Ultrashort pulses of optical superradiance

Stephen G. Benka

George L. Lamb

Ashat M. Basharov

A new type of three-level photon echo has been predicted and analytically described. In contrast to the conventional three-level echo, whose formation involves three resonant ultrashort excitation pulses spaced in time, two of which are resonant to different optically allowed and adjacent transitions with different frequencies, the echo predicted arises under the conditions of formation of the conventional two-pulse echo and requires only two pump pulses of the same frequency. A theory is developed for the conditions of experiments on generation of a superradiance pulse at the 3 P 0-3 H 6 transition in impurity praseodymium ions in the LaF3 matrix upon ultrashort coherent excitation of the adjacent optically allowed 3 H 4-3 P 0 transition in praseodymium. It is shown that the superradiance pulse after its deexcitation does not polarize the medium at the 3 P 0-3 H 6 generation transition and completely eliminates polarization at the 3 H 4-3 P 0 excitation transition. However, simultaneously, the superradiance pulse transfers the optical coherence from the excitation transition to the optically forbidden 3 H 6-3 H 4 transition. Thus, the phase memory about the effect of the excitation superradiance pulse is retained in the medium within a time interval that is shorter than the irreversible relaxation time of the optically forbidden transition.

A. V. Andreev

Rostislav M. Arkhipov, Mikhail V. Arkhipov, A. V. Pakhomov +3 more

Our recent theoretical studies of generation of ultrashort pulses based on collective spontaneous emission from a thin resonant medium layer excited by a pair of high-frequency (compared to the transition frequency of the medium) pulses are reviewed. The source of generated radiation is a resonant polarization pulse in the medium (“stopped polarization pulse”), which is excited and switched off by a pair of light pump pulses. This method allows obtaining attosecond pulses in the optical and ultraviolet ranges, as well as femtosecond terahertz pulses. The effect of the superradiance in generation is discussed. The use of coherent and collective processes makes it possible to achieve a high efficiency of the generation of terahertz radiation. The proposed method is an alternative method of obtaining ultrashort pulses compared to the currently well-developed methods such as the high-harmonic generation method.

P. V. Zinov’ev, Nataliya B. Silaeva, Yu. E. Sheǐbut