We report results and analysis from a series of laser ablation experiments conducted to study high-temperature plutonium (Pu) spectroscopy and gas-phase oxidation. Time-resolved emission spectra were compared to a Pu I spectral model to infer plasma temperature. At later times in the laser-produced plasma evolution, temperatures are lower, and resonant emission bands indicative of molecular species are observed. We tentatively assign these bands to plutonium oxides (PuxOy).

Uranium and plutonium oxidize very rapidly in an oxygen-rich environment like air. Understanding the gas-phase actinide oxide molecular formation through plasma- and thermochemistry is very important for numerous fields including forensic analysis, environmental monitoring, debris analysis in a weapons detonation event, or reactor accident scenario, and actinide nucleation physics. There have been significant recent efforts to understand the chemical progression from U atoms to diatoms (UO) and polyatomic molecules (UxOy).1–3 However, emission analysis of high-temperature gas-phase oxidation of U and Pu and the corresponding plasma chemistry are very complex considering their very congested spectral features. In addition to these, the spectra may contain isotopic shifts and hyperfine structures if the sample is enriched.

Currently, actinide (eg. U, Pu, etc.) analysis at various facilities has been carried out using inductively-coupled plasma mass spectrometry (ICP-MS), inductively-coupled plasma optical emission spectroscopy (ICP-OES), and thermal ionization spectrometry and all these techniques need extensive, and hence time-consuming, laboratory-based sample preparation. Optical spectroscopic tools such as emission, absorption, and fluorescence have the potential to perform in-field, rapid, and non-contact actinide analysis. Laser-induced breakdown spectroscopy which employs emission spectroscopy of laser-produced plasma was previously used for U plasma analysis including isotopic detection. 1 However, the use of emission-based spectroscopic tools for actinide analysis is always challenging considering the extremely congested spectra of all actinides including U and Pu. For example, there exist nearly 100,000 transitions in the UV-VIS spectral range for uranium neutrals and singly ionized species. In addition to these, the emission spectroscopic tools are constrained by instrumental broadening which dictates the available spectral resolution. In this context, laser-induced fluorescence (LIF) and laser-absorption spectroscopy (LAS) are useful tools for obtaining high-resolution spectral features, linewidths, isotopic shifts and hyperfine structures. Although extensive studies have been carried out on optical spectroscopy of U, data on the spectroscopy of Pu is very limited.

Laser imaging techniques for probing the structure and temporal evolution of turbulent flows and flames are illustrated by simultaneous LIF imaging and 3-D velocity field measurements using tomographic PIV at a 10-kHz repetition rate. Rayleigh scattering measurements of transient flows at elevated pressure are demonstrated using a 100-kHz repetition rate pulse-burst laser.

Advances in the emerging field of coherent quantum feedback control (CQFC) have led to the development of new capabilities in the areas of quantum control and quantum engineering, with a particular impact on the theory and applications of quantum optical networks. We consider a CQFC network consisting of two coupled optical parametric oscillators (OPOs) and study the squeezing spectrum of its output field. The performance of this network as a squeezed-light source with desired spectral characteristics is optimized by searching over the space of model parameters with experimentally motivated bounds. We use the QNET package to model the network's dynamics and the PyGMO package of global optimization algorithms to maximize the degree of squeezing at a selected sideband frequency or the average degree of squeezing over a selected bandwidth. The use of global search methods is critical for identifying the best possible performance of the CQFC network, especially for squeezing at higher-frequency sidebands and higher bandwidths. The results demonstrate that the CQFC network of two coupled OPOs makes it possible to vary the squeezing spectrum, effectively utilize the available pump power, and overall significantly outperform a single OPO. Additionally, the Hessian eigenvalue analysis shows that the squeezing generation performance of the optimally operated CQFC network is robust to small variations of phase parameters.

We report an all-fiber passively Q-switched laser using a large mode area (LMA) Yb3+ -doped fiber claddingpumped at 915 nm and an unpumped single-mode (SM) Yb3+-doped fiber as the saturable absorber (SA). The saturable absorber SM fiber and LMA gain fiber were coupled with a fiber taper designed to match the fundamental spatial mode of the LMA fiber and the expanded LP01 mode of the single mode fiber. The amplified spontaneous (ASE) intensity propagating in the single mode SA saturates the absorption before the onset of gain depletion in the pumped fiber, switching the fiber cavity to a high Q-state and producing a pulse. Using this scheme we demonstrate a Q-switched all-fiber oscillator with 32 μJ 93 ns pulses at 1030 nm. The associated peak power is nearly two orders of magnitude larger than that reported in previous experimental studies using a single Yb+3 saturable absorber fiber. The pulse energy was amplified to 0.230 mJ using an Yb3+-doped cladding pumped fiber amplifier fusion spliced to the fiber oscillator, increasing the energy by eight fold while preserving the all-fiber architecture.

We report a passively Q-switched all-fiber laser using a large mode area Yb3+-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb3+-doped saturable absorber fiber. 60 μJ 80 ns pulses at 1030 nm are reported.

We report a passively Q-switched all-fiber laser using a large mode area (LMA) Yb3+-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb3+-doped fiber as the saturable absorber (SA). The saturable absorber and gain fibers were first coupled with a free-space telescope to better study the composite system, and then fusion spliced with fiber tapers to match the mode field diameters. ASE generated in the LMA gain fiber preferentially bleaches the SA fiber before depleting the gain, thereby causing the SA fiber to act as a passive saturable absorber. Using this scheme we first demonstrate a Q-switched oscillator with 40 mu J 79 ns pulses at 1026 nm using a free-space taper, and show that pulses can be generated from 1020 nm to 1040 nm. We scale the pulse energy to 0.40 mJ using an Yb3+-doped cladding pumped fiber amplifier. Experimental studies in which the saturable absorber length, pump times, and wavelengths are independently varied reveal the impact of these parameters on laser performance. Finally, we demonstrate 60 mu J 81 ns pulses at 1030 nm in an all fiber architecture using tapered mode field adaptors to match the mode filed diameters of the gain and SA fibers.

We report a passively Q-switched all-fiber laser using a large mode area (LMA) Yb(3+)-doped fiber cladding-pumped at 915 nm and an unpumped single-mode Yb(3+)-doped fiber as the saturable absorber (SA). The saturable absorber fiber and gain fiber were coupled with a free-space telescope to optimize the coupling efficiency between the disparate fibers, preferentially bleaching the SA fiber before gain depletion in the pumped fiber. Using this scheme we first demonstrate a Q-switched oscillator with 40 μJ 79 ns pulses at 1026 nm, and show that pulses can be generated from 1020 nm to 1040 nm. The associated peak power of the oscillator alone is more than two orders of magnitude larger than that reported in previous experimental studies using an Yb(3+)-doped fiber as a saturable absorber. We further demonstrate an amplified pulse energy of 0.4 mJ using an Yb(3+)-doped cladding pumped fiber amplifier. Experimental studies in which the saturable absorber length, pump times, and wavelengths are independently varied reveal the impact of these parameters on laser performance.

Ultraviolet (UV) Raman scattering with a 244-nm laser is evaluated for standoff detection of explosive compounds. The measured Raman scattering albedo is incorporated into a performance model that focused on standoff detection of trace levels of explosives. This model shows that detection at {approx}100 m would likely require tens of seconds, discouraging application at such ranges, and prohibiting search-mode detection, while leaving open the possibility of short-range point-and-stare detection. UV Raman spectra are also acquired for a number of anticipated background surfaces: tile, concrete, aluminum, cloth, and two different car paints (black and silver). While these spectra contained features in the same spectral range as those for TNT, we do not observe any spectra similar to that of TNT.

We describe a photofragment laser-induced fluorescence (PF-LIF) method that can be applied to the short-range-standoff detection of low-volatility organophosphonate chemical warfare agents (OP-CWAs) on surfaces. It operates by photofragmenting a surface-bound analyte and then actively interrogating a released phosphorous monoxide (PO) fragment using LIF. We demonstrate a single-pulse-pair (pump = 500 mu J @ 266 nm; probe = 20 mu J @ 248 nm) surface detection sensitivity of 30 mu g/cm(2) for the organophosphonate diisopropyl isothiocyanate phosphonate (DIPP) on aluminum and 210 mu g/cm(2) for the same analyte on a more porous concrete surface. By detecting the PO photofragment, the method indicates the presence of organophosphonates; however, we show that it also responds to other phosphorous-containing compounds. Because of its limited specificity, we believe that the method may have most immediate use as a mapping tool to rapidly identify "hotspots" of OP-CWAs. These would then be confirmed using a more specific tool. As one method of confirming the presence of OP-CWAs (and identifying the agent), we demonstrate that the probe beam can be used to acquire Raman-scattering spectra of the target area.