Raman echo under medium excitation by extremely short pulses

A generalization of the Bloembergen-Shen model to Raman active molecules with an arbitrary number of normal modes was suggested. The generalized model was used to study Raman echo signal characteristics when a system of molecules was excited by pulses of widths up to one period of optical oscillations. It was shown that a large number of echo responses on Stokes and anti-Stokes components could arise even under a two-pulse action in a continuous monochromatic pumping field. The number of echo responses depended on the number of molecular normal modes and the geometry of measurements. At small exciting pulse “areas,” the echo responses whose Stokes and anti-Stokes components corresponded to normal vibrational modes of a molecule had the highest intensity, whereas the components formed by normal mode combinations were strongly suppressed.     

Structure of photon echo signals under excitation of a medium by few-cycle optical pulses

The results of original theoretical investigations of the primary and long-lived photon echo, generated by sequences of broadband and quasi-monochromatic pulses, are reported. Both echo responses and the effect of correlation of their profiles with the profiles of excitation pulses have a two-frequency character.     

Photon echo under two-quantum excitation of superradiance in a cavity

The superradiance, photon echo, and coherence transformation in three-level cascade-type atoms have been theoretically investigated for the case where the frequency of an optically allowed transition from the upper level coincides with the cavity frequency.     

Stimulated photon echo under excitation by incoherent and coherent pulses

Excitation of stimulated photon echo by two incoherent pulses obtained from one source and one coherent pulse is considered. The dependence of the average amplitude of stimulated echo on the parameters of noise pulses is determined. The results can be used for analysis of the corresponding algorithm of excitation of stimulated spin echo, as well as in calculations of characteristics of the signal processors based on the phenomena of photon and spin echoes.     

Photon echo excited in multilevel quantum media by ultimately short pulses

The photon echo excitated in a multilevel quantum medium by two or more ultimately short pulses with duration down to one period of optical oscillations is studied theoretically. It is shown that the number of echo responses formed in the system depends on the number of quantum levels covered by the spectrum of the exciting pulses and strongly increases with this number. General equations for the spatio-temporal characteristics of the multipulse echo signals are obtained.     

Primary acoustic echo during excitation of a paramagnetic crystal by picosecond elastic video pulses

The primary acoustic echo formed during excitation of a paramagnetic crystal with effective spin S=1 by two transverse picosecond elastic video pulses is investigated theoretically. Both exciting video pulses are applied perpendicular to the external magnetic field. It is shown that the primary acoustic echo in the general case consists of six longitudinal and transverse signals at the frequencies of the transitions within a Zeeman triplet. The optimal parameters of the exciting video pulses for the appearance of different echo signals are determined. Fiz. Tverd. Tela (St. Petersburg) 41, 623–628 (April 1999)     

Photon number squeezing of ultrabroadband laser pulses generated by microstructure fibers

To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultrabroadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schr?dinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses.     

Two-frequency correlation of photon echo signals in a medium excited by a few-cycle pulses

Two-frequency correlation between the profiles of signals of the primary and long-lived (stimulated) photon echos in a three-level medium excited by combined sequences of resonance quasimonochromatic (encoding) signals and femtosecond pulses consisting of a few optical oscillations (down to one) is predicted. It is shown that the profiles of echo responses of both frequencies correlate with each other and with the profiles of encoding pulses, copy them, and induce mirror rotations, as well as scaling transformations in time in dependence on the methods of forming exciting sequences.     

Soliton structures of a wave field with an arbitrary number of oscillations in nonresonance media

A new class of solitary solutions for a wave field is found. This class describes soliton-like structures of a circularly polarized radiation that propagate in a nonresonance medium and which involve an arbitrary number of field oscillations. A feature peculiar to these solutions is that they undergo a smooth transformation from solitons of the Schrödinger type, which correspond to long pulses involving many oscillations, to extremely short visible pulses, which, in fact, do not extend beyond one period. Realizability of such soliton structures is considered for a field of linear polarization, and their structural stability is shown numerically.     

Energy exchange between laser pulses in an atomic medium with a closed excitation contour

The effect the phase difference between carrier frequencies of two laser pulses has on their propagation in an optically dense medium of three-level point scatterers is investigated. The medium is exposed to constant radiation, creating a closed excitation contour. Situations are considered for pulse durations shorter and longer than the lifetime of the excited state of scatterers.     

Nonlinear gas oscillations in an open tube under anharmonic excitation

Nonlinear gas oscillations excited in a tube with an open end by a piston driven by a crank mechanism are investigated. For the open end of the tube, a nonlinear boundary condition is formulated with allowance for oscillations at the subharmonic resonance frequency. Both first- and second-order approximations to the oscillations at the fundamental frequency and at half this frequency are calculated. The results of theoretical calculations are compared with experimental data.     

Self-division of a pulse consisting of several light-field oscillations in a nonlinear medium with dispersion

The nonparaxial dynamics of light pulses consisting of several light-field oscillations in nonlinear media with dispersion is analyzed. It is shown that the self-action of these extremely short pulses can result in their self-division.     

Formation of a sequence of ultrashort signals in a collision of pulses consisting of a small number of oscillations of the light field in nonlinear optical media

Collisions of pulses consisting of a small number of oscillations and propagating in a nonlinear optical medium unidirectionally but with different group velocities because of a difference in the spectral composition are considered. It is shown that, at intensities of radiation ensuring the superbroadening of its spectrum, the interaction of two pulses can result in the formation of a quasi-discrete spectral supercontinuum whose temporal structure is described by a sequence of ultrashort signals with a nearly rectangular shape.     

Spatial quasi-periodic oscillations of the refractive index in an optically dense medium with a closed excitation contour

A closed contour of excitation (Δ-scheme) of a three-level atom in an optically dense medium under the action of two optical fields and a microwave field has been studied. It is found that phase relations between exciting fields in this medium play a determining role. It is established that, under certain conditions, in an optically dense Δ-atom medium exhibits a quasi-periodic dependence of the refractive index on the coordinate. The conditions under which this dependence is most pronounced are determined.