Generation of high-power, partially coherent light for inertial confinement fusion with dye laser media.

摘要

In one possible approach to generating high-power, partially-coherent light for inertial confinement fusion (ICF), an optical converter containing a liquid organic dye is placed at the output of an existing fusion laser. This device takes the highly coherent radiation from the fusion laser and converts it to spatially and temporally partially-coherent light. To control the divergence and maximize the spectral bandwidth of the light emitted by the converter, a seed laser beam must be copropagated with the fusion laser beam. This injected seed radiation must have a tailored spectrum whose two maxima are located in the wings of the spectral gain curve of the converter medium. The amplitudes of these maxima are adjusted such that at the output of the amplifier or converter they equal the line-center signal amplitude. It is shown in this thesis that high-intensity, broad spectral bandwidth radiation may be generated by employing this tailored spectrum method with three different dye media pumped with a 532 nm wavelength pulsed laser. The outputs from two cavityless dye lasers utilizing different dyes (DCM/DMSO in one, LDS-730/DMSO in the other) were combined and injected into a "combining" pre-amplifier containing a third dye (LDS-698 in a 15/85 mixture of Propylene Carbonate/Ethylene Glycol (PC/EG)). The output from this preamplifier was then passed through an amplifier also containing LDS-698 in PC/EG. The output from this amplifier consisted of {dollar}sim{dollar}5 ns partially coherent light pulses with a peak power of 25-45 MW/cm{dollar}sp2{dollar}, an optical bandwidth of 6-8% (a factor of five greater than without spectral tailoring) centered at 700 nm, and a divergence of 2.3 mrad. Following this amplifier, additional amplifiers could be used to bring the signal up to the desired intensity to drive the converter. A theoretical understanding of the concept and experiments was developed with the aid of a simple time-dependent rate-equation/radiation transport model. Comparison between theory and experiment was good. Radiation polarization measurements showed that, under the slow dye molecule rotational relaxation conditions encountered in the experiment, gain anisotropy occurs. The measured polarization characteristics of the radiation were found to be consistent with an amplification model incorporating dye molecule rotational relaxation dynamics.