Nondestructive analysis of laser fusion microsphere targets using rotational Raman spectroscopy

The use of rotational Raman scattering for nondestructive analysis of laser fusion microsphere targets is reported. Typical hollow-glass-microsphere sample characteristics are 100 μm in diameter, 1.0 μm in glass wall thickness, and 0.5 nl in volume, containing a mixture of hydrogen, deuterium, and tritium gases at pressures of 10–70 atm (total gas sample weights of 5 ng). Relative species mole fraction measurements for all hydrogen isotope species are determined from spectral peak height analysis of rotational Raman spectra. Accuracies of ±0.01 (mole fraction) are obtained from spectra requiring 20 min scan time. Individual species detectability limits are less than 100 picogram. Absolute partial pressure measurements (accurate to ±20%) are obtained using calibration spheres of known diameter and pressure.