figure 7 that the atomic Doppler broadening peak is a Gaussian-like curve, and its full width at half maximum is about 500MHz. Compared with the full width at half maximum (about 10MHz) of the hyperfine peak in the saturated absorption peak, the requirement for frequency stability is greatly reduced . Therefore, the requirement for the stability of the frequency locking device is greatly reduced, the anti-interference ability is strong, and it is suitable for outdoor use and other occasions.

The high-frequency (several kilohertz) modulation signal output by the lock-in amplifier 35 is applied to the injection current of the external cavity semiconductor laser 31, so that the light intensity of the laser superimposes the modulation signal, and the measured Doppler broadening peak also superimposes the modulation signal. Modulated signal. The photodetector 34 converts the Doppler broadened peak superimposed on the modulated signal into a corresponding electrical signal and then inputs it into the lock-in amplifier 35 . The lock-in amplifier 35 demodulates and amplifies the spectral line of the voltage scanning frequency of the piezoelectric ceramic, that is, the low-frequency electrical signal in the Doppler broadening peak is multiplied by the high-frequency electrical signal corresponding to the modulation signal, and then passed through the low-pass filter The filter filters out the high-frequency signal of several kilohertz, and outputs the low-frequency error signal to the proportional-integral-differential controller 36.

Fig. 8 is the oscillogram of the input signal 351 and the output signal 352 of the lock-in amplifier 35 in the frequency locking device shown in Fig. 6, wherein the curve of the input signal 351 of the lock-in amplifier 35 is a Gaussian-like curve with a frequency of 11.88 Hz , the curve of the output low-frequency error signal 352 is similar to a dispersion line. Due to delays in the measurement setup, the displayed low frequency error signal is slightly delayed from the Doppler broadened peak.

The proportional integral differential controller 36 adjusts the voltage of the piezoelectric ceramic in the external cavity semiconductor laser 31 based on the error signal, so as to adjust the external cavity length of the laser tube mode selection, thereby controlling the atomic transition of the laser frequency in the atomic gas chamber 33 Near the frequency, the absorption intensity of the laser 322 by the atomic gas chamber 33 is the maximum. That is, the error signal output by the lock-in amplifier 35 is controlled to be near zero. Based on the negative feedback control of the proportional-integral-differential controller 36, the laser frequency is stabilized.

The embodiments of the present invention lock the laser frequency on the Doppler broadening peak to achieve the purpose of frequency locking. The Doppler linewidth is about 500MHz, which is much larger than the hyperfine peak linewidth (about 10MHz) in the saturated absorption spectrum, which greatly reduces the requirement for frequency stability and improves the reliability of the system.

The optical path of the frequency locking device of this embodiment is simple, the cost and the dependence on frequency stability are reduced, and good conditions are provided for industrialization. And there is no need for high-power consumption equipment to generate a strong magnetic field, which can realize miniaturization and commercialization.

In other embodiments of the present invention, beam splitters such as beam splitters, half mirrors, and Glan Taylor prisms are used instead of the polarizing beam splitter prism 32 in the above embodiments.

In other embodiments of the present invention, a negative feedback controller such as a proportional-integral controller is used to replace the proportional-integral-derivative controller 36 in the above-mentioned embodiments.

In other embodiments of the present invention, the atomic gas cells filled with alkali metal or alkaline earth metal atoms are selected according to the actual required frequency.

In other embodiments of the present invention, tunable lasers such as distributed feedback lasers (DFB) and distributed Bragg reflectors (DBR) are used instead of the aforementioned external cavity semiconductor lasers.

Although the present invention has been described in terms of preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and changes are included without departing from the scope of the present invention.

Claims (10)

1. a kind of atom dopplerbroadening peak laser frequency locking device for tunable laser characterized by comprising

Beam splitting arrangement is used to the laser that tunable laser projects separating first laser；

Atomic air chamber in the optical path of the first laser；

Photodetector is used to the first laser transmitted from the atomic air chamber being converted to electric signal；

Lock-in amplifier receives the electric signal and output error signal of the photodetector output；And

Negative feedback control device, the error signal for being used to be exported according to the lock-in amplifier lock the tunable laser and penetrate The frequency of laser out.

2. the atom dopplerbroadening peak laser frequency locking device according to claim 1 for tunable laser, special Sign is that the negative feedback control device adjusts the tunable laser according to the error signal that the lock-in amplifier exports The frequency of the laser of injection is the atomic transition frequency of the atomic air chamber.

3. the atom dopplerbroadening peak laser frequency locking device according to claim 2 for tunable laser, special Sign is that the negative feedback control device makes the error signal of the lock-in amplifier output near zero.

4. the atom dopplerbroadening peak laser frequency locking device according to claim 1 for tunable laser, special Sign is that the lock-in amplifier also exports in modulated signal to the Injection Current of the tunable laser, the modulation letter Number frequency be higher than the error signal frequency.

5. the atom dopplerbroadening peak laser lock according to any one of claim 1 to 4 for tunable laser Frequency device, which is characterized in that the beam splitting arrangement is polarization beam splitter prism.

6. the atom dopplerbroadening peak laser lock according to any one of claim 1 to 4 for tunable laser Frequency device, which is characterized in that the beam splitting arrangement is Glan-Taylor prism.

7. the atom dopplerbroadening peak laser lock according to any one of claim 1 to 4 for tunable laser Frequency device, which is characterized in that the negative feedback control device is proportional plus integral plus derivative controller.

8. the atom dopplerbroadening peak laser lock according to any one of claim 1 to 4 for tunable laser Frequency device, which is characterized in that the tunable laser is external cavity semiconductor laser, the electricity of the negative feedback control device output Pressure is applied on the piezoelectric ceramics of external cavity semiconductor laser.

9. the atom dopplerbroadening peak laser frequency locking device according to claim 8 for tunable laser, special Sign is that the outer cavity for the laser tube modeling that the piezoelectric ceramics is used to adjust the tunable laser is long.

10. a kind of frequency locking laser characterized by comprising

Tunable laser；And

It is filled as claimed in any one of claims 1-9 wherein for the atom dopplerbroadening peak laser frequency locking of tunable laser It sets.