Yu. P. Malakyan

Selective Addressing of High-Rank Atomic Polarization Moments

We describe a method of selective generation and study of polarization moments of up to the highest-rank kappa=2F possible for a quantum state with total angular momentum F. The technique is based on nonlinear magneto-optical rotation with frequency-modulated light. Various polarization moments are distinguished by the periodicity of light-polarization rotation induced by the atoms during Larmor precession and exhibit distinct light-intensity and frequency dependences. We apply the method to study polarization moments of 87Rb atoms contained in a vapor cell with antirelaxation coating. Distinct ultranarrow (1-Hz wide) resonances, corresponding to different multipoles, appear in the magnetic-field dependence of the optical rotation. The use of the highest-multipole resonances supported by a given system has important applications in quantum and nonlinear optics and in magnetometry.

Nonlinear magneto-optical rotation of frequency-modulated light resonant with a low-J transition

A low-light-power theory of nonlinear magneto-optical rotation of frequency-modulated light resonant with a J=1{yields}J{sup }=0 transition is presented. The theory is developed for a Doppler-free transition and then modified to account for Doppler broadening and velocity mixing due to collisions. The results of the theory are shown to be in qualitative agreement with experimental data obtained for the rubidium D1 line.

Time development of squeezing effects in hyper-Raman scattering

Abstract It is shown that the compound mode of Stokes and parametric fields generated by hyper-Raman scattering (HRS) and four-wave mixing develops a large amount of squeezing, provided that the Stokes mode is amplified in a less degree than the parametric mode is damped. In the opposite case the initial coherent pump field is found to acquire some squeezing which is much higher than that predicted in two-photon absorption.

Suppression of hyper-Raman scattering by destructive interference process

Abstract Selfinduced suppression of hyper-Raman scattering (HRS) in gaseous medium is predicted. The nature of the effect is that the HRS induces four-wave parametric generation of a new field which then participates in destructive interference process leading to the strong suppression of the HRS. The effect occurs only in forward direction and depends on the pump intensity, pulse duration and two-photon detuning.

Features of faraday rotation in cs atomic vapor in a cell thinner than the wavelength of light

Features of the effect of Faraday rotation (the rotation of the radiation polarization plane) in a magnetic field of the D1 line in Cs atomic vapor in a nanocell with the thickness L varying in the range of 80–900 nm have been analyzed. The key parameter is the ratio L/λ, where λ = 895 nm is the wavelength of laser radiation resonant with the D1 line. The comparison of the parameters for two selected thicknesses L = λ and λ/2 has revealed an unusual behavior of the Faraday rotation signal: the spectrum of the Faraday rotation signal at L = λ/2 = 448 nm is several times narrower than the spectrum of the signal at L = λ, whereas its amplitude is larger by a factor of about 3. These differences become more dramatic with an increase in the power of the laser: the amplitude of the Faraday rotation signal at L = λ/2 increases, whereas the amplitude of the signal at L = λ almost vanishes. Such dependences on L are absent in centimeter-length cells. They are inherent only in nanocells. In spite of a small thickness, L = 448 nm, the Faraday rotation signal is certainly detected at magnetic fields ≥0.4 G, which ensures its application. At thicknesses L < 150 nm, the Faraday rotation signal exhibits “redshift,” which is manifestation of the van der Waals effect. The developed theoretical model describes the experiment well.

Absorption of resonance radiation and fluorescence of a layer of an atomic gas with thickness of the order of a wavelength

The features of resonance fluorescence and absorption of resonance laser radiation in atomic vapors in a superthin cell with thickness L of the order of a wavelength lambda are investigated theoretically. Taking into account the Fabry-Perot interference effect, it is found that the dependence of the fluorescence and absorption spectra on the ratio L/lambda is substantially different. Coherent spectral narrowing - the Dicke effect - when L=(2n+1)lambda/2 and broadening of the spectral line when L = n lambda (n is a whole number) are observed in the absorption spectra. This effect is absent in the spector of resonance fluorescence in extended media. It is also shown that the processes of saturation and optical pumping significantly alter the spectral line shape as the laser intensity increases; in particular, additional sub-Doppler dips appear at the frequency of the atomic transitions. Calculated curves are given for the D2 lines of ^85Rb atoms.

Creation of population inversion by Fano interference in three-level cascade-type system

We demonstrate how Fano interference produces a large population inversion in a three-level cascade-type system involving an autoionizing state. We show that when an intense monochromatic field driving the lower transition of the atom by a two-photon resonant interaction creates a pair of dressed states which then are coupled by a second coherent field to ionization continuum and an autoionizing state, the Fano interference prevents the photoionization from the upper dressed state whereas the second state is quickly exhausted, thus making possible the coherent generation of short-wavelength light free of phase-matching condition. We discuss the incoherent processes which can destroy the Fano interference.

Quantum Theory of Hyper-Raman Scattering

Abstract We develop the quantum theory of stimulated hyper-Raman scattering (HRS) and discuss the quantum statistics of pump and Stokes fields. We show that the initially coherent pump field acquires a strong squeezing that exceeds the similar squeezing in other nonlinear processes also involving two-photon absorption. Stokes field statistics are analysed in detail as a function of the initial statistics of both modes. Bunching effects are shown to be amplified in the short-time region, while in asymptotics the antibunching of Stokes photons becomes dominant, which in many cases results in sub-Poissonian statistics of Stokes mode. We also find a number of correlation effects between the photons of the two modes.

Quantum beats in stimulated electronic raman scattering of ultrashort laser pulses

A theory of quantum beats in a Stokes signal observed in pump-probe experiments upon excitation of four-level atoms with two close upper lying levels by femtosecond laser pulses is developed. Quantum beats arise in the intensity of the Stokes field due to the interference of two atomic wave packets generated by ultrashort pump and probe pulses. An analytical solution of the non-steady-state Maxwell-Bloch equations is obtained, and the dependence of the Stokes radiation intensity on the delay time between two laser pulses is investigated. The theoretical results describe qualitatively well the observed features of quantum beats.

Quantum interference in the absorption spectrum of V-type atom with magnetic coherence effects

We study the probe absorption for a three-level atom with a pair of upper levels coupled by a magnetic field. We show the possibility of very narrow absorption resonances due to the quantum interference between two excitation pathways and the coherence induced by magnetic field. The properties of the resonances can be controlled by the strength of magnetic field.