基于多普勒效应的双峰荧光光谱激光稳频技术研究

Laser Frequency Stabilization by Two-peak Fluorescence Spectroscopy Induced by Doppler Effect with Laser at Oblique Incidence

提出了一种使用斜光诱导荧光光谱进行激光稳频的方法,该荧光光谱是通过铯原子束与斜入射激光相互作用产生,具有结构简单、可靠性高的优点。斜光诱导荧光光谱的中心峰的半高宽是可调谐的,在不同入射角度下,分别得到了半高宽为16.3 MHz,18.7 MHz,21.7 MHz,24.4 MHz及26.9 MHz的谱线,这些比单峰荧光光谱(实际测量值为42.5 MHz)的半高宽更加窄。当使用中心峰为24.4 MHz的双峰荧光光谱进行激光稳频时,激光频率波动的峰峰值被限制在70 kHz以内,频率稳定度为2.7×10^(-11)@1s,1.2×10^(-11)@10 s,4.0×10^(-12)@100 s,1.4×10^(-12)@1000 s,优于使用单峰荧光光谱进行激光稳频时的频率稳定度,3.9×10^(-11)@1 s,1.4×10^(-11)@10 s,4.7×10^(-12)@100 s,3.4×10^(-12)@1000 s。该方法有利于提高小型光抽运铯束频标的性能及可靠性。

Improving the stability of laser frequency by reducing frequency fluctuation can enhance the performance of the optically pumped Cs beam frequency standard.It has developed various methods to stabilize the laser frequency,such as the Saturated Absorption Spectroscopy(SAS),Polarization Spectroscopy(PS),Dichroic Atomic-Vapor Laser Lock(DAVLL),Frequency Modulation(FM)spectroscopy,Doppler-free bichromatic spectroscopy.These methods above are mostly based on the thermal vapor cell in a system which is kind of complicated and facing the problems of the temperature of vapor,the light power and the magnetic field,which caused the unstable frequency of laser.For compact optically pumped Cs beam frequency standard,reliability is an important thing that need to be considered,which is probably easier to realize through a simple structure.Therefore,the method of laser frequency stabilization by laser-induced(one-peak)fluorescence spectroscopy is developed.This method has enhanced the system reliability,but introduce a problem of linewidth broadening,which caused by divergent atomic beam.In this paper,we propose a method to stabilize the 852 nm laser frequency by fluorescence spectroscopy with two peaks,which have a simple and reliable structure,and can reduce the Doppler effect caused by divergent atomic beam.The fluorescence spectroscopy with two peaks is induced by two laser beams and atomic beam at oblique incidence.The two laser beams propagate contrarily and coincide exactly with each other.After fluorescence collection and photoelectric conversion,the two-peak fluorescence spectroscopy is formed.By changing the oblique angleθ,the half-width of the central peak of the two-peak fluorescence spectroscopy can be tuned,and we get 16.3 MHz,18.7 MHz,21.7 MHz,24.4 MHz and 26.9 MHz at the different oblique incidence angles separately,which is narrower than the linewidth of one-peak fluorescence spectroscopy whose measured linewidth is about 42.5 MHz.By using the two-peak fluorescence spectroscopy to stabilize the laser,the locking point will be located at the center of the atomic transition when the power of two laser beams is the same and the two laser beams coincide with each other,which is easy to realize.But this method has a drawback of deterioration of the signal-to-noise ratio when the oblique angleθdecreases and tend to zero.When the laser frequency is stabilized by the central peak of a two-peak fluorescence signal with a half-width of about 24.4 MHz,the frequency fluctuation is suppressed to 70 kHz peak-peak and the estimated frequency stability is about 2.7×10^(-11) at 1 s,1.2×10^(-11) at 10 s,4.0×10^(-12) at 100 s,1.4×10^(-12) at 1000 s.In order to compare the performance between the two-peak and one-peak fluorescence spectroscopies,we keep the amplitude of dispersive signals roughly same and the other parameters invariable.And we obtain the error signal by one-peak fluorescence signal with the Allan deviationσy(τ)is about 3.9×10^(-11) at 1 s,1.4×10^(-11) at 10 s,4.7×10^(-12) at 100 s,3.4×10^(-12) at 1000 s.The results show that the method of laser frequency stabilization by two-peak fluorescence spectroscopy is better.This method would help improving the performance and reliability of the compact optically pumped Cs beam frequency standard.For the generation of two-peak fluorescence spectroscopy,further work can be done to simplify the arrangement of the experiment.The laser beam spreads straightly through the optical windows and returns along its original path after reflecting by a mirror.The two-peak fluorescence spectroscopy can also be obtained but exist left-right asymmetry,which will cause the locking point to be shifted from the center of transition.But this character is suitable for laser cooling,because of the frequency locking point can be easily tuned by changing the propagation direction of the Cs atomic beam.