The need for patient-specific photodynamic therapy (PDT) in dermatologic and oncologic applications has triggered several studies that explore the utility of surrogate parameters as predictive reporters of treatment outcome. Although photosensitizer (PS) fluorescence, a widely used parameter, can be viewed as emission from several fluorescent states of the PS (e.g., minimally aggregated and monomeric), we suggest that singlet oxygen luminescence (SOL) indicates only the active PS component responsible for the PDT. Here, the ability of discrete PS fluorescence-based metrics (absolute and percent PS photobleaching and PS re-accumulation post-PDT) to predict the clinical phototoxic response (erythema) resulting from 5-aminolevulinic acid PDT was compared with discrete SOL (DSOL)-based metrics (DSOL counts pre-PDT and change in DSOL counts pre/post-PDT) in healthy human skin. Receiver operating characteristic curve (ROC) analyses demonstrated that absolute fluorescence photobleaching metric (AFPM) exhibited the highest area under the curve (AUC) of all tested parameters, including DSOL based metrics. The combination of dose-metrics did not yield better AUC than AFPM alone. Although sophisticated real-time SOL measurements may improve the clinical utility of SOL-based dosimetry, discrete PS fluorescence-based metrics are easy to implement, and our results suggest that AFPM may sufficiently predict the PDT outcomes and identify treatment nonresponders with high specificity in clinical contexts.
The chemistry of electric discharge driven oxygen iodine lasers (EOIL) has long been believed to have O2(a1▵g) as the
sole energy carrier for excitation of the lasing state I(2P1/2), and O(3P) as the primary quencher of this state. In many sets
of experimental measurements over a wide range of conditions, we have observed persistent evidence to the contrary. In
this paper, we examine comparisons of kinetics analysis and model predictions to experimental results from a supersonic
EOIL research reactor. This analysis leads to identification of important additional production and loss terms for the
lasing species, I(2P1/2), in the EOIL reaction mechanism. These mechanisms are also relevant to the catalytically
enhanced EOIL excitation mechanism. Exploitation of this chemistry can lead to substantial increases in gain and power
extraction efficiency in larger-scale EOIL systems. The analysis points to a significantly higher level of understanding of
this energetic chemical system, which can support application of advanced concepts in power scaling investigations.
We are investigating catalytically enhanced production of singlet oxygen, O2(a1▵g), observed by reaction of O2/He
discharge effluents over an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We have
previously reported a two-fold increase in the O2(a) yields by this process, and corresponding enhancement of I(2P1/2)
excitation and small-signal gain upon injection of I2 and NO2. In this paper we review observed I* excitation behavior and
correlations of the catalytically generated O2(a) with atomic oxygen over a large range of discharge-flow conditions to develop
a conceptual reaction mechanism for the phenomena. We describe a first-generation catalytic module for the PSI supersonic
MIDJet/EOIL reactor, and tests with this module for catalyst coating deposition and enhancement of the small-signal gain
observed in the supersonic flow. The results present compelling evidence for catalytic production of vibrationally excited
O2(X,v) and its participation in the I* excitation process. The observed catalytic effects could significantly benefit the
development of high-power electrically driven oxygen-iodine laser systems.
KEYWORDS: Oxygen, NOx, Data modeling, Chemistry, Chemical analysis, Microwave radiation, Absorption, iodine lasers, Chemical oxygen iodine lasers, Temperature metrology
The chemistry of electric discharge driven oxygen iodine lasers (EOIL) has long been believed to have O2(a1▵g) as the
sole energy carrier for excitation of the lasing state I(2P1/2), and O(3P) as the primary quencher of this state. In many sets
of experimental measurements over a wide range of conditions, we have observed persistent evidence to the contrary. In
this paper, we review our experimental data base in both room-temperature discharge-flow measurements and EOIL
reactor results, in comparison to model predictions and kinetics analysis, to identify the missing production and loss
terms in the EOIL reaction mechanism. The analysis points to a significantly higher level of understanding of this
energetic chemical system, which can support advanced concepts in power scaling investigations.
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.
Scaling of Electric Oxygen-Iodine Laser (EOIL) systems to higher powers requires extension of electric discharge
powers into the kW range and beyond, with high efficiency and singlet oxygen yield. This paper describes the
implementation of a moderate-power (1 to 5 kW) microwave discharge at 30 to 70 Torr pressure 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 is confined near the flow axis by a swirl flow. The discharge effluent,
containing active species including O2(a1▵), 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 monitors the absolute concentrations of O2(a), O(3P), O3, I2, I(2P3/2), I(2P1/2), small-signal
gain, and temperature in both the subsonic and supersonic flow streams. The experimental results include numerous
observations of positive gain and lasing in supersonic flow, and the scaling of gain with a variety of flow and
reaction rate conditions. The results are compared with kinetics modeling predictions to highlight key discrepancies
as well as areas of agreement. The observed gains are generally lower than the predicted values, due in part to
chemical kinetics effects and also due to mixing limitations specific to the reagent injection design. We discuss in
detail the observed effects related to O-atom chemistry, and their import for scaling the gain to higher levels. We
also will present initial beam quality measurements.
We are investigating catalytically enhanced production of singlet oxygen, O2(a1▵g), observed by reaction of O2/He
discharge effluents on an iodine oxide film surface in a microwave discharge-flow reactor at 320 K. We have previously
reported a two-fold increase in the O2(a) yields by this process, and corresponding enhancement of I(2P1/2) excitation and
small-signal gain upon injection of I2. In this paper we report further observations of the effects of elevated temperature up to
410 K, and correlations of the catalytically generated O2(a) with atomic oxygen over a large range of discharge-flow
conditions. We have applied a diffusion-limited reaction rate model to extrapolate the catalytic reaction rates to the highpressure,
fast-flow conditions of the subsonic plenum of a supersonic EOIL test reactor. Using the model and the flow reactor
results, we have designed and implemented a first-generation catalytic module for the PSI supersonic MIDJet/EOIL reactor.
We describe preliminary tests with this module for catalyst coating deposition and enhancement of the small-signal gain
observed in the supersonic flow. The observed catalytic effect could significantly benefit the development of high-power
electrically driven oxygen-iodine laser systems.
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.
Enhanced production of singlet oxygen, O2(a1Δg), was observed by reaction of O2/He discharge effluents on an iodine
oxide film surface in a microwave discharge flow reactor at 320 K. We observed a two-fold increase in the O2(a) yields in
excess of discharge-generated amounts for non-catalytic conditions. The iodine oxide surface appears to catalyze the
heterogeneous reaction to form O2(a) with high collision efficiency. Injection of molecular iodine into the catalytically
enriched active-oxygen flow resulted in excitation of the I(2P1/2) state approaching optical transparency at 1315 nm. Addition
of NO2 resulted in positive small-signal gain in the 320 K subsonic flow. The observed catalytic effect could significantly
benefit the development of electrically driven oxygen-iodine laser systems.
Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315 nm transition of atomic
iodine using the energy transferred to I(2P1/2) from O2(a1Δ) produced by both radio-frequency and microwave electric
discharges sustained in a dry air-He-NO gas mixture. Active oxygen and nitrogen species were observed downstream of
the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower
the temperature of the continuous gas flow. Gain of 0.0062 %/cm was obtained and the laser output power was 32 mW
in a supersonic flow cavity.
Photodynamic therapy (PDT) is a promising cancer treatment that involves optical excitation of photosensitizers that promote oxygen molecules to the metastable O2(a1) state (singlet oxygen). This species is believed to be responsible for the destruction of cancerous cells during PDT. We describe a fiber optic-coupled, pulsed diode laser-based diagnostic for singlet oxygen. We use both temporal and spectral filtering to enhance the detection of the weak O2(aX) emission near 1.27 µm. We present data that demonstrate real-time singlet oxygen production in tumor-laden rats with chlorin e6 and 5-aminolevulinic acid-induced protoporphyrin photosensitizers. We also observe a positive correlation between post-PDT treatment regression of the tumors and the relative amount of singlet oxygen measured. These results are promising for the development of the sensor as a real-time dosimeter for PDT.
Photodynamic therapy (PDT) is a viable treatment option for a wide range of applications, including oncology, dermatology, and ophthalmology. Singlet oxygen is believed to play a key role in the efficacy of PDT, and on-line monitoring of singlet oxygen during PDT could provide a methodology to establish and customize the treatment dose clinically. This work is the first report of monitoring singlet oxygen luminescence in vivo in human subjects during PDT, demonstrating the correlation of singlet oxygen levels during PDT with the post-PDT photobiological response.
Photodynamic therapy (PDT) is a promising cancer treatment. PDT uses the affinity of photosensitizers to be selectively retained in malignant tumors. When tumors, pretreated with the photosensitizer, are irradiated with visible light, a photochemical reaction occurs and tumor cells are destroyed. Oxygen molecules in the metastable singlet delta state O2(1) are believed to be the species that destroys cancerous cells during PDT. Monitoring singlet oxygen produced by PDT may lead to more precise and effective PDT treatments. Our approach uses a pulsed diode laser-based monitor with optical fibers and a fast data acquisition system to monitor singlet oxygen during PDT. We present results of in vitro singlet oxygen detection in solutions and in a rat prostate cancer cell line as well as PDT mechanism modeling.
Predictive modeling of the performance of EOIL laser systems must address the kinetics of the active oxygen flow,
including the production of O3 from recombination of O and O2, and the effects of NO as an additive to remove O and
promote O2(a) formation. This paper describes experimental measurements of the reaction kinetics for active-oxygen
flows generated by microwave discharge of O2/He mixtures at 3 to 10 torr. The concentrations of O2(a1Δ), O, and O3
were directly measured as functions of reaction time in a discharge-flow reactor. Both the O removal rate and the O3
production rate were observed to be significantly lower than expected from the widely accepted three-body
recombination mechanism for O3 production, indicating the existence of a previously unknown O3 dissociation reaction.
Addition of NO to the flow well downstream of the discharge resulted in readily detectable production of O2(a) in
addition to that generated by the discharge. The observed O2(a) production rates were remarkably insensitive to
variations in total pressure, O2 concentration, and NO concentration over the ranges investigated. The mechanism for
this O2(a) production remains to be identified, however it appears to involve a hitherto undetected, metastable, energetic
species produced in the active-oxygen flow.
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.
An analysis of the single point reproducibility of TD-THz based paint thickness measurements demonstrated a precision
of 130 nm, corresponding to 0.1% of the measured thickness. A detailed model of the anticipated TD-THz waveforms
from samples of varying thickness indicates that an intrinsic uncertainty of 0.09% is anticipated in the absence of
environmental fluctuations. Therefore, the influence of oscillations in the THz field associated with the initial reflection
does not adversely impact the ability to extract accurate paint thickness information, and the noise associated with these
oscillations could limit the measurement uncertainty of a calibrated instrument under optimum laboratory conditions. In
the case of a deployed sensor, we anticipate that the accuracy will be degraded by environmental fluctuations.
Laser oscillation at 1315 nm on the I(2P1/2) → I(2P3/2) transition of atomic iodine has been obtained by a near
resonant energy transfer from O2(a1&Dgr;) produced using a low-pressure oxygen/helium/nitric-oxide discharge. In the
electric discharge oxygen-iodine laser (ElectricOIL) the discharge production of atomic oxygen, ozone, and other
excited species adds levels of complexity to the singlet oxygen generator (SOG) kinetics which are not encountered
in a classic purely chemical O2(a1&Dgr;) generation system. The advanced model BLAZE-IV has been introduced in
order to study the energy-transfer laser system dynamics and kinetics. Levels of singlet oxygen, oxygen atoms and
ozone are measured experimentally and compared with calculations. The new BLAZE-IV model is in reasonable
agreement with O3, O2(b1&Sgr;), and O atom, and gas temperature measurements, but is under-predicting the increase in
O2(a1&Dgr;) concentration resulting from the presence of NO in the discharge. A key conclusion is that the removal of
oxygen atoms by NOX species leads to a significant increase in O2(a1&Dgr;) concentrations downstream of the discharge
in part via a recycling process, however there are still some important processes related to the NOX discharge
kinetics that are missing from the present modeling. Further, the removal of oxygen atoms dramatically inhibits the
production of ozone in the downstream kinetics.
Microelectromechanical systems (MEMS) offer a promising approach for creating compact, efficient chemical oxygen
iodine lasers. In this paper we report the demonstration and characterization of a chip-scale, MEMS-based singlet
oxygen generator, or microSOG. The microSOG is a batch-fabricated silicon chip that is micromachined to form
reactant inlets and distribution system, an array of microstructured packed bed reaction channels to ensure good mixing
between the BHP and the chlorine, a gas-liquid separator that removes liquid from the output stream by capillary effects,
integrated heat exchangers to remove the excess heat of reaction, and product outlets. The microSOG has successfully
generated singlet delta oxygen, and the resulting singlet delta concentrations were measured in a quartz test cell
downstream of the chip using absolutely-calibrated near-infrared emission measurements made by an InGaAs array
spectrometer. A kinetics analysis was used to determine the concentration at the chip's outlet from the concentration at
the measurement point. Singlet delta yield at the outlet was determined to be about 81% at 150 Torr plenum pressure
with a 25 sccm flow of chlorine. The corresponding output flow carries about 1.4 W of power at the chip's outlet.
The electric oxygen-iodine laser (EOIL) concept uses an electric discharge plasma to generate an effluent flow
containing singlet oxygen, O2(a1&Dgr;), and atomic oxygen, O, which react with I2 to excite the atomic iodine laser
transition at 1.315 &mgr;m. This chemically rich system has unique characteristics, whose understanding requires
systematic chemical kinetics investigation under carefully selected conditions to isolate the key reaction mechanisms.
We describe a series of reacting flow measurements on the reactions of discharge-excited active-O2 with I2, using a
comprehensive suite of optical emission and absorption diagnostics to monitor the absolute concentrations of O2(a1&Dgr;),
O2(b1summation), O(3P), O3, I2, I(2P3/2), I(2P1/2), small-signal gain, and temperature. These multispecies measurements
help to constrain the kinetics model of the system, and quantify the chemical loss mechanisms for I(2P1/2).
Generation of singlet oxygen metastables, O2(a1Δ), in an electric discharge plasma offers the potential for development of compact electric oxygen-iodine laser (EOIL) systems using a recyclable, all-gas-phase medium. The primary technical challenge for this concept is to develop a high-power, scalable electric discharge configuration that can produce high yields and flow rates of O2(a) to support I(2P1/2->2P3/2) lasing at high output power. This paper discusses the chemical kinetics of the generation of O2(a) and the excitation of I(2P1/2) in discharge-flow reactors using microwave discharges at low power, 40-120 W, and moderate power, 1-2 kW. The relatively high E/N of the microwave discharge, coupled with the dilution of O2 with Ar and/or He, leads to increased O2(a) production rates, resulting in O2(a) yields in the range 20-40%. At elevated power, the optimum O2(a) yield occurs at higher total flow rates, resulting in O2(a) flow rates as large as 1 mmole/s (~100 W of O2(a) in the flow) for 1 kW discharge power. We perform the reacting flow measurements using a comprehensive suite of optical emission and absorption diagnostics to monitor the absolute concentrations of O2(a), O2(b), O(3P), I2, I(2P3/2), I(2P1/2), small-signal gain, and temperature. These measurements constrain the kinetics model of the system, and reveal the existence of new chemical loss mechanisms related to atomic oxygen. The results for O2(a) production at 1 kW have intriguing implications for the scaling of EOIL systems to high power.
KEYWORDS: Energy transfer, Chemical oxygen iodine lasers, Semiconductor lasers, Chlorine, Chemistry, Diagnostics, iodine lasers, Absorption, Iodine, Chemical species
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.
Monitoring singlet molecular oxygen (1O2) produced by photodynamic therapy (PDT) can lead more precise and effective cancer treatment. Physical Sciences Inc. (PSI) has developed a singlet oxygen monitor based on a pulsed diode laser technology. In this paper, we present results of singlet oxygen detection in the solution phase and in a rat prostate cancer cell line, as well as PDT mechanism modeling. We describe an improved detection approach for singlet oxygen monitoring that employs a fiber-coupled optical set-up and fast data acquisition system.
In this paper we discuss several sensitive diagnostics that have specifically developed for application to COIL and other iodine laser concepts such as AGIL and DOIL. We briefly cover the history of some important diagnostics including recently-developed diode laser sensors for a variety of parameters including: water vapor concentration, singlet oxygen yield, small signal gain, and translational temperature. We also discuss new developments and extensions of prior capabilities including: an ultra-sensitive diagnostic for I2 dissociation, a new monitor for singlet oxygen yield, and a novel diode laser-based imaging system for simultaneous, multipoint spatial distributions of species concentration and temperature. Finally, we mention how these diagnostics have bee successfully applied to the emerging DOIL technology.
Recent studies of the iodine dissociation mechanism for COIL systems have prompted new investigations of the energy transfer kinetics of O2(b1Σ+). Additional motivation for these studies, and for investigation of the quenching of I* by O atoms, is derived from efforts to build non-chemical singlet oxygen generators. Discharge generators produce relatively high concentrations of O2(b) and O atoms. Dissociations of I2 by the reagent streams from these generators will follow different kinetic pathways than those that are most important when the flow from a chemical generator is used. To improve our understanding of conventional COIL systems, and gain insights concerning the dissociation kinetics that will be relevant for discharge driven COIL devices we have examined the quenching of O2(b) and O2(a) by I2, and the deactivation of I* by atomic oxygen. The primary findings are: (1) Quenching of O2(b) by I2 is fast (5.8x10-11 cm3 s-1) with a branching fraction of 0.4 for the channel O2(b)+I2→O2(a)+I2. (2) The quantum yield for dissociation of I2 by O2(b) is relatively high (>0.5) and (3) The upper bound for the rate constant for quenching of I* by O atoms is k<2x10-12 cm3 s-1.
In this paper we discuss the application of sensitive, non-intrusive diagnostic techniques to characterize species in the flow that are critical for chemical oxygen iodine laser (COIL) devices and the electric discharge oxygen iodine laser (DOIL) concept. The key diagnostics include chemiluminescence to detect O2(a,b) and I(2P1/2) and tunable diode laser absorption measurements of I* and temperature. We have characterized variations in O and O2(a) yields with discharge power and oxygen mole fraction. We observe O2(a) yields to increase dramatically with decreasing oxygen mole fraction. We also discuss the application of a novel imaging diagnostic to obtain 2-D images of species concentrations and temperature.
In this paper we present results from a spectroscopic and kinetic study of the reaction sequence of NCl3 + H that produces NCl(a1Δ). Using sensitive optical emission diagnostics, we have observed both NCl(a) and (b) 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 2P1/2 → 2P3/2 transition at 1.315 μm. We also used a sensitive diode laser spectrometer to probe the I atom transition and observed transfer of population from ground state (2P3/2) to the excited state (2P1/2) with a concomitant reduction in the measured absorption. We interpret this observation as an approach to optical transparency.
KEYWORDS: Chemical species, Absorption, Oxygen, Energy transfer, Data modeling, Dye lasers, Laser systems engineering, Laser induced fluorescence, Photodiodes, iodine lasers
Dissociation of I2 by O2(b) is a process that is potentially important in iodine laser systems that are driven by discharge and chemical singlet oxygen generators. Recent work on the quenching of singlet oxygen by I2 suggests that the accepted upper bound of <0.2 for the branching fraction for O2(b) + I2 → O2(X) + 2I may be too low. New measurements of the branching fraction have been carried out using transient diode laser absorption technique to monitor I atom formation. The results indicate that the branching fraction may be as high as 0.6.
In this paper we discuss vibrational to electronic energy transfer as a potential method for producing a population inversion in atomic iodine. We discuss the background of this approach and a novel, high-flux F atom source integrated into a small scale supersonic reactor. We present data for energy transfer from HF(v) and H2(v) to the I atom manifold. Using a sensitive diode laser diagnostic we have probed the ground state manifold atomic iodine and observed that the absorption on the I atom line could be reduced to an immeasureably low value. We also describe a novel, diode laser based imaging diagnostic that will have important applications in future chemical or electrical laser development.
This paper discusses methods, using non-intrusive diagnostic techniques, to characterize the detailed dynamics of I* gain and O2(a1Δ) yield on a laboratory microwave-discharge flow reactor, for conditions relevant to the electrically driven COIL concept. The key diagnostics include tunable diode laser absorption measurements of I* small-signal gain and temperature, high-precision absorption measurements of reactor I2 concentrations, absolute and relative spectral emission measurements of O2(a1Δ) and I* concentrations, and air-afterglgow determinations of O concentrations. We have characterized variations in O and O2(a) yields with discharge power and oxygen mole fraction. We observe O2(a) yields to increase dramatically with decreasing oxygen mole fraction. We have also demonstrated a spectral fitting analysis technique capable of quantifying the presence of vibrationally excited O2(a,v). This combined suite of diagnostics offers a comprehensive approach to performance characterization for electrically driven COIL concepts.
In this paper we present results from experiments to develop a real-time, optical monitor for singlet molecular oxygen produced during photodynamic therapy. Using a pulsed diode laser and a sensitive photomultiplier tube, we have obtained signals from singlet oxygen during and following pulsed laser excitation. Several photosensitizers were used, and we obtained strong signals even in the presence of protein laden environments. Values obtained for the lifetimes of the singlet oxygen state and the photosensitizer triplet state are compared to literature values.
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