同位素原子饱和吸收谱稳频的拉曼激光方案

The Frequency-stabilized Raman Laser System Based on Isotope Atom Saturated Absorption Spectrum

提出一种基于同位素原子饱和吸收谱稳频的拉曼激光方案,并应用于原子干涉仪激光系统的小型化。该方案使用同位素原子吸收泡代替现有拉曼光方案中的移频或调制光学器件,以实现拉曼激光的稳频和失谐,使光路和电路同时简化。针对^(85)Rb原子干涉仪,^(87)Rb原子D2线的饱和吸收谱被用于对拉曼激光进行稳频,稳频后的拉曼激光红失谐在GHz量级,线宽约为80 kHz。将该拉曼激光用于原子干涉仪获得了对比度为20%的干涉条纹,重力测量的灵敏度为345μGal/Hz1/2。连续24 h重力测量数据的阿伦方差显示原子干涉仪的分辨率约为2×10^(−8)g@7500 s。该拉曼激光的频率噪声引起的单次重力测量噪声优于1μGal,完全可以满足μGal量级的重力测量需求。该拉曼激光方案有助于推动原子干涉仪激光系统的小型化、轻量化和实用化。

Atom interferometers based on the matter wave interferometry are promising tools for precision measurements.In laboratory,they have been used in the field of fundamental physics research.An important research effort is going on to miniaturize them,which can help to make them play a key role in resource exploration,inertial navigation and gravity mapping from space.The miniaturization of a laser system is a key link to miniaturize an atom interferometer.However,because the atoms used for the frequency stabilization in the existing schemes of the Raman laser system and the atoms used as the test masses in the atom interferometers are of the same type,the special optical elements and their driving devices are used to obtain the far detuning of the Raman lasers by frequency offset locking method,which makes the laser system complex and affects its reliability.Meanwhile,the increase in weight and cost of the laser system is adverse to apply them in the field of inertial navigation and space application.For an atom interferometer using one type of Rb isotope atoms as test mass,a frequency-stabilized Raman laser system based on another type of Rb isotope atoms saturated absorption spectrum is proposed to make the laser system for an atom interferometer compact and robust.This Raman laser system is helpful to miniaturize the laser systems of atom interferometers,and promotes the atom interferometers to be applied in movable platforms or in the weight-sensitive fields.For an 85Rb atom interferometer,the frequency-stabilized Raman laser system based on 87Rb atom saturated absorption spectrum is proposed to make the laser system compact and robust.First,the schematic of the stabilizing frequency and detuning of Raman laser is introduced.Second,the frequencystabilized Raman laser system based on 87Rb atom saturated absorption spectrum is proposed.In this Raman laser system,the frequency of the Raman laser is stabilized to the 87Rb atom saturated spectrum to obtain the far detuning.Then,the laser beam from the Raman laser is modulated by an electro-optic modulator with driving frequency of 3.04 GHz.Amplified by a tapered amplifier,the carrier and+1st bandside in modulated laser beams are used as the Raman beams.The frequency stabilization experiment is done.By scanning the injection current and the voltage of the piezoelectric transducer of the Raman laser,the Rb saturated absorption spectrums are obtained.The frequency of the Raman laser is stabilized to the peak of 87Rb atomF=2→F′=CO2,3transition of D2 line,obtaining a red detuning of a magnitude of GHz and a linewidth of 80 kHz.The Raman beams generated by this Raman laser system are used to one atom interferometer of the atom gradiometer to evaluate its performance.The sensitivity of the atom interferometer using this Raman beams is 345μGal/Hz1/2 with the interference fringe contrast of 20%.And the Allan deviation of the gravity measurement more than one day shows that the resolution of the atom interferometer is 2×10^(-8)g@7500 s.It is calculated that the noise of the gravity measurement per shot contributed by the frequency noise of the Raman laser beams is less than 1μGal.This Raman laser system uses an electro-optic modulator to generate a Raman beams,which inherits the advantages of the existing Raman schemes based on an electro-optic modulator.In this Raman laser system,a Rb cell is used as a substitute for an acousto-optic or electro-optic modulator to stabilize the frequency of the Raman laser and obtain the far detuning,which not only simplifies the light path and electric circuit of the Raman laser system,but also improves the reliability and long-term stability of the Raman beams.Both the atom interference experiment in the atom interferometer and the theoretical evaluation show that this Raman laser system is able to meet the miniaturized atom interferometers applied requirements.This Raman laser system is helpful to realize the miniaturization and weight reduction of the laser systems and promotes the atom interferometers to be applied in the movable platforms and in space.