On transient sub-Doppler spectroscopy of particle spectral lines

L. Hamdi, P. Todorov, Isabelle Maurin +6 more

The collisional effects in nanocell spectroscopy are investigated. Experiments performed on the well-resolved Cs D/sub 1/ line (894 nm), have enabled a simultaneous comparison of /spl lambda//2 and /spl lambda//4 thickness for various densities. Because nanocell spectroscopy, when performed under normal incidence irradiation, allows a sub-Doppler resolution owing to the velocity-selection operated by the transient regime of optical interaction, the pressure behaviour of the various hyperfine components can be studied individually. Considerable differences are found to occur for the pressure-induced shift, as already observed through selective reflection (SR) spectroscopy on the Cs D/sub 2/ line.

Tadeusz Skalinski

А. Ч. Измайлов

The method of sub-Doppler spectroscopy is theoretically elaborated, which is based on the specific dynamics of a number of optically excited atomic particles (atoms or molecules) of a rarefied gas medium in a thin cell after the action of the resonance pulse of the monochromatic radiation. Corresponding calculations are carried out on the basis of density matrix equations for the resonance optical transition between Zeeman degenerate ground and excited quantum levels of particles in case of the linear polarization of the laser pulse at its normal incidence on the cell. The situation is considered when the radiative lifetime of the excited level is much more than the characteristic transit time of particles between nearest plane-parallel walls of the cell. Then the distribution of a number of excited particles versus the pulse frequency detuning narrows in the process of particles collisions with walls of the cell after action of the laser pulse. The factor of such a narrowing (in comparison with the Doppler broadening of the spectral line of the resonance transition) may be more than the ratio of the characteristic transverse size of the thin gas cell to its inner thickness. We discuss possible use of given sub-Doppler resonances (of the number of excited particles) in the high-resolution spectroscopy and also in high-selective processes of photo-ionization and photo-dissociation, especially, for isotope (or isomer) separation and detection of rare (in particular single) atoms or molecules of a gas medium.

Erkki Kyrola, Stig Stenholm

H. Tajalli, S. Ahmadi, А. Ч. Измайлов

A theoretical investigation is carried out through the interaction of the plane running monochromatic light wave, having an arbitrary intensity, with atoms (molecules) of a rarefied gas in the plane cell (at the normal incidence of the wave). Cases of closed and open resonance transitions from the non-degenerate ground (or metastable) quantum level are considered. Possible sub-Doppler resonances are analysed in the wave absorption, caused by the transient establishment of the optical coherence on the transition, Rabi oscillations between its levels, and optical pumping during the free flights of particles between the walls of the cell. Results of the previous works on given problems are generalized, which were obtained at definite restrictions on the wave intensity and cell length. Moreover, non-trivial sub-Doppler spectral structures, resulting as a consequence of the dependence of the absorption saturation on the transit relaxation of particles, have been established and investigated. Such structures may consist of a number of peaks and dips caused by Rabi oscillations between the transition levels. The results obtained can be used in sub-Doppler spectroscopy and for the stabilization of laser frequencies in thin gas cells.

R. Corbalán, Gaspar T. Orriols, L. Roso +2 more