V. V. Samartsev

Coherent optical spectroscopy of promising materials for solid-state optical processors

State of the art of optical coherent spectroscopy of doped solids that are promising as information carriers for optical processors is reviewed. Special attention is paid to optical echo spectroscopy of doped crystals classified as the Van-Vleck paramagnets where the long-lived stimulated echo is observed with the optical-memory time reaching several hours at low temperatures. Modern elaborations of optical echo processors based on this echo phenomenon are discussed. Physical principles of femtosecond echo spectroscopy and coherent four-wave mixing spectroscopy are formulated. The abilities of these methods in the diagnostics of fast processes at room temperature are illustrated using examples of a doped polymer films. The results of elaborations of a new branch of optical spectroscopy (biphoton spectroscopy) are also presented. The advantages and possible applications of this method are demonstrated using an example of two crystals (Er3+:YAG and Cr3+:Al2O3).

Femtosecond primary and stimulated photon echoes in a dye-doped polymer film at room temperature

The signals of both primary and stimulated femtosecond photon echoes are observed and investigated in a dye-doped polymer film at room temperature using a modernized femtosecond echo-spectrometer. It should be noted that stimulated photon echo in the solid-state sample is observed for the first time at such a high temperature. Experimentally obtained decay curves of these signals have a nonexponential character. The spectra of these echo signals are also measured. It is found that the spectrum of the primary photon echo is short-wave shifted with respect to the spectrum of excitation. This can be used for the coherent laser cooling of a sample. The spectrum of the stimulated photon echo is also shifted to the short-wave range relative to the spectrum of excitation, but its shift is much less than that of the primary photon echo. The experiment shows that the femtosecond echo signals at room temperature are excited via the phonon-side band of the absorption line.

Spectroscopic properties and site origin of Shpol'skii system—terrylene in n-nonane

Abstract We present low temperature absorption and fluorescence spectra of terrylene and its derivative di -tert- butylterrylene in a series of n-alkanes: n-octane, n-nonane, n-decane and n-dodecane. Terrylene in n-nonane exhibits the most red-shifted absorption spectrum with clearly distinguished contribution of four sites. Theoretical simulations by means of MM+ and INDO/S methods were carried out with the aim to establish how the guest molecules of chromophore are embedded into the host crystalline lattice of n-alkanes, special attention being paid to the n-nonane matrix.

Advances of laser refrigeration in solids

The physics of laser cooling in solids is discussed. The coherent optical cooling of dye-doped polymer films in regime of anti-Stokes femtosecond photon echo is analyzed. The possibility of improved optical cooling by doped nanocrystalline structures is studied.

The application of the weak magnetic field pulse to measure g-factors of ground and excited optical states by a photon echo method

A new scheme of the definition of g-factors as ground and excited optical states of a paramagnetic ion in zero external constant magnetic field has been proposed and experimentally realized in optical systems in which the Zeeman effect is manifested. A pulse of a weak magnetic field leads to the occurrence of relative phase shifts of the excited dipoles and, as a consequence, to modulation of a photon echo wave form if the magnetic pulse overlaps in time with the echo pulse. The modulation periods of the wave form depend on polarization of the laser light which excites the photon echo. The values of these periods for σ - and π-laser light polarization have been measured and then the g-factors of the ground 4I15/2 and excited 4F9/2 states of the Er3+ ion in the LuLiF4 and the YLiF4 matrices have been determined. The g-factor values have been compared with the known literary data.New scheme of definition of g-factors as ground as excited optical states of a paramagnetic ion in zero external constant magnetic field has been proposed and experimentally realized in optical systems in which Zeeman Effect is manifested. A pulse of a weak magnetic field leads to occurrence of relative phase shifts of the excited dipoles and, as consequence, to modulation of a photon echo waveform if magnetic pulse (MP) overlaps in time with echo-pulse. The modulation periods of the waveform depend on polarization of the laser light, which excites the photon echo. The values of these periods for {\sigma}- and {\pi}- laser light polarization have been measured and then the g-factors of the ground 4I15/2 and excited 4F9/2 states of the Er3+ ion in the LuLiF4 and the YLiF4 matrices have been determined. Values of the g-factors have been compared with the known literary data.

Comparison of spin and electron diffusion coefficients in a two-dimensional electron gas

The results from femtosecond four-wave-mixing experiments carried out in two-dimensional gas at the GaAs/AlGaAs heterojunction boundary under room temperature conditionsare presented. The obtained values of the spin and electron diffusion coefficients are 163.2 and 200 cm2/s respectively. The spin and electron relaxation times are found to be 50.7 ps and 3 ns respectively.

Implementation of room temperature femtosecond echo-processing

Conditions for implementing room temperature femtosecond echo-processing in a phtalocyanine-doped polyvinylbutyral film were studied. A logical operation of bit-by-bit multiplication on the basis of the nonlinear third-order optical response (primary photon echo) of the medium was performed in a time of less than 1 ps.

The application of weak electric field pulses to measure the pseudo-Stark split by photon echo beating

New scheme for determining the pseudo-Stark splitting of optical lines has been proposed and experimentally realized. A pulse of a weak electric field leads to occurrence of relative phase shifts of the excited dipoles and, as consequence, to beating of a photon echo wave form if electric pulse overlaps in time with echo-pulse. The value of the pseudo-stark splitting is the inverse period of the beats. The photon echo beating of the R1-line in Ruby have been observed. The pseudo-Stark splitting has been determined and it’s value have been compared with the known literary data. PACS numbers: 42.50.Md, 42.65.VhA novel scheme for determining the pseudo-Stark splitting of optical lines has been suggested and tested in experiment. The scheme allows one to observe the beating of a photon echo waveform under conditions of overlap in time between a weak electric pulse and its echo-pulse. The pseudo-Stark splitting is equal to the inverse average modulation period of the echo waveform. The photon echo beating of the R1-line in Ruby has been observed. The dependence of the inverse average modulation period of the echo waveform on the average value of the electric field over the optically excited volume has been found. The obtained values of the pseudo-Stark parameter are in good agreement with known literature data.

Multichannel information processing in the optical echo-processors on the basis of Van-Fleck paramagnet crystals

The analysis of various modes of multichannel information recording and readout in conditions of a stimulated (accumulated and long-living) photon echo in the crystals doped with rare earth ions which are known as Van-Fleck paramagnets has been performed in order to utilize them in the operation of low-temperature optical echo-processors.

Femtosecond laser control of intramolecular vibrations in a liquid

Optical control of coherent intramolecular oscillations in chloroform CHCl3 and dimethyl sulfoxide (CH3)2SO is attained experimentally under normal conditions by means of femtosecond polarization spectroscopy. Nonresonant excitation of the medium is accomplished by a sequence of two linearly polarized laser pulses. The state of the medium is probed by the third pulse via the optical Kerr effect. We show that control over the vibrational dynamics of molecules on a sub-picosecond scale can be achieved by varying the delay between the excitation pulses and their relative intensity.