Signals of ultracold plasma are observed by two-photon ionization of laser-cooled caesium atoms in a magnetooptical trap.Recombination of ions and electrons into Rydberg atoms during the expansion of ultracold plasma is investigated by using state-selective field ionization spectroscopy.The dependences of recombination on initial electron temperature(1-70 K) and initial ion density(～10 10 cm-3) are investigated.The measured dependence on initial ion density is N 1.547±0.004 at a delay time of 5 μs.The recombination rate rapidly declines as initial electron temperature increases when delay time is increased.The distributions of Rydberg atoms on different values of principal quantum number n,i.e.n = 30-60,at an initial electron temperature of 3.3 K are also investigated.The main experimental results are approximately explained by the three-body recombination theory.
We present a robust method of single-photon modulation by directly modulating the single photons and observe its frequency spectrum. Compared with conventional photon counting technique, the single-photon modulation spectrum shows that the method could not only realize high-frequency modulation but also obtain higher signal-to-noise ratio. Moreover, the theoretical calculations show good agreement with the experimental results.
Single photon modulation has been proposed to overcome the defects of the low signal-to-noise ratio(SNR)and slow process rate of photon counting. In this paper, we present the quantum theory of single photon modulation, and then experimentally investigate the modulation spectroscopy both in the time domain and frequency domain. It is found that the SNR reached 150 in approximately the MHz modulation bandwidth.
In this paper,ultracold atoms and molecules in a dark magneto-optical trap(MOT) are studied via depumping the cesium cold atoms into the dark hyperfine ground state.The collision rate is reduced to 0.45s-1 and the density of the atoms is increased to 5.6×1011cm-3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15.The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately.The experimental results are analyzed by using the perturbative quantum approach.
A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor.The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts,shaped in an original way,and focused into a room-temperature cesium vapor.We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb,and through absolute frequency measurements.
