Modeling of static K and Rb diode pumped alkali lasers (DPAL) and ion-electron recombination processes in these lasers is reported. The cases of He/CH4 and pure He buffer gases are investigated and the output power and optical efficiency calculated for various pump powers, mole fractions of methane, buffer gas pressures and flow velocities. The model considers the processes of excitation of high levels of K and Rb, ionization, ion-electron recombination and heating of electrons which affect the diffusion coefficient of K and Rb ions. It explains the experimentally observed sharp increase in power in static K DPAL caused by the addition of a few percent of methane to He buffer gas and its decrease with further increase in the methane percentage [B.V. Zhdanov et al, Opt. Exp. 25, 30793 (2017)]. The predictions of the model for different He/CH4 mixtures are presented and verified by comparing them with experimental results for K flowing-gas DPAL [A. J. Wallerstein, Ph.D. dissertation (Air Force Institute of Technology, 2018)] and with the calculated results obtained using a simplified three-level model based on one-dimensional gas dynamics approach reported by A. Gavrielides et al [J. Opt. Soc. Am. B 35, 2202 (2018)]. Calculations of potential energy curves of the 2 K + and 2 Rb + molecular ions and of the diabatic 1ε+, 3ε+, 1Δ, 3Δ, 1 Π 3Π, 1Φ and 3Φ valence states of 2 K + and 2 Rb + that provide the routes for dissociative recombination (DR of the ions are performed. These curves are required for subsequent calculations of DR rate constants. The excited states of K atoms produced by DR are 42P and 52P. Most of the Rb atoms produced by DR are in the 62P excited state. This conclusion contradicts the kinetic scheme for K and Rb DPAL proposed elsewhere, and thus the kinetic schemes of these DPALs should be modified according to the present results.
A comprehensive three-dimensional modeling of static K diode pumped alkali laser (DPAL) and flowing-gas K and Rb DPALs is carried out. The cases of He/CH4 and pure He buffer gases are investigated and the output power and optical efficiency calculated for various pump powers, mole fractions of methane, buffer gas pressures and flow velocities. The model considers the processes of excitation of high levels of K and Rb, ionization, ion-electron recombination and heating of electrons which affect the diffusion coefficient of K and Rb ions. It explains the experimentally observed sharp increase in power in static K DPAL caused by the addition of a few percent of methane to He buffer gas and its decrease with further increase in the methane percentage [B.V. Zhdanov et al, Opt. Exp. 25, 30793 (2017)]. The predictions of the model for different He/CH4 mixtures are presented and verified by comparing them with experimental results for K flowing-gas DPAL [A. J. Wallerstein, Ph.D. dissertation (Air Force Institute of Technology, 2018)] and with the calculated results obtained using a simplified three-level model based on one-dimensional gas dynamics approach reported by A. Gavrielides et al [J. Opt. Soc. Am. B 35, 2202 (2018)].
We report on recent experimental and theoretical studies of cesium laser, where we focused on the beam propagation factor M2 in flowing-gas Cs DPALs with stable optical resonators and of its dependence on the resonator geometry. The measured results were modeled by multi-transverse-mode model [Auslender et al., Opt. Express 25, 19767 (2017)]. Conditions for substantial improvement of the output laser beam quality, reducing M2 to close to unity, are found. In particular we show how changing the length of the resonator, and/or the radius of curvature of the high reflection mirror, leaving all other parameters of the laser unchanged, makes it possible to control the beam quality.
KEYWORDS: Cesium, 3D modeling, Continuous wave operation, Semiconductor lasers, Temperature metrology, Diodes, Gas lasers, Mirrors, Chemical species, Reflectivity
We report on the results of ongoing work in our lab on flowing-gas Cs DPAL. Some of the results have been already reported [Yacoby et al, Opt. Express 26, 17814 (2018)] but we briefly describe them here again to give a full picture of the work. Experimental and theoretical study of continuous wave Cs DPAL with gas circulation (He and CH4), flow velocities of 1-4.5 m/s and pump powers of 30-65 W, is reported. For the theoretical part of the study we used a 3D computational fluid dynamics model, solving the gas dynamics and kinetics equations relevant to flowing-gas laser operation. Maximum CW output power of 24 W and slope efficiency of 48% were obtained. The experimental and theoretical dependence of the lasing power on the flow velocity are in good agreement. The gas temperature rise in the laser cell was measured. The lasing power was not affected by the flow velocity at this range of pump powers and flow velocities due to the fact that the gas temperature rise was only several degrees. It was estimated – using a “fitting” method – that the quenching cross-section of the excited levels of Cs to the ground state is ~ 0.05 Å2 .
The beam quality and efficiency of diode-pumped alkali lasers are strongly dependent on parameters such as the pump beam geometry, the resonator configuration, the gain length and other features. In the present work we studied experimentally and theoretically the dependence of some of these parameters on the laser performance. An optical model of multi-transverse mode operation of alkali vapor lasers [Auslender et al, Opt. Express 25, 19767 (2017)], modified for the current experiments, is applied to the experimental results. The values of the laser power and M2 predicted by the model are in good agreement with the experimental results for different shapes and powers of the pump beam.
Experimental and theoretical parametric study of static and flowing-gas diode-pumped Cs lasers is reported. In the static case dependence of the output laser power and the beam quality factor M2 on the power and spatial shape of the pump beam is studied. An optical model of multi-transverse mode operation of alkali vapor lasers [Auslender et al, Opt. Express 25, 19767 (2017)] is applied to the experimental results. The values of the laser power and M2 predicted by the model are in good agreement with the experimental results for different shapes and powers of the pump beam We also report, briefly, on our recently published work [Yacoby et al, Opt. Express 26, 17814 (2018)] on flowing-gas Cs-DPAL where the output power and gas temperature rise in the laser cell at different flow velocities were studied and the results analyzed by our three-dimensional computational fluid-dynamics) model.
Comprehensive analysis of the performance and beam quality of subsonic flowing-gas K diode-pumped alkali lasers (DPALs) with different pumping geometries, using 3D computational fluid dynamics model, is reported. The model is first applied to a K DPAL with transverse pumping and parameters similar to those of the 1.5 kW K DPAL [Pitz et al, Proc. SPIE 9729, 972902 (2016)] and the calculated results are in satisfactory agreement with the measurements. To study the possibility of scaling up the K DPAL the model is then applied to 100-kW class device with transverse and end pumping geometry. Dependence of the output power on the flow velocity and the pumping geometry is studied. Comparison between end and transverse pumping schemes shows that the output power is almost unaffected by the pumping geometry. However, the spatial intensity distribution of the output laser beam depends on the pumping geometry: it is uniform for the end pumping, whereas for the transverse pumping it is strongly non-uniform at high gas temperature (corresponding to large density of K atoms), becoming more uniform with temperature reduction. The model is applied to evaluation of the beam quality of flowing-gas K DPALs which strongly depends on the refractive index distribution in the gain medium. The beam divergence and the width of the intensity profile in the far field for the end pumping appear to be much smaller than for the transverse pumping. Wave front corrections of the transversely pumped device using cylindrical lens results in substantial reduction of the laser beam divergence and improvement of its quality which becomes comparable with that of the end pumped laser.
In the present paper we use a simple optical model to describe multi-transverse mode operation of alkali lasers. The model is based on calculations of the pump and laser beam intensities in the gain medium, where the laser beam intensity is a linear combination of the azimuthally-symmetric Laguerre-Gaussian modes. The model was applied to optically pumped cesium vapor laser studied experimentally and theoretically previously [Cohen, T., Lebiush, E., Auslender, I., Barmashenko B.D., and Rosenwaks, S., Opt. Exp. 24, 14374 (2016)]. It was found in our calculations that for low pump power and small pump beam radii, only fundamental lasing mode oscillates, just as shown experimentally in this study. However, for higher pump powers and larger pump beam diameters, several transverse modes participate in oscillation. The number and intensities of the oscillating modes as a function of the pump beam power and radius are found. In order to check the validity of the model, it was applied to pulsed static Cs DPAL [Zhdanov, B. et al, Electron. Lett. 44, 582(2008)] with the pump beam radius much larger than that of the fundamental laser mode and constant gas temperature. The model predicts linear dependence of the laser power on the pump power, the values of the former being in agreement with the experimental results.
The pump-to-laser beam overlap and the cell length of static diode-pumped Cs lasers are crucial parameters for optimization of these lasers. In a previous publication we modeled the influence of the pump-to-laser beam overlap on the performance of Ti:Sapphire pumped cesium vapor laser (T. Cohen, E. Lebiush, I. Auslender, B.D. Barmashenko and S. Rosenwaks, Opt. Exp. 24, 14374 (2016)). In the present paper we report on experiments and modeling in progress on diode pumped cesium vapor laser.
Analysis of beam propagation, kinetic and fluid dynamic processes in Cs diode pumped alkali lasers (DPALs), using wave optics model and gasdynamic code, is reported. The analysis is based on a three-dimensional, time-dependent computational fluid dynamics (3D CFD) model. The Navier-Stokes equations for momentum, heat and mass transfer are solved by a commercial Ansys FLUENT solver based on the finite volume discretization technique. The CFD code which solves the gas conservation equations includes effects of natural convection and temperature diffusion of the species in the DPAL mixture. The DPAL kinetic processes in the Cs/He/C2H6 gas mixture dealt with in this paper involve the three lowest energy levels of Cs, (1) 62S1/2, (2) 62P1/2 and (3) 62P3/2. The kinetic processes include absorption due to the 1→3 D2 transition followed by relaxation the 3 to 2 fine structure levels and stimulated emission due to the 2→1 D1 transition. Collisional quenching of levels 2 and 3 and spontaneous emission from these levels are also considered. The gas flow conservation equations are coupled to fast-Fourier-transform algorithm for transverse mode propagation to obtain a solution of the scalar paraxial propagation equation for the laser beam. The wave propagation equation is solved by the split-step beam propagation method where the gain and refractive index in the DPAL medium affect the wave amplitude and phase. Using the CFD and beam propagation models, the gas flow pattern and spatial distributions of the pump and laser intensities in the resonator were calculated for end-pumped Cs DPAL. The laser power, DPAL medium temperature and the laser beam quality were calculated as a function of pump power. The results of the theoretical model for laser power were compared to experimental results of Cs DPAL.
Scaling-up flowing-gas diode pumped alkali lasers (DPALs) to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. We examined the influence of the flow velocity and Mach number M on the maximum achievable power of subsonic and supersonic lasers. For Cs DPAL devices with M = 0.2 - 3 the output power increases with increasing M by only ~20%, implying that supersonic operation mode has only small advantage over subsonic. In contrast, the power achievable in K DPALs strongly depends on M. The output power increases by ~100% when M increases from 0.2 to 4, showing a considerable advantage of supersonic device over subsonic. The reason for the increase of the power with M in both Cs and K DPALs is the decrease of the temperature due to the gas expansion in the flow system. However, the power increase for K lasers is much larger than for the Cs devices mainly due to the much smaller fine-structure splitting of the 2P states (~58 cm-1 for K and ~554 cm-1 for Cs), which results in a much stronger effect of the temperature decrease in K DPALs. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry. However, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.
We present the results of an experimental study of Ti:Sapphire pumped Cs laser and theoretical modeling of these results, where we focused on the influence of the pump-to-laser beam overlap, a crucial parameter for optimizing the output laser power. The dependence of the output laser power on the incident pump power was found for varying pump beam cross-section widths and for a constant laser beam. Maximum laser power > 370 mW with an optical-to-optical efficiency of 43% and slope efficiency ~55% was obtained. Non monotonic dependence of the laser power and threshold power on the pump beam radius (at a given pump power) was observed with a maximum laser power and minimum threshold power achieved at the ratio ~0.7 between the optimal pump beam and laser beam radius. A simple optical model of the laser, where Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams were assumed, was compared to the experiments. Good agreement was obtained between the measured and calculated dependence of the laser power on the incident pump power at different pump beam radii and of the laser power, threshold power and optimal temperature on the pump beam radius. The model does not use empirical parameters such as mode overlap efficiency but rather the pump and laser beam spatial shapes as input parameters. This model can be applied to different optically pumped alkali lasers with arbitrary spatial distributions of the pump and laser beam widths.
We report on the results of an experimental study of Ti:Sapphire pumped Cs laser and theoretical modeling of these
results, where we focused on the influence of the pump-to-laser beam overlap, a crucial parameter for optimizing the
output laser power. Non monotonic dependence of the laser power (optimized over the temperature) on the pump beam
radius was observed with a maximum achieved at the ratio ~ 0.7 between the pump and laser beam radii. The optimal
temperature decreased with increasing pump beam radius. Maximum laser power > 370 mW with an optical-to-optical
efficiency of 43% and slope efficiency ~ 55% was obtained. A simple optical model of the laser, where Gaussian spatial
shapes of the pump and laser intensities in any cross section of the beams were assumed, was compared to the
experiments. Good agreement was obtained between the measured and calculated dependence of the laser power on the
pump power at different pump beam radii and also of the laser power, threshold pump power and optimal temperature on
the pump beam radius. The model does not use empirical parameters such as mode overlap efficiency but rather the
pump and laser beam spatial shapes as input parameters. The present results combined with results of the application of
the model to K DPAL and Ti:Sapphire pumped Cs laser, indicate that the model can describe the operation of different
optically pumped alkali lasers with arbitrary spatial distributions of the pump and laser beam widths.
Modeling of static and flowing-gas subsonic, transonic and supersonic Cs and K Ti:Sapphire and diode pumped alkali lasers (DPALs) is reported. A simple optical model applied to the static K and Cs lasers shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. The model reproduces the observed threshold pump power in K DPAL which is much higher than that predicted by standard models of the DPAL. Scaling up flowing-gas DPALs to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. The performance of subsonic and, in particular, supersonic DPALs is compared with that of transonic, where supersonic nozzle and diffuser are spared and high power mechanical pump (needed for recovery of the gas total pressure which strongly drops in the diffuser), is not required for continuous closed cycle operation. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry, however, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.
We report on a model of highly efficient static, pulsed K DPAL [Zhdanov et al, Optics Express 22, 17266 (2014)], where
Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams are assumed. The model
shows good agreement between the calculated and measured dependence of the laser power on the incident pump power.
In particular, the model reproduces the observed threshold pump power, 22 W (corresponding to pump intensity of 4
kW/cm2), which is much higher than that predicted by the standard semi-analytical models of the DPAL. The reason for
the large values of the threshold power is that the volume occupied by the excited K atoms contributing to the
spontaneous emission is much larger than the volumes of the pump and laser beams in the laser cell, resulting in very
large energy losses due to the spontaneous emission. To reduce the adverse effect of the high threshold power, high
pump power is needed, and therefore gas flow with high gas velocity to avoid heating the gas has to be applied. Thus, for
obtaining high power, highly efficient K DPAL, subsonic or supersonic flowing-gas device is needed.
An analysis of radiation, kinetic and fluid dynamic processes in diode pumped alkali lasers (DPALs) is reported. The
analysis is based on a three-dimensional, time-dependent computational fluid dynamics (3D CFD) model. The CFD code
which solves the gas conservation equations includes effects of natural convection and temperature diffusion of the species
in the DPAL mixture. The gas flow conservation equations are coupled to the equations for DPAL kinetics and to the
Beer-Lambert equations for pump and laser beams propagation. The DPAL kinetic processes in the Cs/CH4 (K/He) gas
mixtures considered involve the three low energy levels, (1) n2S1/2, (2) n2P3/2 and (3) n2P1/2 (where n=4,6 for K and Cs,
respectively), three excited alkali states and two alkali ionic states. Using the CFD model, the gas flow pattern and spatial
distributions of the pump and laser intensities in the resonator were calculated for end-pumped CW and pulsed Cs and K
DPALs. The DPAL power and medium temperature were calculated as a function of pump power and pump pulse duration.
The CFD model results were compared to experimental results of Cs and K DPALs.
Three-dimensional computational fluid dynamics (3D CFD) modeling of subsonic (Mach number M ~ 0.2) and transonic
(M ~ 0.9) diode pumped alkali lasers (DPALs), taking into account fluid dynamics and kinetic processes in the lasing
medium is reported. The performance of these lasers is compared with that of supersonic (M ~ 2.7 for Cs and M ~ 2.4 for
K) DPALs. The motivation for this study stems from the fact that subsonic and transonic DPALs require much simpler
hardware than supersonic ones where supersonic nozzle, diffuser and high power mechanical pump (due to a drop in the
gas total pressure in the nozzle) are required for continuous closed cycle operation.
For Cs DPALs with 5 x 5 cm2 flow cross section pumped by large cross section (5 x 2 cm2) beam the maximum
achievable power of supersonic devices is higher than that of the transonic and subsonic devices by only ~ 3% and ~
10%, respectively. Thus in this case the supersonic operation mode has no substantial advantage over the transonic one.
The main processes limiting the power of Cs supersonic DPALs are saturation of the D2 transition and large ~ 60%
losses of alkali atoms due to ionization, whereas the influence of gas heating is negligible.
For K transonic DPALs both the gas heating and ionization effects are shown to be unimportant. The maximum values of
the power are higher than those in Cs transonic laser by ~ 11%. The power achieved in the supersonic and transonic K
DPAL is higher than for the subsonic version, with the same resonator and K density at the inlet, by ~ 84% and ~ 27%,
respectively, showing a considerable advantaged of the supersonic device over the transonic one. For pumping by
rectangular beams of the same (5 x 2 cm2) cross section, comparison between end-pumping - where the laser beam and
pump beam both propagate at along the same axis, and transverse-pumping - where they propagate perpendicularly to
each other, shows that the output power and optical-to-optical efficiency are not affected by the pump geometry.
However, the output laser beam in the case of end-pumped DPALs has a homogeneous spatial intensity distribution in
the beam cross section, whereas for transverse-pumped DPALs the intensity varies significantly along the pumping axis
(perpendicular to the resonator optical axis) and hence is strongly inhomogeneous in the laser beam cross section. Thus,
higher brightness and better beam quality in the far field is achieved for the end-pumping geometry. Optimization of the
resonator geometry for minimal gas temperature rise and minimal intra-resonator intensity (corresponds to a low
ionization rate) is also reported.
We report on recent progress on our three-dimensional computational fluid dynamics (3D CFD) modeling of supersonic
diode pumped alkali lasers (DPALs), taking into account fluid dynamics and kinetic processes in the lasing medium. For
a supersonic Cs DPAL with laser section geometry and resonator parameters similar to those of the 1-kW flowing-gas
subsonic Cs DPAL [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] the maximum achievable output power, ~ 7
kW, is 25% higher than that achievable in the subsonic case. Comparison between semi-analytical and 3D CFD models
for Cs shows that the latter predicts much higher maximum achievable output power than the former. Optimization of the
laser parameters using 3D CFD modeling shows that very high power and optical-to-optical efficiency, 35 kW and 82%,
respectively, can be achieved in a Cs supersonic device pumped by a collimated cylindrical (0.5 cm diameter) beam.
Application of end- or transverse-pumping by collimated rectangular (large cross section ~ 2 - 4 cm2) beam makes it
possible to obtain even higher output power, > 250 kW, for ~ 350 kW pumping power. The main processes limiting the
power of Cs supersonic DPAL are saturation of the D2 transition and large ~ 40% losses of alkali atoms due to
ionization, whereas the influence of gas heating is negligibly small. For supersonic K DPAL both gas heating and
ionization effects are shown to be unimportant and the maximum achievable power, ~ 40 kW and 350 kW, for pumping
by ~ 100 kW cylindrical and ~ 700 kW rectangular beam, respectively, are higher than those achievable in the Cs
supersonic laser. The power achieved in the supersonic K DPAL is two times higher than for the subsonic version with
the same resonator and K density at the gas inlet, the maximum optical-to-optical efficiency being 82%.
Application of two- and-three dimensional computational fluid dynamics (2D and 3D CFD) models to subsonic flowing-gas DPALs is reported. The 2D model is applied to a DPAL with optical resonator-flow field coaxial configuration and the 3D model is applied to an optical axis transverse to the flow configuration. The models take into account effects of temperature rise and losses of alkali atoms due to ionization. The 2D CFD model is applied to 1 kW flowing-gas Cs DPAL [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] and the calculated results are in good agreement with the measurements. Comparison of the 2D CFD to semi-analytical model [B. D. Barmashenko and S. Rosenwaks, J. Opt. Soc. Am. B 30, 1118 (2013)] shows that for low pump power both models predict very close values of the laser power; however, at higher pump power, corresponding to saturation of the absorption of the pump transition, the laser power calculated using the 2D CFD model is much higher than that obtained using the semi-analytical model. At high pump power, the heat convection out of the laser resonator is more efficient for the transverse case than the coaxial case, the beam temperature is lower and consequently the calculated laser power is higher. Optimization of the Cs DPAL parameters, using 3D CFD modeling, shows that applying high flow velocity and narrowband pumping, maximum lasing power as high as 40 kW can be obtained at pump power of 80 kW for transverse flow configuration in a pumped volume of ~ 0.7 cm3.
Results of recent semi-analytical and three dimensional computational fluid dynamics (3D CFD) modeling of supersonic
diode pumped alkali lasers (DPALs), as well as summary of work in progress, are reported. DPALs have been
extensively studied in the past few years and static and flowing-gas devices have been investigated. Modeling of these
devices has been conducted as well and fluid dynamics and kinetic processes have been taken into account, but until
recently only flowing-gas DPALs with subsonic velocity of the gas were considered. Following our previous work on
supersonic DPALs we further explore in the present study the feasibility of operating DPALs with supersonic expansion
of the gaseous laser mixture, consisting of alkali atoms, He atoms and (frequently) hydrocarbon molecules. The
motivation for this exploration stems from the possibility of fast and efficient cooling of the mixture by the supersonic
expansion. In a recent paper (S. Rosenwaks et al, Proc. SPIE 8962, 896209 (2014)) we have reported on semi-analytical
modeling for a supersonic Cs DPAL with parameters similar to those of the 1-kW flowing-gas subsonic Cs DPAL (A.V.
Bogachev et al, Quantum Electron. 42, 95 (2012)); the maximum power, Plase, for the former was found to be higher than
for the latter by 25%. Optimization of the He/CH4 buffer gas composition and flow parameters using 3D CFD modeling
shows that for Bogachev et al resonator parameters, extremely high lasing power and optical-to-optical efficiency, 33
kW and 82%, respectively, are achievable in the Cs supersonic device. Comparison between the semi-analytical and the
3D CFD models for Cs shows that the latter predicts much higher maximum achievable laser power than the former. For
a supersonic K DPAL the semi-analytical model predicts Plase = 43 kW, 70% higher than for subsonic with the same
resonator and K density at the inlet, the maximum optical-to-optical efficiency being 82%. The paper also includes
estimates for closed cycle supersonic systems.
Comprehensive analysis of kinetic and fluid dynamic processes in flowing-gas diode pumped alkali lasers (DPALs)
using two- and three-dimensional computational fluid dynamics (2D and 3D CFD) models is reported for Cs DPALs.
The models take into account effects of temperature rise and losses of alkali atoms due to ionization. Various gas flow
regimes and transverse and parallel flow-optics directions configurations are studied. Optimization of the Cs DPAL
parameters, using 3D CFD modeling, shows that applying high flow velocity and narrowband pumping, maximum lasing
power as high as 40 kW can be obtained at pump power of 80 kW for transverse flow configuration in a pumped volume
of ~ 0.7 cm3. At high pump power the calculated laser power is higher for the transverse scheme than for the parallel
scheme because of a more efficient heat convection from the beam volume in the transverse configuration. The CFD
models are applied to experimental devices and the calculated results are in good agreement with the measurements.
Comparison between a semi-analytical and two- and-three dimensional computational fluid dynamics (2D and 3D CFD)
models is reported. The models take into account effects of temperature rise and losses of alkali atoms due to ionization
and chemical reactions, resulting in a decrease of the slope efficiency and lasing power. Effects of natural convection in
static DPALs are also taken into account. Both models are applied to Cs DPALs and the results are in good agreement
with measurements in a static [B.V. Zhdanov, J. Sell and R.J. Knize, Electron. Lett. 44, 582 (2008)] and 1-kW flowinggas
[A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] DPALs. Comparison of the models applied to the flowinggas
DPAL shows that for low pump power both models predict very close values of the laser power; however, at higher
pump power, corresponding to saturation of the absorption of the pump transition, the values of the laser power
calculated using the 2D CFD model are much higher than those obtained using the semi-analytical model.
The feasibility of operating diode pumped alkali lasers (DPALs) with supersonic expansion of the gaseous laser mixture, consisting of alkali atoms, He atoms and (frequently) hydrocarbon molecules, is explored. Taking into account fluid dynamics and kinetic processes, both semi-analytical and three-dimensional (3D) computational fluid dynamics (CFD) modeling of supersonic DPALs is reported. Using the semi-analytical model, the operation of supersonic DPALs is compared with that measured and modeled in subsonic lasers for both Cs and K. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. Using the 3D CFD model, the flow pattern and spatial distributions of the pump and laser intensities in the resonator are calculated for Cs DPALs. Comparison between the semi-analytical and 3D CFD models for Cs shows that the latter predicts much larger maximum achievable laser power than the former. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered.
In the last four years, a few research groups worked on the feasibility of compressive sampling (CS) in ultrasound medical imaging and several attempts of applying the CS theory may be found in the recent literature. In particular, it was shown that using iotap-norm minimization with p different from 1 provides interesting RF signal reconstruction results. In this paper, we propose to further improve this technique by processing the reconstruction in the Fourier domain. In addition, alpha -stable distributions are used to model the Fourier transforms of the RF lines. The parameter p used in the optimization process is related to the parameter alpha obtained by modelling the data (in the Fourier domain) as an alpha -stable distribution. The results obtained on experimental US images show significant reconstruction improvement compared to the previously published approach where the reconstruction was performed in the spatial domain.
Kinetic and fluid dynamic processes in diode pumped alkali lasers (DPALs) are analyzed in detail using a semianalytical model, applicable to both static and flowing-gas devices. The model takes into account effects of temperature rise, excitation of neutral alkali atoms to high lying electronic states and their losses due to ionization and chemical reactions, resulting in a decrease of the pump absorption, slope efficiency and lasing power. Effects of natural convection in static DPALs are also taken into account. The model is applied to Cs DPALs and the results are in good agreement with measurements in a static [B.V. Zhdanov, J. Sell and R.J. Knize, Electron. Lett. 44, 582 (2008)] and 1-kW flowing-gas [A.V. Bogachev et al., Quantum Electron. 42, 95 (2012)] DPALs. It predicts the dependence of power on the flow velocity in flowing-gas DPALs and on the buffer gas composition. The maximum values of the laser power can be substantially increased by optimization of the flowing-gas DPAL parameters. In particular for the aforementioned 1 kW DPAL, 6 kW maximum power is achievable just by increasing the pump power and the temperature of the wall and the gas at the flow inlet (resulting in increase of the alkali saturated vapor density). Dependence of the lasing power on the pump power is non-monotonic: the power first increases, achieves its maximum and then decreases. The decrease of the lasing power with increasing pump power at large values of the latter is due to the rise of the aforementioned losses of the alkali atoms as a result of ionization. Work in progress applying two-dimensional computational fluid dynamics modeling of flowing-gas DPALs is also reported.
We explore the feasibility of supersonic operation of diode pumped alkali lasers (DPALs) applying model calculations. The power and efficiency of Cs and K atoms DPALs are estimated based on a semi-analytical model previously used for studying static and subsonic flow DPALs. The operation of supersonic lasers is compared with that measured and modeled in subsonic lasers. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered. Work in progress applying three-dimensional computational fluid dynamics modeling of supersonic DPALs is also reported.
A simple, semi-analytical model of diode pumped alkali lasers (DPALs), applicable to both static and flowing-gas devices, is reported. Unlike other models, assuming a 3-level scheme of the laser and neglecting influence of the
temperature on the lasing power, it takes into account temperature rise and losses of alkali atoms due to ionization and chemical reactions, resulting in a decrease of the pump absorption and slope efficiency. The applicability of the model is demonstrated by (1) obtaining good agreement with measurements in a static DPAL [B.V. Zhdanov, J. Sell and R.J. Knize, Electron. Lett. 44, 582 (2008)], (2) predicting the dependence of power on the flow velocity in flowing-gas DPALs and (3) checking the effect of using a buffer gas with high molar heat capacity and large relaxation rate constant between the 2P3/2 and 2P1/2 fine-structure levels of the of the alkali atom. It is found that ionization processes have a small effect on the laser operation, whereas chemical reactions of alkali atoms with hydrocarbons strongly affect the lasing power. The power strongly increases with flow velocity and by replacing, e.g., ethane by propane as a buffer gas the power may be further increased by up to 30%. 8 kW is achievable for 20 kW pump at flow velocity of 20 m/s.
KEYWORDS: Resonators, Mirrors, Chemical lasers, 3D modeling, Lawrencium, Geometrical optics, Laser resonators, Chemical oxygen iodine lasers, Data modeling, Near field optics
Simple models are developed, describing the power extraction in chemical oxygen-iodine lasers (COILs) with stable and
unstable resonators. For stable resonators the model is applied to the ejector high pressure COIL and the results are
compared with the experimental data (see also a preceding paper by Rosenwaks et al.). The positive and negative branch
unstable resonators with cylindrical mirrors that have been recently used in COILs are studied theoretically using a
geometrical optics model. The optical extraction efficiency, spatial distributions of the intracavity radiation intensity in
the flow direction and the intensity in the far field are calculated for both kinds of resonators as a function of both the
resonator and COIL parameters. The optimal resonator magnifications corresponding to the maximum intensity in the far
field are found.
The kinetics of the chemical oxygen-iodine laser (COIL) has been studied alongside the technological efforts in COIL
development. In particular, many efforts have been devoted to the study of the mechanism of I2 dissociation in the COIL
medium. Since O2(a) is the energy reservoir of the COIL, it must be involved in the dissociation of I2. Therefore,
understanding the dissociation mechanism may help in finding ways of minimizing the O2(a) consumption for
dissociation and increasing the chemical efficiency of the laser. In the present paper previously suggested mechanisms
of I2 dissociation are briefly overviewed and recent measurements and modeling of the gain and the power in supersonic
COILs carried out in our laboratory are presented. Our studies employ both an analytical model and numerical
calculations which are outlined in the present paper, with more details on the models given in a following paper by
Barmashenko et al. To unravel the I2 dissociation mechanism we utilize kinetic-fluid dynamics three-dimensional
modeling, where pathways involving the excited species I2(X, 10 ≤ v < 25), I2(X, 25 ≤ v ≤ 47), I2(A, A'), O2(X, v), O2(a,
v), O2(b, v) and I(2P1/2) as intermediate reactants are included. Both the gain and the power studies show good agreement
between calculations and experiments. We believe that future modeling should include the above pathways and
additional pathways should be considered when additional kinetic data is available.
KEYWORDS: Resonators, Mirrors, Geometrical optics, Chemical lasers, Lawrencium, Near field optics, Chemical analysis, Chemical oxygen iodine lasers, Oxygen, Differential equations
A simple geometrical optics model is developed, describing the power extraction in chemical oxygen-iodine lasers with
unstable resonators. The positive and negative branch unstable resonators with cylindrical mirrors that were recently
used in the COIL are studied. The optical extraction efficiency and intensity spatial distributions in the flow direction for
both kinds of resonators are calculated.
KEYWORDS: 3D modeling, Chemical oxygen iodine lasers, Oxygen, Chemical lasers, Computational fluid dynamics, Mirrors, Iodine, Chlorine, Modeling, Systems modeling
Experimental and theoretical work in progress on supersonic COILs at Ben-Gurion University is reported. Following the
achievement of a record value (40%) for the chemical efficiency of a supersonic 5-cm gain length COIL in our lab, a 10-
cm gain length device was experimentally studied. Maximum output power exceeding 0.6 kW with chemical efficiency
of 35% was obtained for 1% total mirror transmission in preliminary studies. Comparing the results of three-dimensional
computational fluid dynamics model calculations to available experimental results [Nikolaev et al., IEEE J. Quantum
Electron. 38, 421 (2002)], we show that the model is applicable to high pressure, ejector type chemical oxygen-iodine
laser (COIL), reasonably reproducing the measured gain and temperature.
The results of three-dimensional computational fluid dynamics model calculations are reported in detail and compared to
available experimental results [Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is
applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured
gain, temperature, static pressure and gas velocity. A previous model which included I2(A' 3Pi2u), I2(A 3Pi1u) and O2(a 1Deltag,
v) as significant intermediates in the dissociation of I2 [Waichman et al., J. Appl. Phys. 102, 013108 (2007)] reproduced
the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by
adding the effects of turbulence, which play an important role in high pressure COILs.
KEYWORDS: 3D modeling, Iodine, Chemical oxygen iodine lasers, Chemical lasers, Chemical species, 3D metrology, Temperature metrology, Diagnostics, Oxygen, Resonators
The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied via
detailed measurements and three dimensional computational fluid dynamics calculations. Comparing the measurements
and the calculations enabled critical examination of previously proposed dissociation mechanisms and suggestion of a
mechanism consistent with the experimental and theoretical results obtained in a supersonic COIL for the gain,
temperature and I2 dissociation fraction at the optical axis. The suggested mechanism combines the recent scheme of
Azyazov and Heaven (AIAA J. 44, 1593 (2006)), where I2(A'3Π2u), I2(A3Π1u) and O2(a1&Dgr;g, v) are significant dissociation
intermediates, with the "standard" chain branching mechanism of Heidner et al. (J. Phys. Chem. 87, 2348 (1983)),
involving I(2P1/2) and I2(X1&Sgr;+g, v). In addition, we examined a new method for enhancement of the gain and power in
a COIL by applying DC corona/glow discharge in the transonic section of the secondary flow in the supersonic nozzle,
dissociating I2 prior to its mixing with O2(1&Dgr;). The loss of O2(1&Dgr;) consumed for dissociation was thus reduced and the
consequent dissociation rate downstream of the discharge increased, resulting in up to 80% power enhancement. The
implication of this method for COILs operating beyond the specific conditions reported here is assessed.
KEYWORDS: Iodine, Chemical oxygen iodine lasers, Chemical lasers, Molecules, Chemical analysis, Oxygen, Chemical species, Absorption, Resonators, Diagnostics
The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied
experimentally as a function of I2 flow rate. The measurements revealed that the number of consumed O2(1&Dgr;) molecules
per dissociated I2 molecule depends on the experimental conditions: it is 4.2 ± 0.4 for typical conditions and I2 densities
applied for the operation of the COIL, but increases at lower I2 densities. In addition, a new method for dissociating I2
prior to its mixing with O2(1&Dgr;) and thus reducing the loss of O2(1&Dgr;) is reported. The method is based on applying
corona/glow electrical discharge in the transonic section of the secondary flow in the COIL supersonic nozzle. 1.7% of I2
is dissociated by the discharge resulting in 70% power enhancement at rather high I2/O2 ratio, 1.6%, close to the optimal
value (~ 2.5%) for operation of COILs with supersonic mixing.
KEYWORDS: 3D modeling, Chemical lasers, Chemical oxygen iodine lasers, Iodine, Computational fluid dynamics, Molecules, 3D metrology, Computer simulations, Optical simulations, Chemical reactions
The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied via detailed measurements and three dimensional computational fluid dynamics calculations. Comparing the measurements and the calculations enabled critical examination of previously proposed dissociation mechanisms and suggestion of a mechanism consistent with the experimental and theoretical results. The gain, I2 dissociation fraction and temperature at the optical axis, calculated using Heidner's model (R.F. Heidner III et al., J. Phys. Chem. 87, 2348 (1983)), are much lower than those measured experimentally. Agreement with the experimental results was reached by using Heidner's model supplemented by Azyazov-Heaven's model (V.N. Azyazov and M.C. Heaven, AIAA J. 44, 1593 (2006)) where I2(A') and vibrationally excited O2(a1&Dgr;) are significant dissociation intermediates.
KEYWORDS: Iodine, Chemical oxygen iodine lasers, Mirrors, Chemical analysis, Temperature metrology, Oxygen, Chlorine, Chemical lasers, Molecules, Laser development
We report on a detailed gain measurements and analysis of the extremely efficient supersonic chemical oxygen-iodine laser (COIL) recently developed in our laboratory (Appl. Phys. Lett., 85, 5851 (2004)). The power and spatial distributions of the gain and temperature across the flow were measured for different supersonic nozzles with both staggered and non-staggered iodine injection holes, different injection locations along the flow and nozzle throat-heights. 40.0% efficiency was measured for 1 s at the early stage of operation, followed by a sustained 35.5% chemical efficiency for 20 s. By carefully studying and optimizing the operation of the chemical generator, 0.73 yield of singlet oxygen was obtained for conditions corresponding to the highest efficiency.
We report on recent studies aimed at improving the chemical efficiency of the supersonic chemical oxygen-iodine laser (COIL). Efficiencies around 30% for the supersonic COIL have been the state-of-the-art in the last decade. By carefully studying and optimizing the operation of the chemical generator, the mixing of reagents in different nozzles and the optical extraction efficiency, we achieved a new record (40%) for the chemical efficiency of the supersonic COIL and approached the theoretical limit for this efficiency. The effects of the partial pressure of O2 and the residence time of the flow in the generator, as well as the heating of the nozzle, are discussed and shown to be crucial in attaining this high efficiency.
We report on a detailed parametric study of an extremely efficient supersonic chemical oxygen-iodine laser (COIL) with supersonic mixing of iodine and oxygen. Output power exceeding 0.5 kW with chemical efficiency of ~33% was obtained in a 5 cm gain length for Cl2 flow rate of 17 mmole/s. 33% efficiency is the highest reported chemical efficiency of any supersonic COIL. Comparison between different mixing schemes shows that for supersonic mixing the output power and chemical efficiency are about 20% higher than for transonic mixing scheme. The optimal conditions for the efficient operation are investigated. Diagnostic measurements of the small-signal gain shows that the value of the gain for the supersonic mixing scheme corresponding to the maximum efficiency is about 0.75%/cm, about 1.5 times larger than for transonic mixing scheme. Studies of different supersonic mixing schemes show that to achieve further power increase the injection location should be moved downstream.
KEYWORDS: Iodine, Chemical oxygen iodine lasers, Diagnostics, Chemical lasers, Temperature metrology, Oxygen, Semiconductor lasers, Systems modeling, Nitrogen, Fluid dynamics
Spatial distributions of the gain, temperature and I2 across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser (COIL) as a function of the iodine and secondary nitrogen flow rate and jet penetration parameter. The mixing efficiency for supersonic injection of iodine (~ 0.85) is found to be much larger than for transonic injection (~ 0.5), the maximum values of the gain being ~ 0.65%/cm for both injection schemes. Spatial distributions of the gain corresponding to the maximum power are found. A simple one-dimensional model is developed for the fluid dynamics and chemical kinetics in the COIL. Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heaven’s dissociation mechanism is much lower than the measured one. Employing Heidner’s mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of flow parameters.
KEYWORDS: Iodine, Chemical lasers, Chemical oxygen iodine lasers, Diagnostics, Nitrogen, Oxygen, Molecules, Semiconductor lasers, Temperature metrology, Chemical species
Spatial distributions of the gain and temperament across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter and gas pumping rate. The mixing efficiency for supersonic injection of iodine is found to be much larger than for transonic injection, the maximum values of the gain being approximately 0.65 percent/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI2 were carried out. For transonic injection the optimal value of nI2 at the flow centerline is smaller than that at the off axis location. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decease the Mach number results in a decrease of the gain and increase of the temperature. The mixing efficiency in this case is much larger than for closed leak.
KEYWORDS: Iodine, Chemical oxygen iodine lasers, Chemical lasers, Temperature metrology, Chemical reactions, 3D modeling, Oxygen, Resonators, Chemical species, Molecules
We report on a simple one-dimensional model developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two dissociation mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heaven's dissociation mechanism is much lower than the measured one. Employing Heidner's mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of the flow parameters. Other predictions of the model (larger mixing efficiency and higher temperature with a leak opened downstream of the resonator and gain decrease along the flow) are also in agreement with the experimental observations.
KEYWORDS: Iodine, Resonators, Chemical lasers, Chemical oxygen iodine lasers, Oxygen, Chlorine, Diagnostics, Temperature metrology, Chemical species, Molecules
The chemical oxygen-iodine laser (COIL) is one of the most promising and extensively studied chemical lasers. Nevertheless, the mechanisms governing its operation are not yet fully understood and efforts are underway to find better singlet oxygen chemical generators and improve oxygen/iodine mixing schemes. The latter efforts are briefly reviewed and recent results of parametric studies of an efficient supersonic COIL operating in our laboratory are presented. The laser is energized by a jet type generator, operating without primary buffer gas and applies simple nozzle geometry and mixing of iodine and oxygen at or after the critical cross section.
We report on a detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser operating without primary buffer gas and on preliminary power measurements in this laser. In particular, a study is carried out to find optimal values of the flow parameters corresponding to the maximum gain. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using a diode laser based diagnostic, the gain and temperature in the cavity are studied. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. Preliminary power measurements are performed. For slit nozzle with iodine injection in the diverging part ofthe nozzle output power of 287 W with chemical efficiency of 21% was measured at 15.1 mmole/s of Cl2 with no primary buffer gas. This is the highest reported chemical efficiency of a supersonic COIL operating without primary buffer gas.
An analytical model is developed for calculating the iodine dissociation fraction F and the number N of O2(1Æ)molecules lost in the region of iodine dissociation per I2 molecule in slit nozzles. The model is applied to results obtained for different mixing schemes.
We report on diagnostic measurements in a small scale supersonic chemical oxygen iodine laser (COIL) with transonic mixing. Using diode laser based diagnostics we measured the O2(1(Delta) ) yield and water vapor fraction at the exit of a jet type singlet oxygen generator (JSOG) and the gain in the resonator. In addition the chlorine utilization and gas temperature at the generator exit were measured. For conditions corresponding to the maximum chemical efficiency of the supersonic COIL energized by the JSOG the O2(1(Delta) ) yield, water vapor fraction, chlorine utilization and temperature at the generator exit are 0.65, 0.08, 0.92 and 30 C. Small signal gain and temperature at the resonant optical axis are 0.25%/cm and 280 K, respectively. Dependence of the yield on the generator pressure and variation of the temperature along the flow in the diagnostic cell are consistent with rate constant of the O2(1(Delta) ) energy pooling reaction of 2.7 X 10-17 cm3s-1.
KEYWORDS: Iodine, Chemical lasers, Oxygen, Mirrors, Chlorine, Chlorine gas, Chemical oxygen iodine lasers, Chemical analysis, Resonators, Chemical species
Recent results of parametric studies of an efficient supersonic chemical oxygen-iodine laser are presented. The laser is energized by a jet type singlet oxygen generator, operated without primary buffer gas and applies simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 190 W with chemical efficiency of 18% was obtained in a 5 cm gain length for Cl2 flow rate of 11.8 mmole/s. The power is studied as a function of the distance between the optical axis and the supersonic nozzle exit plane, the molar flow rates of various reagents, the BHP and gas pressures in the generator, the type of the secondary buffer gas (N2 or He) and the stagnation temperature of the gas. It is found that the power under the present operation conditions is almost unaffected by water vapor in the medium. The role of buffer gas under different conditions is discussed.
Optical extraction efficiency of the COIL is calculated for (transverse) multimode oscillation. The effects of hyperfine and velocity cross-relaxation and changes of the gain and intraresonator intensity in the flow direction are taken into account.
We report on studies of a 5 cm gain length chemical oxygen- iodine laser (COIL) energized by a jet-type singlet oxygen generator (JSOG) are presented. For 10 mmole/s of Cl2 flow rate, output power of 132 W with chemical efficiency of 14.5% were obtained without a water vapor trap. One-hundred-sixty- three watts and 18% were achieved when cooled (173 K) He was introduced downstream of the JSOG; under these conditions the small signal gain was estimated to be 0.32% cm-1. Wattage of 190 and 10.5% were obtained for 20 mmole/s of Cl2 flow rate. Replacing He by N2 as a buffer gas resulted in a 13% power decrease only. The main key for increasing the chemical efficiency of a COIL without a water vapor trap for a given iodine-oxygen mixing system is found to be high oxygen pressure and low water vapor pressure inside the reaction zone of the JSOG. The last goal was achieved by optimizing the composition and temperature of the basic hydrogen peroxide solution (BHP). The experimental results are discussed and related to the composition and flow conditions of the gaseous reactants and of the BHP. We also report on preliminary results of efficient COIL operation without primary buffer gas using rectangular nozzles with iodine injection in the throat.
KEYWORDS: Iodine, Chemical lasers, Oxygen, Chemical oxygen iodine lasers, Helium, Chlorine, High power lasers, Mirrors, Chemical analysis, Chemical species
Parametric studies of the gain and the power of a small scale supersonic chemical oxygen- iodine laser are presented. The laser is of 5 cm long active medium, and utilizes a simple sparger-type O2(1(Delta) ) chemical generator and a medium size pumping system. A grid nozzle is used for iodine injection and supersonic expansion. 45 W of CW laser emission at 1315 nm are obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long periods make it a convenient tool for studying parameters important for high power supersonic iodine lasers and for comparison to model calculations. The gain and the lasing power are studied as a function of the molar flow rates of the various reagents, and conditions are found for optimal operation. Good agreement is found between the experimental results and calculations based on a simple 1D semi-empirical model, previously developed in our laboratory and modified in the present work. The model is used to predict optimal values for parameters affecting the laser performance that are difficult to examine in the present experimental system.
A theoretical model is developed for chemical generators producing O2(1(Delta) ) at high pressure. Such generators are especially important for supersonic chemical oxygen-iodine lasers. The model treats different types of generators, e.g., bubble column, film, aerosol, and jet generators. The main factor affecting the O2(1(Delta) ) yield under high pressure is liquid-phase quenching enhanced by depletion of HO2- ions near the gas/liquid interface. Simple analytical expressions are derived for the O2(1(Delta) ) yield at the exit of the generator. Output characteristics of different specific generators are calculated and compared with available experimental results. O2(1(Delta) ) yield > 0.5 can be achieved for oxygen pressure up to 50 Torr and flowrates of 3 mmol/cm2s. For equal velocities of the gas and the liquid the maximum flux of the energy carried by O2(1(Delta) ) for jet or aerosol generators reaches 200 W/cm2. It can be increased by increasing the liquid velocity in the generator.
KEYWORDS: Iodine, Chemical lasers, Chemical oxygen iodine lasers, Diffusion, Oxygen, Performance modeling, Data modeling, Chemical reactions, NOx, Radon
A simple, one-dimensional leak flow tube model was used to calculate the effect of mixing on the performance of chemical oxygen-iodine lasers (COIL). Both the maximum gain and the characteristic length of the iodine dissociation are shown to be nonmonotonic functions of the iodine flow rate, nI2. The maximum nI2 for which lasing is possible is less than 1 - 2% of the oxygen flow rate. This is in agreement with experimental data and is not explained by models assuming premixed flows. The present model was applied to calculations of the performance of supersonic COILs.
KEYWORDS: Chemical lasers, Molecules, Chemical reactions, Infrared lasers, Molecular lasers, Energy efficiency, Chemical analysis, Semiconductors, Lawrencium, Arsenic
Theoretical investigation shows that during the chemical pumping of high vibrational levels of diatomic molecules partial population inversion between these levels can exist much longer than that for vibrational transition 1?0. In case of fast VV-exchange the ”long" inversion appears long after finishing of the inversion for the transition I?0. It lasts up to the completion of chemical pumping reaction. The calculations are made for H2-F2-He mixture.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.