Narrow resonances of two-photon absorption of super-narrow pulses in a gas

M. S. Pindzola

Eugeniy E. Mikhailov, Vladimir A. Sautenkov, Yuri V. Rostovtsev +1 more

We observe a narrow, isolated, two-photon absorption resonance in 87Rb for large one-photon detuning in the presence of a buffer gas. In the absence of a buffer gas, a standard Λ configuration of two laser frequencies gives rise to electromagnetically induced transparency (EIT) for all values of one-photon detuning throughout the inhomogeneously (Doppler) broadened line. However, when a buffer gas is added and the one-photon detuning is comparable to or greater than the Doppler width, an absorption resonance appears instead of the usual EIT resonance. We also observe a large negative group delay (≈−300 μs for a Gaussian pulse that propagates through the media with respect to a reference pulse not affected by the media), corresponding to a superluminal group velocity vg=−c/(3.6×106)=−84 m/s.

А. В. Тайченачев, Anatolii M Tumaikin, Valeriy I. Yudin

A gas of three-level atoms with Λ configuration of energy levels was taken as an example to demonstrate that the influence of particle motion on the two-photon resonances extends further than the residual Doppler shift ( k 1 − k 2 ) v . In particular, a narrow dip in the absorption spectrum (“dark” resonance) undergoes substantial narrowing, as compared to the atoms at rest. The width of this resonance is studied nonperturbatively as a function of the intensities of probe and strong fields.

Gerard Nienhuis

Ye. V. Baklanov, Veniamin P. Chebotayev, B. Dubetsky

E. V. Baklanov, V. P. Chebotaev

Two-photon absorption of a continuous train of ultrashort pulses in a gas gives rise to resonances when the sum of the frequencies of two locked modes coincides with the transition frequency in the gas. It is shown that the width of these resonances is not governed by the pulse duration but by the width of the twophoton transition. Resonance intensities are of the same order of magnitude as in the single-frequency regime at the same power level. It is worth noting an important feature of the use of ultrashort pulses in studies of two-photon resonances due to the 1S-2S transition in the hydrogen atom: there is a strong increase in the efficiency of conversion of dye laser radiation to the ultraviolet range.