Collisional Dynamics of Bi\u3csub\u3e2\u3c/sub\u3e A(0\u3csub\u3eu\u3c/sub\u3e\u3csup\u3e+\u3c/sup\u3e). II. State-to-state Rotational Energy Transfer

Rotational-to-translational (R–T) energy transfer within v′=1 of the A(0+u) state of Bi2 has been investigated using spectrally resolved, laser induced fluorescence techniques. Spectrally resolved emissions from collisionally populated rotational levels of Bi2(A,v′=1) were observed for helium, neon, and argon collision partners after laser excitation of the high rotational levels J′=171, 201, and 231. Total rotational removal rates from the initially prepared state range from 2.8–8.9×10−10 cm3/molecule s. Collisional population of rotational states with |ΔJ|⩽56 was observed at pressures of 0.09–1.4 Torr. The state-to-state rates are adequately modeled by the energy based statistical power gap law

Spatial and spectral performance of a chromotomosynthetic hyperspectral imaging system

The spatial and spectral resolutions achievable by a prototype rotating prism chromotomosynthetic imaging (CTI) system operating in the visible spectrum are described. The instrument creates hyperspectral imagery by collecting a set of 2D images with each spectrally projected at a different rotation angle of the prism. Mathematical reconstruction techniques that have been well tested in the field of medical physics are used to reconstruct the data to produce the 3D hyperspectral image. The instrument operates with a 100 mm focusing lens in the spectral range of 400–900 nm with a field of view of 71.6 mrad and angular resolution of 0.8–1.6 μrad. The spectral resolution is 0.6 nm at the shortest wavelengths, degrading to over 10 nm at the longest wavelengths. Measurements using a point-like target show that performance is limited by chromatic aberration. The system model is slightly inaccurate due to poor estimation of detector spatial resolution, this is corrected based on results improving model performance. As with traditional dispersion technology, calibration of the transformed wavelength axis is required, though with this technology calibration improves both spectral and spatial resolution. While this prototype does not operate at high speeds, components exist which will allow for CTI systems to generate hyperspectral video imagery at rates greater than 100 Hz

Spin-Orbit Relaxation of Cesium 7 \u3csup\u3e2\u3c/sup\u3eD in Mixtures of Helium and Argon

Pulsed excitation on the two-photon Cs 62S1/2 -\u3e 72D3/2,5/2 transition results in time-resolved fluorescence at 697 and 672 nm. The rates for fine-structure mixing between the 72D3/2,5/2 states have been measured for helium and argon rare-gas collision partners. The mixing rates are very fast, 1.26±0.05×10−9 cm3/atom s for He and 1.52±0.05×10−10 cm3/atom s for Ar, driven by the small energy splitting and large radial distribution for the valence electron. The quenching rates are considerably slower, 6.84±0.09×10−11 and 2.65±0.04×10−11 cm3/atom s for He and Ar, respectively. The current results are placed in context with similar rates for other alkali-metal–rare-gas collision pairs using adiabaticity arguments

Collisional Dynamics of Bi\u3csub\u3e2\u3c/sub\u3e A(0\u3csub\u3eu\u3c/sub\u3e\u3csup\u3e+\u3c/sup\u3e). I. Quantum-resolved Vibrational Energy Transfer for v′=0–4

Vibrational-to-translational energy transfer between the lowest vibrational levels (v′=0–4) of the A(0+u) state of Bi2 has been investigated using spectrally resolved, laser-induced fluorescence techniques. The small vibrational spacing (ω′e≃132 cm−1) leads to highly nonadiabatic conditions, particularly for the Bi2(A)–He collision pair. However, the Δv=−1 transition probabilities for collisions with the rare gases range from 0.75% to 1.75% per collision, considerably lower than would be anticipated from standard vibrational energy transfer theory. Multiquantum (Δv′=±2) transfer rates are low, consistent with the low anharmonicity of the A(0+u) state. The rates for Δv′=±1 transitions scale linearly with vibrational quantum number as expected near the bottom of this nearly harmonic potential

Comparison of Plume Dynamics for Laser Ablated Metals: Al and Ti

Emissive plumes from pulsed laser ablation of bulk Ti and Al from KrF laser irradiation at laser fluence up to 3.5 J/cm2 and argon background pressures of 0–1 Torr have been observed using gated intensified charged-coupled device imagery. Mass loss for Ti increases from 0.1 to 0.8 μg/pulse as pulse energy increase from 174 to 282 mJ/pulse (35–170 photons/atom) and decreases by ∼30% as pressure increases from vacuum to 1 Torr. Early plume energies are described by the free expansion velocities of 1.57 ± 0.02 and of 1.81 ± 0.07 cm/μs for Ti and Al, respectively, and up to 90% of the incoming laser energy can be attributed to the Al shock front in the mid-field. The ablation thresholds of 90 ± 27 mJ (1.12 ± 0.34 J/cm2) for Ti and 126 ± 13 mJ (1.58 ± 0.16 J/cm2) for Al also represent 30%–70% of the incident laser energy. The decrease in mass loss at higher pressures is attributed to plasma shielding of the target surface

Pressure Broadening and Shift of the Cesium D\u3csub\u3e1\u3c/sub\u3e Transition by the Noble Gases and N\u3csub\u3e2\u3c/sub\u3e, H\u3csub\u3e2\u3c/sub\u3e, HD, D\u3csub\u3e2\u3c/sub\u3e, CH\u3csub\u3e4\u3c/sub\u3e, C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e6\u3c/sub\u3e, CF\u3csub\u3e4\u3c/sub\u3e, and \u3csup\u3e3\u3c/sup\u3eHe

The pressure broadening and shift rates for the cesium D1 (62P1/2 ← 6 2S1/2) transition with the noble gases and N2, H2, HD, D2, CH4, C2H6, CF4, and 3He were obtained for pressures less than 300 torr at temperatures under 65 °C by means of laser absorption spectroscopy. The collisional broadening rate, γL, for He, Ne, Ar, Kr, Xe, N2, H2, HD, D2, CH4, C2H6, CF4, and 3He are 24.13, 10.85, 18.31, 17.82, 19.74, 16.64, 20.81, 20.06, 18.04, 29.00, 26.70, 18.84, and 26.00 MHz/torr, respectively. The corresponding pressure-induced shift rates, δ, are 4.24, −1.60, −6.47, −5.46, −6.43, −7.76, 1.11, 0.47, 0.00, −9.28, −8.54, −6.06, and 6.01 MHz/torr. These rates have then been utilized to calculate Lennard-Jones potential coefficients to quantify the interatomic potential surfaces. The broadening cross section has also been shown to correlate with the polarizability of the collision partner

Spectral broadening Effects on Pulsed-source Digital Holography

Using a pulsed configuration, a digital-holographic system is setup in the off-axis image plane recording geometry, and spectral broadening via pseudo-random bit sequence is used to degrade the temporal coherence of the master-oscillator laser. The associated effects on the signal-to-noise ratio are then measured in terms of the ambiguity and coherence efficiencies. It is found that the ambiguity efficiency, which is a function of signal-reference pulse overlap, is not affected by the effects of spectral broadening. The coherence efficiency, on the other hand, is affected. As a result, the coherence efficiency, which is a function of effective fringe visibility, is shown to be a valid performance metric for pulsed-source digital holography

Time-of-flight Emission Profiles of the Entire Plume Using Fast Imaging During Pulsed Laser Deposition of YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7−x\u3c/sub\u3e

Emission time-of-flight (TOF) profiles have been obtained using gated imagery to further the process control during the pulsed laser deposition of the high temperature superconductor, YBa2Cu3O7−x⁠. An intensified charge coupled device array was used to obtain a sequence of plume images at 10ns temporal resolution and 0.2mm spatial resolution. Plume imagery is transformed to TOF profiles and pulse-to-pulse variations removed using physically based smoothing techniques. Comparison with non-imaging sensors establishes excellent agreement, with systematic uncertainties in streaming speed and temperatures of less than 15% and 8%, respectively. The resulting streaming speeds of 0.4–1.2×106 cm/s and characteristic temperatures of 20000–200000K are characterized across the full plume. This new imaging TOF technique enables the monitoring of the complete evolution of speed distributions. Indeed, significant deviations from the forward-directed Maxwellian speed distributions are observed

Deep-turbulence Wavefront Sensing using Digital Holography in the On-axis Phase Shifting Recording Geometry with Comparisons to the Self-referencing Interferometer

In this paper, we study the use of digital holography in the on-axis phase-shifting recording geometry for the purposes of deep-turbulence wavefront sensing. In particular, we develop closed-form expressions for the field-estimated Strehl ratio and signal-to-noise ratio for three separate phase-shifting strategies—the four-, three-, and two-step methods. These closed-form expressions compare favorably with our detailed wave-optics simulations, which propagate a point-source beacon through deep-turbulence conditions, model digital holography with noise, and calculate the Monte Carlo averages associated with increasing turbulence strengths and decreasing focal-plane array sampling. Overall, the results show the four-step method is the most efficient phase-shifting strategy and deep-turbulence conditions only degrade performance with respect to insufficient focal-plane array sampling and low signal-to-noise ratios. The results also show the strong reference beam from the local oscillator provided by digital holography greatly improves performance by tens of decibels when compared with the self-referencing interferometer

Metastable Ar(1s\u3csub\u3e5\u3c/sub\u3e) Density Dependence on Pressure and Argon-helium Mixture in a High Pressure Radio Frequency Dielectric Barrier Discharge

Simulations of an α-mode radio frequency dielectric barrier discharge are performed for varying mixtures of argon and helium at pressures ranging from 200 to 500 Torr using both zero and one-dimensional models. Metastable densities are analyzed as a function of argon-helium mixture and pressure to determine the optimal conditions, maximizing metastable density for use in an optically pumped rare gas laser. Argon fractions corresponding to the peak metastable densities are found to be pressure dependent, shifting from approximately 15% Ar in He at 200 Torr to 10% at 500 Torr. A decrease in metastable density is observed as pressure is increased due to a diminution in the reduced electric field and a quadratic increase in metastable loss rates through Ar*2 formation. A zero-dimensional effective direct current model of the dielectric barrier discharge is implemented, showing agreement with the trends predicted by the one-dimensional fluid model in the bulk plasma