Ultrafast intrinsic optical switching in a dense medium of two-level atoms

Abstract

We performed a numerical investigation of the dynamics of the Bloch equations, extended for dense media (media having many atoms within a cubic resonance wavelength), for optical pulses whose duration is much less than an induced-dipole dephasing time. We find a signature of near dipole-dipole interaction which may provide a useful method for validating the first-principles model, for measuring the strength of the interaction, and for coherent pumping. Further, we demonstrate a new and unique optical switching mechanism which may lead to the development of important devices.PACS numbers: 42.65.Pc, 42.50.Hz, 42.79.Ta In dense media, of densities such that there are many atoms within a cubic atomic resonance wavelength, induced near dipole-dipole (NDD) interactions can cause a dynamic frequency chirp in the system [l-4]. In the steady-state limit, NDD interactions may cause bistability that is intrinsic to the material and does not require an external feedback mechanism [I]. Intrinsic optical bistability (IOB) can have important device applications in optical computing and optical data processing [5]. Other effects of NDD interactions which have been analyzed include conditions for self-induced transparency (SIT) in isotropic, homogeneously broadened media [2], and selfphase modulation in SIT [3], as well as linear and nonlinear shifts in the absorption spectrum [4]. Both linear and nonlinear spectral effects due to NDD interactions have recently been observed in reAectivity spectrum measurements using a sapphire window to form an interface with a dense potassium vapor [6].In this Letter, we consider optical pulses, whose temporal duration is assumed to be much less than an induced-dipole dephasing time, incident upon a thin film of homogeneously broadened material composed of twolevel atoms with NDD interactions.In this limit, the induced-dipole dephasing time and the population-decay time can be neglected. We consider the film thickness in the propagation direction to be much smaller than the atomic resonance wavelength so that propagation effects may be neglected.Under these conditions, we find that the inversion w that remains after a pulse has passed has a nearly stepfunction response to the peak value of the time-varying field, largely independent of the pulse shape and pulse area. A peak Rabi frequency, Ao=pEo/h, is associated with the peak amplitude Fo of the field envelope, where p is the matrix element of the transition dipole moment.The system, initially in the ground state, w = -I, is always returned to the ground state when the peak Rabi frequency is less than the strength of the NDD interaction~. However, the final state of the inversion is the fully excited state, w =1, when Qo is nearly equal to e. This suggests that the strength of the NDD interaction can be measured by increasing the field amplitude and interrogating the system after the pulse has passed, in a pulseprobe scenario, to determine whether the system is in the ground or excited state. Furthermore, the nearly stepfunction response of...

Condition for resonant optical bistability

“…Later it was conjectured that local-field corrections alone could give rise to mirrorless OB [9]. This type of bistability was extensively studied [10][11][12][13][14] and observed experimentally [15].The practical interest in all-optical devices faded to some extent as their solid-state counterparts proved to perform better in terms of switching speed and device density. However, OB and optical hysteresis remain of considerable interest from the fundamental standpoint as a clear manifestation of a nonlinear light-matter interaction.…”

Optical solitons in periodic media with resonant and off-resonant nonlinearities

“…Although this approach is not rigorous, it clearly demonstrates that, sufficiently far from the above-mentioned NLS (small-frequency small-amplitude) limit, Bragg-grating solitons can be unstable. Later, a rigorous analysis of the same stability problem was developed by Barashenkov, Pelinovsky and Zemlyanaya [1998] and by de Rossi, Conti and Trillo [1998]. It has been demonstrated that the Bragggrating solitons indeed have instability regions in their parametric (ω, v) plane, which are close to those originally predicted by means of the variational approximation.…”

“…This behavior is more remarkable than the response of conventional two-level systems, because the medium can only be found in one of two states: either fully inverted, or in the ground state, depending (quasi-periodically) on the ratio between the peak fieldstrength and the NDD coupling strength. This feature was found to be impervious to changes in pulse shape, and independent of the pulse area (Crenshaw, Scalora and Bowden [1992]). …”

“…When the excitation frequency is somewhat larger than the original resonant frequency, the transmission of the layer exhibits a transient bistable behavior on the time scale of superradiance (Basharov [1988], Benedict, Malyshev, Trifonov and Zaitsev [1991]). It was shown that if an ultrashort pulse is allowed to interact with a thin film of optically dense two-level systems, the medium response is characterized by a rapid switching effect (Crenshaw, Scalora and Bowden [1992], ). This behavior is more remarkable than the response of conventional two-level systems, because the medium can only be found in one of two states: either fully inverted, or in the ground state, depending (quasi-periodically) on the ratio between the peak fieldstrength and the NDD coupling strength.…”

“…Current experiments are conducted in short fiber pieces, which do not allow us to test the solitons' stability. Approximate and rigorous treatments of the stability problem (Malomed and Tasgal [1994], Barashenkov, Pelinovsky and Zemlyanaya [1998], de Rossi, Conti and Trillo [1998]) have demonstrated that the Kerr-nonlinear Bragg-grating solitons have instability regions in their frequency-amplitude parametric plane, far from the PBG-center, small-amplitude limit. The generation of a slow gap soliton in a Kerr -nonlinear periodic grating via Raman transfer of en-1.…”