Generation of ultrahigh intensity laser pulses

Abstract

Mainly due to the method of chirped pulse amplification, laser intensities have grown remarkably during recent years. However, the attaining of very much higher powers is limited by the material properties of gratings. These limitations might be overcome through the use of plasma, which is an ideal medium for processing very high power and very high total energy. A plasma can be irradiated by a long pump laser pulse, carrying significant energy, which is then quickly depleted in the plasma by a short counterpropagating pulse. This counterpropagating wave effect has already been employed in Raman amplifiers using gases or plasmas at low laser power. Of particular interest here are the new effects which enter in high power regimes. These new effects can be employed so that one high-energy optical system can be used like a flashlamp in what amounts to pumping the plasma, and a second low-power optical system can be used to extract quickly the energy from the plasma and focus it precisely. The combined system can be very compact. Thus, focused intensities more than 10 25 W/cm 2 can be contemplated using existing optical elements. These intensities are several orders of magnitude higher than what is currently available through chirped pump amplifiers.

Reaching the Nonlinear Regime of Raman Amplification of Ultrashort Laser Pulses

“…The nonlinear regime, the socalled -pulse regime, is characterized by pump depletion and the simultaneous temporal compression of the amplified pulse. In this regime, the Raman amplification and compression of ultrashort pulses in a plasma allow intensities to reach 10 20 -10 21 W=cm 2 in a compact universityscale device, and unprecedented high intensity on the order of 10 25 W=cm 2 in a larger system [9]. Such intensities open new frontiers in physics and should also lead to practical applications such as fast ignition for inertial fusion [10], x-ray lasers [11], or laser wake field accelerators [12].…”

“…pe , the efficiency can be as high as 90%. What makes the resonant Raman backscatter regime attractive is that it is a simple resonant interaction, with the seed amplification strong enough to outrun other deleterious competing instabilities (such as modulational instability that can lead to the filamentation of the laser beam) [6] or to avoid superluminous precursor solutions [8], and with realizable highly compressed ultrashort pulse solutions [9].The Raman backscattering (RBS) amplification can be divided into linear and nonlinear regimes. In the linear regime the pump depletion is negligible and the gain is independent of the seed intensity.…”

Demonstration of laser pulse amplification by stimulated Brillouin scattering

“…The plasma can support intensities of up to 10 17 W cm −2 , i.e., 5 orders of magnitude larger than solid-state systems, before disruption to the medium occurs [1] . Laser pulse amplification in plasma rests upon an energy transfer between a relatively long duration pump pulse and a shorter seed pulse through the generation of either an electron plasma wave, known as stimulated Raman scattering (SRS), or an ion-acoustic wave, known as stimulated Brillouin scattering (SBS).…”

Formation of laser plasma channels in a stationary gas

“…The resonant Raman backscattering scheme can be extrapolated to high powers conveniently using optical systems. 5 Being essentially a resonant three-wave process, SRB amplification is rather sensitive to the plasma frequency ω p . Detuning of the resonance caused by longitudinal fluctuations of the electron density δn ez is due to corresponding fluctuations of the electron plasma wave frequency 6 δω p = ω p δn ez /2n e0 .…”

“…For experimental beam parameters and l || ≈ 0.2 mm, the density nonuniformity has to be δn ez /n e < 3-4 %. 5 In the first experimental arrangement, plasma with a density of n e ~ 10 20 cm -3 and a temperature of T e ~ 20 eV was created in a capillary by KrF laser. 8,9 It was shown, however, that the effective length of the plasma channel in copper and LiF capillaries did not exceed 0.2 mm, presumably due to intense pump absorption via an inverse Bremsstrahlung mechanism and initial nonuniformity of the plasma density in the capillary.…”