Abstract
The energy and spectrum of the reflected 248 nm radiation are studied from solid targets up to 1.15 × 1018 W cm−2 intensity. The experiments used the 700 fs directly amplified pulses of the KrF system which was cleaned from prepulses with the new Fourier-filtering method providing 12 orders of magnitude temporal contrast. Increasing the intensity from 1015 W cm−2 results in increasing absorption up to more than 90% above 1018 W cm−2. This is accompanied by increasing x-ray conversion exhibiting a less steep power law dependence for low-Z matter than for gold. Strong blue shift of the reflected radiation from the backward propagating plasma was observed. It is shown that in the case of KrF laser pulses of highest contrast, vacuum heating can be one of the dominant absorption mechanisms.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.
Highlights
KrF lasers have been and even presently are regarded as possible alternative laser drivers for inertial confinement fusion (ICF) [1]
Note that former plasma mirror experiments performed with KrF lasers where increasing reflectivity was measured for the 45° angle of incidence showed saturation above 1014 W cm−2 and a strong decrease above 1015 W cm−2 intensity [30]
The reflectivity drops below 10% above 1018 W cm−2, i.e. the absorption surpasses 90%. This tendency is similar to that found by Ziener et al [31] for infrared pulses, who observed an increase of absorption up to the same Iλ2 value, i.e. up to several times 1016 W cm−2 infrared intensity
Summary
KrF lasers have been and even presently are regarded as possible alternative laser drivers for inertial confinement fusion (ICF) [1]. The short wavelength and the high beam quality make them attractive as a driver. As a fast ignitor [2] because the electrons will not be accelerated much above 1 MeV even in the nonlinear interactions with the short pulse. The energy of the accelerated electrons royalsocietypublishing.org/journal/rsta Phil.
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