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.     

Excitation of photon echo by noise pulses

The excitation of photon echo by noise pulses that are formed by modulation of the carrying frequency with Gauss noise is modeled. The modeling is based on optical Bloch equations the solution of which for noise pulse realizations is constructed by their stepwise approximation. In terms of the formalism of state transfer matrices, the two- and three-pulse excitation modes are analyzed. The complex envelopes of the primary and stimulated echo responses are determined. In the linear (low-level-signal) mode, the shape of the two-pulse echo corresponds to that of the time delayed and inverted noise pulse. The boundary of the linear mode, upon exceeding of which distortions of the shape of the noise pulse become noticeable, is determined. The shape of the stimulated (three-pulse) echo in the linear mode corresponds to that of the autocorrelation function of the noise pulse realization. Upon passage beyond the boundary of the linear mode, the shape of the three-pulse echo corresponds either to the cross-correlation function of distorted noise pulses (with different intensities) or to the autocorrelation function of distorted pulses (with the same intensities). The modeled photon echo excitation modes can be used in photon echo processors to process signals in the light range.     

Time-domain Fresnel-to-Fraunhofer diffraction with photon echoes

A photon echo experiment in Tm(3+):YAG is reported that shows, for the first time to the authors' knowledge, the time-domain equivalent of the transition from near- to far-field diffraction, including Talbot self-imaging effects. The experiment demonstrates the huge dispersion capability of photon echoes and opens the way to further exploration of space-time duality.     

Spectrally coded optical data storage by metal nanoparticles

In metal nanoparticles the resonance wavelength of light-driven collective electron oscillations is determined by the particle shape. This shape dependence can be used for optical data storage by spectral coding. In this way the storage density can be increased by at least a factor of 5 compared with that for conventional optical storage principles.     

Stimulated photon echo with temporal data coding in the Hopfield-Little regime

A model of an optical neural network with associative memory using stimulated photon echo (SPE) with temporal data coding is presented. The electrical field’s calculation of the SPE signals is carried out for case of multiple influences on the resonant medium by optical pulses. A computer model of an optical echo processor with associative retrieval of information is elaborated.     

Effect of locking of photon echo signals in multichannel data recording

The effect of locking of a long-lived photon echo is investigated in the case where nonresonant laser radiation (a standing or traveling wave with an artificially created spatial inhomogeneity) serves as an inhomogeneous external perturbation, which results in random shifts or splitting of the initial monochromatic components of the inhomogeneously broadened line. The use of the mutual spatial orientation of the gradients of electric fields as an associative key of access to recorded information allows one to produce a large number of independent channels of data recording. It is demonstrated that the proposed scheme for recording and associative sampling of information has the advantage that, in each channel, information is recorded simultaneously at all optical centers (the whole inhomogeneously broadened resonance line), which does not decrease the intensity of the response from each channel. Moreover, the echo holographic information coded in the wavefronts of the exciting pulses can also be recorded in each channel, which does not affect the independence of individual channels of data recording.     

Multifrequency photon echo generated by extremely short pulses

A photon echo in a multilevel quantum medium excited by two extremely short pulses with durations of less than one period of oscillation of the light is investigated theoretically. It is shown thatQ echo signals (Q is the number of allowed transitions) can form at each frequency of the allowed transitions, and the number of echo responses for all the allowed transitions equalsQ ². Of these,Q(Q?1) signals are separated in both time and space. The otherQ echo signals of all the allowed frequencies all arise at the time 2τ ₂₁ (τ ₂₁ is the time interval between application of the first and second pulses to the medium) and are collinear with one another.     

Modeling of the multipulse photon echo and its application in specialized optical computers

A physical principle of the design of two parallel coprocessors for solving the knapsack problem was proposed. These coprocessors operate on the basis of polarization properties of multipulse excitation and recording of the photon echo signals. The exciting pulse area is optimized to improve the resolution in solving combinatory problems.     

Multipulse excitation of photon echo and its application for developing the principle of design of an optical echo processor

A method for optical data processing, based on the mode of multipulse excitation of photon echo signals, has been proposed and applied to solution of the knapsack problem. In this case, along with the recognition of solvability, the solution itself is found in the optical processor. A scheme of a possible optical echo processor on molecular iodine vapor is presented.     

Laser-modified luminescence for optical data storage

The yearly growing quantities of dataflow create a desired requirement for advanced data storage methods. Luminescent materials, which possess adjustable parameters such as intensity, emission center, lifetime, polarization, etc., can be used to enable multi-dimensional optical data storage (ODS) with higher capacity, longer lifetime and lower energy consumption. Multiplexed storage based on luminescent materials can be easily manipulated by lasers, and has been considered as a feasible option to break through the limits of ODS density. Substantial progresses in laser-modified luminescence based ODS have been made during the past decade. In this review, we recapitulated recent advancements in laser-modified luminescence based ODS, focusing on the defect-related regulation, nucleation, dissociation, photoreduction, ablation, etc. We conclude by discussing the current challenges in laser-modified luminescence based ODS and proposing the perspectives for future development.     

Locking of a stimulated photon echo

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 1, pp. 84–88, July, 1991.     

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.     

Excitation of photon echo by pulses modulated with Barker codes

The excitation of the primary and stimulated photon echoes by pulses modulated in phase with Barker codes is modeled. The shape of the complex envelopes of the primary and stimulated echoes is found by solving the optical Bloch equations. Linear and nonlinear excitation modes are considered. In linear modes, it is possible to realize a time delay and form the correlation function of modulated pulses. The results obtained can be used in modeling and analyzing the corresponding algorithms of the photon echo excitation and in calculating the characteristics of signal processors based on the phenomena of photon and spin echoes.     

Femtosecond photon echo in a dye-doped polymer film and the possibility of coherent optical cooling

The signals of primary and stimulated femtosecond photon echoes are investigated in a dye-doped polymer film at room temperature. The homogeneous S ₀ → S ₁ spectral line width, which is due to the interaction between the impurity molecules and the quasi-local low-frequency modes, is estimated (≈5 × 10¹² Hz). Special attention is paid to the study of spectra of femtosecond echo signals. The short-wave shifts of these spectra, with respect to the spectrum of femtosecond exciting pulses, are observed. These shifts indicate that the anti-Stokes regime of femtosecond pulse emission is realized. Therefore, the coherent regime of laser cooling of solids appears to be possible. The prospects of using of this new cooling regime in the function of a solid-state optical refrigerator are discussed.     

Anti-Stokes femtosecond photon echo in dye-doped polymer films and the possibility of coherent optical cooling

An anti-Stokes model is proposed to explain the known experimental data on the femtosecond photon echo in dye-doped polymer films at room temperature. The possibility of implementing the anti-Stokes mode of coherent laser cooling of such films is analyzed.     

Photon echo and stimulated photon echo study of various collisional-relaxation channels

Collisional relaxation in SF₆ gas and its mixtures with He and Xe is studied by photon echo and stimulated photon echo methods from the standpoint of the possibility of identifying the contributions of different types of collisions. The nonexponential nature of the kinetic curve of the photon echo is clearly observed for pure SF₆, it is weaker in the mixture SF₆+Xe, and it is virtually completely absent for high degrees of dilution of SF₆ with helium. These features can be explained on the basis of estimates, made from experimental data, of the critical delay between the exciting pulses (for which the nonexponential behavior should be most strongly manifested). In pure SF₆ it is possible to distinguish the contribution of the inelastic channel (rotational relaxation) and the contribution of weak collisions. To distinguish successfully the relaxation channels in mixtures with buffer gases a heavier buffer gas and a much better time resolution must be used. It is shown that data obtained on the orientation and alignment relaxation rates by the stimulated photon echo method can serve as an upper limit for the rates of inelastic processes which cannot be measured by the photon echo method. The combined use of photon echo and stimulated photon echo methods made it possible to obtain data on the cross sections for elastic and inelastic scattering of the collisional pairs SF₆–SF₆, SF₆–Xe, and SF₆–He. Zh. éksp. Teor. Fiz. 116, 47–56 (July 1999)     

Spatial regularities in the effect of locking of photon echo signals and associative optical memory

The efficiency of suppression of the generation of a photon echo response depending on the mutual spatial orientation of gradients of external nonumform electric fields acting on a resonant medium is studied. The possibility of creating an associative memory where the mutual orientation of the gradients of external electric fields is an associative key is discussed.