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Photonic Doppler Velocimetry is an interferometric technique for measuring the beat frequency of a moving surface, from which the calculated velocity profile of the surface can be used to describe the physical changes the material undergoes after high-impact shock. Such a technique may also be used to characterize the performance of small detonators and determine the time at which the surface began moving. In this work, we develop a semi-automated technique for extracting the time of initial movement from a normalized lineout of the power spectrogram near the offset frequency of each probe. We characterize the response bias of this method and compare with the time of initial movement obtained by hand calculation of the raw voltage data. Results are shown on data from shock experiments such as gas gun setups and explosives-driven flyer plates.

The spin temperature of neutral hydrogen, which determines the optical depth and brightness of the 21 cm line, is determined by the competition between radiative and collisional processes. Here we examine the role of proton-hydrogen collisions in setting the spin temperature. We use recent fully quantum mechanical calculations of the relevant cross sections, which allow us to present accurate results over the entire physically relevant temperature range 1-10,000 K. For kinetic temperatures T_K>100 K, the proton-hydrogen rate coefficient exceeds that for hydrogen-hydrogen collisions by about a factor of two. However, at low temperatures (T_K < 5 K) H-p collisions become several thousand times more efficient than H-H and even more important than H-e^- collisions., submitted to MNRAS, 5 pages, 2 figures, typos corrected

ArnCl− clusters have been investigated by anion zero electron kinetic energy (ZEKE) and partially discriminated threshold photodetachment spectroscopy. The experiments yield size-dependent electron affinities (EAs) and electronic state splittings for the X, I, and II states accessed by photodetachment. Cluster minimum energy structures have been determined from calculations based on a “simulated annealing” approach employing our recently presented Ar–Cl(−) pair potentials from anion ZEKE spectroscopy [T. Lenzer, I. Yourshaw, M. R. Furlanetto, G. Reiser, and D. M. Neumark, J. Chem. Phys. 110, 9578 (1999)] and various nonadditive terms. The EAs calculated without many-body effects overestimate the experimental EAs by up to 1500 cm−1. Repulsive many-body induction in the anion clusters is found to be the dominant nonadditive effect. In addition, the attractive interaction between the chloride charge and the Ar2 exchange quadrupole is important. These findings are consistent with our earlier results for XenI−...

Xe n I − clusters ( n ⩽13) have been studied by anion photoelectron (PE) spectroscopy at a photon energy of 4.661 eV and an electron energy resolution of 10 meV. Electron affinities (EA's) as a function of cluster size are extracted and compared to previous PE and tunable laser photodetachment spectra of these species. The EA's found in this study lie between those of the two earlier experiments. These discrepancies are attributed to calibration issues in the earlier PE spectra and the influence of charge-transfer-to-solvent states in the tunable laser experiments.

The first demonstration of a technique for the vibrational spectroscopy of anions, stimulated Raman pumping-anion photoelectron spectroscopy is reported. It combines the high spectral resolution of stimulated Raman pumping with the high detection efficiency, mass-selectivity, and wide applicability of anion photoelectron spectroscopy. The vibrational spectrum of a test system, C2−, is recorded and the frequency of the 1←0 vibrational transition is determined to be 1757.8±0.1 cm−1. The Q-branch is partially rotationally resolved.

Zero electron kinetic energy (ZEKE) spectroscopy has been utilized to study the 40 Ar 35 Cl − anion and the X1/2, I3/2 and II1/2 electronic states of neutral ArCl. Well-resolved progressions in the low-frequency vibrations of the anion and the neutral complexes are observed in the ZEKE spectra. From our spectroscopic data we construct model potential functions for the anion and three neutral states. This yields refined values for the neutral state splittings and the first accurate experimental ArCl − anion potential. Absolute uncertainties for R m and e in all potentials are estimated to be ±0.08 A and ±0.6 meV, respectively.

XenI− van der Waals clusters have been investigated by anion zero electron kinetic energy (ZEKE) and partially discriminated threshold photodetachment (PDTP) spectroscopy. The experiments yield size-dependent electron affinities (EAs) and electronic state splittings between the X, I, and II states accessed by photodetachment. Cluster minimum energy structures have been determined by extensive simulated annealing molecular dynamics calculations using Xe–I(−) pair potentials from anion ZEKE spectroscopy and various nonadditive terms. The EAs calculated without many-body effects overestimate the experimental EAs by up to 3000 cm−1. Repulsive many-body induction in the anion clusters is found to be the dominant nonadditive effect, though the attractive interaction between the iodide charge and the Xe2 exchange quadrupole is also important. Unique global minimum energy structures for the anion clusters arise from the influence of the many-body terms, yielding, e.g., arrangements with a closed shell of xenon at...

The XeI− anion and the corresponding neutral X1/2, I3/2, and II1/2 electronic states have been studied by means of zero electron kinetic energy (ZEKE) and photoelectron spectroscopy. The ZEKE spectra show rich and well-resolved progressions in the low-frequency vibrations of the anion and the neutral van der Waals complexes. From our spectroscopic data we construct model potentials for the anion and three neutral states, which are compared to previously obtained potential functions for this system. The intensity of the I3/2←anion transitions relative to the X1/2←anion transitions in the XeI− ZEKE spectrum is considerably lower than expected from a Franck-Condon simulation based on the model potentials. Comparison with the photoelectron spectrum of XeI− indicates this is due to a small s-wave partial cross section for photodetachment to the I3/2 state.

Our goal is to collect x-ray images of different sized targets, which are positioned inside a containment vessel, onto different sized CCD cameras.

A new fisheye lens design is used as a miniature probe to measure the velocity distribution of an imploding surface along many lines of sight . Laser light, directed and scattered back along each beam on the surface, is Doppler shifted by the moving surface and collected into the launching fiber. The received light is mixed with re ference laser light in each optical fiber in a technique called p hoton ic Doppler velocimetry, providing a continuous time record . An array of single -mode optical fibers sends laser light through the fisheye lens . The lens consists of an index- matching posi tive element, two positive doublet groups, and two negative singlet elements. The optical design minimizes beam diameters, physical size, and back reflections for excellent signal collection. The fiber array projected through the fisheye lens provides many measurement points of surface coverage over a hemisphere with very little crosstalk. The probe measures surface movement with only a small encroachment into the center of the cavity.

A novel fiber -optic probe measures the velocity distribution of an imploding surface a long many lines of sight. Reflected light from each spot on the moving surface is Doppler shifted with a small portion of this light propagating backwards through the launching fiber. The reflected light is mixed with a reference laser in a technique called photon Doppler velocimetry, providing continuous time records. Within the probe, a matrix array of 56 single -mode fibers sends light through a n optical relay consisting of three types of lenses. Seven sets of these relay lenses are grouped into a close -packed array allowing the interrogation of seven regions of interest. A six -faceted prism with a hole drilled into its center direct s the light beams to the different regions. Several types of relay lens systems have been evaluated, including doublets and molded aspheric singlets. The optical design minimizes beam diameters an d also provides excellent imaging capabilities. One of the fiber matrix arrays can be replaced by a n imaging coherent bundle. This close -packed array of seven relay systems provides up to 476 beam trajectories. The pyramid prism has its six facets polished at two different angles that will vary the density of surface point coverage. F iber s in the matrix arrays are angle polished at 8° to minimize back reflections. This causes the minimum beam waist to vary along different trajectories. Precision metrology o n the direction cosine trajectories is measured to satisfy environmental requirements for vibration and temperature. Keywords: photon Doppler v elocimetry, PDV, pyramid prism, optical metrology, velocimetry, optical alignment

Anion photoelectron spectroscopy is performed on the C(5)H(-) species. Analogous to C(3)H(-) and C(3)D(-), photodetachment transitions are observed from multiple, energetically close-lying isomers of the anion. A linear and a cyclic structure are found to have electron binding energies of 2.421+/-0.019 eV and 2.857+/-0.028 eV, respectively. A cyclic excited state is also found to be 1.136 eV above the linear (2)Pi C(5)H ground state. Based on our assignments of the observed transitions and previous calculations on the energetics of neutral C(5)H isomers, the cyclic (1)A(1) anion state is found to lie 0.163 eV below the (3)A linear anion.

A velocimetry experiment has been designed to measure shock properties for small cylindrical metal targets (8-mm-diameter by 2-mm thick). A target is accelerated by high explosives, caught, and retrieved for later inspection. The target is expected to move at a velocity of 0.1 to 3 km/sec. The complete experiment canister is approximately 105 mm in diameter and 380 mm long. Optical velocimetry diagnostics include the Velocity Interferometer System for Any Reflector (VISAR) and Photon Doppler Velocimetry (PDV). The packaging of the velocity diagnostics is not allowed to interfere with the catchment or an X-ray imaging diagnostic. A single optical relay, using commercial lenses, collects Doppler-shifted light for both VISAR and PDV. The use of fiber optics allows measurement of point velocities on the target surface during accelerations occurring over 15 mm of travel. The VISAR operates at 532 nm and has separate illumination fibers requiring alignment. The PDV diagnostic operates at 1550 nm, but is aligned and focused at 670 nm. The VISAR and PDV diagnostics are complementary measurements and they image spots in close proximity on the target surface. Because the optical relay uses commercial glass, the axial positions of the optical fibers for PDV and VISAR are offset to compensate for chromatic aberrations. The optomechanical design requires careful attention to fiber management, mechanical assembly and disassembly, positioning of the foam catchment, and X-ray diagnostic field-of-view. Calibration and alignment data are archived at each stage of the assembly sequence.

The spin temperature of neutral hydrogen, which determines the 21 cm optical depth and brightness temperature, is set by the competition between radiative and collisional processes. In the high-redshift intergalactic medium, the dominant collisions are typically those between hydrogen atoms. However, collisions with electrons couple much more efficiently to the spin state of hydrogen than do collisions with other hydrogen atoms and thus become important once the ionized fraction exceeds ~1%. Here we compute the rate at which electron-hydrogen collisions change the hydrogen spin. Previous calculations included only S-wave scattering and ignored resonances near the n=2 threshold. We provide accurate results, including all partial wave terms through the F-wave, for the de-excitation rate at temperatures T_K < 15,000 K; beyond that point, excitation to n>=2 hydrogen levels becomes significant. Accurate electron-hydrogen collision rates at higher temperatures are not necessary, because collisional excitation in this regime inevitably produces Lyman-alpha photons, which in turn dominate spin exchange when T_K > 6200 K even in the absence of radiative sources. Our rates differ from previous calculations by several percent over the temperature range of interest. We also consider some simple astrophysical examples where our spin de-excitation rates are useful., submitted to MNRAS, 9 pages, 5 figures