Optical echo holography

Population difference gratings created on vibrational transitions by nonoverlapping subcycle THz pulses

“…Because of high dipole moments in the THz range, one needs significantly smaller field amplitudes than in the optical range, of the order of kV/cm. This opens a new opportunity for an ultrafast THz spectroscopy with subcycle THz pulses to determine the resonance frequencies and the corresponding dephasing and relaxation times via diffraction of a weak probe pulse on the induced gratings 12 – 14 . The investigated phenomenon can be also used for creation of ultrafast beam deflectors and switches on molecular systems in the THz range.…”

“…That is, so called coherent interaction regime takes place, and effects of resonant light-matter interactions such as Rabi oscillations may arise 11 . If a resonant medium interacts coherently with a train of few-cycle pulses and the pulses do not overlap in the medium, population density gratings can be created in a two-level medium as it was shown in optical range using long nanosecond 12 – 14 , femtosecond and attosecond pulses 15 – 17 as well as in THz range using multi-cycle THz 18 pulses.…”

“…Furthermore, creation of the gratings on vibrational transitions in different systems opens novel opportunities in THz ultra-fast spectroscopy. For instance, diffraction of a weak probe pulse on such gratings can be used for spectroscopic measurements of – a task which is otherwise proved to be quite difficult experimentally 12 – 14 . As we show below, such gratings can be also used for control of THz radiation, for instance ultrafast pulse reshaping using fast mirrors.…”

Population density gratings induced by few-cycle optical pulses in a resonant medium

“…This induced polarization grating can interact with other pulses, leading to modification of population inversion and thus to a grating. Such gratings were observed in the first experiments on photon echo on the nanosecond time scale 20 and were used in the so-called echo holography 21 .…”

“…For instance, if the pulse amplitude is strong enough, it can propagate in a resonant absorbing medium practically without losses in the regime of self-induced transparency (SIT) 19 . Due to the presence of phase memory, a direct intersection of the pulses for grating creation 20 , 21 is not required anymore. The reason for this is the appearance of polarization oscillations at the optical frequency, which remains after the pulse passage.…”