Effects of continuous phase plate on plasma corona homogeneity and laser-plasma instabilities in experiments with three target materials

Abstract

Corona homogeneity and spectra of scattered light and hot electrons produced by laser-plasma instabilities inside laser-produced plastic, aluminum, and gold plasmas were investigated with and without the use of continuous phase plate (CPP) to the laser beam. Improvement of the corona homogeneity was observed for all three materials after applying CPP, while the inhibition of the intensity of backward-scattered light and the amount of emitted hot electrons was not always synchronous for different materials, which is interpreted as a result of the changes in thresholds of the stimulated Raman scattering (SRS) and the two-plasmon decay (TPD) instability before and after the application of CPP. By comparing the changes of SRS scattered light intensity with the amount of hot electrons in different kinetic energy ranges for all three target materials in our experiments, we conclude that SRS is more responsible for the diagnosed hot electrons between 50-150 keV, and those above 150 keV should be generated by TPD, which could be explained by the difference in phase velocity of electron plasma waves between SRS and TPD calculated from measured and simulated parameters of corona and laser-plasma instabilities.

Spectral characteristics of laser-plasma instabilities with a broadband laser

“…Outside this range, the intensity is much lower, which is similar to the typical SRS backscatter spectral characteristics of an ultraviolet laser. [39] In the broadband case, the scattering region density is significantly expanded -the redshift edge is close to 0.25n cr , and there is no obvious short cutoff usually believed to be related to the Landau damping. As mentioned earlier, SRS under the broadband condition is believed to be reduced by the mitigation of filamentation by the introduction of bandwidth.…”

Spatially and temporally discontinuous two-plasmon decay with relatively low laser irradiance

“…Time-resolved 3ω 0 /2 spectra in directdrive ICF experiments using an ultraviolet laser were obtained by Seka et al [23], indicating a TPD threshold, could be reasonably predicted by the linear theory of absolute instability. Kang et al obtained a clear threshold, linear growth and saturation stages of TPD for aluminum targets by the angularresolved measurement of 3ω 0 /2 emission [20], and they found the threshold condition proposed by Simon et al [19] can be used to roughly explain the experimental results for the difference on TPD of plastic, aluminum and gold planar targets with an irradiance of ∼10 15 W cm −2 [24]. Beyond the topic of threshold, growth and saturation of TPD, measurements of 3ω 0 /2 spectra were performed to estimate the plasma conditions.…”

“…Beyond the topic of threshold, growth and saturation of TPD, measurements of 3ω 0 /2 spectra were performed to estimate the plasma conditions. Seka et al [25] and Giulietti et al [26] proposed formulas to calculate plasma temperature based on the wavelength shifts and the diagnostic angle, which were applied in the analyses on the spectra measured by Basov et al [27], Amiranoff et al [28] and Kang et al [24]. Young [29] and Kondrashov [30] studied the characteristics of blue and red peaks of 3ω 0 /2, and they found that the ratio of intensity of the two peaks may be related to either the target material or the plasma conditions.…”