Resonant Medium Research Articles

Compression of few-cycle optical pulses and unipolar pulse generation due to coherent interaction with nonlinear resonant medium

Compression of few-cycle optical pulses and unipolar pulse generation due to coherent interaction with nonlinear resonant medium

Imbalance of group velocities for amplitude and phase pulses propagating in a resonant atomic medium

The dynamics of light pulses with amplitude and phase modulations is investigated for a medium of resonant two-level atoms. It is shown that the pulse-like variations of the phase can be also described in terms of group velocity. It is found that in the nonlinear regime of atom-field interaction, the group velocities of amplitude and phase pulses can have a large imbalance. Namely, amplitude pulses travel at a velocity less than $c$, whereas the group velocity of phase pulses is greater than the velocity of light in free space or it is even negative. The predicted imbalance of the group velocities can be important in the case of chirped pulses propagating in a resonant medium.

Few-cycle pulse-driven excitation response of resonant medium with nonlinear field coupling

We study theoretically the optical response of the resonant medium on the few-cycle pulse-driven excitation for different types of the coupling strength to the field. It is demonstrated that the medium can exhibit a specific excitation response depending on the field coupling nonlinearity. Remarkably, the analysis of this response revealed the possibility of the controllable generation and shaping of unipolar optical pulses, which can be important in real-time observation and time-domain control of ultrafast processes in matter.

Formation and erasure of population difference gratings in the coherent interaction of a resonant medium with extremely short optical pulses

In the regime of coherent interaction of short optical pulses with a resonant medium, which is implemented with a pulse duration shorter than the relaxation times in the medium, the formation of population gratings can occur without overlapping the pulses therein. In this case, there are new possibilities for controlling optical pulses, which are especially pronounced for extremely short pulses. It is shown that, with the proper choice of the parameters of a sequence of extremely short optical pulses, not only the formation of population gratings, but also their erasure are possible. It is demonstrated that this effect can be used for the creation of an ultrahigh-speed optical deflector.

Analytic study on certain solitons in an erbium-doped optical fibre

()-dimensional non-linear optical waves through the coherently excited resonant medium doped with the erbium atoms can be described by a -dimensional non-linear Schrödinger equation coupled with the self-induced transparency equations. For such a system, via the Hirota method and symbolic computation, linear forms, one-, two- and N-soliton solutions are obtained. Asymptotic analysis is conducted and suggests that the interaction between the two solitons is elastic. Bright solitons are obtained for the fields E and P, while the dark ones for the field N, with E as the electric field, P as the polarization in the resonant medium induced by the electric field, and N as the population inversion profile of the dopant atoms. Head-on interaction between the bidirectional two solitons and overtaking interaction between the unidirectional two solitons are seen. Influence of the averaged natural frequency on the solitons are studied: (1) can affect the velocities of all the solitons; (2) Amplitudes of the solitons for the fields P and N increase with decreasing, and decrease with increasing; (3) With decreasing, for the fields P and N, one-peak one soliton turns into the two-peak one, as well as interaction type changes from the interaction between two one-peak ones to that between a one-peak one and a two-peak one; (4) For the field E, influence of on the solitons cannot be found. The results of this paper might be of potential applications in the design of optical communication systems which can produce the bright and dark solitons simultaneously.

Tunable Electromagnetically Induced Transparency-Like in Plasmonic Stub Waveguide with Cross Resonator

An analog of electromagnetically induced transparency (EIT) is investigated in a metal-insulator-metal (MIM) waveguide structure consisting of a stub waveguide and a side-coupled cross resonator. The transmission properties of this plasmonic MIM waveguide structure are numerically studied by the finite element method. The results show that there are double EIT-like phenomena as well as multiple EIT-like peaks in the transmission spectra by adding another stub. The transparency windows not only can be manipulated by changing the coupling distance between the stub and the cross resonator and the length of the horizontal and vertical cavity but also show a red shift with the increase of the refractive index n of the medium in the cross resonator. The designed plasmonic MIM waveguide structure is able to serve as a filter with a transmission rate of over 80 % and is easy to detect the refractive index of the filled media in the cross resonator, which indicates the potential applications in filtering and sensing.

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.

Electromagnetic field of a charge moving in a waveguide and intersecting a boundary between vacuum and a resonance dispersion medium

Electromagnetic field of a charge that uniformly moves in a circular waveguide from a vacuum into a dielectric possessing frequency dispersion of a resonant type is under consideration. The main attention is paid to the analytical and numerical investigation of the waveguide modes excited by the charge. It is shown that there is a region in the medium where partial compensation of Cherenkov radiation (CR) takes place similar to the case of a nondispersive dielectric. However, the electromagnetic field pattern is complex and the role of resonant dispersion is essential. In the vacuum area of the waveguide, the main part of the field is a response from the resonant medium with frequency which is close to the resonance frequency. This effect might be used for diagnostics of medium properties. The typical plots for the field demonstrate the process of forming the so-called ‘wakefield’ in the dielectric part of waveguide.

Frequency–time correlation of inhomogeneous broadening in a three-level system and the stimulated photon echo locking effect

The frequency–time correlation of inhomogeneous broadening on different transitions in a threelevel resonant medium in the presence of external spatially nonuniform electric fields is considered. It is shown that, under a certain relationship between the magnitudes of gradients of external nonuniform electric fields acting at different moments of time, it is possible to control the magnitude of the frequency–time correlation on different frequency transitions. An increase in the frequency–time correlation coefficient with certain strengths of external spatially nonuniform electric fields leads to the recovery of the phase memory of the system and an increase in the stimulated photon echo intensity.

Rogue wave triggered at a critical frequency of a nonlinear resonant medium.

We consider a two-level atomic system interacting with an electromagnetic field controlled in amplitude and frequency by a high intensity laser. We show that the amplitude of the induced electric field admits an envelope profile corresponding to a breather soliton. We demonstrate that this soliton can propagate with any frequency shift with respect to that of the control laser, except a critical frequency, at which the system undergoes a structural discontinuity that transforms the breather in a rogue wave. A mechanism of generation of rogue waves by means of an intense laser field is thus revealed.

Broadband Transmission Loss Using the Overlap of Resonances in 3D Sonic Crystals

The acoustic properties of a three-dimensional sonic crystal made of square-rod rigid scatterers incorporating a periodic arrangement of quarter wavelength resonators are theoretically and experimentally reported in this work. The periodicity of the system produces Bragg band gaps that can be tuned in frequency by modifying the orientation of the square-rod scatterers with respect to the incident wave. In addition, the quarter wavelength resonators introduce resonant band gaps that can be tuned by coupling the neighbor resonators. Bragg and resonant band gaps can overlap allowing the wave propagation control inside the periodic resonant medium. In particular, we show theoretically and experimentally that this system can produce a broad frequency band gap exceeding two and a half octaves (from 590 Hz to 3220 Hz) with transmission lower than 3%. Finite element methods were used to calculate the dispersion relation of the locally resonant system. The visco-thermal losses were accounted for in the quarter wavelength resonators to simulate the wave propagation in the semi-infinite structures and to compare the numerical results with the experiments performed in an echo-free chamber. The simulations and the experimental results are in good agreement. This work motivates interesting applications of this system as acoustic audible filters.

Generation of terahertz radiation in the interaction of coherent electromagnetic wave with a resonant medium in a constant external electric field

The paper shows that it is sufficient to place a resonance medium in an external dc electric field for the generation of low-frequency radiation at the resonant interaction of the medium and a coherent wave with carrier frequency of the optical range. Under certain conditions the carrier frequency of the generated radiation equals the Rabi frequency of the resonant interaction.

Attosecond transient absorption in dense gases: Exploring the interplay between resonant pulse propagation and laser-induced line-shape control

We investigate the evolution of extreme ultraviolet (XUV) spectral lineshapes in an optically-thick helium gas under near-infrared (IR) perturbation. In our experimental and theoretical work, we systematically vary the IR intensity, time-delay, gas density and IR polarization parameters to study lineshape modifications induced by collective interactions, in a regime beyond the single atom response of a thin, dilute gas. In both experiment and theory, we find that specific features in the frequency-domain absorption profile, and their evolution with propagation distance, can be attributed to the interplay between resonant attosecond pulse propagation and IR induced phase shifts. Our calculations show that this interplay also manifests itself in the time domain, with the IR pulse influencing the reshaping of the XUV pulse propagating in the resonant medium.

Controlling the Radiation Parameters of a Resonant Medium Excited by a Sequence of Ultrashort Superluminal Pulses

We investigate the possibility of controlling the radiation parameters of a spatially periodic one-dimensional medium consisting of classical harmonic oscillators by means of a sequence of ultrashort pulses that propagate through the medium with a superluminal velocity. We show that, in the spectrum of the transient process, in addition to the radiation at a resonant frequency of oscillators, new frequencies arise that depend on the period of the spatial distribution of the oscillator density, the excitation velocity, and the angle of observation. We have examined in detail the case of excitation of the medium by a periodic sequence of ultrashort pulses that travel with a superluminal velocity. We show that it is possible to excite oscillations of complex shapes and to control the radiation parameters of the resonant medium by changing the relationship between the pulse repetition rate, the medium resonant frequency, and the new frequency.

Controllable frequency hysteresis in semiconductor lasers

Optical feedback with orthogonal polarization enables frequency sweep of semiconductor lasers and leads to frequency bistability when a resonant medium is used to filter the reinjected radiation. Here, we explore a configuration with two lasers coupled through mutual injection. Each laser injects and receives light with a polarization orthogonal to the plane of emission. Both injections are independently filtered by a resonant atomic vapor. We show that this more versatile version also exhibits bistable states, and that it is possible to reduce the laser frequency jitter as well as to invert its frequency hysteresis cycle on demand (from counterclockwise to clockwise and vice versa). Experimental demonstration is done with diode lasers emitting around 780 nm, using Rb thermal vapors as nonlinear filters.

Soliton Solutions of a Generalised Nonlinear Schrödinger–Maxwell–Bloch System in the Erbium-Doped Optical Fibre

Abstract In this article, the generalised nonlinear Schrödinger–Maxwell–Bloch system is investigated, which describes the propagation of the optical solitons in an optical fibre doped with two-level resonant impurities like erbium with the fourth-order dispersion taken into account. Bilinear forms are derived via the Hirota method, symbolic computation, and the auxiliary function. Bright solitons can be obtained for the complex envelope of the field and the measure of the polarisation for the resonant medium, while the dark ones have been deduced for the extant population inversion. Propagation of the one and two solitons is analysed with the results that the solitons keep their shapes unchanged after the interaction, except for the phase shifts, which means that the interaction is elastic. Velocities of the solitons decrease when the effect of discreteness and higher-order dispersion increases. For the bound-state solitons, which can be formed among the solitons at the same velocity, the period decreases when the effect of discreteness and higher-order dispersion increases.

Abnormal enhancement against interference inhibition for few-cycle pulses propagating in dense media

We numerically study the reflected spectrum of a few-cycle pulse propagating through an ultrathin resonant medium. According to the classical interference theory, a destructive interference dip is expected at the carrier frequency ωp for a half-wavelength medium. In contrast, an abnormal enhanced spike appears instead. The origin of such an abnormal enhancement is attributed to the coherent transient effects. In addition, its scaling laws versus medium length, pulse area and duration are obtained, which follow simple rules.

Solitons and Rogue Waves for a Higher-Order Nonlinear Schrödinger–Maxwell–Bloch System in an Erbium-Doped Fiber

AbstractUnder investigation in this article is a higher-order nonlinear Schrödinger–Maxwell–Bloch (HNLS-MB) system for the optical pulse propagation in an erbium-doped fiber. Lax pair, Darboux transformation (DT), and generalised DT for the HNLS-MB system are constructed. Soliton solutions and rogue wave solutions are derived based on the DT and generalised DT, respectively. Properties of the solitons and rogue waves are graphically presented. The third-order dispersion parameter, fourth-order dispersion parameter, and frequency detuning all influence the characteristic lines and velocities of the solitons. The frequency detuning also affects the amplitudes of solitons. The separating function has no effect on the properties of the first-order rogue waves, except for the locations where the first-order rogue waves appear. The third-order dispersion parameter affects the propagation directions and shapes of the rogue waves. The frequency detuning influences the rogue-wave types of the module for the measure of polarization of resonant medium and the extant population inversion. The fourth-order dispersion parameter impacts the rogue-wave interaction range and also has an effect on the rogue-wave type of the extant population inversion. The value of separating function affects the spatial-temporal separation of constituting elementary rogue waves for the second-order and third-order rogue waves. The second-order and third-order rogue waves can exhibit the triangular and pentagon patterns under different choices of separating functions.

Effective Medium-Based Plasmonic Waveguides for Tailoring Dispersion

We propose a waveguide configuration with a plasmonic grating for tailoring dispersion characteristics. The unit-cell of the plasmonic grating encompasses the subwavelength distribution of metal nanowires forming a highly resonant effective medium. The configuration enables independent control of the coupling between the plasmonic and waveguide modes via the resonant strength of the effective medium. Numerical simulations show that the line shapes of the coupled modes can be varied from Fano to electromagnetically induced transparency-like. Furthermore, we use the structure to enhance the group index from 250 to 850 and to broaden the associated band from 40 to 180 meV.

Time spectrum of a coherent pulse propagating through a single resonant medium

A new formula for the delayed electromagnetic field and the time spectrum of a coherent synchrotron radiation pulse propagating through a single resonant medium is obtained. Unlike the commonly accepted one-term formula for such a time spectrum, our formula contains an additional term arising from the secondary radiation. This term helps to overcome some shortcomings of the accepted formula. Using the experimental data from the time spectrum of an enriched stainless-steel foil obtained recently at PETRA III (DESY, Hamburg) as a test case, our new formula provides a quality fit. Unlike the commonly available computer programs used by experimentalists, our fit does not require the averaging of the thickness parameter.