Robert K. Sander

Cascaded electro-optic scanning of laser light over large angles using domain microengineered ferroelectrics

We present a device concept based on cascaded electro-optic deflection in a domain microengineered ferroelectric chip. In our design, large deflection angles are achieved by cascading several smaller scanners in a single ferroelectric chip, such that each successive scanner stage builds upon the deflection of the previous stage. We demonstrate the basic concept using a two-stage device fabricated in a single crystal wafer of ferroelectric LiTaO3. By operating the device using a specially designed programmable multichannel driver that provides ±1.1 kV per stage, a total scan angle of 25.4° at 5 kHz was demonstrated. Even larger angles of deflection are possible with additional scanner stages.

Resonantly enhanced vacuum ultraviolet generation and multiphoton ionization in carbon monoxide gas

Competition between three‐photon resonantly enhanced vacuum ultraviolet third‐harmonic generation and six‐photon multiphoton ionization using the A state in gaseous carbon monoxide is observed. Excitation spectra of the third‐harmonic emission exhibit increasing blue shifts and broadening with increasing pressure due to the phase matching requirements. Estimates for the efficiency and tunability show that third‐harmonic generation in carbon monoxide molecules is a promising source for coherent vacuum ultraviolet light.

ArF laser enrichment of oxygen isotopes

Absorption by air in the optical cavity of an ArF discharge laser removes the 16O2 Schumann‐Runge lines from the broad lasing output centered at 193 nm. Subsequent irradiation of an oxygen cell induces photochemistry of 17O and 18O, resulting in isotopically enriched ozone.

Optical properties of PbSe nanocrystal quantum dots under pressure

The optical properties of PbSe nanocrystal quantum dots (NQDs) were studied as a function of applied hydrostatic pressure over the range from ambient to 5.4GPa. PbSe NQDs exhibit an energy gap that is dominated by quantum confinement. Despite such strong confinement, the authors find that the energy gaps of 3, 5, and 7nm diameter PbSe NQDs change monotonically with pressure with a dependence that is almost entirely determined by the bulk deformation potential. The sizable dependence of the NQD energy gap with pressure invites applications in the areas of high speed pressure sensing and tunable IR lasers.

Quantitative chemical identification of four gases in remote infrared (9–11 µm) differential absorption lidar experiments

A combined experimental and computational approach utilizing tunable CO(2) lasers and chemometric analysis was employed to detect chemicals and their concentrations in the field under controlled release conditions. We collected absorption spectra for four organic gases in the laboratory by lasing 40 lines of the laser in the 9.3-10.8-mum range. The ability to predict properly the chemicals and their respective concentrations depends on the nature of the target, the atmospheric conditions, and the round-trip distance. In 39 of the 45 field experiments, the identities of the released chemicals were identified correctly without predictions of false positives or false negatives.

Electro-optic coefficients of lithium tantalate at near-infrared wavelengths

The unclamped linear electro-optic coefficients r13 and r33 for lithium tantalate are known at only one wavelength, 632.8 nm, whereas the clamped coefficients are also known at 3.39 μm. In the unclamped mode the effects of mechanical changes caused by piezoelectric and elasto-optic effects are accounted for in the electro-optic coefficient. We demonstrate a novel technique that uses a ferroelectric domain micropatterned electro-optic deflector to measure the unclamped linear electro-optic coefficients r13 and r33 at any wavelength. Using this method, we have determined these values for lithium tantalate at 980, 1330, and 1558 nm.

Importance of the gas phase role to the prediction of energetic material behavior: An experimental study

Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase las...

Quenching of C2H emission produced by vacuum ultraviolet photolysis of acetylene

Excited C2 H* is produced by vacuum ultraviolet photolysis of acetylene using a frequency tripled laser. Time‐dependent emission is measured from 400–940 nm. The use of a coherent photolysis source produces an excitation spectrum in which the rotational band contour is resolved. The absorption spectrum of C2 H2 taken in the same apparatus closely resembles the excitation spectrum indicating a homogeneous predissociation. Time‐dependent quenching of the C2 H* emission by Xe, Kr, Ar, He, N2, H2, D2, and C2 H2 is measured. The rapid quenching rates and lack of strong dependence on atomic weight suggest a spin‐allowed process is involved in this channel of C2 H2 photolysis. Quench rates are compared with several theoretical models.

The mechanism of energy decrease in the XeBr laser

The xenon bromide discharge laser utilizes the reaction of Xe* with HBr to produce XeBr* in a dilute mixture with He or Ne buffer gas. XeBr lasers previously reported suffer from a high gas usage rate under static fill conditions. This is caused by the decomposition of HBr in the laser discharge to bromine and hydrogen. This reaction can be reversed using a catalyst in an external gas circulating system. We demonstrate a tenfold reduction in the consumption of the laser mix, namely 126 shots per liter of gas mix for decay of laser energy to 75% of maximum.

Ignition dynamics of high explosives

Mechanical insults of granular high explosives (HE) can result in localized areas of elevated temperature, or hot spots. The evolution of these hot spots is a central issue of HE science. Because of the complexity involved, it is worthwhile to study mechanical and reaction processes in isolation. Mechanical processes are isolated and studied using inert materials or weak insults where reaction may be minimal. Likewise, purely thermal processes can be considered to isolate HE reaction response. In this work the authors study the radiant ignition of various HEs of interest, including HMX (C{sub 4}H{sub 8}N{sub 8}O{sub 8}), PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), RDX (C{sub 3}H{sub 6}N{sub 6}O{sub 6}), TATB (C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502. Initial work has included unconfined samples at ambient pressure in air. Diagnostics have included photodiodes to record first light emission, high speed photography, microthermocouple and IR emission measurement to obtain surface temperature, IR emission of gases above the pellet, and a novel nonlinear optical technique to characterize the dynamic {beta}-{delta} solid phase transformation and the formation of a liquid layer. The authors find that ignition delays at various power levels is very similar for HMX and RDX; except that the minimum radiant flux needed for RDX ignition is higher. The addition of only 5% binder (PBX 9501) causes significantly longer ignition delays at lower heat fluxes compared with HMX alone. TATB and TATB-based explosives exhibit much longer ignition delays than HMX. In contrast to HMX, however, no measurable difference is observed in TATB by the addition of a binder (PBX 9502, aged or pristine).