Search

We discuss an efficient all-optical switching scheme with ultrafast switching times and high switching contrast which satisfies fan-out [1] , one difficult challenge to be met in all optical computing. To this end, a nonlinear interaction mechanism provides a means to control light by light [2] , [3] , realizing switching between different parts of soliton-fission induced supercontinuum spectra. The experimental setup employed a NL-PM-750 photonic crystal fiber (NKT Photonics), and the complementing numerical simulations were performed using a generalized nonlinear Schrodinger equation [1] , [3] .

This work reports the observation of rogue waves in a Ti: sapphire laser containing a coherent absorber cell with Rb and Cs vapors. Extreme events were observed with an interval of one to ten seconds when several dissipative self-induced transparency solitons could be simultaneously present in the cavity. An extremely rare event was the fusion of solitons into one.

In this talk, existence of unipolar pulses, methods of their generation and interaction with quantum objects are revised. The effective influence of unipolar pulses in comparison with bipolar pulses on quantum systems is shown. The question of mutual attraction and repulsion of unipolar impulses is also considered.

Passive mode-locking is one of the main methods for generation of ultra-short pulses in lasers [1]. The critical part of a passively mode-locked lasers is a nonlinear absorber placed in a cavity. It was shown to be possible [2, 3], in the coherent regime of light-matter interaction (in particular using self-induced-transparency (SIT) effects), to achieve a mode-locking (so called coherent or SIT mode-locking) with a pulse duration smaller than the polarization relaxation time T2 of the medium - the limit which can be not be conquered by other mode-locking approaches.

In this talk, the rule of conservation of the electric field area of the pulse is tested for the absorption and amplification of light in a resonance medium. The results of numerical simulations show that, contrary to the intuitive representation, this rule is satisfied. The conservation of the electric area of the pulse makes it possible to solve qualitatively the problems of changing the parameters of the pulses in propagation problems.

The possibility of passive mode locking in a laser containing an amplifier and an absorber is theoretically analyzed in the case when the length of the laser cavity is extremely small and the duration of one light pass between the mirrors of the cavity is less than the relaxation times of the polarization of the amplifier and absorber.

Quantum cascade lasers (QCLs) are unipolar semiconductor devices emitting in the mid-and far-infrared spectral ranges. Due to their relatively narrow linewidths and short gain recovery times, these lasers have been deemed difficult, if not impossible, to passively mode lock (PML) [1, 2]. However, the successful mode locking of QCLs is of utmost importance as it could allow generation of ultrashort pulses and also formation of broadband frequency combs. As a consequence, the research community invested substantial effort and funds in devising methods for active mode locking of QCLs with some limited success achieved [1, 2]. In this submission, we revise the prospect of passively mode locking a THz QCL via a fast saturable absorber (FSA). Our results, based on the numerical solution of the Maxwell-Bloch equations, show that it could be possible to implement a “text-book” FSA-PML mechanism, robust over large variations of the experimental parameters.

Generation of ultrashort pulses of few-cycle or even subcycle duration made it possible to observe previously inaccessible ultrafast processes in matter [1]. On the other hand, ultrashort pulses can coherently interact with a resonant medium since their duration can be much smaller than the medium relaxation times T 1 and T 2 .

Coherent mode-locking (CML) is based on intracavity self-induced transparency phenomena and allows generating single-cycle laser pulses. We propose a new technique based on McCall and Hahn Area theorem, allowing to predict the main features of CML regimes, study theoretically the possibility of single-cycle optical pulse generation and provide experimental study of mode-locked regimes in laser with a coherent absorber.

We consider theoretically a possibility of creating and control of population inversion gratings in two-level resonant medium coherently interacting with few-cycle light pulses. It is shown that it is possible to create, erase, and modify the spatial period of such gratings.

we consider an optical response of one-dimensional string made of dipoles with a periodically varying density excited by a laser pulse moving along the string at the superl uminal velocity. We demonstrate that the Cherenkov radiation arising in such system is rather unusual, possessing both transient and reson ant character. Our analysis indicates that in addition to the resonanc e frequency of the medium another Doppler-like frequency appears in the radiation spectrum.

In the present work we perform numerical analysis of coherent mode-locking in lasers containing either coherent gain and absorbing medium or only one gain medium. Our numerical simulations indicate the possibility of mode-locked pulse formation when coherence time of the medium is larger than the pulse duration Keywords— coherent effects, passive mode-locking, selfinduced transperency Passive mode-locking is a technique for generation of short optical pulses with high repetition rates [1]. Commonly in passive mode-locked lasers coherence time of the medium T2 is much smaller than the pulse duration, so medium polarization is adiabatically eliminated [1]. Another situation arises when the interaction between light and matter is coherent, i.e. pulse duration is smaller than the medium coherence time T2. In this case coherent effects of pulse propagation in a resonant absorbing and amplifying medium can take place [2]. A well-known coherent phenomenon which was discovered by Mcall and Hahn is the self-induced transparency (SIT) [3]. This phenomenon arises when pulse duration is smaller than polarization relaxation time T2 and leads to a soliton-like pulse propagation in a resonant medium. In the Ref. [4-5] theory of coherent mode-locking based on SIT in a 2 section laser was developed. It has been demonstrated that when the interaction between light and matter in the cavity is coherent mode-locked pulse in the absorbing medium is 2π pulse of SIT and in the gain medium it propagates as a π pulse. In [5] the authors proposed a quantum cascade lasers (QCLs) structure for experimental observation of the coherent mode-locking in QCL. In the [4,5] it was assumed that the electric field interacts with absorber and amplifier simultaneously, i.e. both absorber and amplifying “mixed” medium are homogeneously distributed in the laser cavity. This situation is however not entirely realistic but it can be applied to the designed structure of QCL proposed in [5]. In the real laser systems gain and absorber medium are separated in space. In the present work we perform a more detailed numerical analysis of passive mode-locking in a 2 and 1 section laser including coherent effects when absorber and gain medium are placed separately in the cavity. We demonstrate numerically the possibility of mode-locked pulse formation in a two section and in a single section laser (selfsynchronization). We perform numerical simulations for the ring and linear cavities and compare the results. Our numerical analysis is based on the system of MaxwellBloch equations for slow envelopes of the polarization of 2level gain and absorbing medium, population difference of the medium and slow envelope of the electric field. This model allows to perform sufficiently complete modeling of evolution of an extended two-level medium in a cavity, taking into account multi-mode character of radiation and the nonlinear coherent effects accompanying light interaction with two-level medium [2]. Our numerical simulations indicate that when medium coherence time is too large, coherent mode-locked pulse arises. But the area of this pulse in absorbing medium is smaller than 2π, so the medium does not become completely inverted and then returns to the ground state during the pulse propagation as in the case of classical SIT. Moreover we have found that the pulse area in the gain medium is differs from π but is quite close to it. Finally our numerical simulations demonstrated that presence of the absorbing medium is unnecessary – stable coherent self mode-locking regime is preserved when absorbing medium is absent in the cavity. R.M. Arkhipov would like to acknowledge the support of EU FP7 ITN PROPHET, Grant No. 264687. R.M. Arkhipov would like to acknowledge Dr. I.A. Chekhonin and Dr. A.G. Vladimirov for helpful discussions.