A new energy transfer chemical laser at 1.315 μm

Article abstract of DOI:10.1016/S0009-2614(00)00687-4

CW laser action has been demonstrated on the electronic I^*(²P_1/2)→I(²P _3/2) transition of atomic iodine at 1.315 μm from the NCl (a¹Δ)+I(²P _3/2) energy transfer reaction. The stimulated emission was generated in a transverse subsonic flow device when hydrogen azide, HN₃, was injected into a flow of iodine and chlorine atoms. The measured laser output power was 180 mW.

Full text of DOI:10.1016/S0009-2614(00)00687-4

4
August 2000
Chemical Physics Letters 325 Ž2000. 537–544
www.elsevier.nlrlocatercplett
A new energy transfer chemical laser at 1.315 mm
)
Thomas L. Henshaw , Gerald C. Manke II, Timothy J. Madden,
1
Michael R. Berman , Gordon D. Hager
Gas and Chemical Lasers Branch, Directed Energy Directorate, Air Force Research LaboratoryrDELC, 3550 Aberdeen AÕe. SE,
Kirtland AFB, NM 87117-5776, USA
Received 23 May 2000
Abstract
CW laser action has been demonstrated on the electronic I Ž P
)
2
2
.
IŽ P . transition of atomic iodine at 1.315 mm
1
r2
3r2
1
2
from the NCl Ža D.qIŽ P
. energy transfer reaction. The stimulated emission was generated in a transverse subsonic
flow device when hydrogen azide, HN , was injected into a flow of iodine and chlorine atoms. The measured laser output
3
r2
3
power was 180 mW. q 2000 Elsevier Science B.V. All rights reserved.
1
. Introduction
first purely chemical laser using fluorine atom com-
bustion technology to initiate lasing in the DFrCO
2
Chemical lasers are devices that derive their popu-
w x
system 2 . It was not until 1978 that McDermott and
co-workers demonstrated the first chemically pumped
lation inversions from exothermic chemical reac-
tions, whether directly or indirectly, and include
photochemical-induced bond dissociation, radiative
recombination of atoms or molecules and energy
transfer ŽET. processes. In view of their generally
electronic transition laser 3,4 . Continuous wave
w
x
Ž
I
cw laser oscillation was achieved on the
.
)
2
2
Ž
P1r2 –I P
.
Ž
.
transition via the ET reaction
between the oxygen metastable, O a D , and
a ground state iodine atom, I P
3r2
1
Ž
.
2
2
efficient conversion of chemical potential into laser
radiation, chemical lasers have been sought after for
numerous applications in which lightweight, self-
contained lasers are utilized. The advent of chemical
lasers began with experiments conducted by Kasper
and Pimentel in 1965, who successfully demon-
strated lasing on various vibrational levels of HCl
obtained by photolysis of H rCl mixtures w1x. A
Ž
.
. This che-
3
r2
mistry forms the basis of the high-powered Chemical
Oxygen Iodine Laser, or COIL, which operates in
the near-infrared at 1.315 mm with cw power up to
4
0 kW.
Long lived metastables are noted for their impor-
tance as energy carriers in chemical laser media and
identifying suitable electronically excited metasta-
bles for short wavelength laser utility has been the
focus of extensive work over several decades w5–9x.
2
2
short time thereafter, Cool et al. demonstrated the
Of considerable interest are the nitrene metastables
)
Corresponding author. Fax: q1-505-846-4807; e-mail:
thomas.henshaw@kirtland.af.mil
Air Force Office of Scientific ResearchrNL, 801 North Ran-
dolph Street, Room 732, Arlington, VA 22203-1977, USA.
1
1
NCl Ža D. and NF Ža D., which are isovalent with
1
1
Ž
.
O2 a D and possess many favorable properties as
energy carriers in a chemically pumped laser system.
0
009-2614r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.
PII: S0009-2614Ž00.00687-4

5
38
T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
Among these are long radiative lifetimes w10,11x and
efficient gas phase chemical generation w10–13x. In
fact, following the discovery of the efficient elec-
tronic ET between NCl Ža D. and atomic iodine
w14,15x,
elsewhere w19–21x and only a brief discussion is
presented here.
The laser cavity consisted of 5 cm wide times 2
cm high stainless steel duct Žcross-sectional area
1
2
s10 cm . whose inner surfaces were lined with
Teflon ramps and flow shrouds to minimize wall
deactivation and help confine the active gain zone to
a nominal 5 cm length. The resonator mirrors ŽM1
and M2 in Fig. 1. were 2.54 cm in diameter and
were mounted on two 2.54 cm ŽOD. vacuum tubes
1
2
3
qI) P1r 2
2
NCl
Ž
a D
.
qI P
NCl
Ž
X S
.
ž
3r 2
/
ž /
Ž
1
2
.
.
I) P1r 2
2
2
/ ž 3r 2 /qhn Ž
I P
1.315 mm
.
,
Ž
ž
with mirror bellows and micrometers for alignment.
The mirrors were separated by 1.15 m and purged
with He during laser operation. The reactor wall
height Ž2 cm. and the inside diameter of the mirror
several laboratories have attempted the demonstra-
tion of gain and or lasing on the 1.315 mm transition
of atomic iodine using this mechanism. In 1992,
)
2
Ž
.
Yang et al. provided evidence of an I Ž P .–
mount 2 cm adjoining the mirrors to the vacuum
tubes defined the minimum aperture of the cavity.
Laser power measurements were conducted under a
variety of optical resonator conditions. However,
owing to the potentially small signal gain of the
system, the initial resonator was fitted with two
symmetric 5 m concave ultra-high finesse cavity
mirrors ŽResearch Electro Optics Corp.. These mir-
1
r2
2
IŽ P . population inversion in a subsonic flow
3
r2
1
using chemically generated NCl Ža D. w16x and
shortly thereafter near threshold laser oscillation was
1
)
2
observed in the NCl Ža D.–I Ž P . system by Ray
and Coombe from the pulsed ArF laser photolysis of
ClN and CH I w17x. Recently, this laboratory re-
ported for the first time a direct and quantitative
measurement of the population inversion between
1
r2
3
2 2
rors were primarily used to overcome cavity losses
and confirm the presence of stimulated emission.
The high finesse mirrors were characterized by cav-
ity-ring-down spectroscopy ŽLos Gatos Research, Los
Gatos, CA. which revealed a high reflectivity of
2
2
the Ž P . and Ž P . states of atomic iodine pro-
3
r2
1r2
1
duced by energy transfer from NCl Ža D. w18x. This
effort represented a significant milestone in the de-
velopment of a chemically pumped, all gas phase
iodine laser. In continuing our investigation into the
9
9.998"0.001% at 1.32 mm; however, measure-
1
)
2
NCl Ža D.rI Ž P . ET system, we report for the
ment of transmission and substrate absorptionr
scattering losses were not performed. Subsequent to
the initial laser demonstration, additional power ex-
traction experiments were conducted using various
output couplers listed at a nominal 99.9% reflectivity
ŽCVI, Inc.. and the high finesse back reflector of
1
r2
)
2
first time an example of continuous wave I Ž P .–
1
r2
2
IŽ P . laser oscillation resulting from entirely gas
3
r2
phase chemical generation.
9
9.998% reflectivity. Coarse alignment was obtained
2
. Experimental
The demonstration of I Ž P .–IŽ P . laser
by first superimposing a He:Ne laser beam through
the centerline of the flow reactor and then adjusting
the resonator mirrors such that reflected beams from
the resonator mirrors are collinear with the reactor
centerline. The laser power output was measured
with an Ophir power meter ŽModel PD 300-IR Nova.
)
2
2
1
r2
3r2
action was performed in a transverse subsonic flow
reactor shown in Fig. 1. The essential features
of this apparatus are a dc discharge for F atom
production, an axial injector for DCl injection, and
two side-wall transverse injectors for HI and HN3
admission into the flow stream. In addition, the
apparatus is equipped with sensitive optical diagnos-
for tests in the 0–30 mW range and a Coherent
meter ŽModel 210. for powers above 30 mW.
The observation of small signal gain on the
2
)
2
IŽ P .–I Ž P . transition was measured with a
continuously tunable, single-mode 1.315 mm diode
laser with a spectral line width of less than 500 kHz
ŽFWHM. over 30 GHz from 7602.4 to 7603.5 cm
3
r2
1r2
2
tics for measuring optical gain between the IŽ P .–
3
r2
)
2
I Ž P . states. Experimental details of the gain
1
r2
y1
measurement and methodology have been described
.

T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
539
Fig. 1. Schematic representation of the subsonic flow device and optical resonator showing Ž1. dc discharge, Ž2. axial injector ŽDCl., Ž3.
first set of transverse wall injectors ŽHI., Ž4. second set of transverse wall injectors ŽHN . and Ž5. flow confinement shrouds. The optical
3
cavity, consisting of mirrors M1 and M2, is joined to the flow tube by two tubes containing mirror mounts, bellows and micrometers for
alignment. Each tube is purged with He and the out-coupled laser power measured with a power meter ŽPM..
This performance allows the laser to scan across the
double-pass arrangement providing a pathlength of
10 cm.
Fluorine atoms are generated using a 10 kW dc
discharge Ž1.75 kW actual power load when running.
2
)
2
entire IŽ P .–I Ž P . transition with complete
3
r2
1r2
hyperfine resolution. Since the FŽ3,4. transition in
iodine exhibits the highest gain among the hyperfine
2
lines, it was used to monitor the IŽ P
.
of F or NF in helium. The pressure in the system
3
r2
2
3
)
2
I Ž P . gain. The diode laser is operated in a
was regulated by flowing N 1.5 m downstream of
1
r2
2

5
40
T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
1
the reactor cavity through a 3 cm choke orifice. Flow
reactor pressures were measured with calibrated ab-
solute capacitance manometers. Reagents introduced
into the flow stream were measured with either
calibrated mass flow controllers or sonic orifices.
Hydrogen azide was synthesized by the reaction of
molten stearic acid ŽCH ŽCH . COOH. with
hence, NCl Ža D. density would be generated via
this reaction. However, a recent temperature-depen-
dent study on the ClqHN reaction rate coefficient
over the 300–500 K range reveals a significant
3
temperature dependence with kŽT.s1.2"0.3=
y11 1r2
10
T
expŽy1514 " 93rT. w24x. Using the
1.315 mm diode laser, an analysis of the I-atom line
shape shows a Doppler broadened linewidth that
corresponds to an apparent temperature upwards of
650 K. In this regard, a strong enhancement in this
reaction rate is expected and a sizable portion of N3
density is subsequently generated through this reac-
tion chemistry. Furthermore, since both the branch-
3
2 16
sodium azide ŽNaN ., under vacuum at 1108C. A
3
1
0:1 molar excess of stearic acid over sodium azide
was used. The gaseous HN was stored as a 10%
3
mixture in helium. Helium diluent ŽMatheson,
9
9.995%., F ŽMatheson, 20% in He., NF ŽSpectra
2
3
Gas, 99%., DCl ŽCambridge Isotopes, 99%., HI
ŽMatheson, 99%. were used without further purifica-
tion.
1
)
2
ing fractions for NCl Ža D. and I Ž P . in reac-
1
r2
tions Ž6. and Ž7. are reported to exceed 50%, the
mechanism described here depicts an efficient gas
phase chemical process for the production of NCl
)
2
The chemical generation of I Ž P
. and subse-
1
r2
quent lasing is based on a sequential process in
which Cl and I atoms are produced,
1
)
2
Ža D. and I Ž P . w12,13,15x.
1
r2
)
2
Experimentally, the I Ž P . inversion density is
FqDCl
see Ref. w22x ;
DFqCl, k300 K s1=10y11 cm rs;
3
1r2
obtained by an ordered injection of DCl, followed by
HI and finally HN into the flow reactor. The staging
of this injection sequence is important for the follow-
ing considerations. First, a condition of excess F
atoms must be avoided to eliminate the competing
reactions:
Ž
3
.
.
3
2
ClqHI HClqI P
,
ž
3r 2
/
y10
3
k300K s1.0=10
followed by NCl Ža D. production,
cm rs; see Ref. w23x ;
Ž
4
1
FqHN3 HF
Ž
Õ
y10
.
qN3 ,
ClqHN3 HCl
Ž
Õ
.
qN ,k
3
300K
3
k300K s1.1=10
cm rs;
Ž
9
.
s1=10y12 cm rs; see Ref. w24x ;
3
Ž
5
.
.
1
FqN3
NF
Ž
a D
.
qN2 ,
3
1
1
3
1
ClqN3 NCl
Ž
a D,b S,X S
.
qN2
Ž
X S ,k300K
.
y11
k300K s5=10
FqNCl
k300K s2=10
cm rs;
Ž
Ž
10
.
.
s2=10y11 cm rs; see Refs. w12,13x ;
3
Ž
a
.
products,
y11
Ž
6
3
cm rs; see Ref. w13x ,
11
1
1
and finally the ET reaction between NCl Ža D. and
2
)
2
which ultimately deplete the system of NCl Ža D.
production and hence, I Ž P .. Thus, the DCl flow
is typically run in two-fold excess over the measured
F atom flow rate. Further, utilizing DCl as a Cl atom
source is necessary to eliminate the production of
HF, which is an effective quencher of I Ž P . w25x.
Once the F atoms are converted into Cl, the reactions
of Cl with HI and HN proceed with production of
IŽ P . to generate I Ž P .: w12,15x
3
r2
1r2
)
2
1
r2
1
2
3
qI) P1r 2
2
NCl
Ž
a D
.
qI P
NCl
Ž
X S
.
/,
ž
3r 2
/
ž
y11
3
k300K s2=10
I) P1r 2
cm rs
Ž
7
.
.
2
2
)
2
I P
3r 2 /qnhn
Ž
1.315 mm .
.
ž
/qhn
ž
1r2
Ž
8
3
1
The magnitude of these room temperature rate
coefficients indicate a rapid mechanism for the gen-
ground state I, NClŽa D. and HCl, which is a rela-
tively benign quencher of NClŽa D. and I Ž P ..
The injection of HI precedes HN in order to
1
)
2
1
r2
1
)
2
eration of NCl Ža D. and I Ž P ., notwithstanding
1
r2
3
2
the small room temperature ClqHN rate coeffi-
have IŽ P . atoms present in the flow stream
3
3r2
1
cient in reaction Ž5.. Indeed, its value suggests it is
when NCl Ža D. is produced. This minimizes the
1
rate limiting and that minimal N3 formation, and
bimolecular NCl Ža D. self-annihilation rate,

T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
541
y12
3
ks7=10
cm rs, a deleterious effect that would
The gain measured in Fig. 2 represents the neces-
sary but not sufficient condition for laser oscillation.
The conditions under which laser action will occur
depends on the mirror reflectances; strictly speaking
this is when the gain exceeds or is at least equal to
the losses in the resonator. Thus, the immediate goal
is to identify what cavity parameters, specifically
mirror reflectance values, over which power can be
extracted. Considering only the optical losses occur-
ring at the mirror ports, the useful power Žthat is, the
power transmitted to the power meter. is constrained
by mirror reflectivity ŽR., transmittance ŽT., scatter-
ing ŽS. and absorbance ŽA.. Since the scattering-ab-
sorption losses and, to a lesser degree, transmission
of available laboratory mirrors have not been quanti-
fied, a rigorous maximization of output power via
mirror reflectivity was not performed. Nevertheless,
the outcoupling power of the laser exhibits certain
characteristic features; namely there exists a range of
mirror reflectivities over which power can be ex-
tracted and an optimum reflectivity that determines
maximum output power. In this regard, the gain
measurements obtained here are used to determine
the required range of mirror reflectivities where laser
power can be extracted but not necessarily the opti-
mum power.
be considerable at the densities present in these
experiments w26x.
3
. Results and discussion
Although F has been successfully used to gener-
ate gain in this system, the best peak gains were
obtained when NF was used as an F atom source.
As such, Fig. 2 presents a summary of gain scaling
2
3
with respect to various HN flows ranging from 2.0
3
to 5.3 mmolrs for fixed flows of NF at 2.4 mmolrs,
3
DCl at 2.0 mmolrs and HI at 0.07 mmolrs and a
total pressure of 16 Torr. The data was collected 7
cm downstream from the HN injection point, which
3
is the stream-wise position of maximum gain for the
)
2
2
I Ž P .–IŽ P . transition. It is not clear as to
1
r2
3r2
what the operative mechanism is that facilitates the
improved gain with NF . However, in a previous
study it was determined that conversion of F to F
atoms in the discharge is incomplete and significant
3
2
amounts of F flow into the reactor cavity w27,28x.
2
This may result in IF production through the sec-
ondary F qI
IF reaction which promotes effi-
2
)
2
cient I Ž P . quenching.
1
r2
The gain, g, in the active medium when lasing is
present in this analysis is given by
2
7
l A
1
2
3
,4
2
2
gs 1
f
Ž
n0
.
I) P1r 2
/ y
I P
3r 2
ž
ž
/
12
ž
/
.
2
8p
ss3,4 D N
where l is the wavelength Ž1.315 mm., A is the
Einstein coefficient Ž5.08 s . and fŽn . is the nor-
malized line shape function for spectral broadening.
In the absence of stimulated emission, the population
Ž
3
,4
y1
)
2
2
density of I Ž P
. and IŽ P
. are not perturbed
3r2
2
1
r2
)
and Eq. Ž12. is distinguished by g ss
ŽwI Ž P
0
3,4
2
.
x –1r2wIŽ P
.x ., which is the small signal
1
r2
0
3r2
0
gain. Under steady state conditions, where the only
losses are assumed to be occurring at the mirror
output ports, the saturated gain, g, is
Fig. 2. A summary of gain scaling with respect to various HN3
flows ranging from 2.0 to 5.3 mmolrs for fixed flows of NF s2.4
3
mmolrs, DCls2.0 mmolrs, HIs0.07 mmolrs, and a total
pressure of 16 Torr. The He bath gas constitutes 95% of the total
gas flow. The data was collected 7 cm downstream from the HN3
injection point, which is the stream-wise position of maximum
yln R R
1
2
gs
Ž
13
.
2 L
)
2
2
gain for the I Ž P .–IŽ P . transition. Under these condi-
1
r2
3r2
y4
y1
where R and R are mirror reflectivities and L is
tions, the maximum small signal gain, g s2.1=10
was obtained at an HN flow of 5.3 mmolrs.
cm
,
1
2
0
the cavity path length. This relates the minimum gain
3

5
42
T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
to the design features of the oscillator. When Rs
, the minimum reflectance at threshold, the I and
)R)0.9979, were examined for their effect on
extracting higher laser power.
The high finesse optical cavity consisted of two
symmetric mirrors ŽM1 and M2 in Fig. 1. with
0.99998 reflectivity at 1.32 mm and 5 m radius of
curvature. The flow reactor and resonator conditions
for demonstrating lasing are tabulated in Trial 1,
Table 1. Evidence of laser action was demonstrated
by measuring the output power on a calibrated power
R
min
)
I
inversion density is unperturbed and gsg and
0
the laser just begins to oscillate. As the reflectivity is
increased the cavity losses are overcome and the
output power increases concurrently until a maxi-
mum is reached. In the limit as the cavity losses go
to zero, the optimum reflectivity approaches unity
and the maximum power occurs at zero output cou-
pling. However, when R
1 small but finite losses
meter. Thus, upon adding HN to a steady stream of
3
such as a distributed non-saturable loss, diffraction,
scattering and mirror absorption can become compa-
rable to the transmitted power in which case the
power falls off.
Cl and I atoms, 3 mW of power was measured per
mirror port for a total of 6 mW. In addition, the
mode pattern of the laser was easily observed on a
near-IR phospor card Ž1.3 mm. at a distance of 2 m
from the output coupler ŽM1.. In contrast, upon
The mirror reflectivity, R , that is required to
1
overcome losses due to threshold laser action is
misaligning the cavity or turning off any of the fuels,
the laser power signal was immediately extinguished
and returned to baseline. The laser run time is typi-
cally 20–30 s; however, this period of operation
simply was performed only to conserve the HN3
fuel. Longer run times of up to several minutes are
possible and are only limited by the storage volume
ey2 L g0
R s
.
Ž
14
.
1
R2
Accordingly, using the maximum g s2.1=
0
y4
y1
1
0
cm
obtained from Fig. 2, Ls5 cm and
letting R s0.99998, the minimum reflectivity R
and pressure of our HN reservoir Ž300 L..
2
1
3
required to overcome cavity losses is 0.9979. Simi-
In keeping with the measured g and reflectance
0
larly, allowing R sR s0.99998, the minimum
range defined above, attempts at extracting more
power from the cavity were performed by replacing
the output coupler ŽM1. with a more transmissive
1
2
y6
y1
gain at threshold is 4=10
cm . Consequently,
the values of R Žtaken as R . and R Ž0.99998.
1
min
2
bound the extractable power to range of mirror trans-
mirror. In this vein, two mirrors with vendor quoted
nominal reflectance values of 0.998 R Ž2 m cc. and
0.999 R Ž2 m cc. were tested for output power. In an
y5
missions, Ts1yR, between 2=10
and 2.1=
y3
1
0
. Since this is a very narrow transmission re-
gion, a resonator was specifically designed with two
ultra-high finesse mirrors in order to confidently
overcome cavity losses and ensure laser action, but
not necessarily achieve maximum laser power. Thus,
once lasing was demonstrated output couplers of
lower nominal reflectivity, within the range 0.99998
effort to characterize these mirrors more fully, sev-
eral independent in-house transmission measure-
ments were performed on these mirrors using the
1.315 mm gain probe laser. However, no attempt at
specifying the mirror scattering or absorption was
performed. For purposes of clarity, the 0.998 R and
Table 1
)
2
2
Flow reactor and resonator conditions for achieving laser action on the I Ž P .–IŽ P . transition
1
r2
3r2
Trial
Flow reactor conditions
Resonator conditions
He
NF3
DCL
HN3
HI
P
Zone
HR
OC
Power
Žmmolrs.
Žmmolrs.
Žmmolrs.
Žmmolrs.
Žmmolrs.
ŽTorr.
Žcm.
ŽmW.
1
2
3
4
128.80
127.86
149.78
141.73
1.08
1.02
1.53
1.51
2.11
2.20
2.22
2.40
3.16
3.03
4.36
4.59
0.04
0.04
0.07
0.07
15.73
15.61
14.67
14.95
15
15
15
15
0.99998
0.99998
0.99998
0.99998
0.99998
6
19
110
180
0.9988 ŽI.
0.9988 ŽI.
0.9988 ŽII.

T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
543
0
.999 R mirrors were labeled OC I and OC II,
and the subsequent role they play on laser perfor-
mance.
respectively. Accordingly, results from these mea-
surements give an average transmisson of 1.2"0.1
y3
=
10
ŽRs0.9988"0.0001. for both OC I and
OC II and thus, within experimental uncertainty,
there is no apparent difference in the reflectance
values between these two mirrors. Trial 2 in Table 1
shows the effect of substituting the high finesse
outcoupler with OC I, Rs0.9988. For near identical
flow conditions, the output power more than triples.
Indeed, using OC I under the enhaced NF , HN and
Acknowledgements
The authors wish to acknowledge Brian Ander-
son, Ralph Tate, Dr. John Herbelin, Vaughn Halford,
Richard Hagenloh and Dr. Shiv Dass for their techni-
cal assistance in these studies.
3
3
HI flow conditions shown in Trial 3 the power
increases considerably to 110 mW. Interestingly, in
Trial 4 the power extraction is repeated with OC II,
Rs0.9988, and a significant power enhancement to
References
w1x J.V.V. Kasper, G.C. Pimentel, Appl. Phys. Lett. 5 Ž1964.
1
80 mW is observed. Since the transmission mea-
2
31.
surements for OC I and II are somewhat limited in
accuracy, the power enhancement shown with OC II
may be attributed to slight variations in the magni-
tude of the mirror transmission that are not discern-
able by these measurements, or possibly by other
systematic effects such as better cavity alignment. It
should be noted that although attempts were made at
keeping the flow rates constant, the recorded HN3
and DCl flow rates in Trial 4 were slightly higher
and thus may also have contributed to the overall
increase in power.
2 T.A. Cool, R.R. Stevens, T.J. Falk, Int. J. Chem. Kinet. 1
w x
Ž1970. 295.
w3x W.E. McDermott, N.R. Pchelkin, D.J. Benard, R.R. Bousek,
Appl. Phys. Lett. 32 Ž1978. 469.
w4x D.J. Benard, W.E. McDermott, N.R. Pchelkin, R.R. Bousek,
Appl. Phys. Lett. 34 Ž1979. 40.
w x
5
J.M. Herbelin, N. Cohen, Chem. Phys. Lett. 20 1973 605.
w6x T.C. Clark, M.A.A. Clyne, Trans. Faraday Soc. 66 Ž1970.
77.
w7x C.T. Cheah, M.A.A. Clyne, J. Chem. Soc. Faraday Trans.
r76 Ž1980. 1543.
w8x A.T. Pritt Jr., R.D. Coombe, Int. J. Chem. Kinet. 12 Ž1980.
41.
Ž
.
8
2
7
w9x M.A.A. Clyne, A.J. MacRobert, J. Brunning, C.T. Cheah, J.
Chem. Soc. Faraday Trans. 2r79 Ž1983. 1515.
w10x J. Habdas, S. Watengaonkar, D.W. Setser, J. Phys. Chem. 91
Ž1987. 451.
4
. Summary and conclusion
w11x D.R. Yarkony, J. Chem. Phys. 86 Ž1987. 1642.
A new, chemically pumped, continuous wave laser
w
1
2
x
Ž
.
R.J. Malins, D.W. Setser, J. Phys. Chem. 95 1981 1342.
w13x T.L. Henshaw, S.D. Herrera, L.A. Schlie, J. Phys. Chem. A
02 Ž1998. 6239.
2
)
2
operating on the IŽ P .–I Ž P . transition of
3
r2
1r2
1
iodine at 1.315 mm has been demonstrated. The laser
w14x G.C. Manke II, D.W. Setser, J. Phys. Chem. A 102 Ž1998.
is based on the ET reaction between metastable NCl
1
2
7257.
Ža D. and ground state IŽ P . atoms. This repre-
3
r2
w
15x
x
Ž
.
R.D. Bower, T.T. Yang, J. Opt. Soc. Am. B 8 1991 1583.
sents a significant step in the development of a
chemically pumped, all gas phase iodine laser. The
efficiency of the laser at this time is not fully charac-
terized since the current device features small gain,
pathlength and limitations in the amount of fluorine
atoms that can be generated in this device. Future
work will be directed at constructing a larger device
with longer pathlength and higher mass flow rates to
enhance the single-pass gain and mode volume of
this system. In addition, continued efforts will be
directed at obtaining a more detailed understanding
of the mixing and chemical kinetics of this system
w
Ž
.
1
6
A.J. Ray, R.D. Coombe, J. Phys. Chem. 97 1993 3475.
w17x T. Yang, V.T. Gylys, R.D. Bower, L.F. Rubin, Opts. Lett. 24
Ž1992. 1803.
w18x A.J. Ray, R.D. Coombe, J. Phys. Chem. 99 Ž1995. 7849.
w19x J.M. Herbelin, T.L. Henshaw, B.D. Rafferty, B.T. Anderson,
R.F. Tate, T.J. Madden, G.C. Manke II, G.D. Hager, Chem.
Phys. Lett. 299 1999 583.
Ž
.
w20x R.F. Tate, B.T. Anderson, P.B. Keating, G.D. Hager, Proc.
SPIE Gas Chem. Lasers Intense Beam Appl. 3268 Ž1998.
1
15.
w21x B.D. Rafferty, B.T. Anderson, T.L. Henshaw, J.M. Herbelin,
G.D. Hager, Lasers 97 Ž1997. 23.
w22x T.L. Henshaw, T.J. Madden, J.M. Herbelin, G.C. Manke II,
B.T. Anderson, R.F. Tate, G.D. Hager, Paper 3612-24, SPIE

5
44
T.L. Henshaw et al.rChemical Physics Letters 325 (2000) 537–544
Conference on Gas and Chemical Lasers and Intense Beam
Applications II, San Jose, CA, January 1999.
w26x R.D. Coombe, A.T. Pritt Jr., J. Chem. Phys. 66 Ž1977. 5214.
w27x T.L. Henshaw, S.D. Herrera, L.A. Schlie, J. Phys. Chem. A
101 Ž1997. 4048.
w28x G.C. Manke II, T.L. Henshaw, T.J. Madden, J.M. Herbelin,
B.D. Rafferty, G.D. Hager, accepted for publication in J.
AIAA, April 2000.
w23x M.A.A. Clyne, W.S. Nip, Int. J. Chem. Kinet. 10 Ž1978. 367.
w24x F.J. Wodarczyk, C.B. More, Chem. Phys. Lett. 26 Ž1974.
4
84.
w25x G.C. Manke II, T.L. Henshaw, T.J. Madden, G.D. Hager,
Chem. Phys. Lett. 310 Ž1999. 111.