Research On High-resolution Optical Frequency Comb Spectrum Of Rubidium Atoms

Spectral measurement technology is an important method to study the basic physical structure of atoms and molecules.With the development of laser and nonlinear optics,the spectral measurement sensitivity,spectral resolution,spectral time and spatial resolution increased by several orders of magnitude,which laid the foundation for the high sensitive spectroscopy technology and promoted greatly the development of atomic and molecular physics.In the last century 90's,the femtosecond optical frequency comb not only realizes the connection of optical and microwave frequencies,but also promotes the development of precision measurement technology of the spectrum,forming a very promising frequency comb spectroscopy.This technique overcomes the disadvantages of continuous spectrum of laser absorption spectroscopy data within the long acquisition time and low spectral sensitivity of Fourier transform.In the wide frequency range,it can achieve the spectral measurement of atoms and molecules within a short period of time and a wide wave band.It is widely used in researches of atomic and molecular constants of basic measurement,atmospheric chemical kinetics and pollution control.In this paper,the high resolution two-photon spectrum of Rb atoms is studied based on the optical frequency comb,the main contents are as follows:1.The two-photon excitation transitions for 5 S1/2 to 5D5/2 of Rb are performed with two counter propagating femtosecond pulses.The high resolution rubidium atom(87Rb and 85Rb)5S1/2--5P3/2-5D5/2 two-photon spectroscopy are obtained by scanning the repetition frequency of the optical frequency comb and detecting 6P3/2-5S1/2 transition fluorescence signal.The temperature of rubidium atom and the average output power of optical frequency comb dependence of two-photon spectroscopy are studied..The two-photon spectral signal-to-noise ratio is greatly improved by intensity modulation of the femtosecond pulses via chopper.2.We obtained two-photon spectrum of rubidium atoms using a femtosecond optical frequency comb and a cw laser.The technology can effectively overcome the disadvantage of the spectrum sensitivity limitation which is caused by the low power of each frequency comb.The cw laser excites 5 S1/2-5P3/2 transition of rubidium atoms,the optical frequency comb excites 5P3/2-5D5/2 transition rubidium atoms.Through scanning cw laser frequency in the rubidium D2 line,we obtain high resolution rubidium atomic 5S1/2--5P3/2-5D5/2 transitions spectrum by detecting 6P3/2-5S1/2 fluorescence signal.We study the influences of temperature and cw laser power on the two-photon spectrum.The theoretical fitting results are consistent with experimental results.3.With the beat frequency signal of a femtosecond optical frequency comb and a cw laser,we get the interference spectrum and measure the relationship between the interference frequency distances of the two signals and output frequency of cw laser.The results can be used to realize fast measurement of cw laser frequency.