Show all abstracts
View Session
- Front Matter: Volume 7581
- Iodine Transfer Lasers (COIL, EOIL, AGIL)
- Short Pulse Lasers and Laser Applications I
- Short Pulse Lasers and Laser Applications II
- Alkali Atom Lasers
- Poster Session
Front Matter: Volume 7581
Front Matter: Volume 7581
Show abstract
This PDF file contains the front matter associated with SPIE
Proceedings Volume 7581, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Iodine Transfer Lasers (COIL, EOIL, AGIL)
Enhanced performance of an electric oxygen-iodine laser
Show abstract
Experiments and modeling have led to continued enhancements in the Electric Oxygen-Iodine Laser (ElectricOIL)
system. This continuous wave (cw) laser operating on the 1315 nm transition of atomic iodine is pumped by the
production of O2(a) in a radio-frequency (RF) discharge in an O2/He/NO gas mixture. New discharge geometries
have led to improvements in O2(a) production and efficiency. A 95% enhancement in cw laser power was achieved
via a 50% increase in gain length, flow rates, and discharge power. A further 87% increase in extracted laser power
was obtained using a larger mode volume resonator. The gain has improved by more than 100-fold from the initial
demonstration of 0.002% cm-1 to 0.26% cm-1, and similarly the outcoupled laser power has improved more than
500-fold from 0.16 W to 102 W.
Transverse gas flow RF slab discharge generator of singlet delta oxygen for oxygen-iodine laser
Show abstract
Results of experimental and theoretical study of singlet delta oxygen (SDO) production in transverse gas flow RF slab
discharge for an electric discharge oxygen-iodine laser are presented. The electric discharge facility operating in both
pulse-periodic and CW mode was manufactured: gas flow duct including multi-path cryogenic heat exchanger, dielectric
slab channel, and slab electrode system incorporated in the channel for RF discharge ignition. Experiments on SDO
production in transverse gas flow RF discharge were carried out. SDO production depending on gas mixture content and
pressure, gas flow velocity, and RF discharge power was experimentally studied. It was shown that SDO yield increased
with gas pressure decrease, gas flow deceleration and helium dilution of oxygen at the same input power. CW RF
discharge was demonstrated to be the most efficient for SDO production as compared to pulse-periodic RF discharge
with the same averaged input power. SDO yield was demonstrated to be not less than 10 percent. The model developed
was further modified to do simulations of CW and pulse periodic RF discharges. A reasonable agreement between
experimental and theoretical data on SDO production in CW and pulse-periodic RF discharges in oxygen is observed.
Kinetics and scaling of gain and lasing in a 1-5 kW microwave discharge oxygen iodine laser
Show abstract
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.
Iodine dissociation in the photochemistry of N[sub]2[/sub]O/I[sub]2[/sub] mixtures
Show abstract
A new kinetic scheme for the dissociation of I2 by O2(a) has been proposed by Azyazov et al. (J. Chem. Phys. 130,
104306/9 (2009)). In principle, the reactions initiated by UV photolysis of N2O/I2 mixtures can be used to probe the
chain propagation stage of this dissociation model, and provide additional validation. In the present study, 193 nm laser
photolysis of N2O/I2 mixtures was used to initiate secondary chemical reactions and to produce iodine atoms. Singlet
oxygen was generated in this system by the fast reaction O(1D)+N2O→ O2(a)+N2. Emission spectroscopy and laser
induced fluorescence techniques were used to follow the time evolutions of I* and I2. The photolysis of N2O/I2 mixtures
creates all of the species needed to sustain the chain propagation stage of I2 dissociation process. However, it was found
that the high pressures of N2O needed to generate sufficient concentrations of O2(a) suppressed the I2 dissociation
process. Computational modeling indicated that suppression of the chain propagation reactions under the conditions
examined was consistent with the revised dissociation model.
An all gas-phase iodine laser based on NCl3 reaction system
Show abstract
Theoretical and experimental studies of the amine-based all gas-phase iodine laser (AGIL) are conducted. The numerical
simulation code is a detailed one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known
rate equations to date. Using this code, we find that the key reactions to achieve positive gain are the deactivation
reaction of excited iodine atoms by chlorine atoms and the self annihilation reactions of NCl(1Δ). The order of the
injection nozzles is crucial to suppress these reactions. Following the calculations, we fabricate a flow reactor apparatus
and demonstrate laser action for the 2P1/2-2P3/2 transition of iodine atom pumped by energy transfer from NCl(1Δ)
produced by a set of amine-based, all gas-phase chemical reactions. Continuous-wave laser output of 50 mW with 40%
duty factor is obtained from a stable optical resonator consisting of two 99.99% reflective mirrors. The observed laser
characteristics are reasonably explained by numerical calculations. To our knowledge, this is the first achievement of
amine-based AGIL oscillation.
Catalytic enhancement of singlet oxygen for hybrid electric discharge oxygen-iodine laser systems
Show abstract
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.
O[sub]2[/sub](a[sup]1[/sup]Delta) quenching in O/O[sub]2[/sub]/O[sub]3[/sub]/CO[sub]2[/sub]/He/Ar mixtures
Show abstract
The development of discharge singlet oxygen generators (DSOG's) that can operate at high pressures is required
for the power scaling of the discharge oxygen iodine laser. In order to achieve efficient high-pressure DSOG
operation it is important to understand the mechanisms by which singlet oxygen (O2(a1Δ)) is quenched in these
devices. It has been proposed that three-body deactivation processes of the type O2(a1Δ))+O+M→2O2+M
provide significant energy loss channels. To further explore these reactions the physical and reactive quenching
of O2(a1Δ)) in O(3P)/O2/O3/CO2/He/Ar mixtures has been investigated. Oxygen atoms and singlet oxygen
molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O2(a1Δ)) quenching were
followed by observing the 1268 nm fluorescence of the O2 a1Δ-X3Ε transition. Fast quenching of O2(a1Δ)) in the
presence of oxygen atoms and molecules was observed. The mechanism of the process has been examined using
kinetic models, which indicate that quenching by vibrationally excited ozone is the dominant reaction.
Short Pulse Lasers and Laser Applications I
Direct generation of femtosecond laser pulses with a peak power exceeding 18 MW without external amplification
Show abstract
We report on our latest results in the development of high-energy, long-cavity Chirped Pulse Oscillators (CPOs). Our
concept allows the generation of ultrashort laser pulses at MHz repetition rates with a pulse duration of less then 50fs
and an energy approaching the μJ-level directly out of an oscillator. Thus, our unique approach completely avoids the
need for any additional amplification stages. This paper is, to the best of our knowledge, the first demonstration that
laser pulses with a peak power exceeding 18MW can be generated directly out of a femtosecond oscillator.
Optical-field-induced-ionization Ar[sub]2[/sub][sup]*[/sup] excimer amplifier for intense femtosecond vacuum ultraviolet pulse generation
Show abstract
We report the optical amplification characteristics of an optical-field-induced-ionization (OFI) Ar2
* excimer
vacuum ultraviolet (VUV) amplifier at 126 nm by using two experimental approaches. We have observed the
amplification of OFI Ar2
* excimer emission and evaluated the gain length product of 1.0 by using an optical cavity.
We also achieved the gain length product of 5.0 by measuring the one pass amplification inside a hollow fiber with
the length of 5 cm. The use of a hollow fiber was effective to guide the VUV emission and to extend a gain length.
A small signal gain coefficient of 1.0 cm-1 was evaluated in both experimental approaches.
Short Pulse Lasers and Laser Applications II
Excimer laser deposition of super-hard coatings
Show abstract
Super-hard functional coatings are obtained by high power excimer laser based PLD. Diamond-like,
tetrahedral amorphous carbon (ta-C) is grown on substrates moderately heated to below 90°C inside a
vacuum chamber upon ablating a graphite target by means of a high pulse energy excimer laser at a
wavelength of 248 nm. The fast evaporation of the target material induced by the high photon energy of 5
eV, the short temporal width of 30 ns and the high fluence of the excimer laser pulses generates plume
species with a high degree of ionisation and high kinetic energies. As a consequence, the kinetic energies
resulting from excimer based PLD are significantly higher than those associated with the thermal
evaporation and the ion sputtering deposition methods. In fact, the mean kinetic energy of the atoms and
ions in the plume are in the range of 30 eV to 80 eV for fluencies of 5 J/cm2 to 20 J/cm2. Such large ontarget
UV fluences are easily provided by high energy excimer lasers such as the Coherent LPXpro and by
LSX laser models which can operate at output energies up to 1 J and average output powers up to 540 W.
Time-resolved imaging of material response following laser-induced breakdown in the bulk and surface of fused silica
Show abstract
Optical components within high energy laser systems are susceptible to laser-induced material modification when the
breakdown threshold is exceeded or damage is initiated by pre-existing impurities or defects. These modifications are the
result of exposure to extreme conditions involving the generation of high temperatures and pressures and occur on a
volumetric scale of the order of a few cubic microns. The response of the material following localized energy deposition,
including the timeline of events and the individual processes involved during this timeline, is still largely unknown.
In this work, we investigate the events taking place during the entire timeline in both bulk and surface damage in
fused silica using a set of time-resolved microscopy systems. These microscope systems offer up to 1 micron spatial
resolution when imaging static or dynamic effects, allowing for imaging of the entire process with adequate temporal
and spatial resolution. These systems incorporate various pump-probe geometries designed to optimize the sensitivity for
detecting individual aspects of the process such as the propagation of shock waves, near-surface material motion, the
speed of ejecta, and material transformations. The experimental results indicate that the material response can be
separated into distinct phases, some terminating within a few tens of nanoseconds but some extending up to about 100
microseconds. Overall the results demonstrate that the final characteristics of the modified region depend on the material
response to the energy deposition and not on the laser parameters.
Distortion free pulse stretching and compression by chirped volume holographic gratings
Show abstract
We have developed a novel method to correct the spatial distortion resulting from temporally stretching/compressing
optical pulses with a chirped volume holographic grating (CVHG) in glass. We show that the inherent spatial beam
distortion can be corrected to produce a distortion-free round beam output. We fabricated a 30 mm long CVHG with 9
nm bandwidth, 300 ps delay at 1031nm exhibiting a smooth round spatial Gaussian profile after compression. Coupling
efficiencies for the compressed pulse exceeds 75% into a single mode fiber. The spatial profile is maintained over a wide
temperature range from 10 to 60 degrees Celsius. We believe that the spatial beam profile improvements of CVHG
demonstrate herein enables the practical realization of ultra-compact and efficient chirped pulse amplification laser
systems.
Alkali Atom Lasers
Scaling of diode-pumped Cs laser: transverse pump, unstable cavity, MOPA
Show abstract
There has been recent interest in Diode Pumped Alkali Lasers (DPALs) and their scaling to higher powers. Scaling of
DPALs to high powers requires using multiple pump sources such as laser diode arrays or stacks of arrays. Coupling of
multiple pump beams into the laser gain medium can be realized using a transverse pumping scheme that is most
efficient for the laser operating with large mode volume. We have demonstrated Cs laser with unstable resonator
transversely pumped by 15 narrowband diode laser arrays. This laser operates on lowest transverse mode with a diameter
of 7 mm with an optical-to-optical efficiency higher than 30%. An alternative power scaling approach: Master
Oscillator and power Amplifier (MOPA) system with transversely pumped by multiple diode lasers Cs amplifier was
studied experimentally and demonstrated high optical efficiency.
Alkali-vapor lasers
Show abstract
We report on the results from several of our alkali laser systems. We show highly efficient performance from an
alexandrite-pumped rubidium laser. Using a laser diode stack as a pump source, we demonstrate up to 145 W of
average power from a CW system. We present a design for a transversely pumped demonstration system that will show
all of the required laser physics for a high power system.
Modeling laser performance of scalable side pumped alkali laser
Show abstract
Diode pumped alkali lasers (DPAL) offer the potential for high power and efficient operation. The extremely low
quantum defect of the alkali system minimizes thermal management requirements. At the same time DPALs keep
advantages of gas lasers (no thermal stresses, high intrinsic beam quality). Side pumped geometry simplifies system
design, separating laser and pump light and providing physical space for a large number of diode stacks needed for
power scaling. The three-level nature of these lasers complicates modeling, making numerical simulation the most viable
option for system studies in this geometry.
We have built a simplified numerical code for simulation of CW laser performance in different side pumped geometries
and studied performance of a rubidium DPAL with helium and methane buffer gases at high pump power. We observed
dramatic differences in pump absorption with the laser turned off compared to an operating laser. Cell temperature is a
key parameter that controls effective absorption length. If pump density is sufficiently high, we can find an operating
point with optical to optical efficiency above 60% with reasonably homogenous spatial laser output profile even for a
single side pumped laser cell.
Potential energy surfaces for alkali plus noble gas pairs: a systematic comparison
Show abstract
Optically Pumped Alkali Lasers (OPAL) involve interactions of alkali atoms with a buffer gas typically consisting
of a noble gas together with C2H4. Line broadening mechanisms are of particular interest because they can
be used to match a broad optical pumping source with relatively narrow alkali absorption spectra. To better
understand the line broadening processes at work in OPAL systems we focus on the noble gas collisional partners.
A matrix of potential energy surfaces (PES) has been generated at the multi-configurational self consistent field
(MCSCF) level for M + Ng, where M=Li, Na, K, Rb, Cs and Ng=He, Ne, Ar. The PES include the X2Σ
ground state surface and the A2II, B2Σ excited state surfaces. In addition to the MCSCF surfaces, PES for
Li+He have been calculated at the multi-reference singles and doubles configuration interaction (MRSDCI) level
with spin-orbit splitting effects included. These surfaces provide a way to check the qualitative applicability of
the MCSCF calculations. They also exhibit the avoided crossing between the B2Σ and A2II1/2 surfaces that is
partially responsible for collision induced relaxation from the 2P3/2 to the 2P1/2 atomic levels.
Extended saturation analysis and analytical model of diode-pumped alkali lasers
Show abstract
An analytic model for the cw diode pumped alkali laser is developed by considering the longitudinally averaged number
densities of the ground 2S1/2 and first excited 2P3/2, and 2P1/2 states. The pump intensity to reach threshold requires fully
bleaching the pump transition and exceeding optical losses, typically about 200 Watts/cm2. Slope efficiency depends
critically on the fraction of incident photons absorbed and the overlap of pump and resonator modes, approaching the
quantum efficiency of 0.95 - 0.98. For marginal cavity transmission losses, peak performance is achieved for low output
coupling. For efficient operation, the collisional relaxation between the two upper levels should be fast to prevent bottlenecking.
By assuming a statistical distribution between the upper two levels, the limiting analytic solution for the quasitwo
level system is achieved. For properly designed gain conditions, the quasi two level solution is usually achievable
and represents ideal performance.
Excimer-pumped alkali vapor lasers: a new class of photoassociation lasers
J. D. Readle,
C. J. Wagner,
J. T. Verdeyen,
et al.
Show abstract
Excimer-pumped alkali vapor lasers (XPALs) are a new class of photoassociation lasers which take
advantage of the spectrally broad absorption profiles of alkali-rare gas collision pairs. In these systems,
transient alkali-rare gas molecules are photopumped from the thermal continuum to a dissociative X2Σ+
1/2 interaction potential, subsequently populating the n2P3/2 state of the alkali. The absorption profiles ≥5 nm and
quantum efficiencies >98% have been observed in oscillator experiments, indicating XPAL compatibility
with conventional high power laser diode arrays.
An alternative technique for populating the n2P3/2 state is direct photoexcitation on the n2P3/2←n2S1/2 atomic
transition. However, because the XPAL scheme employs an off-resonant optical pump, the strengths of
resonantly-enhanced nonlinear processes are minimized. Additionally, the absorption coefficient may be
adjusted by altering the number densities of the lasing species and/or perturbers, a valuable asset in the design
of large volume, high power lasers.
We present an overview of XPAL lasers and their operation, including the characteristics of recently
demonstrated systems photopumped with a pulsed dye laser. Lasing has been observed in Cs at both
894 nm and 852 nm by pumping CsAr or CsKr pairs as well as in Rb at 795 nm by pumping RbKr. These
results highlight the important role of the perturbing species in determining the strength and position of the
excimer absorption profile. It is expected that similar results may be obtained in other gas mixtures as similar
collision pair characteristics have historically been observed in a wide variety of transient diatomic species.
Multi-dimensional modeling of the XPAL system
Show abstract
The exciplex pumped alkali laser (XPAL) system was recently demonstrated in mixtures of Cs vapor, Ar, and ethane, by
pumping Cs-Ar atomic collision pairs and subsequent dissociation of diatomic, electronically-excited CsAr molecules
(exciplexes or excimers). Because of the addition of atomic collision pairs and exciplex states, modeling of the XPAL
system is far more complicated than classic diode pumped alkali laser (DPAL) modeling. In this paper we discuss
BLAZE-V multi-dimensional modeling of this new laser system and compare with experiments.
Spectroscopic studies of alkali atom-rare gas systems
Show abstract
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.
Poster Session
Fiber-based drive laser systems for the Cornell ERL electron photoinjector
Show abstract
Cornell University is developing a high brightness, high average current electron source for the injector of an Energy
Recovery Linac (ERL) based synchrotron radiation source. Master oscillator-power amplifier (MOPA) laser systems
have been developed to satisfy the requirements of the Cornell ERL high brightness electron photoinjector. One system
operates at 50-MHz and low average power, and the second system operates at 1.3 GHz and high average power. The
GHz system is comprised of a commercial harmonically mode-locked Yb-fiber oscillator, a SMF pre-amplifier, and a
double-clad, large-mode area Yb-doped fiber amplifier. Currently, the system provides 45 watts infrared power in a train
of 3-ps-long pulses at 1.3 GHz in a near diffraction-limited beam. A BBO Pockels cell is used to generate macropulse
trains at various repetition rates. The infrared pulses are frequency-doubled to produce green beam average power of 15
watts. The green pulses (Gaussian shape, FWHM 2.5 ps) are efficiently shaped to flat-top pulses with sharp rise and fall
times through differential delay in a set of birefringent crystals (YVO4). The transverse shaping is implemented with
commercial refractive beam shaper (Newport). The laser systems design and characterization will be presented. Future
work will address achieving of even larger average powers.
A 20fs synchronization system for lasers and cavities in accelerators and FELs
Show abstract
A fiber-optic RF distribution system has been developed for synchronizing lasers and RF plants in short pulse FELs.
Typical requirements are 50-100fs rms over time periods from 1ms to several hours. Our system amplitude modulates a
CW laser signal, senses fiber length using an interferometer, and feed-forward corrects the RF phase digitally at the
receiver. We demonstrate less than 15fs rms error over 12 hours, between two independent channels with a fiber path
length difference of 200m and transmitting S-band RF. The system is constructed using standard telecommunications
components, and uses regular telecom fiber.
KC Space Pirates and NASA's Power Beaming Challenge
Show abstract
The Space Elevator Games with $2 Million in prize money is one of the most exciting challenges in the NASA
Centennial Challenges program. We had an 8kW TRUMPF laser beaming power straight up 1 kilometer to a moving
vehicle. This paper is the team captain's analysis of the state of the art in power beaming, and the excitement and
challenge of the games themselves. Predictions are made of what new technology we will see in the next round of the
games coming spring 2010.