We consider the possibility of observing a femtosecond correlated photon echo (FCPE) under two-photon excitation of CdS crystal by two pairs of crossed laser beams. The peculiarities of FCPE signals and their possible applications are discussed.
A new method of two-photon excitation of femtosecond signals of ``entangled'' free induction decay (EFID) by two crossed 790-nm laser beams in a CdS crystal at room temperature has been realized for the first time. This ``entangled'' (through the wave vectors) coherent response appears only in the case when the photons involved to the process of two-photon excitation of the sample belong to the different laser beams. This technique allows one to separate the EFID signal from the exciting femtosecond pulses and to vary the response wavelength by varying the angle between their wave vectors. The most optimal case occurs when the angle between the wave vectors of exciting pulses as well as the angle between each of these wave vectors and that of the response is equal to 60°.
Entangled free induction decay (EFID) femtosecond signals are experimentally observed for the first time at a wavelength of 790 nm in a cadmium sulfide (CdS) crystal in the two-photon absorption (TPA) regime upon excitation by two crossed (angle, 60°) laser beams. The sample emitted two EFID signals simultaneously in opposite directions. The signals were diffracted by nonequilibrium electric polarization gratings induced by two laser beams in accordance with the laws of energy and momentum conservation. The possibility of exciting EFID signals in the three-photon absorption regime is discussed.