Dynamics in direct two-photon transition by frequency combs

Abstract

Based on the proposed theoretical model of a three-level system, the optical Bloch equations including the direct two-photon transition (DTPT) process using the optical frequency comb (OFC) were derived and the population distribution of particles in the upper states varying with the velocity of the atoms was obtained. Comparing to the resonance two-photon transition process, that population was increased by a factor of 1.4 without the Doppler shift, which is consistent with our previous experimental results. Simultaneously, the relationship between momentum transfers, and atomic velocity and pulse number were analyzed. When applied to a multi-level system it was found the population of particles in the excited states increased by a few percentages. The novel approach of DTPT using OFC improved the utilization of comb teeth and atoms, increased the momentum transfer path, reduced the reachable Doppler temperature limit, and encouraged us to use OFC to cool multiple elements simultaneously through the DTPT process. By analyzing the Doppler temperature of 133Cs and 87Rb in one dimension, it was found that this process can lower a temperature below 100 mK and generate dipolar molecules 133Cs87Rb via photoassociation, which provides us a new tool to create dipolar molecules and to investigate their complex rovibrational spectra in ultra-cold chemistry.

Laser frequency stabilization for continuous-wave laser enhanced direct frequency comb spectroscopy system

“…The two-photon transition DFCS also opens the door to the study of nonlinear optical phenomena and quantum control for alkali metal, for instance, studies of time-domain dynamics in cold rubidium (Rb) atoms [9,10], investigations of velocity selective TPTs DFCS in room temperature rubidium and cesium vapor [11][12][13], research on numerous pulse shaping schemes to improve the precision of DFCS which includes pulse chirping, pulse delaying, and pulse spectrally controlling [14][15][16][17]. Very recently, a powerful dual-comb technique for Fourier-transform TPT spectroscopy has been proposed in rubidium vapor [18,19].…”

“…However, despite significant advances in the use of frequency combs for high-precision spectroscopy, DFCS has remained challenging owing to the low intensity of each comb line and the difficulty of resolving features while the repetition rate f rep of the OFC is less than the Doppler width of the resonance. We can induce that the spectrum has a folding feature and that their spectra lines are indistinguishably overlapped [2,9,16,17]. Some experiments have tried to solve the low intensity of per comb line by amplifying the power of OFC output pulses and enhancing the atom-light interaction [4,8,10].…”

Frequency Stabilization of diode laser via Two-photon transitions spectroscopy induced by optical frequency comb pulses combined with diode laser

“…The approach of DFCS uses laser from a comb of appropriate structure became an ultimate technique to directly simultaneous measurements of all transitions for atomic levels within the comb bandwidth, studies time-dependent quantum coherence, and extends high-resolution spectroscopy to far inaccessible XUV wavelength regions where CW laser does not exist. [6][7][8] The two-photon transitions DFCS also opens the door to study nonlinear optical phenomena and quantum control for alkali mental, for instance, studies of time-domain dynamics in cold rubidium (Rb)atoms, [9,10] investigations of velocity-selective twophoton transitions DFCS in room temperature rubidium and cesium vapor, [11][12][13] researches on numerous pulse shaping schemes to improve precision of DFCS which includes pulse chirping, pulse delaying and pulse spectrally controlling. [14][15][16][17]Very recently, a powerful dual-comb technique of Fourier-transform two-photon transitions spectroscopy has been proposed in rubidium vapor.…”