arXiv subjects

S. A. Saakyan

Publications and source records attributed to S. A. Saakyan.

7 recordsLinked to original sources

arXiv2026

Influence of Many-Body Dipole-Dipole Interactions on Excitation Transfer in a Dense Gas

We study non-radiative dipole-dipole induced excitation transfer in dense Rb vapour. We show that density dependence of characteristic time of the excitation diffusion changes from linear to non-linear for high Rb density. It is attributed to the breakdown of binary collisions approach to the dipole-dipole excitation transfer. It is shown that the observed result can be qualitatively described if the mean free path is replaced by mean interatomic distance for the chracteristic diffusion length.

physics.atom-ph↗

arXiv2026

Hollow Beam Optical Ponderomotive Trap for Ultracold Neutral Plasma

Rapidly oscillating, inhomogeneous electromagnetic field from laser exert a force that repels charged particles from regions of high light intensity. We propose and analyze a flat-bottomed hollow-beam ponderomotive optical trap for an ultracold neutral plasma (UNP), driven by a high-power CO$_2$ laser. Molecular dynamics simulations show that the plasma and Rydberg atoms are effectively trapped within a nearly uniform dark region bounded by repulsive light walls. In contrast to RF traps, flat-bottomed traps yield a small density-weighted mean ponderomotive energy per electron, while the UNP collision frequency is far below the laser frequency, thereby making collisional absorption negligible and does not limit the lifetime of the trap. This approach could enhance antimatter production and storage.

physics.plasm-ph↗

arXiv2025

Optical-field-induced dips and splits in nonlinear spectra of selective reflection from high-density atomic vapor

We discuss nonlinear spectra of selective reflection from high-density rubidium atomic vapor, where the self-broadening of the resonant transition $5S_{1/2}-5P_{3/2}$ dominates over the Doppler width. In the experiments, the hole-burning technique with probe and pump lasers is used. The reflection of weak probe beam is investigated at four atomic densities in the range $(1.2\text{--}3.6)\times10^{17}$~cm$^{-3}$ and various pump beam intensities. To enhance the spectral resolution, the frequency derivative $\text{d}R/\text{d}ν$ of the reflection coefficient $R$ is analyzed. Increasing the atomic number density changes the character of self-broadening from inhomogeneous to homogeneous. At the highest density, the strong pump field splits the observed spectra into two homogeneously broadened symmetric resonances. The appearance of the optical-field-induced resonances can be explained within the framework of "dressed atomic states" approach. At lower densities the spectral profiles are inhomogeneously broadened. Spectral profiles of the frequency derivative are separated by optically saturated dips. The width of such dips is a combination of the homogeneous component of self-broadening and intensity-dependent field broadening. Careful study of the transition from inhomogeneous to homogeneous broadening may initiate further development of the theory of interatomic interactions in high density atomic gas media.

physics.atom-ph↗

arXiv2024

Pump-probe studies of resonantly saturated selective reflection from high-density rubidium vapor

Nonlinear selective reflection from the interface YAG window-high density rubidium vapor in the high-temperature cell is studied at the transition 5S$_{1/2}$-5P$_{3/2}$. In the experiment tunable pump and probe lasers are used. The selective reflection spectra for the laser probe beam are investigated at four different rubidium atomic densities and five different pump beam intensities. The estimated dipole-dipole interaction-induced line broadening varies from $13.2$ to $39.6$ GHz, the measured pumped intensities change from $1.2$ to $8.8$ kW$\cdot$cm$^{-2}$. Growth of the pump intensity causes reduction of the magnitude and the width of the recorded selective reflection resonance. We suggest developing all-optical modulators on the basis of nonlinear selective reflection.

physics.atom-ph↗

arXiv2023

Electronic resonances in expanding non-neutral ultracold plasma

We present a calculation of the natural oscillation spectrum of inhomogeneous non-neutral ultracold plasma. The collective modes of these plasma oscillations are recorded in experiments as absorption resonances of radio-frequency electric field. It is shown that in the presence of friction of the electronic component, a discrete spectrum of plasma eigenoscillations is formed. Dependence of the frequency of these resonances on the charge imbalance and on the expansion time is obtained. Good agreement with the experiments of different authors is noted.

physics.plasm-ph↗

arXiv2022

Steady-State Ultracold Plasma

A strongly coupled ultracold plasma can be used as an excellent test platform for studying many-body interactions associated with various plasma phenomena. In this paper we discuss an approach that makes possible creation of the steady-state ultracold plasma having various densities and temperatures by means of continuous two-step optical excitation of calcium atoms in the MOT. The parameters of the plasma are studied using laser-induced fluorescence of calcium ions. The experimental results are well described by a simple theoretical model involving equilibration of the continuous source of charged particles by the hydrodynamical ion outflux and three-body recombination. The strongly coupled plasma with the peak ion density of $6\cdot10^5$ cm$^{-3}$ and the minimum electron temperature near 2 K has been prepared. Our steady-state approach in combination with the strong magnetic confinement of the plasma will make it possible to reach extremely strong coupling in such system.

physics.plasm-ph↗

arXiv2018

Self-focusing of CW Laser Beam with Variable Radius in Rubidium Atomic Vapor

Self-focusing of a cw laser beam in rubidium atomic vapor was studied. The beam power and beam spot size at entrance of a glass cell with the rubidium vapor were variable parameters. A steep grow of the threshold power of self-focusing for the small beam radii (< 30 μm) was observed. Our experimental data are in an agreement with the theoretical results published by Semak and Shneider in 2013. Additional experiments in resonance and transparent media are suggested in order to check and extend our measurements.

physics.optics↗