Self-induced Transparency Regime Research Articles

Experimental study of self-induced transparency mode-locking in Ti:sapphire laser

In this paper, passive mode-locking in Ti:sapphire laser with a coherent absorber cells with rubidium vapor placed in the cavity is demonstrated experimentally. For the best of our knowledge these experiments are the first time experimental demonstration of passive mode-locking based on self-induced transparency regime in the coherent absorber. Up to now, such a regime has not been observed experimentally and was predicted only theoretically.

Generation of terahertz radiation by optical rectification in presence of resonance impurities

We demonstrate the possibility of an efficient generation of terahertz radiation under optical rectification in a uniaxial crystal containing impurities with resonance two-level quantum transitions. The group velocity of an optical pulse entering the regime of self-induced transparency decreases to the value of phase velocity of the terahertz radiation, which results in phase matching of long- and short-wavelength waves. The terahertz generation is accompanied by strong self-modulation of the optical pulse. Two-component soliton-like structures can be formed at long distances accompanied by spectral red shift of the optical component.

The generation of terahertz radiation via optical rectification in the self-induced transparency regime

The possibility of efficient terahertz generation via optical rectification in electro-optic crystal doped with the two-level resonant impurities is demonstrated. Under conditions of the self-induced transparency regime the laser pulses slows down to achieve the phase matching condition. The terahertz generation is accompanied by periodic modulation and spectral deformation of the laser pulse. The most efficient generation occurs under condition of small negative detuning from the resonant frequency of the two-level system.

Soliton self-frequency shift, non-solitonic radiation and self-induced transparency in air-core fibers

We report numerical investigation of several effects accompanying propagation of femtosecond pulses in air-core photonic crystal fibers.We have found that the strong Raman response of air does not always result in the large soliton self-frequency shift, because it can simultaneously stimulate energy losses into non-solitonic radiation. We demonstrate that the pronounced spectral tails seen in many recent experiments on the short wavelength side of the soliton spectra can be associated with emission of Airy waves by the decelerating solitons. For pulse durations close to 10fs all radiation effects due to Raman response of air become negligible for a special choice of the peak power leading to propagation in the self-induced transparency regime.

Optical nonlinear waves in semiconductor quantum dots: Solitons and breathers

A general theory of optical resonance solitons and breathers in the presence of single-excitonic and biexcitonic transitions in an ensemble of inhomogeneously broadened semiconductor quantum dots is constructed. Optical plane wave solitons ($2\ensuremath{\pi}$ pulses) are formed in stacked layer structures (many-layered systems) of semiconductor quantum dots. Optical small-amplitude bright breathers ($0\ensuremath{\pi}$ pulses) in semiconductor quantum dot waveguides are considered. Explicit analytical expressions for the shape and parameters of the solitons and breathers in the regime of self-induced transparency are obtained as well as simulations of the space-time dynamics of two-dimensional breathers presented with realistic parameters which can be reached in current experiments. It is shown that, unlike for plane wave breathers, the parameters additionally depend on the waveguide mode. In the special case of plane wave breathers in semiconductor quantum dots, known analytical results are recovered.

Surface optical solitons in semiconductor quantum dot layers

A theory of optical solitons under the condition of nonlinear coherent interaction of surface TM-modes with a layer of inhomogeneously broadened semiconductor quantum dots is developed. Explicit analytical expressions for a surface soliton (2π-pulse) in the presence of single and biexciton transitions are obtained in the regime of self-induced transparency with realistic parameters which can be reached in current experiments.

Nonlinear regimes of propagation of resonant pulses in multilevel quantum media

An approximate operator approach that is equivalent to the mathematical Wentzel-Kramers-Brillouin method and allows one to solve the set of constitutive equations for an N-level quantum medium resonantly interacting with multifrequency optical pulses is proposed. The transitions occurring via a common level with the ordinal number j are considered in detail. It is shown that, for j=1, the self-induced transparency regime is realized, whereas, at j=N, the regime of electromagnetically induced transparency is realized. Within the framework of the WKB approximation, an expression that represents the area theorem for multifrequency resonant pulses is derived.

Self-induced transparency of hydrogen-containing ferroelectrics for extremely short pulses in the vicinity of the curie temperature

Nonlinear propagation of extremely short (carrierless) electromagnetic pulses in a KDP-type ferroelectric is investigated at temperatures close to the phase transition point. It is demonstrated that, although weak monochromatic signals undegro a sharp attenuation at these temperatures, an extremely short high-power pulse can propagate in the self-induced transparency regime and the associated soliton is stable to transverse perturbations.

Strain wave evolution equation for nonlinear propagation in materials with mesoscopic mechanical elements.

Nonlinear wave propagation in materials, where distribution function of mesoscopic mechanical elements has very different scales of variation along and normally to diagonal of Preisach-Mayergoyz space, is analyzed. An evolution equation for strain wave, which takes into account localization of element distribution near the diagonal and its slow variation along the diagonal, is proposed. The evolution equation provides opportunity to model propagation of elastic waves with strain amplitudes comparable to and even higher than characteristic scale of element localization near Preisach-Mayergoyz space diagonal. Analytical solutions of evolution equation predict nonmonotonous dependence of wave absorption on its amplitude in a particular regime. The regime of self-induced absorption for small-amplitude nonlinear waves is followed by the regime of self-induced transparency for high-amplitude waves. The developed theory might be useful in seismology, in high-pressure nonlinear acoustics, and in nonlinear acoustic diagnostics of damaged and fatigued materials.

Electromagnetic energy penetration in the self-induced transparency regime of relativistic laser-plasma interactions.

Two qualitatively different scenarios for the penetration of relativistically intense laser radiation into an overdense plasma, accessible by self-induced transparency, are presented. In the first one, penetration of laser energy occurs by solitonlike structures moving into the plasma. This scenario occurs at plasma densities less than approximately 1.5 times the critical one (depending on ion mass). At higher background densities, laser light penetrates only over a finite length which increases with incident intensity. In this regime the plasma-field structures represent alternating electron (and, on longer time scales, ion) layers separated by about half a wavelength of cavitation with concomitant strong charge separation.

Self-induced transparency in plasmas with sharp boundary

We study fully relativistic nonlinear 1D fluid equations describing steady-state solutions for an electromagnetic wave interacting with plasma in the self-induced transparency regime. In addition to the well-known solution that corresponds to the transmission of the electromagnetic wave into plasma, another steady-state solution is shown to exist in a certain range of the amplitude of the wave. The latter one satisfies the same boundary conditions but corresponds to the full reflection of the incident wave. The co-existence of the two solutions indicates a rich structure of the interface between the opaque and transparent phases in ultraintense laser interactions with near-critical and overdense plasmas—in particular, one may expect hysteresis-like behavior when a current state of the system depends on its history.

Self-induced transparency and self-induced opacity in laser-plasma interactions

The interaction of a strong electromagnetic wave with a layer of overdense plasma is considered under conditions that allow for self-induced transparency (SIT). In a certain range of the amplitude of the incoming wave, the corresponding nonlinear one-dimensional (1D) set of equations is shown to admit two competing steady-state solutions that satisfy the same boundary conditions. One of those solutions describes just the well-known SIT regime of propagation, the other one corresponds to the full reflection of the incident wave. Their coexistence indicates the possibility of hysteresis-like effects in ultraintense laser interactions with overdense plasmas. 1D Particle-In-Cell simulations confirm analytical results and suggest the dominance of the opaque solution over the entire parameter window where it is possible. Fast longitudinal heating of plasma electrons occurs then in a natural way as a result of the breakup of the opaque solution above some threshold in laser intensity.

On self-induced transparency in laser-plasma interactions

We study fully relativistic nonlinear one-dimensional equations describing steady-state solutions for an electromagnetic wave interacting with a plasma in the self-induced transparency regime. In addition to the well-known solution that corresponds to the transmission of the electromagnetic wave into plasma, another steady-state solution is shown to exist in a certain range of amplitudes of the wave. The latter solution corresponds to total reflection of the incident wave. The coexistence of the two solutions indicates the possibility of hysteretic behavior in the self-induced transparency.

Breakdown of the Area Theorem: Carrier-Wave Rabi Flopping of Femtosecond Optical Pulses

By solving Maxwell's curl equations coupled to a two-level atom, a theoretical study of carrier-wave Rabi flopping of femtosecond optical pulses of only several carrier-cycles time duration is reported. For pulse areas of $2\ensuremath{\pi}$, the usual self-induced transparency regime is essentially recovered. However, for larger pulse areas, carrier-wave Rabi flopping occurs that manifests in local carrier reshaping and subsequently to the production of significantly higher spectral components on the propagating pulse. These new features are not predicted by employing the area theorem or a slowly-varying-envelope approximation for the amplitude and phase terms---which is the usual approach.

Intracavity self-induced transparency of a multilevel absorber

Intracavity self-induced transparency of a three-level absorber is studied in the scope of solid-state laser generation of an ultrabroadband electromagnetic pulse that drives the population of all absorber levels through complete Rabi flopping. We show that at sufficient pump rates a Ti:sapphire laser forces an intracavity GaAs single quantum-well absorber, which provides an inter-valence-band transition in the THz domain in addition to two direct optical interband transitions, into the self-induced transparency regime and acts as an all-solid-state ultrabroadband pulse emitter. In dependence on the resonator bandwidth, the intracavity pulse energy and the absorber dipole moments we obtain a multilevel self-induced transparency pulse spectrum which extends from the THz domain up to the ultraviolet. The steady-state sub-10-fs pulse consists of only a few optical cycles with the high-frequency components at its leading edge and a single to subcyclic THz component at its trailing edge.

Coherent-absorber mode locking of solid-state lasers

We study solid-state laser mode locking in the self-induced transparency regime of an intracavity absorber. Depending on the absorber dephasing, pulse energy, and resonator dispersion, we find stable coherent 2pi -pulse operation, pulse splitting, oscillatory pulse shapes, and smooth transition to incoherent saturable-absorber mode locking.

Soliton formation processes in optically dense media

Numerical methods are used to investigate the characteristics of soliton formation when optical pulses of arbitrary shape and duration propagate in resonantly absorbing media of large optical thickness. It is shown that a regime of soliton propagation in a resonant medium, characterized by a nonlinear Schrodinger equation model, changes to a self-induced transparency regime. Incoherent steady-state interaction conditions are then replaced by coherent interaction. This effect can be utilized to compress laser pulses.

Steady-state 2π pulses under conditions of passive locking of laser modes

A theoretical study is made of laser mode locking in the regime of self-induced transparency of a passive filter. It is shown that there is a solution in the form of ultrashort steady-state 2π pulses. The range of stability of this regime and its characteristics are determined. By way of example, estimates are obtained of parameters of a steady-state pulse emitted by an alexandrite laser with a potassium absorption cell.