Intensity-Dependent Absorption in 10.6-μm Laser-Illuminated Spheres

Abstract

An intensity dependence of the absorption of 10-/u m laser light on C02-laser-fusion targets has been observed. Absorption on gold spheres increases from 25%--30% at 10^^ W/cm^ to 50%-60% at 10^^ W/cm^, with most of the variation occurring above 10^^ W/cm^ Concurrently, hot-electron temperature scales as T^ot ^I^'^^ over the entire range. The absorption variation is interpreted as enhanced resonant absorption. It is su^ested that as intensity is increased, the critical surface in the irradiated region becomes increasingly unstable, thereby permitting greater surface distortion and more favorable coupling conditions for resonant absorption.

Absorption of ultrashort, ultra-intense laser light by solids and overdense plasmas

“…For US-UI pulses, this happens quite early in the interaction, and so most of the pulse interacts with a plasma, as opposed to an unionized solid. The relativistically correct dispersion relation (for circular polarization) that governs the propagation of light waves in a plasma is given by (3) where is the wavenumber (frequency) of the laser light, is the relativistic factor, and is the plasma frequency. First consider the nonrelativistic case where , which is valid up to (normalized) intensities of about 5 10 W m /cm .…”

“…Never before has it been possible to deposit so much laser energy in such a short amount of time, in such a tiny volume on the front of a solid target. Previously, the intense CO lasers were nanoseconds long, unavoidably creating large preformed plasmas that the laser had to interact with [3]. This led to a considerable amount of absorption in the underdense part of the plasma, as well as enough time for the laser to filament on its way to the critical surface.…”

Effect of pulse width and fluence of femtosecond laser on the size of nanobump array

“…When the fluence was 87 mJ/cm 2 , the size of nanobump decreased at the pulse width longer than 350 fs, which is due to the loss of energy. The loss of energy can be due to the change of the absorbance of laser [11] or heat radiation, or due to the diffusion of high energy electrons from excited region to not-excited region, or heat conduction from excited region to not-heated region or to transparent substrate. There is quite few data of these phenomena between gold film and quartz glass substrate, so it is difficult to speculate about energy loss paths in detail.…”

Study of the Stimulated Brillouin Scattering in a Dissipative Two‐Ion Species Plasma

“…Now differentiating equation (8) with respect to time t and using equations (6) and (9), we have derived the expression for the low frequency density fluctuation of the electrons assuming a/at Q wpe, kvre as where and iwovo* w&(l + k21',2,) .…”

“…Recently BACH et al [6] have observed the intensity dependent absorption in the laser-illuminated spheres. Thus the theoretical and experimental studies of different nonlinear mechanisms which may cause the saturation of the instabilities in plasma have received much attention in the recent years.…”