An all gas-phase iodine laser based on NCl3 reaction system
Taizo Masuda*a, Tomonari Nakamurab, Masamori Endob, Taro Uchiyamaa
a
Department of System Design Engineering, Keio University, 3-14-1 Hiyoshi, Kohokuku,
Yokohama, 223-0061, Japan
b
Department of Physics, Tokai University, 1117 Kita-Kaname, Hiratsuka, 259-1292, Japan
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.
Keywords: chemical laser, iodine laser, nitrogen trichloride, metastable NCl, AGIL, COIL.
1. INTRODUCTION
The chemical oxygen-iodine laser (COIL) system, in which stimulated emission of the magnetic dipole transition of
atomic iodine produces laser output at 1315 nm wavelength, was first demonstrated by McDermott et al.1 as a promising
technology for high-power chemical laser. Owing to its scalability to a megawatt-level output, high atmospheric
transmittance and capability with glass optics for flexible beam delivery, COIL system have been expected not only for
military application, but also civilian applications such as disaster relief activities and space debris removal and so force.
However, the COIL has an inherent drawback for mobile laser platform. First, it is necessary to prepare the basic
hydrogen peroxide which is the energy source of the COIL immediately before laser oscillation because it is unsuitable
to long preservation. Second, the generators constitute a large fraction of the overall weight of the COIL system and add
water vapor, a relatively strong deactivator of excited iodine atoms.
Consequently, there has been considerable interest in developing alternate systems that use the iodine atoms as the laser
species but different energy transfer partners which is produced by all gas-phase chemical reactions because iodine is an
ideal for the lasing species. As a compound that meets such a requirement, only the nitrene metastables NCl(a1Δ) and
NF(a1Δ) have been found so far. Both compounds are isovalent with O2(a1Δ) which is the energy carrier of COIL and
possess many favorable properties as energy carriers in a chemically pumped laser system, and have long radiative
lifetime and can be generated efficiently via gas phase chemical reactions.2,3
In 2000, Henshaw et al. succeeded in operating the first continuous wave atomic iodine laser pumped by chemically
produced NCl(a1Δ) using all gas-phase reactionts.4 This laser is called all gas-phase iodine laser or AGIL. The energy
carrier of this system is a NCl(a1Δ) produced from fluorine atoms and hydrogen azide, NH3, and iodine atoms were
excited by energy transfer reaction from NCl(a1Δ) according to Eq. (1).
NCl(a1Δ) + I → I* + NCl(X)
(1)
While this scheme avoids wet chemistry, it still requires highly toxic and explosive hydrogen azide, highly corrosive
fluorine, and expensive DCl. Therefore, a scheme of producing NCl(a1Δ) without using these species is highly
preferable.
*[email protected]; phone +81-45-566-1725; fax +81-45-566-1720
High Energy/Average Power Lasers and Intense Beam Applications IV, edited by
Steven J. Davis, Michael C. Heaven, J. Thomas Schriempf, Proc. of SPIE Vol. 7581,
758106 · © 2010 SPIE · CCC code: 0277-786X/10/$18 · doi: 10.1117/12.840785
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Coombe et al. developed an amine-based chemistry for producing NCl(a1Δ) which scheme does not require any of above
unfavorable species.5,6 This alternate process uses the following two-step reactions.
NCl3 + H → NCl2 + HCl
(2)
NCl2 + H → NCl(a1Δ) + HCl
(3)
1
They also demonstrated an efficient energy transfer to iodine atoms from the NCl(a Δ) produced by the above reactions.
The amine-based chemistry offers an attractive alternative to the azide-based chemistry used in the original AGIL
because NCl3 is inherently more stable than hydrogen azide and can be stored as liquid phase. Although many thorough
experiments have been conducted7,8,9, the achievement of laser oscillation has not been reported yet from any laboratory.
In this paper, we report on the establishment of the detail conditions that should allow us to achieve laser oscillation by
using numerical simulation code developed in our laboratory. Following the calculations, we fabricated a flow reactor
and demonstrated a laser action for the 2P1/2-2P3/2 transition of iodine atom pumped by energy transfer from NCl(a1Δ)
produced by a set of amine-based, all gas-phase chemical reactions for the first time.
2. NUMERICAL SIMULATION
2.1 Model description
We have applied the simulation code originally developed for COIL10 to an amine-based AGIL system. Fig. 1 shows a
schematic drawing of the one-dimensional, multiple-leaky-stream-tubes kinetics model. The flow field is divided into n
stream tubes of primary flow layers, secondary flow layer, third flow layer, and fourth flow layer. The main-flow
direction is defined as x and the perpendicular axis is
defined as y. The secondary flow, third flow, and fourth
flow layers are not mixed with adjacent layer until the
predefined nozzle position is reached. Downstream of the
each nozzle position, diffusive mixing of adjacent layers
is assumed. Downstream of the fourth flow injector, a
rooftop optical resonator is placed where the interaction
of iodine atoms and photon flux is calculated. Flow field
is discretized in the x coordinate by a 1 mm grid, and in
the y direction, the width of the duct is divided into n
primary layers and the width of the other three flow layers
is determined in accordance with their molar flow rates.
Both top and bottom boundaries in Fig. 1 are assumed to
be symmetric. Therefore, layer 0 represents the center of
the duct, while the (n+2)th layer represents the top and
Fig. 1: Schematic drawing of the one-dimensional, multiplebottom walls of the flow duct if a wall injection scheme is
leaky-stream-tubes kinetics model.
assumed.
The partial differential equation governing the flow field is as follows.
∂M i ( x, y, t )
=
∂t
∑C
2
g [T ( x,
y, t )]M j ( x, y, t ) M k ( x, y, t )
g
+
∑C
3
h [T ( x,
y, t )]M o ( x, y , t ) M p ( x, y, t ) M q ( x, y, t )
h
∂
− {M i ( x, y, t ) H ( x)v( x)} / H ( x)
∂x
∂n p ( x, t )
∂ 2 M i ( x, y , t )
− Da
−δ
2
∂t
∂y
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(4)
Here, M i ( x, y, t ) is the number density of the ith species [1/cm3], C g2 [T ] is the rate constant of the gth reaction of 2nd
order [cm3/s], Ch3 [T ] is the rate constant of the hth reaction of 3rd order [cm6/s], T is the gas temperature [K], H(x) is the
height of the duct [cm], v(x) is the gas velocity at position x [cm/s], Da is the artificial diffusion constant, and np is the
photon density [1/cm3]. δ=–1 if i represents the upper state of the iodine atom, δ=1 if i represents the ground state of the
iodine atom, and δ=0 for the other cases.
The differential equation is discretized by the upwind finite difference method. The upstream boundary condition is
given by the set of equations,
M i (0, t ) = M 0i
(5)
The difference equation is explicitly integrated in the time domain with first-order accuracy.
The rate equation set used in this work is not shown here, but the readers would find the complete description of the
model in Ref. 11.
2.2 Results of calculations
We investigated the detailed conditions such that laser oscillation of an amine-based AGIL system can be achieved with
facilities available in our laboratory. The schematic of the apparatus, namely, the mixing nozzle configurations and
hydrogen atom generation scheme were assumed the same as that of developed by Physical Science Inc. (PSI).9
First, we calculated the small signal gain under the condition that the nozzle configuration was the same as that of PSI
and molar fraction of each chemical species was varied. By optimizing the flow rates of each species, maximum small
signal gain was found to be 1.0×10–2 %/cm. Table 1 shows the optimum molar fractions of each chemical species.
Table 1: Optimum molar fractions of each chemical species for the PSI setup.
Species
Flow rate (mmol/s) Mole fraction (%) Pressure (Pa)
HI
0.08
0.13
0.9
NCl3
0.2
0.32
2.1
H2
H
1.0
1.0
1.61
1.61
10.8
10.8
Ar (NCl3 carrier)
30
48.17
322.7
He (HI and H2 carrier)
Total
30
62.3
48.17
-
322.7
670
This value is not high enough to start lasing because it was estimated that the threshold of the small signal gain that
should start lasing is about 1.2×10–4 cm-1 when the mirror is the same as in the original AGIL12. Close examination of the
elementary processes in the active zone revealed that there are two critical reactions that affect small signal gain
evolution. The first one is the self annihilation reactions between two NCl(a1Δ) molecules and the second one is
deactivation of exited iodine atoms, I*, by chlorine atoms. The impacts of these reactions were confirmed by deleting one
of these reactions from the rate equation set and calculated small signal gain. Because of these two reactions, no matter
how much flow rates of NCl3 and HI are increased, the small signal gain didn’t grow further.
We tried to circumvent these negative reactions by modifying injection order of the species. To reduce the influence of
the self annihilation reaction, it is necessary to lower the probability of the collision between generated NCl(a1Δ)
molecules, by homogenizing the local concentration of NCl(a1Δ) molecules. To achieve this, we thought of mixing NCl3
to the main flow in advance, and then injecting HI and H2/H as secondary and tertiary flows. Calculations were
conducted under the conditions that the NCl3 flow rate was fixed and injection positions of secondary and tertiary flows
were varied. In these calculations, the molar fractions of NCl3, H2, H and HI were fixed at the same values as in the first
calculation which gave the highest small signal gain, and only molar fractions of carrier gases were changed to maintain
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With this new nozzle arrangement a small signal gain
of 2.1×10–2 %/cm was obtained. This value is
equivalent to the gain measured in the original AGIL
based on azide chemistry 12.
In conclusion, we have shown that the nozzle order is
crucial for achieving a positive gain in amine-based
AGIL and the key is the reduction of deactivation
reaction of excited iodine atoms by chlorine atoms
and of the self-annihilation reactions.
0.025
0.020
Small signal gain (%/cm)
the total flow rate unchanged. Fig. 2 shows the
calculated results of the peak small signal gain as a
function of the HI nozzle position relative to the
H2/H nozzle position. The minus sign represents that
the HI nozzle is located upstream of the H2/H nozzle.
As seen in the figure, the highest small signal gain
was obtained when HI nozzle and H2/H nozzle were
positioned at the same point of the flow duct.
0.015
0.010
0.005
H2/H nozzle positon
0.000
-20
-15
-10
-5
0
5
10
15
Relative position (mm)
Fig. 2: Calculated peak small signal gain as a function of the
HI nozzle position relative to the H2/H nozzle position.
3. EXPERIMENT
3.1 Experimental setup
We have fabricated a flow reactor based on the knowledge from the calculated results. A block diagram of the
experimental setup is shown in Fig.3. The apparatus consisted of an upstream mixing section and downstream gain
section. The upstream section was a Pyrex glass circular tube of 20 mm in diameter, and the downstream section was a
rectangular duct with an optical cavity, 50 mm in width and 10 mm in height. Three injectors were located on branches
of the mixing tube, supplying NCl3, atomic hydrogen, and HI. The HI and H2/H injectors were located at the same point
on the mixing tube. The NCl3 was synthesized prior to the experiment, and stored in a dry ice/methanol bath. The
detailed synthesis process of NCl3 is described in our previous publication13.
The hydrogen atoms were produced by a microwave discharge in the H2/He admixture. The microwave generator was
built from a commercially available magnetron (SANYO 2M217J) originally designed for a microwave oven, operating
at 2.45 GHz. Since it was driven by a simple half-wave rectification circuit, the magnetron worked only at half cycle of
the commercial power source (50 Hz). Microwave power was coupled with plasma in a rectangular cavity resonator
through which the hydrogen tube passed. The dimensions of the resonator box were 100 × 50 × 150 mm3. The intensity
of the discharge plasma emission was measured using a Si photodetector at the stem of the H/H2 branch. In all the
experiments, we ran the magnetron at an output of 600 watts. To achieve a higher dissociation level of hydrogen
molecules, the H2/He mixture was precooled in a dry ice/methanol bath before admitting it to the microwave resonator.
The optical resonator consisted of two symmetric mirrors having R ≥ 99.984% and T=0.004% at 1315 nm (Showa
Optronics) and a 2 m radius of curvature; the mirrors were mounted on bellows with threaded screw adjuster for
alignment. The mirrors were separated by 340 mm and purged with nitrogen gas during laser operation. The resonator
was placed at the center of the gain section, whose optical axis was 170 mm from the mixing point of H and HI. The
resonator’s clear aperture was 30 mm.
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Laser power was measured with an Ophir L30A-SH power meter. An infrared detection card (Quantex Q-32-R) was
illuminated from the backside to observe the intensity profile of the output beam. Transient laser power and small signal
gain were also measured with a Ge photodiode (Hamamatsu B1919-01) with amplifier and tunable laser diode,13
respectively.
3.2 Results and discussion
A. Demonstration of a laser action.
The typical gas-flow conditions for the laser oscillation experiments are given in Table 2. We were unable to measure the
molar flow rate of NCl3, however, it should have been somewhere between 0.05 and 0.1 mmol/s, judging from the total
Cl2 dose in a NCl3 production batch and the typical yield of NCl3 reported.7
Table 2. Typical operating conditions.
Species
Flow rate (mmol/s)
Mole fraction (%)
Pressure (Pa)
HI
H2
H
NCl3
Ar (NCl3 carrier)
He (H2 carrier)
total
0.003
0.21
0.18
0.05-0.1
6.7
8
15
0.02
1.4
1.2
0.3-0.6
balance
53
100
negligible
13
11
418
492
934
When a flow of the NCl3/Ar mixture was admitted to a stream containing H atoms, a red flame produced by the
NCl(b1Σ) → NCl(X3Σ) transition was clearly visible. The intensity of the red emission increased with time because the
flow rate of NCl3 increased as the temperature of the NCl3 container increased gradually. For safety reasons, the NCl3
container was taken out from the cold bath immediately before the experiment, and no heat was adapted to it.
Fig. 4 shows the time-resolved measurement of the Ge photodiode signal and the voltage of the commercial power
source. The measurement result of small signal gain is also shown in Fig. 4. It is clearly seen that the laser oscillated
during half of the alternating current cycle, during which the magnetron was working and positive gain was obtained.
The observations suggest that the production of the hydrogen atom was incomplete, making it currently the limiting
factor of the laser power as we suggested in our previous publication.13 Fig. 4 also suggested that the small signal gain of
7.8×10–3 %/cm was obtained.
H2/He
Oscilloscope
Dry ice-MeOH
bath
Amplified Si
photodiode
Ge
Photodiode
Mirrors
Pump
Magnetron
50 mm
NCl3/Ar
Power meter
HI
Mixing section
Gain section
Fig. 3: Schematic drawing of the experimental setup.
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Small signal gain (NCl3 on)
Small signal gain (NCl3 off)
0.015
Laser power
0.010
3000
0.005
2000
0.000
NCl3 on
-0.005
Applied voltage
1000
-0.010
-0.015
Transient laser power (arb.unit)
A transverse mode pattern observed on the phosphor is
shown in Fig. 6. The rhombic shape is familiar to us,
reminiscent of the subsonic COIL experiments in the
middle 1980’s. Judging from the width of the beam and
its insensitivity to misalignment, the positive gain was
distributed over an area wider than the optical aperture of
the resonator.
4000
0.020
Small signal gain (%/cm)
Stable output power was observed for several minutes.
Fig. 5 shows the averaged laser output power measured
by power meter and NCl(b1Σ) → NCl(X3Σ) emission
intensity as a function of time. As the NCl(b1Σ) signal
intensity became strong, observed laser power became
strong. We typically turned off the laser at 300 s or less to
change operating conditions or measurement equipments.
The peak value of the average output power was 10 mW.
As the output was extracted equally from both mirrors,
and the duty factor of the laser was 40% from Fig. 4, the
total output power during the ‘on’ cycle was calculated to
be 50 mW.
NCl3 off
-0.020
0
0
5
10
15
20
Time (ms)
Fig.4: Results of measured laser power signal, the voltage
of power source and small signal gain.
In conclusion, we achieved laser action on the I(2P1/2)I(2P3/2) electric transition of the iodine atom at 1315 nm, pumped by an energy transfer from NCl(a1Δ) produced by an
amine-based, all gas-phase chemical reaction system.
25000
Laser power
Emission intensity
Laser power (mW)
10
20000
NCl(1Σ) emission
(667 nm)
8
15000
6
10000
4
Laser power
5000
2
0
0
0
100
200
Flow
NCl(1Σ) emission intensity (photon/s)
12
1 cm
300
Time (s)
Fig.5: The measured averaged laser output power and
NCl(b1Σ) → NCl(X3Σ) emission intensity as a
function of time.
Fig.6: The observed mode pattern of the laser.
B. Laser characteristics of amine-based AGIL.
Next, we measured distribution of small signal gain and laser output power at three positions in the flow duct to
understand detailed laser characteristics of amine-based AGIL. Table 3 shows the results. In this table, the ‘position’
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refers to the distance measured from the mixing point of H and HI. The highest small signal gain and laser power were
recorded at 170 mm downstream from the mixing point. Nevertheless, the small signal gain recorded at the upstream and
downstream positions (±40mm) were high enough to start lasing. It is in contrary to our intuitive understanding, since the
characteristic length of major chemical reactions occurred in a few centimeters in our numerical simulations. We
hypnotized that the long positive-gain region is owed to the inefficient mixing characteristic of the NCl3 main flow and
the injected flows. To prove this, we measured gas temperature and characteristic mixing length of the flow, then
conducted a series of numerical simulations.
Table 3 The measurement results of small signal gain and laser output power.
Position (mm)
Small signal gain (%/cm)
130
170
210
CW laser output power (mW)
7.2×10
–3
45
7.8×10
–3
50
6.1×10
–3
35
The gas temperature was measured by applying the Gaussian curve fitting to the results of diode laser absorption traces
of the iodine atom (3-4) hyperfine line using the same apparatus as gain measurements. Fig. 7 shows the fitting result.
The temperature measured were 530±35 K and they did not depend on the measurement position, namely, three optical
axes shown in Table 3. The velocity of the flow is then estimated from the temperature measurement and molar flow,
which turned to be 160±15 m/s.
The characteristic mixing length of the flow was measured by observing the distribution of plasma glow along the gas
flow. We operated the apparatus without providing NCl3 and photographed the plasma glow from the side of the mixing
section. Fig. 8 shows the result. The string-like plasma glow is seen beyond the end of the mixing section, and it is seen
that the mixing is still incomplete even the gas enters the gain section. From the figure, the characteristic mixing length
was determined to 120 mm. This value is extremely long compared to conventional subsonic or transonic COILs, or our
initial simulations. Then the question arises: Is it still possible to achieve the amount of gain we observed by this poor
mixing?
Small signal loss (arb.unit)
Experimental
Gaussian fit
0
0
500
1000
1500
2000
2500
Relative frequency (MHz)
Fig.8: Plasma radiation viewed from the side of the
mixing section.
Fig.7: Iodine atom absorption measurement and its
Gaussian fit.
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C. Numerical simulations.
We calculated small signal gain and laser output power under the conditions that gas flow rate, residual loss of the
resonator, transmittance of the mirrors, gas temperature and mixing length were fixed at measured conditions. The
residual loss of the resonator was estimated from the measured results of lasing threshold. The dissociation fraction of
hydrogen molecule was varied as a parameter, since the fraction was the only unknown parameter, which was necessary
for the calculations.
Fig. 9 shows the comparison of the experimentally measured small signal gain distribution along the gas flow and the
calculated results. The horizontal line in Fig. 9 indicates the lasing threshold of our AGIL system. The calculated and
experimental results are very close when the dissociation fraction of hydrogen molecule is 30%. Fig. 9 also suggested
that the positive gain is distributed over an area wider than 200 mm.
We then calculated the laser output power under the
condition that hydrogen dissociation fraction was fixed
at 30%. Table 4 shows the comparison of experimental
and calculated results. The calculated results were in
very good agreement with the experimental results.
Therefore, it can be concluded that the observed laser
characteristics are reasonably explained by the
hypothesis, that the mixing length of our AGIL
apparatus was quite long as we see in Fig. 8.
0.010
Experimental
20%
Small signal gain (%/cm)
0.008
From the calculated results shown in Fig. 9, another
interesting phenomenon is seen. The peak value of
positive gain is reached when the dissociation fraction
is 30%, and higher dissociation fraction merely
shortens the positive gain region without increasing its
peak value. In the course of experiments, we sometimes
experienced that the better coupling of microwave to
the plasma reduced laser output power, and the
calculation in Fig. 9 qualitatively explains that
observation.
10%
0.006
0.004
50%
0.002
Lasing threshold
40%
30%
0.000
-0.002
-0.004
-0.006
0
0.05
0.10
0.15
0.20
0.25
0.30
Distance (m)
Fig.9: Calculated and experimentally measured small
signal gain distribution,
Finally, we conducted the calculation under the conditions that the mixing length was varied as a parameter to see what
happens if we improved mixing. Fig. 10 shows the results. Unexpectedly, the peak gain was not increased as the mixing
length was shortened. On the other hand, the distribution of positive gain was shortened. It can be explained as follows;
both rapid mixing and high dissociation fraction of hydrogen molecule are equivalent from the viewpoint of hydrogen
atom injection rate to the main flow and that results in acceleration of self annihilation reaction of NCl(a1Δ). In addition,
the self-annihilation reaction generates chlorine atoms as shown in Fig. 11, whose density is a determinative factor of
amine-AGIL gain evolution.11 The negative influence of rapid mixing or high dissociation rate was only seen when
molar flow rate of HI was extremely low compared to that of NCl3 like our experimental conditions (Table 2). Higher
gain was seen only when the short mixing length was combined with a high HI flow rate. In these cases, high H atom
flow rate should be accompanied, and that was beyond the specification of current experimental apparatus.
Table 4 Calculated and experimental results of CW laser output power
Position (mm)
130
170
210
CW laser output power (mW)
Simulation
Experimental
42.3
47.5
38.3
45
50
35
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3.0×1014
0.010
80mm
100mm
120mm
2.5×1014
40mm
0.006
60mm
80mm
2.0×1014
Density (cm-3)
Small signal gain (%/cm)
0.008
0.004
0.002
60mm
40mm
0.000
1.5×1014
100mm
120mm
1.0×1014
0.5×1014
-0.002
0
-0.004
-0.006
0
0.05
0.10
0.15
0.20
0.25
-0.5×1014
0
0.30
Distance (m)
0.05
0.10
0.15
0.20
0.25
0.30
Distance (m)
Fig.10: The calculated results of small signal gain
distribution. Iodine dissociation was fixed at 30%
and the characteristic mixing length was varied.
Fig.11: The calculated results of chlorine atom density
distribution. The condition was same as the
calculations shown in Fig. 10.
4. SUMMARY
Theoretical and experimental studies of an amine-based all gas-phase iodine laser (AGIL) were conducted. The
numerical simulation code was a detailed one-dimensional, multiple-leaky-stream-tubes kinetics code. Using this
simulation code, we established the detail conditions required to achieve laser oscillation based on NCl3 reaction system.
Based on these calculation results, we fabricated a flow reactor apparatus. We demonstrated laser action on the I(2P1/2)I(2P3/2) electric transition of the iodine atom at 1315 nm, pumped by an energy transfer from NCl(a1Δ) produced by an
amine-based, all gas-phase chemical reaction system. Stable CW output power of 40 % duty factor was observed for
several minutes. The laser output power during the on cycle was 50 mW. To our knowledge, this is the first achievement
of amine-based AGIL oscillation. Small signal gain and laser power were measured at three different positions in the
flow reactor. The observation was in good agreement with the numerical calculations. To explain the experimental
observations, we assumed that the hydrogen dissociation rate was 30% and mixing length was 120 mm. Both of them
was not perfect from the viewpoint of intuitive understanding, however, the calculation indicated that increasing the
dissociation rate, nor improvement of mixing length did not contribute to the small-signal gain improvement. The reason
was explained as the higher hydrogen atom concentration results in faster self-annihilation NCl(a1Δ), and subsequent Cl
atom generation, which is the determinative factor of amine-AGIL gain evolution. To achieve higher gain, fast mixing
should be accompanied by high HI and atomic H flow rate.
ACKNOWLEDGMENTS
The authors are very grateful to Dr. Steven J. Davis of Physical Sciences Inc. for his useful advices. We are also grateful
to Kawasaki Heavy Industries Ltd, for the lease of their vacuum system and measurement devices.
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REFERENCES
1
McDermott, W. E., N. R. Pchelkin, D. J. Benard, and R. R. Bousek. "An. Electronic Transition Chemical Laser,"
Applied Physics Letters, 32, (1978) 469.
2
J. Habdas, S. Watengaonkar, D.W. Setser, “The F + HN3 System: A Chemical Source for NF(a1∆)”, J. Phys. Chem.
91 (1987) 451.
3
D.R. Yarkony, “On the radiative lifetimes of the B 1-Sigma-+ and A 1-delta states in NCl”, J. Chem. Phys. 86
(1987) 1642.
4
Henshaw, T.L., et al., “A new energy transfer chemical laser at 1.315 μm.”, Chemical Physics Letters, 2000.
325(5,6): p.537-544.
5
D.B. Exton, J.V. Gilbert, and R.D. Coombe, “Generation of Excited NCl by the Reaction of Hydrogen Atoms with
NCl3,” J. Phys. Chem. 91, 2692 (1991).
6
Schwenz, R. W., Gilbert, J.V. and R.D. Coombe, “NCl(a1∆) and I(52P1/2) production in a D/NCl3/HI transverse flow
reactor,” Chem. Phys. Lett., vol. 207, No. 4,5,6, 1993 P.526.
7
McDermott, W.E., Robert Coombe, Julanna Gilbert, Zane Lambert, Mikailia Heldt. , “Flow Tube Studies of NCl3
Reactions”, Gas and Chemical Lasers, and Applications III, Proc. SPIE 5334, pp.11-17. 2004.
8
McDermott, W.E., Robert Coombe, Julanna Gilbert, Zane Lambert, Mikailia Heldt. , “NCl3 as a source of NCl(a)
for an NCl(a)-I laser”, XV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, Proc. SPIE
5777, pp.243-252. 2005.
9
Amy J. R. Bauer, Seonkyung Lee, Danthu Vu, Kristin L. Galbaly, William J. Kessler, and Steven J. Davis, “Studies
of an Advanced Iodine Laser Concept”, in AIAA2005-5040, AIAA 36th Plasmadynamics and Lasers Conference,
Toronto, Ontario, Canada, 2005.
10
M. Endo, T. Masuda, and T. Uchiyama, “Development of Hybrid Simulation for Supersonic Chemical OxygenIodine Laser”, AIAA Journal, Vol.45, No.1, pp.90-97. 2007.
11
T. Masuda, M. Endo and T. Uchiyama, “Numerical simulation of an all gas-phase iodine laser based on NCl3
reaction system,” J. Phys. D: Appl. Phys. 41 055101, 2008.
12
C. Manke II, C. B. Cooper, S. C. Dass, T. J. Madden, G. D. Hager, “A multiwatt All gas-phase Iodine laser
(AGIL)”, IEEE J. Quantum Electron. 39, No.8, pp. 995-1002, 2003.
13
T. Masuda, T. Nakamura, M. Endo, and T. Uchiyama, “Observation of Pumping Reaction in an Amine-Based All
Gas-Phase Iodine Laser Medium”, Jpn. J. of Appl. Phys. 48 (2009) 032501.
Proc. of SPIE Vol. 7581 758106-10
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