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.

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.

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.

A method is described for generating shock waves with 10–20 ps risetime followed by &gt;200 ps constant pressure, using spectrally modified (clipped) chirped laser pulses. The degree of spectral clipping alters the chirped pulse temporal intensity profile and thereby the time-dependent pressure (tunable via pulse energy) generated in bare and nitrocellulose-coated Al thin films. The method is implementable in common chirped amplified lasers, and allows synchronous probing with a &lt;200 fs pulse.

We have applied ultrafast time-resolved two-dimensional interferometric microscopy to the measurement of shock wave breakout from thin metal films. This technique allows the construction of a two-dimensional breakout profile for laser generated impulsive shocks with temporal resolution of &lt;300 fs and out-of-plane spatial resolution of 0.5 nm using 130 fs, 800 nm probe pulses. Constraints placed on the spatial extent of the probed region and on the spatial resolution of the technique by the short duration of the probe pulses are discussed. In combination with other techniques, such as spectral interferometry, this technique provides a powerful means of investigating shock dynamics in a variety of materials.