In this experiment, eight of the laser beams at Nova are used to heat the opacity sample. Other x-rays from the same point backlight bypass the sample, but are still diffracted from the crystal onto the film record. Because the crystal disperses the spectrum, the result is an image that is both spatially and spectrally resolved. Temporal resolution is provided by backlight duration. Schematic of point projection spectroscopy method for measuring opacity.
Proper collimation allows a highly quantitative analysis of the spectrum.
Careful attention was paid to the sample conditions. It was required that the sample be uniform throughout in both temperature and density. Uniformity of temperature was attained by heating the sample in a special hohlraum. The hohlraum also kept a uniform temperature throughout the sample, and this, along with the relatively high density of the sample, ensured that the sample was in local thermodynamic equilibrium. Further, the samples were tamped by plastic so that the density throughout the sample was constant as the sample expanded.