High-intensity Laser Propagation Research Articles

The mobile ultrafast high energy laser facility - A new facility for high-intensity atmospheric laser propagation studies

We present the design, performance, and initial activation of the Mobile Ultrafast High Energy Laser Facility, a 5 TW near-infrared laser source located on a multi-km test range at Kennedy Space Center. The system is compact, readily transportable, and provides a robust, tunable output suitable for long range studies of high intensity laser propagation. The supporting testing infrastructure, which includes stand-alone beam diagnostic stations and atmospheric monitoring capabilities, makes this facility ideal for the development of stand-off high energy ultrafast applications and fundamental studies of atmospheric laser science.

Evolution of laser pulse shape in a parabolic plasma channel

During high-intensity laser propagation in a plasma, the group velocity of a laser pulse is subjected to change with the laser intensity due to alteration in refractive index associated with the variation of the nonlinear plasma density. The pulse front sharpened while the back of the pulse broadened due to difference in the group velocity at different parts of the laser pulse. Thus the distortion in the shape of the laser pulse is expected. We present 2D particle-in-cell simulations demonstrating the controlling the shape distortion of a Gaussian laser pulse using a parabolic plasma channel. We show the results of the intensity distribution of laser pulse in a plasma with and without a plasma channel. It has been observed that the plasma channel helps in controlling the laser pulse shape distortion. The understanding of evolution of laser pulse shape may be crucial while applying the parabolic plasma channel for guiding the laser pulse in plasma based accelerators.

High-power, high-intensity laser propagation and interactions

This paper presents overviews of a number of processes and applications associated with high-power, high-intensity lasers, and their interactions. These processes and applications include: free electron lasers, backward Raman amplification, atmospheric propagation of laser pulses, laser driven acceleration, atmospheric lasing, and remote detection of radioactivity. The interrelated physical mechanisms in the various processes are discussed.

Characterization of High-Intensity Laser Propagation in the Relativistic Transparent Regime through Measurements of Energetic Proton Beams

Experiments were performed to investigate the propagation of a high intensity (I approximately 10(21) W cm(-2)) laser in foam targets with densities ranging from 0.9n(c) to 30n(c). Proton acceleration was used to diagnose the interaction. An improvement in proton beam energy and efficiency is observed for the lowest density foam (n(e)=0.9n(c)), compared to higher density foams. Simulations show that the laser beam penetrates deeper into the target due to its relativistic propagation and results in greater collimation of the ensuing hot electrons. This results in the rear surface accelerating electric field being larger, increasing the efficiency of the acceleration. Enhanced collimation of the ions is seen to be due to the self-generated azimuthal magnetic and electric fields at the rear of the target.

Effect of focus position on a high intensity laser propagation in a dense plasma

A tightly focused laser pulse with relativistic intensity propagating in a dense plasma is studied by means of 2D particle-in-cell simulation. The results demonstrate that the laser propagation in the plasma is strongly dependent on the laser focus position. It is found that the laser can penetrate deeper in the plasma and create an on-axis plasma channel at certain focus positions, which is due to the suppression of the filamentation instability in the laser plasma interactions. The results are of interest for understanding of the fast ignition related experiments.

High Intensity Laser Propagation though Overdense Plasmas

High intensity laser propagation in plasmas is one of the key issues in fast ignition scheme of laser fusion energy. We have investigated experimentally and computationally the laser propagation in dense plasmas. The experiment demonstrates plasma channel formation and indicates laser propagation through overdense plamsas with relativistic self-focusing. The channel direction coincides with the laser axis. Two and three-dimensional particle-in-cell simulation reproduces the plasma channel and reveals that the laser propagation is dependent on the laser focus position in plasmas.

Vacuum ultraviolet argon excimer production by use of an ultrashort-pulse high-intensity laser

We report on the observation of ${\mathrm{Ar}}_{2}^{*}$ emission at 126 nm by use of a hollow fiber to guide the high-intensity laser propagation in high-pressure Ar. A small-signal gain coefficient of $0.05{\mathrm{cm}}^{\ensuremath{-}1}$ was measured at 126 nm by this method. The increase of the ${\mathrm{Ar}}_{2}^{*}$ emission intensity was measured to be $\mathrm{exp}(2.5),$ with an increase of the fiber length up to 50 cm. Kinetic analysis revealed that the ${\mathrm{Ar}}_{2}^{*}$ production processes were initiated by the electrons produced by the high-intensity laser through an optical-field-induced ionization (OFI) process. A rapid conductive cooling of the OFI electrons is favorable to initiate the ${\mathrm{Ar}}_{2}^{*}$ formation kinetics more efficiently. This high-density cold plasma production method should be applicable for other vacuum ultraviolet rare-gas excimer lasers.

Observation of vacuum-ultraviolet Ar2* radiation gain at 126 nm produced by an ultrashort high-intensity laser pulse propagating in a hollow fiber.

We observed a small-signal gain of Ar2* emission at 126 nm by use of a hollow fiber to guide the high-intensity laser propagation in high-pressure Ar. The small-signal gain coefficient was measured to be 0.05 cm(-1) at 126 nm. Kinetic analysis revealed that the electrons produced by the high-intensity laser through an optical-field-induced ionization process initiated the Ar2* production processes. The increase in the emission intensity was measured to be exp(2.5), with an increase in the fiber length.

The effect of high intensity laser propagation instabilities on channel formation in underdense plasmas

Experiments have been performed using high power laser pulses (up to 50 TW) focused into underdense helium plasmas (ne⩽5×1019 cm−3). Using shadowgraphy, it is observed that the laser pulse can produce irregular density channels, which exhibit features such as long wavelength hosing and “sausage-like” self-focusing instabilities. This phenomenon is a high intensity effect and the characteristic period of oscillation of these instabilities is typically found to correspond to the time required for ions to move radially out of the region of highest intensity.

Ultra-high-intensity laser propagation through underdense plasma

Picosecond resolution shadowgraphy is a powerful tool for measurement of high-intensity laser propagation instabilities through underdense plasma. It is shown that as the plasma density increases, the laser beam is subject to severe filamentation instabilities-likely due to the effect of stimulated Raman side-scattering. At higher plasma densities, scattering and absorption are so severe that the propagation distance of the high intensity laser pulse is reduced.