Absolutely Calibrated Vacuum Ultraviolet Spectra in the 150 nm to 250 nm Range from Plasmas Generated by the NIKE KrF Laser; Journal article

摘要

High resolution vacuum ultraviolet (VUV) spectra were recorded from plasmas generated by the NIKE KrF laser for the purpose of observing emission from the two-plasmon decay instability (TPDI) at 2/3 the NIKE wavelength (165 nm). The targets were irradiated by up to 43 overlapping beams with intensity up to &(number sign)8776;1014 W/sq cm and with beam smoothing by induced spatial incoherence (ISI). The targets consisted of planar foils of CH, BN, Al, Si, S, Ti, Pd, and Au. Titanium-doped silica aerogels in pyrex cylinders were also irradiated. Spectra of the target elements were observed from charge states ranging from the neutral atoms to 5 times ionized. The spectrometer was absolutely calibrated using synchrotron radiation, and absolute VUV plasma emission intensities were determined. Emission from the TPDI at 165 nm wavelength was not observed from any of the irradiated targets. An upper bound on the possible TPDI emission was less than 4x10-8 the incident NIKE laser energy. The NIKE laser radiation backscattered from the silica aerogel targets at 248 nm was typically 6x10-6 the incident NIKE laser energy, and the spectral broadening corresponded to the 1 THz bandwidth of the ISI smoothing. The spectra from the moderately charged plasma ions (up to 5 times ionized), spectral line widths, absolute continuum emission level, and slope of the continuum were consistent with plasma temperatures in the 100 eV to 300 eV range.