Propagation Of Short Laser Pulses Research Articles

Photon acceleration and polariton wakefields in dielectric crystals

Nonlinear processes associated with short laser pulse propagation in dielectric crystals are considered. They include photon acceleration of probe high frequency photons interacting with long wavelength polariton fields, and polariton wakefield excitation by short laser pulses. This could be useful to the understanding of tera-Hertz radiation sources.

High energy electron transport in solids

With the addition of recent PW shots, the propagation of short-pulse laser generated electron beams have been studied using laser pulse energies from 30 J to 300 J, generating currents up to ∼15 MA in solid Al:Cu targets. This is ∼5% of the current that will be required in an ignition pulse. To this level, the current appears to simply scale with laser power, the propagation spread not change at all. The resistance of the aluminum does not seem to play a role in the propagation characteristics, though it might in setting the current starting parameters. We do find that at the highest currents parts of these targets reach temperatures high enough to modify the Cu-K, emission spectrum rendering our Bragg imaging mirrors ineffective; spectrometers will be needed to collect data at these higher temperatures.

Propagation of short pulses through a Bose-Einstein condensate

We study propagation of short laser pulses in a Bose-Einstein condensate taking into account dispersive effects under the conditions for electromagnetically induced transparency. We calculate dispersion coefficients using typical experimental parameters of slow-light schemes in condensates. By numerically propagating the laser pulse, and referring to theoretical estimations, we determine the conditions for which dispersion starts to introduce distortions on the pulse shape.

Near-field imaging of nonlinear pulse propagation in planar silica waveguides

A simplified near-field scanning optical microscope is employed to image the propagation of short laser pulses in planar silica waveguides, in the anomalous dispersion regime, under varying conditions of input beam power and width. Our results show a complex evolution of the transverse intensity profiles of the beam when there is a pronounced difference between the input diffraction and dispersion lengths. Numerical simulations confirm that these complex spatial dynamics are intimately related to the temporal and spectral evolution of the pulse.

Effect of pulse slippage on resonant second harmonic generation of a short pulse laser in a plasma

The process of second harmonic generation of an intense short pulse laser in a plasma is resonantly enhanced by the application of a magnetic wiggler. The wiggler of suitable wave number provides necessary momentum to second harmonic photons to make harmonic generation a resonant process. The laser imparts an oscillatory velocity to electrons and exerts a longitudinal ponderomotive force on them at , where ω1 and are the frequency and the wave number of the laser, respectively. As the electrons acquire oscillatory velocity at the second harmonic, the wiggler magnetic field beats with it to produce a transverse second harmonic current at , driving the second harmonic electromagnetic radiation. However, the group velocity of the second harmonic wave is greater than that of the fundamental wave, hence, the generated pulse slips out of the main laser pulse and its amplitude saturates.

Experimental and numerical analysis of short-pulse laser interaction with tissue phantoms containing inhomogeneities.

The objective is to perform an experimental and numerical study to analyze short-pulse laser propagation through tissue phantoms without and with inhomogeneities embedded in them. For a short-pulse laser the observed optical signal has a distinct temporal shape, and the shape is a function of the medium properties. The scattered temporal transmitted and reflected optical signals are measured experimentally with a streak camera for tissue phantoms irradiated with a short-pulse laser source. A parametric study involving different scattering and absorption coefficients of tissue phantoms and inhomogeneities, as well as the detector positions and orientations, is performed. The temporal and spatial profiles of the scattered optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation by using the discrete ordinates technique.

Short pulse laser propagation through tissues for biomedical imaging

An experimental and numerical study is performed to analyse short pulse laser propagation through tissue phantoms with and without inhomogeneities embedded in it. Short pulse laser probing techniques have distinct advantages over conventional very large pulse width or cw lasers primarily due to the additional information conveyed about the tissue interior by the temporal variation of the observed signal. Both the scattered temporal transmitted and reflected optical signals are measured experimentally using a streak camera for samples irradiated with a short pulse laser source. Parametric study involving different scattering and absorption coefficients of tissue phantoms and inhomogeneities as well as the detector position and orientation is performed. The temporal and spatial profiles of the scattered optical signals are compared with the numerical modelling results obtained by solving the transient radiative transport equation using the discrete ordinates technique.

Analysis of short-pulse laser photon transport through tissues for optical tomography

We describe a method for analyzing short-pulse laser propagation through tissues for the detection of tumors and inhomogeneities in tissues with the goal of developing a time-resolved optical tomography system. Traditional methods for analyzing photon transport in tissues usually involve the parabolic or diffusion approximation, which implies infinite speed of propagation of the optical signal. To overcome such limitations we calculate the transmitted and reflected intensity distributions, using the damped-wave hyperbolic P(1) and the discrete-ordinates methods, for a wide range of laser, tissue, and tumor parameters. The results are compared with the parabolic diffusion P(1) approximation.

Photon kinetics for laser-plasma interactions

A photon kinetic formalism is employed to describe the propagation of short laser pulses in tenuous plasmas. The photon kinetic theory contains all of the ingredients necessary to describe the relativistic nonlinear optics of short laser pulses in plasmas, and the shortest time scale is determined by the local evolution of the index of refraction. We use this feature to implement a photon in cell code, in which the typical time step is much bigger than is the laser field time scale. Additional information provided by the photon kinetic framework is illustrated by one-dimensional (1-D) and two-dimensional (2-D) simulations.

Separate observation of ballistic and scattered photons in the propagation of short laser pulses through a strongly scattering medium

The conditions are identified for simultaneous observation of the peaks of scattered and unscattered (ballistic) photons in a narrow pulsed laser beam crossing a strongly scattering medium. The experimental results are explained on the basis of a nonstationary two-flux model of radiation transport. An analytic expression is given for the contribution of ballistic photons to the transmitted radiation, as a function of the characteristics of the scattering medium. It is shown that the ballistic photon contribution can be increased by the use of high-contrast substances which alter selectively the absorption and scattering coefficients of the medium.

Instabilities of Short-Pulse Laser Propagation through Plasma Channels.

The stability of short laser pulses propagating through plasma channels is investigated theoretically. Perturbations to the laser pulse are shown to modify the ponderomotive pressure, which distorts the dielectric properties of the plasma channel. The channel perturbation then further distorts the laser pulse. A set of coupled mode equations is derived, and a matrix dispersion relation is obtained analytically for the special case of a quadratic radial density variation. As an example, the spatiotemporal growth of a pure dipole perturbation is evaluated in various parameter regimes. Mechanisms for suppressing the instability are discussed.

Propagation of short laser pulses under kinetic cooling conditions

A study is made of the instability of a short laser pulse under kinetic cooling conditions and the feasibility of suppressing such an instability is considered.