We have measured the rise time of laser-generated shock waves in vapor plated metal thin films using frequency-domain interferometry with subpicosecond time resolution. 10%- 90% rise times of <6.25 ps were found in targets ranging from 0.25 to 2.0 microm in thickness. Particle and average shock velocities were simultaneously determined. Shock velocities of approximately 5 nm/ps were inferred from the measured free surface velocity, corresponding to pressures of 30-50 kbar. Thus, the shock front extends only a few tens of lattice spacings.

We observe terahertz emission by optical rectification of an intense 1.5-eV, 50-fs pulse in single-crystal iron thin films grown by molecular beam epitaxy. The azimuthal dependence of the emission indicates the presence of a magnetic nonlinearity and a nonmagnetic surface nonlinearity.

The vibrational spectra of the R, β, and δ phases of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been investigated by complimentary theoretical and experimental approaches. Density functional theory and the scaled quantum mechanical force-field method have been used to calculate the vibrational spectra of the H 8 C 4 N 8 O 8 molecule in C i and C 2V symmetry conformations in the gas phase. By comparing the calculated molecular vibrational frequencies of the H 8 C 4 N 8 O 8 molecule with the experimental infrared and Raman spectra of HMX crystalline samples, we attempt to assign the intramolecular motions that correspond to the measured bands in the experimental spectra of HMX in R-, β-, and δ-phase crystal lattices. Our analysis of the vibrational spectra verifies that the particular conformation of the H 8 C 4 N 8 O 8 molecule in each crystal lattice of HMX determines, to a great extent, the general pattern of the vibrational spectrum of the crystal lattice. We also compare our detailed motion assignments with the general assignments proposed in previous experimental work. Good agreement is found between the calculated geometry of the H 8 C 4 N 8 O 8 molecule in the C i symmetry conformation and the experimental geometry of molecules in the β-phase lattice of HMX and between the calculated geometry of the H 8 C 4 N 8 O 8 molecule in the C 2V symmetry conformation and the experimental geometry of molecules in the Rand δ-phase lattices of HMX.

Survey spectra of single-crystal HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and PETN (pentaerythritol tetranitrate) were acquired in the region from 10 to 80 cm(-1) using terahertz time-domain spectroscopy. The spectra were taken at temperatures ranging from 8.4 to 300 K. Generally, the spectra show multiple absorption peaks in the range 50-80 cm(-1), with PETN (110) showing strong absorption features at room temperature. RDX (210) is the most notable in the region 10-40 cm(-1), showing multiple spectral features, while HMX (010) shows a very broad absorption at 47.8 cm(-1) with a fwhm of 37.3 cm(-1). Future plans include polarization-dependent investigations for multiple crystallographic orientations over an increased spectral range and higher-level theoretical calculations.

We report a direct measurement of temperature in a shocked metal using Doppler broadening of neutron resonances. The 21.1-eV resonance in 182 W was used to measure the temperature in molybdenum shocked to 63 GPa. An explosively launched aluminum flyer produced a planar shock in a molybdenum target that contained a 1-mm thick layer doped with 1:7 at: % 182 W. A single neutron pulse, containing resonant neutrons of less than 1 s duration, probed the shocked material. Fits to the neutron time-of-flight data were used to determine the temperature of the shocked molybdenum.