The Measurement Of The Fine Structure Of Cesium Atom Rydberg States

Because of huge volume,long lifetimes as well as high polarizability,Rydberg atoms play an important role in atomic and molecular field.Spectroscopy of Rydberg atoms is of great significance for studying the energy level of Rydberg atoms and the interaction between neutral atoms,especially,the high-resolution spectroscopy of Rydberg atoms can be used to measure the energy level shifts of Rydberg atoms resulting from the dipole-dipole interactions in room-temperature vapor cells.Based on electromagnetic-induced transparency?EIT?,the ladder-type EIT spectra of Rydberg atoms can be obtained experimentally.In the experiment,we use the cascade two-photon excitation with852nm and 509nm lasers to prepare the Rydberg states of cesium atoms.The continuous tunable range of 1018nm external cavity diode laser?ECDL?is1016nm-1020nm,and the 1018nm optical fiber amplifier has a maximum output power of 5W while the injected power of seed laser is 10mW.Based on periodically-poled KTP?PPKTP?crystal?1mm×2mm×10mm?,four-mirrors bow-tie ring cavity is set up,the 509nm laser is produced by the frequency doubling through the cavity-enhanced second-harmonic generation and the maximum output power is¹W.The 852nm laser is produced by an ECDL laser.The focused 852nm and 509nm lasers counter-propagate into the room-temperature cesium cell,when the laser frequency is resonance to the corresponding energy level,¹³³Cs Rydberg states and its EIT spectra can be prepared.Tuning wavelength of 1018nm laser,¹³³Cs can be prepared to different Rydberg states.Simultaneously,the ladder-type 6S_1/2-6P_3/2-nS?D?EIT spectra with high-resolution are realized in the cesium cell,with principle quantum number n of 41 to 90 in the experiment.With velocity-selective RF sideband modulated technology,the frequency interval of the the spectrum has been calibrated.Then fine splitting of nD_3/2 and nD_5/2Rydberg states are measured.The experimental data of the fine structure splitting is in keeping with theoretical calculated value when principle quantum number n is less than 70;otherwise,there is a large deviation.It may be result from the stronger interaction between higher Rydberg states which can be lead to frequency shift.The main factors influencing the precision of the measurement to splitting interval between nD_3/2 and nD_5/2 are the broadening of the electromagnetic induced and the non-linear of the scanning to 509nm laser'frequency.This paper mainly carry out the realization and measurement of the EIT spectrum to ¹³³Cs atom based on the ladder-type EIT.The main contents are as follows:1)The related information of Rydberg atoms and EIT theory as well as the status and development of the research on the EIT spectrum of Rydberg state has been introduced;2)The density matrix theory of the interaction mechanism between field and atoms and EIT process in experiments was introduced.And the quantum defect theory was presented in details,which makes it clear to calculate the energy level of Rydberg states;3)Based on PPKTP crystal,we designed and built a four-mirror bow-tie ring cavity,in which the 1018nm laser was frequency doubling to the 509nm laser.The high power 1018nm laser is produced by an ECDL and a 1018nm optical fiber amplifier;4)Setting up the optical system of EIT,we obtained the EIT spectrum of nD Rydberg states of ¹³³Cs.By detecting the 852nm probe laser with RF modulation,we calibrated the frequency of spectra.Finally,we obtained the fine splitting of nD_3/2 and nD_5/2,and the measurement results are analyzed.The innovations of the above work are as follows:1)In the experiment of achieving the EIT of nD Rydberg states of ¹³³Cs based on 852nm and 509nm lasers,by scanning frequency of 509nm coupling laser,the doppler background of EIT spectra was eliminated,it is benificial to measure the EIT interval accurately;2)With the method of RF modulation,we calibrated the frequency of spectra.The RF-sideband modulation of 30MHz was added to the 852nm laser by the electro-optical phase modulator,and the EIT spectrum was calibrated to achieve the measurement of the fine splitting of Rydberg states.