Dense Resonant Medium Research Articles

Generation of Isolated Attosecond Pulses with Large Electric Area in a Dense Resonant Medium

Generation of Isolated Attosecond Pulses with Large Electric Area in a Dense Resonant Medium

Generation of isolated attosecond pulses with large electric area in a dense resonant medium

Obtaining unipolar half-cycle optical pulses of femto- and attosecond duration with a large electrical area is an urgent but difficult task. The reason for the emerging difficulties lies in the existence of the rule of conservation of the electrical area of the pulse, which does not allow converting a bipolar pulse into a unipolar one. In this work, it is shown that in a resonant medium a few-cycle pulse can be converted into two unipolar pulses separated in time by a distance that is an order of magnitude or more longer than the duration of the initial pulse. This allows in a number of problems to consider such pulses separately as unipolar. The estimation of the electric area value relative to its "atomic scale" is carried out. Keywords: attosecond pulses, unipolar pulses, subcycle pulses, electrical area of pulses.

Single-cycle pulse compression in dense resonant media.

We propose here a new approach for compression and frequency up-conversion of short optical pulses in the regime of extreme nonlinear optics in optically dense absorbing media, providing an alternative route to attosecond-scale pulses at high frequencies. This method is based on dynamics of self-induced transparency (SIT) pulses of nearly single cycle duration, leading to single-cycle-scale Rabi oscillations in the medium. The sub-cycle components of an incident pulse behave as separate SIT-pulses, approaching each other and self-compressing, resulting in the threefold compression in time and frequency up-conversion by the same factor. As we show, the scheme can be cascaded, staying at the subsequent stage with nearly the same compression and up-conversion ratio. In this way, as our simulations show, after only few micrometers of propagation, a 700 nm wavelength single cycle pulse can be compressed to a pulse of 200 attoseconds duration located in XUV frequency range.

Ultra high-speed all-optical coherent memory cell

We study the interaction of two counterpropagating unipolar video pulses of electromagnetic radiation in a dense resonant two-level medium. The pulse durations are less than one oscillation period of an atomic transition. We show that a polariton cluster (i.e. the compact long-living strongly coupled state of electromagnetic field and matter polarization) is created, when two unipolar pulses collide in a resonant medium of the frequency ω0 (the pulses correspond to self-induced transparency solitons of the same amplitudes and opposite polarities).We have studied for the first time the conditions of maximal excitation of a resonant polarization in the polariton cluster volume. We show that there exist optimal durations and amplitudes of the recording pulses. We studied the processes of double and multiple recording and erasing of an optical memory cell in a thin layer of a resonant medium (quantum dots). We demonstrated that the pulse rate of the recording-erasing pulses can reach 60 000 GHz and higher, which happens under the coherent regime of the interaction between the electromagnetic field and polarization of the medium.

New ultra high-speed all-optical coherent D-trigger

We study the interaction of two counterpropagating unipolar video pulses of electromagnetic radiation in a dense resonant two-level medium. The pulse durations are less than one oscillation period of an atomic transition. We show that a polariton cluster (i.e. the compact long-living strongly coupled state of electromagnetic field and matter polarisation) is created, when two unipolar video pulses collide in a resonant medium of the frequency ωo (the pulses correspond to self-induced transparency solitons of the same amplitudes and opposite polarities).We studied for the first time multiple recording and erasing of a polariton cluster in a thin layer of a resonant medium (quantum dots) placed on the mirror surface. We showed that dynamics of the medium population difference N(x,t) is analogous to the operation of a D-trigger of the pulse rate 60 000 GHz and higher. We found such a method of the polariton cluster recording and erasing that excludes the accumulation of erasing errors. Therefore, the total duration of the optical D-trigger operation time can strongly exceed the phase relaxation time T2.

Observation of parametric nonadiabatic excitation of collective resonances under femtosecond optical pumping of a dense resonant extended medium without population inversion under the conditions of strong light-matter coupling

We experimentally studied the superradiance of the resonant line of rubidium under femtosecond optical pumping of a dense extended medium without population inversion under conditions of strong lightmatter coupling. Substantial self-splitting of superradiance components is observed.

Light-induced polariton clusters and their application in optical signal processing

The properties of coupled long-lived states of the electromagnetic field + matter system that are induced by a collision of two counter-propagating coherent pulses in a dense resonant media are discussed. It is demonstrated that the system possesses properties of a mirrorless polariton nanocavity with a high Q-factor.

Study of four-wave mixing in the femtosecond laser pulse propagation near the resonance rubidium doublet

In this paper, we investigated the coherent degenerate and nondegenerate four-wave interaction in the propagation of a femtosecond laser pulse in atomic rubidium vapor. In the case of degenerate four-wave interaction, the mechanism for optical switching in an optically dense resonant medium is considered. The third-order nonlinear interaction of the laser beams intersecting in the cell at a small angle leads to a nonlinear response in the form of a fourth beam, which occurs as a result of the interaction between the two pump beams and the third signal laser beam.

Dynamical instabilities of spectroscopic transitions in dense resonant media

We consider the influence of the near dipole–dipole interaction, underlying the local field, on the dynamics of two-level and V-type three-level atoms exposed to cw-laser radiation. The near dipole–dipole interaction between the V-type three-level atoms is shown to give rise to the Poincaré–Andronov–Hopf bifurcation in steady-state solution of the equations of motion. As a result, the populations of the energy levels periodically vary in time. In the framework of the nondegenerate two-level model, dynamical instabilities are proved to be impossible.

Resonance reflection of light by a thin layer of a dense nonlinear medium

The possibility of hysteretic behavior of resonant reflection spectral curves is determined analytically for the conditions of the dipole-dipole interaction and spectral shift of the field. The phase shift of the acting field is associated with the variation of the energy state of a dense resonant medium forming a thin boundary layer. The problem is considered for the parameters of quantum-size structures based on semiconductors used in optics.

啁啾超短激光脉冲对稠密共振介质特性的调控

According to the semi-classical theory of light-matter interaction,the Bloch equations with chirped terms were established in a dense two-level medium,and an accurate and efficient fourth-order Runge-Kutta method was applied for solving the equations.After numerical simulation,the interactions between a chirped ultra-short pulse and dense resonant two-level medium were investigated,and the influences of local-field effects and chirp on Bloch vectors were gained.The numerical results show that,the evolutions of Bloch vectors and the final state of inversion are strongly modulated by the local-field effects correction coefficient and chirp parameter,which provides a method to achieve stable population inversion of control by adjusting the linear chirp parameter and local-field correction coefficient.

Reversible absorption of weak fields revealed in coherent transients

It is shown that the absorbtion of a weak field in a thick resonant absorber is a reversible process even in the case of the homogeneous broadening of the absorption line. As an example, the propagation of a long rectangular pulse with sharp edges in an optically dense resonant medium is studied theoretically in the linear response approximation. Transient nutation (TN), free induction decay (FID), and transients, induced by the phase switch of the incident pulse, are considered. It is shown that in exact resonance the amplitude of FID increases with the length of the medium. FID arises due to the scattered radiation field (dipoles ringing). In a thick medium the scattered field is almost of the same amplitude but opposite in phase with the incident radiation field. Both fields interfere destructively to produce what is seen as radiation damping at the output of the medium. The scattered field needs time to develop. Therefore, the leading edge of the pulse is not absorbed, demonstrating temporal transparency followed by TN. Phase shift (180${}^{\ensuremath{\circ}}$) of the pulse brings the incident pulse in phase with the scattered radiation. Constructive interference of the pulse with the scattered radiation field produces a short pulse with an amplitude that is two times larger than the amplitude of the incident pulse. If the input pulse is detuned from resonance, for a particular detuning and optical thickness of the medium the amplitude of the transient pulse, induced by the phase shift, is nearly three times larger than the amplitude of the incident pulse. This is explained by the interference of the scattered field, the phase-shifted input field, and the slowly propagating part of the pulse, developed before the phase shift.

Femtosecond pulses in a dense two-level medium: Spectral transformations, transient processes, and collisional dynamics

Propagation of ultrashort optical pulses in a dense resonant medium is considered in the semiclassical limit. In our analysis, we place emphasis on several main points. First, we study transformations of spectra in the process of pulse propagation and interactions with another pulse. The second point involves the transient processes (including pulse compression) connected with self-induced transparency soliton formation inside the medium. Finally, the third aspect is the study of collisions of co- and counter-propagating pulses in the medium. In the last case, the investigation of symmetric and asymmetric collisions shows the possibility of effectively controlling the parameters of transmitted radiation.

Logic gate based on a one-dimensional photonic crystal containing quantum dots

The feasibility of using quantum dots as a dense resonant medium with large transition dipole moments is analyzed. The possibility of creating one-dimensional photonic crystals containing quantum dots is examined on the basis of published experimental and theoretical data and the basic parameters of such systems are discussed. A numerical solution of the generalized Maxwell–Bloch equations is used to show that the interaction of coherent light pulses with a photonic structure containing quantum dots can be used to create optical logical operations of types that will depend on the spectral properties of the crystal.

Effect of frequency detuning on pulse propagation in one-dimensional photonic crystal with a dense resonant medium: application to optical logic

We consider propagation of light pulses detuned from the atomic resonance in a dense two-level medium and the photonic structures with it. The large density of the medium is important for decreasing the spatial scale of nonlinear effects such as pulse compression, though it does not provide any fundamentally new phenomena as compared to dilute media. Frequency detuning decreases the effectivity of nonlinear phenomena such as pulse compression and dispersion-spreading compensation as well. We propose simple logic gates based on interaction between two pulses in one-dimensional nonlinear photonic crystal. We found that frequency detuning is necessary to obtain ultrafast AND gates, while OR and NOT gates can be realized in the system without detuning.

Excitation dependence of resonance line self-broadening at different atomic densities

We study the dipole–dipole spectral broadening of a resonance line at high atomic densities when the self-broadening dominates. The selective reflection spectrum of a weak probe beam from the interface of the cell window and rubidium vapour is recorded in the presence of a far-detuned pump beam. The excitation due to the pump reduces the self-broadening. We found that the self-broadening reduction dependence on the pump power is atomic density independent. These results provide experimental evidence for the disordered exciton based theory of self-broadening, and can be useful for the description of the interaction of a strong optical field with a dense resonance medium.

Compression of an intensive light pulse in photonic-band-gap structures with a dense resonant medium

Intensive light pulse interaction with a dense resonant medium is considered. The possibilities of optical switching and pulse compression at realistic parameters of the medium are analyzed. Pulse-shape transformation in different photonic-band-gap structures containing a dense resonant medium is studied. In particular, the effect of dispersion compensation due to nonlinear interaction with a medium is reported. The possibility of pulse control with another pulse is considered in the schemes of copropagating and counterpropagating pulses. It is shown that a photonic crystal makes controlling more effective, at least in the case of copropagating pulses.

Bistable behavior of reflection and transmission of a one-dimensional photonic crystal with a dense resonant medium as a defect

We consider the optical response of a one-dimensional photonic crystal with a dense resonant medium as a defect. Using the iteration matrix approach, we calculate the intensity distribution in this structure and the reflection and transmission properties of it. We discuss the influence of photonic crystal on the bistable behavior of a dense resonant medium both within and outside the region of intrinsic optical bistability. Finally we compare our results with the case without taking into account near dipole-dipole interaction.

Bistability of an optical response of a photonic crystal with a dense resonant medium as a defect

Optical characteristics of a system consisting of a photonic crystal with a defect layer of a dense resonant medium described by the modified Bloch equation are considered. Transmission spectra are calculated and regions of existence of bistable optical response of the system are found. It is shown that the effect of internal reflection demonstrated by the dense resonant medium results in variation of reflection and transmission spectra of the photonic crystal and the loop width of the bistable response of the dense resonant medium is determined by the structure of the photonic crystal.

Effect of the local field on the soliton generation mechanism of passively mode-locked ultrashort laser pulses

The generation of solitons is considered in the model of a two-component dense resonance medium having the amplifying and absorbing components when the both components or one of them (amplifying) can exhibit near dipole—dipole interactions depending on the concentration of resonance atoms and dipole transition moments. The features of formation of phase-modulated π- and 2π-pulses are studied. The stability of the obtained solutions to small perturbations is analysed. It is shown that the 2π-pulse is stable, whereas the π-pulse is unstable.