Physical Sciences Inc. (PSI) is developing a sensitive, rugged, person-portable, and safe instrument for the quick analysis of metals in jet fuels in fuel depots and transfer stations. The instrument fills a needed role for easy and affordable analysis of catalyzing metals content in fuel batches before they are used in, or shipped to, critical engines such as military aviation platforms. The instrument targets a panel of most likely and problematic metals that are often found in kerosene-based fuels, both refined and synthetic. The cause for concern lies in the potential for many metals, even at part per billion (ppb) concentrations, to catalyze rapid degradation of fuel performance, especially at elevated storage temperatures. The laser-induced breakdown spectroscopy (LIBS) technology development reported here has demonstrated a robust and viable measurement system for multiple contaminants of importance to military (and commercial) fuel distribution. Estimated detection limits for all elements of interest, save phosphorus, are at sub-ppm levels. Signal normalization with an added internal reference has demonstrated an adjusted concentration measurement accuracy <95% and useful operation of the method near the noise floor of the instrument. The accomplishments are strong indicators for commercial potential for the technology as a useful tool in the intended fuel monitoring application, as well as other industrial sample analysis needs.
The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkaliexciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms at number densities in excess of 1012 cm-3 in a continuous-wave electric discharge in flowing gas mixtures with helium diluent. This paper describes continuing investigations of the use of linear microwave micro-discharge arrays to generate metastable argon atoms, Ar (4s, 1s5) (Paschen notation), in flowing mixtures of Ar and He at atmospheric and reduced pressures, in optical pump-and-probe experiments for laser development. We describe initial experimental investigations of several key aspects of concepts for scaling to higher output powers. This includes initial data on the dependence of argon metastable production and optically pumped gain on micro-discharge gap size, pressure, and discharge power. We have observed clearly measureable gain at pressures down to 85 Torr. We have also developed an overlapping dual-array micro-discharge-flow configuration, to conduct detailed measurements of Ar(1s5) production and loss. Spatially resolved measurements of Ar(1s5) distributions in discharge-flow provide preliminary indications of 20-50 μs collisional lifetimes of argon metastable atoms after they exit the active microplasma. This information is relevant to modeling the recycling of Ar(1s5) in the optically pumped laser, and to the scaling architecture of the optically pumped system. The dual-discharge investigations demonstrate the potential for volume scaling of the active gain medium in a simple multi-discharge, flow-through configuration.
The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkali-exciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at atmospheric pressure. This paper describes initial investigations of the use of linear microwave micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure in optical pump-and-probe experiments for laser development. Power requirements to ignite and sustain the plasma at 1 atm are low, <30 W. We report on the laser excitation dynamics of argon metastables, Ar (4s, 1s5) (Paschen notation), generated in flowing mixtures of Ar and He at 1 atm. Tunable diode laser absorption measurements indicate Ar(1s5) concentrations near 3 × 1012 cm-3 at 1 atm. The metastables are optically pumped by absorption of a focused beam from a continuous-wave Ti:S laser, and spectrally selected fluorescence is observed with an InGaAs camera and an InGaAs array spectrometer. We observe the optical excitation of the 1s5→2p9 transition at 811.5 nm and the corresponding laser-induced fluorescence on the 2p10→1s5 transition at 912.3 nm; the 2p10 state is efficiently populated by collisional energy transfer from 2p9. Using tunable diode laser absorption/gain spectroscopy, we observe small-signal gains of ~1 cm-1 over a 1.9 cm path. We also observe stable, continuous-wave laser oscillation at 912.3 nm, with preliminary optical efficiency ~55%. These results are consistent with efficient collisional coupling within the Ar(4s) manifold.
Diode-pumped alkali laser (DPAL) technology offers a means of achieving high-energy gas laser output through optical pumping of the D-lines of Cs, Rb, and K. The exciplex effect, based on weak attractive forces between alkali atoms and polarizable rare gas atoms (Ar, Kr, Xe), provides an alternative approach via broadband excitation of exciplex precursors (XPAL). In XPAL configurations, we have observed multi-quantum excitation within the alkali manifolds which result in infrared emission lines between 1 and 4 μm. The observed excited states include the 42FJ states of both Cs and Rb, which are well above the two-photon energy of the excitation laser in each case. We have observed fluorescence from multi-quantum states for excitation wavelengths throughout the exciplex absorption bands of Cs-Ar, Cs-Kr, and Cs-Xe. The intensity scaling is roughly first-order or less in both pump power and alkali concentration, suggesting a collisional energy pooling excitation mechanism. Collisional up-pumping appears to present a parasitic loss term for optically pumped atomic systems at high intensities, however there may also be excitation of other lasing transitions at infrared wavelengths.
In this paper we present experimental results on several features of optically excited alkali atoms. We describe small
signal gain measurements including spatially-resolved gain in atomic Cs. We discuss observations of numerous near- to
mid-IR emissions from states that are higher in energy than the pump beam photons. Finally we outline a measurement
scheme to determine the threshold pump intensities for two types of optically excited alkali lasers.
In this paper we describe a platform for small signal gain measurements for alkali atom laser systems based on the
DPAL excitation method. We present initial results that clearly show the transition from absorption on the alkali atom D1
lines in Cs and Rb to optical transparency and positive gain. The achievement of optical gain is critically dependent upon
alkali cell conditions and collision partners. We also present the first spatially resolved gain measurements in a DPAL
system. The small signal gain methods described will be valuable tools for power scaling of these laser systems.
In this paper we describe several diagnostics that we have developed to assist the development of high power gas
phase lasers including COIL, EOIL, and DPAL. For COIL we discuss systems that provide sensitive measurements
of O2(a), small signal gain, iodine dissociation, and temperature. These are key operational parameters within COIL,
and these diagnostics have been used world-wide to gain a better understanding of this laser system. Recently, we
have developed and integrated a similar suite of diagnostics for scaling the EOIL system and will provide examples
of current studies. We are also developing diagnostics for the emerging DPAL laser. These include monitors for
small signal gain that will provide both a more fundamental understanding of the kinetics of DPAL and valuable
data for advanced resonator design. We will stress the application of these diagnostics to realistic laser systems.
Photodynamic therapy (PDT) is a light activated chemotherapy that is dependent on three parameters: photosensitizer
(PS) concentration; oxygen concentration; and light dosage. Due to highly variable treatment response, the development
of an accurate dosimeter to optimize PDT treatment outcome is an important requirement for practical applications.
Singlet oxygen is an active species in PDT, and we are developing two instruments, an ultra-sensitive singlet oxygen
point sensor and a 2D imager, with the goal of a real-time dosimeter for PDT researchers. The 2D imaging system can
visualize spatial maps of both the singlet oxygen production and the location of the PS in a tumor during PDT. We have
detected the production of singlet oxygen during PDT treatments with both in-vitro and in-vivo studies. Effects of
photobleaching have also been observed. These results are promising for the development of the sensor as a real-time
dosimeter for PDT which would be a valuable tool for PDT research and could lead to more effective treatment outcome.
We summarize recent results in this paper.
We describe a series of measurements of absorption and laser induced fluorescence on cells that contained cesium and
rubidium and a rare gas: He, Ar, Kr, or Xe. These studies showed strong blue wing absorption to the short wavelength
side of the alkali atom D2 lines due to collisionally formed Cs- or Rb-rare gas excimers. We also have observed an
efficient two photon excitation of higher lying states in Cs and Rb that produces both intense blue emission and IR
atomic emission in the 1.3 to 3.8 μm spectral region.
In this paper we describe the development and testing of instruments to measure singlet molecular oxygen produced by
the photodynamic process. Singlet oxygen is an active species in photodynamic therapy, and we are developing two
instruments for PDT researchers with the goal of a real-time dosimeter for singlet oxygen. We discuss both an ultrasensitive
point sensor, and an imaging system that provides simultaneous 2D maps of the photosensitizer fluorescence
and the singlet oxygen emission. Results of in vitro tests to characterize the sensors and preliminary in vivo results are
presented.
We describe a series of measurements of absorption and laser induced fluorescence using cells that contained cesium and
rubidium and krypton as a bath gas. These studies showed strong blue wing absorption to the short wavelength side of
the alkali atom D2 lines due to collisionally formed Cs-Kr or Rb-Kr excimers. These studies indicate that these species
may be appropriate candidates for optically excited Rb and Cs atomic lasers.
Scaling of EOIL systems to higher powers requires extension of electric discharge powers into the kW range and
beyond with high efficiency and singlet oxygen yield. We have previously demonstrated a high-power microwave
discharge approach capable of generating singlet oxygen yields of ~25% at ~50 torr pressure and 1 kW power. This
paper describes the implementation of this method in a supersonic flow reactor designed for systematic investigations of
the scaling of gain and lasing with power and flow conditions. The 2450 MHz microwave discharge, 1 to 5 kW, is
confined near the flow axis by a swirl flow. The discharge effluent, containing active species including O2(a1Δg, b1Σg+),
O(3P), and O3, passes through a 2-D flow duct equipped with a supersonic nozzle and cavity. I2 is injected upstream of
the supersonic nozzle. The apparatus is water-cooled, and is modular to permit a variety of inlet, nozzle, and optical
configurations. A comprehensive suite of optical emission and absorption diagnostics is used to monitor the absolute
concentrations of O2(a), O2(b), O(3P), O3, I2, I(2P3/2), I(2P1/2), small-signal gain, and temperature in both the subsonic and
supersonic flow streams. We discuss initial measurements of singlet oxygen and I* excitation kinetics at 1 kW power.
The paper presents results of singlet delta oxygen yield (SDO) measurements in a high-pressure, non-self-sustained discharge and small signal gain measurements on the 1315 nm iodine atom transition in the M=3 supersonic cavity downstream of the discharge. The results demonstrate operation of a stable pulser-sustainer discharge in O2-He flows at pressures of up to 120 torr and discharge powers of up to 2.2 kW. The reduced electric field in the DC sustainer discharge ranges from 6 to 12 Td. SDO yield in the discharge is up to 5.0-5.7% at the discharge temperatures of 400-420 K. The results suggest that SDO yield exceeds the gain threshold yield at the M=3 cavity temperature by up to a factor of three, which is confirmed by gain measurements. The highest gain measured in the supersonic cavity is 0.01%/cm.
KEYWORDS: Chemical species, Iodine, Absorption, iodine lasers, Diagnostics, Chemistry, Chlorine, Semiconductor lasers, Chemical oxygen iodine lasers, Energy transfer
We discuss experimental results from spectroscopic and kinetic investigations of the reaction sequence starting with
NCI3 + H. Through a series of abstraction reactions, NCI (a1Δ) is produced. We have used sensitive optical emission
diagnostics and have observed both [NCI(a1Δ)]and [NCI(b1Σ)] produced by this reaction. Upon addition of HI to
the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(2P1/2) state, and we
observed strong emission from the I atom 2P 1/2 -> 2P3/2 transition at 1.315 μm. With a tunable diode laser we probed
the I atom transition and observed significant transfer of population from ground state (2P3/2) to the excited state
(2P1/2) and have observed optical transparency within the iodine atom energy level manifold.
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