Interaction Of Optical Pulses Research Articles

Microfiber-Knot-Resonator-Induced Energy Transferring From Vector Noise-Like Pulse to Scalar Soliton Rains in an Erbium-Doped Fiber Laser

We report on scalar soliton rains (SRs) shedding from vector square-wave noise-like pulse (NLP) by introducing a microfiber-knot-resonator (MKR) into an erbium-doped fiber (EDF) laser. The EDF laser has an ultralong cavity of ∼3.07 km and a large anomalous cavity-dispersion, facilitating the formation of NLP. Once an MKR was further incorporated, comb-like filtering effect could be clearly observed on the emission spectrum. Apart from that, SRs shedding from the NLP were observed, which resulted from the MKR-induced energy transferring effect from the NLP to SRs. It was further found that the SRs existed only along a particular polarization direction, whereas the NLPs could be found in any pair of orthogonal polarization directions, despite some differences in pulse peak power. These suggest that the SRs possess scalar feature, whereas the co-circulating NLP is a package of vector pulses. Our results represent the first observation of MKR-induced pulse energy transferring effect and also the first observation of the co-existence of scalar and vector pulses in a single fiber system. Besides enriching the dynamics and interactions of optical pulses in fiber lasers, our results extend the applications of MKR to the area of pulse manipulations through spectral tailoring and local nonlinearity engineering.

X-ray and optical pulse interactions in GaAs.

Absorption of hard x-rays in GaAs creates excitations that can dramatically alter the propagation of optical laser pulses with photon energies near the bandgap. Measurements of optical transmission through a thin crystalline wafer of GaAs after absorption of an intense x-ray synchrotron pulse demonstrate how x-ray induced optical transparency depends on the recombination of excited conduction band electrons and valence band holes via Auger, spontaneous emission, and especially stimulated emission processes. The x-ray induced band fluorescence spectrum also reveals amplified spontaneous emission at the high x-ray fluences used, confirming the importance of stimulated emission. For laser pulses with sufficiently high fluence, the interaction of optically excited electrons with x-ray excited electrons can quench the enhanced laser transmission.

Modeling of ultrabroadband and single-cycle phenomena in anisotropic quadratic crystals

We present a comprehensive model to describe the propagation of single-cycle and broadband optical pulses in anisotropic, dispersive, and nonlinear materials. Two nonlinear coupled wave equations describe the dynamics and interactions of optical pulses in uniaxial second-order nonlinear materials. The equations are first order in the propagation coordinate and are valid for arbitrarily wide pulse bandwidth, providing an accurate modeling of the evolution of ultrabroadband pulses also when the separation into different coupled frequency components is not possible or not profitable. We exploit this model to simulate recently observed femtosecond single-cycle multiterahertz transients in gallium selenide and to predict harmonic generation and spectral broadening in the visible and mid-infrared in lithium niobate.

The Suppression of Four-Wave Mixing by Random Dispersion

Pairwise interactions of optical pulses lead to the creation of four-wave mixing (FWM) products in the presence of periodic damping and amplification. In this manuscript, we examine how these FWM products grow in the presence of small to moderate random dispersion. Namely, we show that (i) the growth of the FWM products in the presence of white noise is inversely proportional to the noise strength $\bar{D}$, confirmed by both analytical and numerical results; (ii) the FWM products as a function of $\bar{D}$ obey a gamma-type probability distribution function; and (iii) the presence of either white or Ornstein–Uhlenbeck (OU) noise has a similar influence on the growth of these FWM products. This work shows that small random dispersion can effectively mitigate the deleterious effects of FWM in wavelength-division–multiplexed optical communications systems for either sech-type or Gaussian-type input pulses.

Advanced soliton-train generation through drive field enhancement and multiple light storage effect in cold rubidium atoms

We report triple-colour time dependent excitation technique to generate atomic soliton-train via simultaneous light storing and enhancement of the retrieved consumed triple interaction of optical pulses. The constituents of the soliton train are shown to be Gaussian in shape and advancing in time. These solitons are the one dimensional solution of the coupled Liouville-von Neumann equation for the density matrix of the dressed atom and the reduced Maxwell's field equations.

All-optical coherent control of spin dynamics in semiconductor quantum dots

A new model for rigorous theoretical description of circularly (elliptically) polarized ultrashort optical pulse interactions with singly charged quantum dots embedded in semiconductor optical waveguides and microcavities is proposed. The method is based on self-consistent solution in the time domain of the vector Maxwell equations coupled via microscopic polarization to the coherent time-evolution equations of a discrete N-level quantum system in terms of the real pseudospin (coherence) vector. The model is applied to a 4-level system describing the optical dipole transitions of the trion state in a singly charged quantum dot. Selective optical excitation of specific spin states by predefined helicity of the optical field and an onset of self-induced transparency and polarized soliton formation in the nonlinear regime are numerically demonstrated

Spin‐dependent dynamics of ultrafast polarised optical pulse propagation in coherent semiconductor quantum systems

AbstractA new model for rigorous theoretical description of circularly (elliptically) polarised ultrashort optical pulse interactions with the resonant nonlinearities in semiconductor optical waveguides is proposed. The method is based on self‐consistent solution in the time domain of the vector Maxwell equations coupled via microscopic polarisation to the coherent time‐evolution equations of a discrete N‐level quantum system in terms of the real pseudospin (coherence) vector. The model is initially applied to a generic two‐level quantum system and subsequently to a 4‐level system describing the heavy‐hole excitonic transitions in low‐dimensional semiconductor systems, such as quantum wells and quantum dots. Selective optical excitation of specific spin states by predefined helicity of the optical field in the linear regime and an onset of self‐induced transparency and polarised soliton formation in the nonlinear regime are numerically demonstrated in both discrete‐level systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamical model of coherent circularly polarized optical pulse interactions with two-level quantum systems

We propose and develop a method for theoretical description of circularly (elliptically) polarized optical pulse resonant coherent interactions with two-level atoms. The method is based on the time-evolution equations of a two-level quantum system in the presence of a time-dependent dipole perturbation for electric dipole transitions between states with total angular-momentum projection difference $(\ensuremath{\Delta}{J}_{z}=\ifmmode\pm\else\textpm\fi{}1)$ excited by a circularly polarized electromagnetic field [Feynman et al., J. Appl. Phys. 28, 49 (1957)]. The adopted real-vector representation approach allows for coupling with the vectorial Maxwell's equations for the optical wave propagation and thus the resulting Maxwell pseudospin equations can be numerically solved in the time domain without any approximations. The model permits a more exact study of the ultrafast coherent pulse propagation effects taking into account the vector nature of the electromagnetic field and hence the polarization state of the optical excitation. We demonstrate self-induced transparency effects and formation of polarized solitons. The model represents a qualitative extension of the well-known optical Maxwell-Bloch equations valid for linearly polarized light and a tool for studying coherent quantum control mechanisms.

Mitigation of thermal blooming and diffraction effects with high-power laser beams

The three-dimensional (3-D) pulse propagation code, pulsed ultrashort laser simulation emulator (PULSE), has been used to model the interaction of thermal blooming, diffraction, and nonlinear self-focusing in the atmosphere. PULSE is a derivative of the free-electron laser (FEL) simulation code, free-electron laser experiment (FELEX) [Nucl. Instrum. Methods Phys. Res. A250, 449 (1986)] that was used for many years to model the 3-D interaction of optical pulses with electron beams. This code has now been modified to model nonlinear material interactions. In its current configuration, an electromagnetic pulse is modeled on a Cartesian grid, thereby allowing for arbitrary amplitude and phase modulations in the transverse (x, y) and longitudinal (z) directions. The code includes models for thermal blooming (in a laminar transverse wind field), diffraction, Kerr self-focusing and self-phase modulation, plasma defocusing and absorption, and multiphoton and avalanche ionization. Simulation of picosecond length pulses indicate that the defocusing effects of thermal blooming and diffraction can be effectively eliminated by Kerr self-focusing. Simulation results show that the beam arrives at the target with a spot size comparable to (or less than) its initial spot size. For propagation distances of many kilometers, this can result in order-of-magnitude increases of the on-target intensity at range, which can significantly reduce the average power requirement of the laser required to provide a given irradiance level.

Experimental investigation of resonant enhancement of the acoustic interaction of optical pulses in an optical fiber

The acoustic interaction of optical pulses in optical fibers is investigated directly by time-resolved pump-probe measurements of the transmission of a fiber Sagnac-loop interferometer. Resonant enhancement of the refractive-index change deltan(ac) induced by the acoustic waves is observed when the repetition frequency of the pulse train is close to a vibrational eigenfrequency of the fiber. For standard fiber deltan(ac) is enhanced by a factor of ~3 at the 465-MHz eigenmode frequency, and this factor increases to ~10 when the polymer jacket is removed from the fiber. The guided acoustic wave Brillouin scattering spectrum that arises from spontaneous thermal excitation of the acoustic eigenmodes of the fibers is also measured. The results suggest that the resonant enhancement of deltan(ac) is limited by dampling that is due to the polymer jacket and by inhomogeneous broadening that is due to fiber diameter variations.

Generation of up-converted or down-converted photon echoes in three-level resonant medium

Abstract The equations describing the interaction of optical pulses with three-level resonant media are considered. It is shown that the resonant medium, if excited by suitable sequences of ultrashort optical pulses, can generate up-converted or down-converted photon echoes.