Energetic material response to ultrafast indirect laser heating.

The initial evolution of thermal energy transfer into a solid explosive is studied using an indirect femtosecond laser heating technique on a picosecond timescale in order to elucidate the role of temperature in the shock-induced initiation of explosives. The indirect laser heating method is presented; time-resolved visible transient absorption (TA) spectroscopy was used to monitor the energetic material response following heat transfer from the laser-heated gold (Au) layer to the sample. Reported here are visible TA data in the spectral region from 500 to 750 nm for indirect laser-heated thin films of cyclotrimethylene trinitramine (RDX), oxidized polyethylene (OPE), and RDX with 1%, 2.5%, 5%, or 10% OPE prior to decomposition. TA was observed for RDX and RDX with OPE; however, no TA was observed for pure OPE. Compared to pure RDX, the TA intensity of RDX with OPE decreases as the OPE content increases and the time required to observe the TA signal from RDX increases. Our results suggest that the thermal energy produced by a femtosecond laser pulse with an energy of 15 mJ cm-2 is sufficient to induce changes in the electronic structure of RDX, resulting in promotion of the RDX molecules into an excited state. We also determined that the heat transfer rate in RDX depends on its homogeneity and degree of purity.

Shock induced chemistry in liquids studied with ultrafast dynamic ellipsometry and visible transient absorption spectroscopy.

The response to ultrafast laser shock loading of nine liquids was monitored in an effort to reveal evidence of chemical changes occurring during the first 350 ps following the shock front. In an effort to compare molecular structures possessing a variety of common bonding patterns, data were acquired for the liquids: cyclohexane, cyclohexene, 1,3-cyclohexadiene, benzene, water, acetonitrile, acrylonitrile, tert-butylacetylene, and phenylacetylene. Transient absorption spectra were measured in the spectral region from 440 to 780 nm over shock stress states from 7 to 20 GPa. Ultrafast dynamic ellipsometry was used to measure the shock and particle velocity as well as the shocked refractive index. Significant transient absorption attributed to chemical reaction was observed for shocked phenylacetylene and acrylonitrile. Evidence of volume decreasing chemical reactions was also observed in the ultrafast dynamic ellipsometry data for phenylacetylene and acrylonitrile. The liquid 1,3-cyclohexadiene exhibited volume decreasing reaction in the ultrafast dynamic ellipsometry data but did not exhibit an increase in the transient absorption spectra. There was no evidence of chemical reaction in cyclohexane, cyclohexene, benzene, water, acetonitrile, or tert-butylacetylene in the first 350 ps, despite the application of shock stress that was in many cases well above the reaction threshold observed at microsecond time scales.

Femtosecond stimulated Raman scattering picosecond molecular thermometry in condensed phases.

We demonstrate the capability of femtosecond stimulated Raman scattering (FSRS) data to measure the temperature of condensed matter at the molecular vibrational level. We report the temperature dependence of Raman loss to Raman gain ratios for low frequency modes (<300 cm(-1)) in a CaCO3 single crystal from cryogenic to room temperature, which is shown to be in agreement with theoretical predictions. We also report the measurements of nonequilibrium time evolution of mode specific vibrational temperatures in the CaCO3 single crystal to demonstrate that FSRS can measure temperature on picosecond time scales. Finally, we point out the unique origin of this temperature dependent anti-Stokes to Stokes ratio in stimulated Raman, which is not present in other coherent Raman spectroscopies. These measurements require no material dependent parameters or prior calibration.

Temperature dependence of hole growth kinetics in aluminum-phthalocyanine-tetrasulfonate in hyperquenched glassy water.

The temperature (T) dependence of hole growth kinetics (HGK) data that span more than four decades of burn fluence are reported for aluminum-phthalocyanine tetrasulfonate (APT) in fresh and annealed hyperquenched glassy water (HGW) for temperatures between 5 and 20 K. The highly dispersive HGK data are modeled by using the "master" equation based on the two level system (TLS) model described in 2000 by Reinot and Small [J. Chem. Phys. 2000, 113, 10207]. We have demonstrated that thermal line broadening is not enough to account for temperature-dependent HGK for temperatures greater than 10 K. To overcome the discrepancy, the hole growth model must account for thermal hole filling (THF) processes. For the first time, the "master" equation used for HGK simulations is modified to take into account both the temperature dependence of the (single site) absorption spectrum and THF processes, effectively turning off those TLS which do not participate in the hole burning process at higher temperatures. A single set of parameters, some of which were determined directly from the hole spectra, was found to provide satisfactory fits to the HGK data for APT in fresh and annealed HGW for holes burned in the 679.7-676.9 nm range from the high to low energy sides of the Qx absorption band. Furthermore, we propose that HGK modeling at high burn fluences requires that the TLS model be further modified to take into account the existence of extrinsic multiple level systems.

Malignant chest wall tumors in children and young adults.

PURPOSE: Primary chest wall malignancies, which occur infrequently in children, can pose complex technical challenges to the surgeon. This study was undertaken to evaluate the pathology, treatment approaches, role of surgical resection and reconstruction, and outcomes of patients with these tumors. METHODS: This is a retrospective review of all patients with malignant primary chest wall tumors treated at our institution between February 1983 and July 1998. RESULTS: Nineteen cases were identified: malignant small round cell type (MSRCT, also called Ewing's sarcoma, primitive neuroectodermal tumor [PNET], and Askin's tumor; n = 8), rhabdomyosarcoma (RMS; n = 6), and other tumors (n = 5). Three patients underwent "upfront" complete resections. Sixteen patients underwent initial biopsy, followed by chemo- or radiotherapy. Nine of these 16 survived to undergo delayed chest wall resections. Six of the 12 "resected" patients required en bloc resection of adjacent muscles or organs; 7 required complex chest wall reconstruction. Eight of 19 patients (42%) have survived (median follow-up of survivors, 4 years), all with no evidence of disease; the remaining 11 patients died of progressive disease. Local invasion did not alter chance of survival. Two of the 10 patients with metastases at diagnosis (20%) survived. Six of the 9 patients (67%) with localized disease survived. All five patients with tumor types other than MSRCT or RMS, metastatic or not at diagnosis, are alive with no evidence of disease. There were no local recurrences. CONCLUSION: Surgical resection, with en bloc removal of involved structures and chest wall reconstruction, provides excellent local control of malignant chest wall tumors.