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A theoretical investigation is performed to determine the possibility of and conditions for self-induced transparency on Wannier–Mott excitons in a layer of semiconductor quantum dots.

The possibility and conditions of recording and reading out two-quantum transient holograms on the exciton levels of CdSe/CdS/ZnS-type semiconductor quantum dots are studied theoretically.

The possibility of observing the exciton nutation in a thin layer of CdSe/CdS/ZnS semiconductor quantum dots is demonstrated theoretically.

The possibility of and conditions for creating a quantum gate and exciton coherence on semiconductor quantum dots are investigated theoretically. Prospects for observing exciton echoes on quantum dots are discussed.

A theoretical investigation is performed for the possibility and conditions of the stimulated induction of excitons in a thin layer of semiconductor quantum dots upon excitation by continuous-wave laser radiation.

We discuss the possibility of exciting a stimulated excitonic induction in a thin film of semiconductor quantum dots and analyze the possibility of writing and reading out the two-quantum excitonic transient holograms in such samples.

Results from femtosecond coherent spectroscopy of four-wave mixing in GaAs/AlGaAs semiconductor heterostructures at room temperature are presented. Electron diffusivities and their spins are found via spectroscopy of transient gratings. Investigations in the field of spin transport in GaAs/AlGaAs heterostructures are performed with the aim of their possible use in spintronics applications.

We have studied theoretically a possibility to construct a quantum gate on the basis of semiconductor quantum dots of a core/shell type.

The possibility and conditions of an incoherent exciton echo excitation in a thin layer of the CdSe/CdS/ZnS semiconductor quantum dots spread on a glass substrate are discussed.

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.

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°.

The signals of photon echo (PE) are investigated firstly in a ruby crystal doped only by the 53Cr isotope ions in a concentration of 0.03 – 0,05 wt%. The optical experiments were performed in backward regime at the wavelength of 693.4 nm both with a low magnetic field (200 G) and without it. Since the 53Cr isotope ions have hyperfine structure of levels the special attention was paid to the study of the stimulated photon echo and primarily to the investigation of its decay kinetics. It is established that this decay has a form which is typical to the signals of long-lived PE. But in contrast to the long-lived PE the decay time in our case is less than the lifetime of the excited 2E(Ē) state. The signals of primary photon echo and stimulated photon echo at a low longitudinal magnetic field and their decay curves are investigated. We observed the beats of temporal shape of these signals with a period of several tens of nanoseconds. Theoretical analysis shows that they are due to the hyperfine interaction of valence electrons of 53Cr isotope ions with their own nuclei. The obtained decay curves allow us to estimate the phase relaxation time at the presence of a magnetic field. It proves to be equal to 98 ns. The spectrum of stimulated photon echo signal in the doped ruby exposed to a magnetic field is measured.

The absorption spectrum of Er3+ ions in YAG crystal in the range from 645 nm to 655 nm was measured with the resolution of 0.01 nm using the frequency-anticorrelated broadband photon pairs (biphotons) generated by spontaneous parametric down-conversion. The spectrum of the sample was measured by counting the coincidences when the impurity crystal was placed in front of the signal photon detector, whilst the wavelength of the idler photons was resolved by a monochromator which was placed in front of another photon detector. The results are in agreement with those obtained by the usual intensity measurements with a classical light source and a monochromator. It was shown experimentally that the biphoton spectroscopy, unlike the usual single photon spectroscopy, allows one to obtain the spectroscopic information in the presence of an external noise such as background thermal radiation.

The features of superfluorescence (SF) in nanoclusters, which consist of a few neighboring particles interacting with each other by exchange or/and electrostatic forces, are investigated theoretically. It is shown that there are two types of cooperatively SF depending on the ratio between the linear size of a nanocluster and the cooperative interaction range. Experiments on cooperative luminescence in Ytterbium-doped silica fibers are analyzed. It is shown that the intensity of cooperative SF in such a system should be proportional to the fourth degree of Ytterbium concentration.

The results of an experimental investigation of the incoherent photon echo in ruby (with Cr3+ concentration equal to 0.16 wt%) at T=1.7 K are presented. Optical fiber with length 3 m and diameter 100 μm was used for delivery of the first exciting pulse to a sample. The dependence of the IPE intensity on the excitation wavelength within the width of R1 absorption line was studied. The IPE decay curve was obtained and the phase relaxation time was found to be equal to 98 ns.

The possibility of an observation of correlated signals of the accumulated photon echo under a three-photon excitation of a sample, which is an ensemble of semiconductor nanoparticles of "core – shell" type, by a femtosecond radiation of Ti:Sa laser is discussed. The phase matching conditions of such signals are obtained.

The possibility and conditions for generation of the correlated signals of cluster superfluorescence (CSF) under two and three-quantum excitation of nanostructured samples CdSe/CdS by two crossed at the angle of 60° femtosecond beams of the Ti:Sapphire laser radiation are investigated. It is shown that intensity of the CSF signals is proportional to the cube of the number of clusters and that these collective signals are generated in mutually opposite directions k 1 – k 2 and k 2 – k 1 , where k 1 , k 2 are the wavevectors of the exciting pulses.

In the paper the solution of the following inverse problem of electrostatics is suggested. An electric field created by a point charge with a dipole moment is known at a, certain point of space. The tensor of the first derivatives of the electric field with respect to the coordinates is known at the same point. It is required to find the coordinates and magnitudes of the charge and dipole moment.

The absorption spectrum of Cr3+ ions in Al2O3 crystal in the range from 691 nm to 697 nm was measured at the room temperature using the biphoton light generated by nondegenerate spontaneous parametric down-conversion of the He-Cd laser radiation (325 nm) in the LiIO3 crystal. The spectrum of the sample was measured by counting the coincidences when signal photons go through the impurity crystal, whilst the wavelength of the idler photons is resolved by a monochromator. A strongly nondegenerate regime of SPDC, when the difference in frequencies of correlated photons exceeds significantly their spectral width, was used in the biphoton spectroscopy for the first time. Such a regime allows one to obtain an absorption spectrum by measuring the wavelength in a completely different spectral range.

The possibility and conditions of the correlated signals of stimulated photon echo (SPE) generation under three-photon femtosecond excitation of a sample, which is an ensemble of N semiconductor nanoparticles, are investigated. Each of these nonoparticles consists of a CdSe core covered by a CdS shell. The phase matching conditions for correlated SPE signal formation in such a sample are obtained.

This article presents a review of many years of study of the physical principles of optical memory based on light (photon) echoes.

Temporal shape of a primary photon echo (PPE) in a ruby is experimentally investigated. Using of special equipment, including a dye laser and a stroboscopic oscilloscope, allows to observe the "beats" of temporal shape of primary photon echo. Analysis shows that these "beats" are due to the hyperfine interaction of electrons of "Cr-53" isotope ions with their nuclei.

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.

It is assumed that the Lienard-Wiechert fields of an arbitrary moving charge is measured or predefined as a function of time. The position of the charge is calculated as a function of the retarded time., Comment: LaTeX2e, 6 pages, published in Physics Letters A

A review of femtosecond experiments on photon echo (PE) and four-wave mixing (FWM) performed at room temperature is presented. The Weiner–Ippen technique of FWM spectroscopy is demonstrated in dye-doped polymer films (such as polyvinilbutural doped with phthalocyanine), semiconductors (CdS) and heterostructures (GaAs/AlGaAs). The experimental setup used in these experiments is described. The dephasing times are estimated and the relaxation mechanisms are discussed.

Possibilities of photon echo technique in sensing of atmosphere are explored. As example the vapor of molecular iodine is considered as the promising resonant medium for the photon echo lidar (PE-lidar). The two schemes of PE-lidar are discussed and the ways of their optimal use for the atmosphere sensing are analyzed.

Spectrum of radiation of a relativistic particle moving in a nonhomogeneous magnetic field is considered. The spectrum depends on the pitch-angle $\alpha$ between the velocity direction and a line tangent to the field line. In case of very small $\alpha$ the particle generates so-called curvature radiation, in an intermediate case undulator-kind radiation is produced. In this paper we present the calculations of radiation properties in a case when both curvature and undulator radiation is observed., Comment: 5 pages, 2 figures. Talk given at 9th Lomonosov Conference on Elementary Particle Physics: Particle Physics on the Boundary of the Millenium, 20-26 Sep 1999. Moscow, Russia. CNUM: C99-09-20.3

In this letter the electron and spin dynamics at GaAs/AlGaAs heterojunction was studied by ultrafast spectroscopy techniques (photon echo and transient grating studies). Relaxation times and diffusion coefficients of photoexcited electrons and spins were obtained using pure optical setup. The estimated spin diffusion coefficient value of 160 cm2/s is relatively high and comparable to the electron diffusion coefficient of 200 cm2/s. This feature makes GaAs/AlGaAs heterosructure a promising material for practical application in semiconductor spintronics.

Triggering optical superradiance, which allows a control of spontaneous emission with the use of an injection optical pulse, is considered. The multipulse regime of excitation of optical superradiance and the long-lived optical superradiance are analyzed as the generalizations of the triggering regime of superradiance excitation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The application of laser cooling to facilitate the superradiance process is considered. The possibilities to quench homogeneous and inhomogeneous relaxation processes, to create inversion and to ensure superradiance without inversion are analyzed. The corresponding kinetic equations are constructed. Their solutions are obtained in order to estimate the conditions for observation of superradiance induced by laser cooling process.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The problem of the optical memory using the long-lived photon echo is analyzed. The results of our experiments on this problem are discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.