An optical kink is a shock-wave-like field structure which can appear in a resonant two-level medium as a result of the nonlinear process of self-steepening. We numerically simulate this process using an adiabatically switching wave form as an input and confirm the self-similarity of resulting kinks. The analysis is also applicable to a more general wave form with a decaying trailing edge which we call a kinklike pulse. We study in detail collisions of kinks with other kinks and ultrashort pulses and demonstrate the possibility to control kink speed by changing the parameters of counterpropagating fields. The effects considered can be treated as belonging to a wide class of unexplored phenomena in the regime of incoherent light-matter interaction.
An optical kink is a shock-wave-like field structure which can appear in a resonant two-level medium as a result of the nonlinear process of self-steepening. We numerically simulate this process using an adiabatically switching wave form as an input and confirm the self-similarity of resulting kinks. The analysis is also applicable to a more general wave form with a decaying trailing edge which we call a kinklike pulse. We study in detail collisions of kinks with other kinks and ultrashort pulses and demonstrate the possibility to control kink speed by changing the parameters of counterpropagating fields. The effects considered can be treated as belonging to a wide class of unexplored phenomena in the regime of incoherent light-matter interaction.
We show that self-similar optical waves with a kink structure exist in a wide class of resonant nonlinear media, adequately treated in the two-level approximation. The self-similar structure of the present kinks is reflected in the time evolution of the field profile, atomic dipole moment, and one-atom inversion. We develop an analytical theory of such kinks. We show that the discovered kinks are accelerating nonlinear waves, asymptotically attaining their shape and the speed of light. We also numerically explore the formation and eventual disintegration of our kinks due to energy relaxation processes. Thus, the present kinks can be viewed as intermediate asymptotics of the system.
Investigating the behavior of an atom in response to the applied electric field when the latter frequency is in resonance with the natural frequency of the atom is an interesting subject. Near resonance, some of the most interesting optical phenomena such as dispersion, and absorption are more pronounced. Moreover, considering resonant and near resonant interaction of light with two-level atoms, uncovers fascinating physical phenomena such as area theorem and self-induced transparency describing stable pulse propagation regimes in which the pulses maintain their identity. Existence of these optical structures in on-resonance optical media has not been investigated in detail. In this thesis, the on-resonance interaction of optical field with atoms is considered and the formation of several novel self-similar and kink waves in linear and nonlinear resonant media is discovered and theoretically explored. First, self-similar pulse formation in homogeneous broadened linear amplifiers in a vicinity of an optical resonance is analyzed. It is demonstrated that the self-similar pulses serve as universal asymptotics of any near resonance short pulses propagating in coherent linear amplifiers. Second, ultrashort self-similar pulse propagation in coherent linear absorbers near optical resonance is investigated. Third, existence of self-similar optical waves with kink structure in resonant optical systems is discovered. Fourth, it is found that self-induced transparency quadratic solitons are realizable in the media with quadratic optical nonlinearities, doped with resonant impurities. Finally, stable spatial similaritons supported by homogeneous conservative optical media with quintic nonlinearities are explored. To experimentally realize the presented results, physical models are presented for all systems under consideration. The stability of the proposed near resonance optical systems is demonstrated through a series of numerical case studies.
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 counterpropagating 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.
We investigate a light-pulse propagation with negative group velocity in a nonlinear coherent medium. We show that the necessary conditions for nonlinear superluminal effects to be observable are realized in a three-level $\ensuremath{\Lambda}$ system interacting with a linearly polarized laser field in the presence of a static magnetic field. The initially prepared Zeeman coherence cancels the resonant absorption of the medium almost completely, but preserves its dispersion anomalous and very high. In this medium the light pulse propagates superluminally in the sense that the peak of the transmitted pulse exits the medium before the peak of the incident pulse enters. At the same time the pulse group velocity is intensity dependent, which leads to the self-steepening of the pulse trailing edge due to the fact that the more intense parts of the pulse travel slower. This is in contrast with the shock wave generation in a nonlinear medium with normal dispersion. The predicted effect can be easily observed in the well-known schemes employed in the studies of nonlinear magneto-optical rotation. The upper bound of sample length is found from the criterion that the pulse self-steepening and group-advance time are observable without pulse distortion caused by the group-velocity dispersion.
We examine the dynamics of counterpropagating self-induced transparency solitons in three-level media. In a multilevel system, self-induced transparency gives rise to soliton solutions if the propagation is unidirectional, but the collision of counterpropagating pulses destroys the integrability of the underlying equations. We consider the collision of a rightward and a leftward moving self-induced transparency solitary wave by solving the full Maxwell-Bloch equations numerically using a finite-difference time-domain approach. Depending on pulse duration, amplitude and relative polarizations of the initial solitary waves we observe different regimes of interaction. For high group velocities and orthogonal polarizations, secondary solitary waves are born during the interaction, whereas the collision of solitary waves with the same polarization never produces secondary solitary waves but leaves behind a population grating in the interaction region. Because the crucial parameters can be controlled, an experimental confirmation of the predicted interaction regimes should be feasible.
Optical bistability is the basic nonlinear phenomenon mediating the control of light by light, being of ultimate demand for a plethora of applications in laser information technologies. The two most general designs are driven by the presence or absence of an external feedback, among which the mirrorless architecture seems promising, being free of bulky mirrors, resonant cavities, photonic crystals, etc. In this Letter, we propose a method to achieve optical quasi-bistability governed by the formation of specific nonlinear waveforms called “kinks.” We show that a thin layer of the relatively dilute resonant medium specially designed to support kinks could serve as a platform for compact, ultrafast, low-power optical switching. This mechanism does not require high densities of resonant particles specific for the feedback-free devices driven by dipole–dipole interactions, and enhances the overall practical relevance of such devices for optical computing.