Resonant Fast-Beam/Laser Interactions: Saturated Absorption and Two-Photon Absorption

Nis Bjerre, M. Kaivola, U. Nielsen +3 more

Pengyuan Chang, Duo Pan, Haosen Shang +2 more

Abstract We report on a global crossover saturated-absorption spectroscopy (SAS) of Cs D 2 transition using a dual-frequency laser field with a frequency difference of less than the Doppler width. With two pairs of dual-frequency laser beams counter-propagating through the vapor cell, the line shape and non-linear features observed in the transmission spectra of the probe beam change with the frequency difference of the dual-frequency laser. The superficially complicated transmission signal includes two sets of common single-frequency SAS and several velocity-selective resonances (VSRs), we call these VSR peaks ‘global crossover SAS’. This phenomenon is explained by VSR effect. The global crossover SAS is formed by the atomic velocity groups resonance with both the initial and modulated laser fields, which are counter-propagated. Moreover, the global crossover SAS dips having the separation of allowed hyperfine transitions move along with the two sets of common single-frequency SAS while the frequency difference of the dual-frequency laser is changed. This indicates a resonance between the velocity shifted pump laser frequency and the velocity shifted probe laser frequency. The results obtained in this system are of great interest for laser spectroscopy. Furthermore, the application of the counter-propagating laser beams in the dual-mode regime increase the number of atoms that effectively interact with the field, hence, this scheme has a potential advantage for laser frequency stabilization.

Gerard Nienhuis

Ming-Chiang Li

Vl. V. Pokasov, D.Yu. Primakov, Sergei N Bagayev +1 more

We present a new scheme of laser spectrometer based on an active optical cavity containing saturated absorbing and amplifying media. Such an active cavity may ensure enhancement in the amplitude of nonlinear optical resonances of saturated absorption at least by one order of magnitude as compared with similar passive system. The efficiency of the spectrometer was demonstrated by the observation of saturated absorption resonances in methane at a wavelength of 3.39 /spl mu/m under transit-time conditions. In these conditions, the contribution of fast molecules can be greatly reduced because of a finite interaction time of particles with the radiation field. In our work with a light beam 0.6 cm in diameter, we eliminated the transit-time broadening limit by using optical selection of slow methane molecules with a transverse velocity 20 times less than the mean thermal one, and obtained sub-DoppIer resonances with a homogeneous width less than 5 kHz.

清 西川, 昭 佐道, Hiroshi Sekiya +3 more