Note: Descriptions are shown in the official language in which they were submitted.
1038953
This invention relates to a chemical laser wherein
chlorine dioxide is reacted with nitric oxide to produce ato~ic
chlorine, which in turn is reacted with hydrogen iodide to form
hydrogen chloride at excited energy levels. The hydrogen chloride
may itself be lased, preferably in a transverse flow laser, or its
vibrational energy may be transferred to another molecule such
as carbon dioxide to produce hybrid chemical laser action.
Longitudinal flow and transverse flow laser apparatus adapted to
- implement the foregoing reactions constitute additional aspects
of the present invention. Furthermore, proposals are made for
: extending the transverse flow laser operation to supersonic
flow rates.
SUMMARY OF THE PRIOR ART
For the purposes of this discussion, a chemical laser
is defined as a laser in which the lasing constituent or con- -
stituents are directly derived from exothermic chemical reactions,
requiring no energy input for production of any of the reagunts.
(Energy will normally be required to exhaust spent reagents from
the laser.)
The reactions required in continuous wave (C~ chemical
lasers are ordinarily arranged to occur in flowing gases. -
Accordingly, ~ chemical lasers are made in two general configu-
rations with respect to the direction of gas flow. In the first,
the gas flow is parallel to the optical axis, i.e. the line
connecting the laser mirrors. Such lasers are referred to as
longitudinal flow lasers, wherein the excited gases enter the
optical cavity near one end and flow parallel to the optical
axis to be exhausted near the other end. Since the gases have an
appreciable dwell time in the optical cavity, the properties of
- 30 the mixture will change as the gases flow from one end to the other.
- 2 - ~ "
- - ~ ..... .. . . ..... . .
- :'~ - ' ' ' . ' `' ' .
.}w
¢;..
. ~ . . .
1038953
It is not possible to specify the conditions of the laser medium
without taking account of the evolution of the gases with time
as they make their passage through the optical cavity.
Transverse flow lasers are those in which the gases
flow through the optical cavity at right angles to the line
connecting the mirrors. In this flow configuration, all the
molecules along the optical axis are at generally the same
stage of time development. The dwell time of the gases in the ?;
cavity can be made relatively much shorter than in the case of
the longitudinal flow lasers. Since the excited molecules
reach a maximum concentration at a definite time, the transverse
flow geometry allows the optical axis to be coincident with this
region of maximum concentration.
The general problem in the development of chemical ~-
lasers is to discover chemical reactions that generate products
in an excited state. This excitation must be such as to
exhibit a "population inversion" between the excited states(s)
and a state lying lower in energy; an optical transition
(laser transition) must be possible between the two states.
Many such reactions are currently known,for example:
,
F + H2 ) HF + H
Cl + HI ) HCl + I
o + cs ) cot + s : '
where the superscript t indicates a vibrationally excited
molecule. These reactions are now substantially exploited in ~
the present state of the art (see for example Cool et al., ,
Journal of Applied Physics, Vol, 41, No. 10, Sept. 1970,
p. 4038).
The population inversion required may be produced
in a multi-step process, where excitation is generated in one
- 3 -
: ' : - : ~ . .' : " . , - : , . :
1038953
step, and, by subsequent energy transfer, the population
; inversion is produced in another molecule. This is also
currently exploited in the art in so-called "hybrid chemical
lasers." For example, the following sequence of processes
F + H2 > HF + H
H + F2 > HFt + F
HF + CO2 ) HF + CO2
provide inversion in CO2 according to a well-known CO2 laser
transition populated by vibrationally excited HF.
Many chemical lasers require a gaseous atomic species
(as distinguished from the usual molecular state) as one of the
reagents. For example, molecular chlorine (C12) is not known
to be directly useful, but must first be dissociated into Cl
atoms. Much chemical laser research has been directed to
finding efficient atom production methods. Atomic species such
as those mentioned above are conventionally produced by using
external sources of energy to dissociate molecules (e.g. by
using electrical energy or ultra-violet or other electromagnetic
radiation.)
In a few cases it has proven possible to produce the
atomic species by a chemical reaction. The reaction of nitric ~ -
oxide with fluorine (NO + F2 ) NOF + F), and combustion
of fluorine-rich, hydrogen-fluorine mixtures are examples of
known chemical reactions for production of fluorine atoms.
In this way purely chemical laser operation has been
demonstrated for hydrogen fluoride and deuterium fluoride
lasers operating simultaneously on several transitions near 2.8
microns and 3.9 microns respectively. The vibrationally excited
hydrogen fluoride and deuterium fluoride have also been used to
excite hybrid carbon dioxide lasers at 10.6 microns.
.. , .~ .
'
lQ38953
Continuous wave chemical lasers are known (see for
example, United States Patent 3,668,215 of August 29th, 1972
assigned to the United States of America as represented by the '
Secretary of the Air Force and naming Donald J. Spencer, Harold
Mirels, Theodore A. Jacobs and Rolf W. F. Gross as inventors).
In this patent the inventors teach the operation of a continuous
wave chemically pumped laser in which the pumping action is
achieved by a chemical reaction and in which a supersonic jet
containing fluorine atoms, produced in an arc, and an inert gas
is reacted with hydrogen or deuterium and hydrogen fluoride
is obtained in a vibrationally excited state which can then
lase in a suitable optical laser cavity. As taught in this
patent, the laser action is of the continuous-wave type and is
capable of providing sustained laser power for long time
durations. Such lasers are referred to as "chemically pumped" ~ ~ -
because the vibrational population inversion and radiation
energy are obtained directly by a chemical reaction.
United States Patent 3,560,876, granted the 2nd of
February, 1971, discloses a supersonic flow chemically pumped
- 20 gas laser in which hydrogen chloride, hydrogen bromide, or
hydrogen fluoride are used as a lasing medium which is formed
in a supersonic mixing chamber. Once again the halogen
component is dissociated by means of an electrial discharge as
is the case in United States Patent 3,688,215 previously
referred to.
Although atomic chlorine is known to be a useful ~ -
reagent for generating excited molecules, as in the reaction
Cl + HI ) HClt + I -
the prior art does not disclose chemical production of -
chlorine atoms for use in chemical lasers. However, various
.. .
- 5 -
.. . . .. . , . , ,- , . : , ~. , . ~ . ...
1038953
lasers based on the electrical production of chlorine atoms have
been reported. A chemical laser using chlorine rather than
fluorine would be desirable because of the lower cost of chlorine
and the lower corrosive activity of chlorine as compared with
fluorine.
A hybrid continuous-wave (CW) chemical laser based on
the reaction of chlorine atoms with hydrogen iodide and the
subsequent energy transfer to carbon dioxide has been previously
disclosed. See for example, T. A. Cool and R. R. Stephens,
International Journal of Chemical Kinetics, 1, 495 (1969). This
hydrogen chloride/carbon dioxide hybrid laser operates on the
following chemical processes:
CI + HI ) HCl + I
HCl + CO2 ~ HCl + CO2
where the CO2t thus formedsupportslaser action near 10.6 microns.
Lasing of the excited HClt intermediate at 3.8 microns
has also been effected both in longitudinal flow lasers: see
for example, T. A. Cool et al, as aforesaid, and in transverse
flow lasers: see for example, J. A. Glaze, J. Finzi, and W. F.
Krupke, Applied Physics Letters, 6, 121 (1970).
The chlorine atoms required for these devices were
generated by the electrodeless discharge tvia applied microwave~
or radio-frequency electromagnetic radiation) of C12 diluted in
a suitable inert gas such as helium.
An early transverse flow CW HCl flow laser was
developed by D. W. Naegeli and C. J. Ultee, as described in
Chem Phys. Letters 6, p. 121 (1970). In their device, C12, mixed
with He, was dissociated in a two-stage electrical discharge and
then allowed to flow through a duct and mixed with HI. This
reacting mixture then flowed across the optical cavity in the
-- 6 --
- .,
1038953
transverse sense. The flow was subsonic (about 165 m/s). Total
power consumption in the discharges and total output power were
not reported.
The most recent work on transverse flow HCl CW lasers
known to the inventors is that of M. J. Linevsky and R. A. Carbetta,
described in "Chemical Laser Systems", General Electric Space
Sciences Laboratory Semi-Annual Technical report, March-Sept. 1973,
73SD4278, and in Paper MB-7 of the Fourth Conference on Chemical
and Molecular Lasers, St. Louis, MO., October 1974. These authors
worked with an apparatus similiar to that to be described in the
present specification, with the exception that the flow of
chlorine atoms was generated by means of a 200W electrical discharge
- in He-C12 mixtures. The Cl atoms thus formed were reacted with ~
HI immediately before the flow passed through the optical cavity, ~ -
in common with the other transverse flow devices described above.
When the flow was 0.5 mmol s 1 Cl atoms, a power of about 5 Watts
could be extracted. The pressure in the cavity was near 4 torr.
A chemical method of producing atomic chlorine is
known as follows: -
2 1 ClO + NO2 Kl = 3.4 x 10 13cm3~~1
ClO + NO ~ Cl + NO2 K2 = 1.7 x 10 11cm3s 1
Cl + ClO2 ~ 2ClO K3 = 5.9 x 10~11c~3s~
From these reactions and rate constants, it is seen that, when
two volumes of NO are mixed with one of ClO2, the overall ;
reaction produced Cl and 2NO, as:
C1O2 + 2NO ~ CL + 2No2
See. P. P. Bemand, M. A. A. Clyne and R. T. Watson, Journal of the
Chemical Society, Faraday Transactions 1, 69, 1356 (1973):
J. A. Coxon, Transactions of the Faraday Society, 64, 2118
30 (1968).
-- 7 --
.. ' ,' ' .
1038953
Chemical methods of deriving chlorine dioxide (ClO2)
are also known, although never previously used in a laser context.
According to one such method, loosely packed sodium chlorite
(NaClO2) is flushed with molecular chlorine and helium. The
following reaction occurs between the gaseous C12 and the solid
NaClO2 packing material:
C12 + 2NaClO2 5 ~ 2 NaCl + 2ClO2
See Woodward et al, Trans. Am. Inst. ~hem. Engrs. 40, p. 27,
(1945).
Chlorine dioxide is also available as a commercial pro-
duct stored in an aqueous solution. The required ClO2 may be
liberated from the solution by bubbling a counter current of an
appropriate inert gas such as helium therethrough. Since this
activity would liberate not only the ClO2 but also a certain
amount of water vapour, it would be necessary to pass the effluent
through a drying stage to eliminate most of the water vapour,
since the water vapour would tend to quench the laser activity.
Thehelium is useful for two reasons: (a) Firstly,
since it is convenient to operate the ClO2 generator at atmos-
pheric pressure and since, to avoid risks of explosion, the ClO2pressure should be less than 60 torr, then it is desirable to
include a flow of inert gas through the ClO2 generator. Further-
more, for a fixed pressure of ClO2, the presence of inert diluent
gas reduces the risk of explosions. (b) Secondly, in any case,
efficient lasing action requires that the potential temperature
rise due to the heat liberated from the various reactions be -
reduced by the presence of inert gas.
SUMMARY OF THE INVENTION
In accordance with the present invention, the lasing of
excited hydrogen chloride is accomplished by purely chemical means.
:
` ~0389S3
To this end, either of two processes is employed.
In sccordance, therefore, with one aspect of this invention there
is provided a method for producing continuous wave chemical laser activity
consisting of injecting gaseous nitric oxide from a first injector into a flow
path upstream from an optical resonator cavity, separately injecting gaseous
supplies of chlorine dioxide and hydrogen halide selected from the group con- -
sisting of hydrogen iodide and hydrogen bromide from a second injector into
the flow path upstream from the optical resonator cavity, whereby said flow
path contains a mixture consisting of the reactant gases of hydrogen halide,
nitric oxide and chlorine dioxide, wherein said nitric oxide reacts with the
chlorine dioxide to produce chlorine atoms, which atoms in turn react with
the hydrogen halide to form vibrationally excited hydrogen chloride, the
hydrogen chloride being at a sufficiently elevated energy level that the popu-
lation of some of the energy states are inverted, wherein the resulting gaseous
medium is laseable in the optical resonator cavity and the sequence of injec-
tion of the hydrogen halide is such that the reaction of the hydrogen halide :
with the chlorine atoms is in a time period which is less than the time period
for 63% loss of the chlorine atoms by recombining into chlorine molecules.
By another aspect of this invention, there is provided a method of
effecting continuous wave chemical laser activity, consisting essentially of ~ - . . .
continuously injecting and reacting gaseous supplies of nitric oxide, a hydrogen
halide consisting of one of hydrogen bromide and hydrogen iodide, a suitable
inert gas, and a gaseous compound of chlorine and oxygen into a flow path in
a chamber, and expanding and accelerating the gases to a supersonic velocity
so as to yield a supersonic flow including vibrationally excited gaseous
hydrogen chloride; and using the vibrationally excited gaseous hydrogen
chloride immediately downstream of the region of formation thereof for con-
tinuous wave laser activity, wherein the sequence of injection of the hydrogen
halide is such that the reaction of the hydrogen halide with the chlorine atoms
is in a time period which is less than the time period for 63% loss of the
chlorine atoms by recombining into chlorine molecules.
d~
_ 9 _
B
MB/~ ~.............................................................. .
. ~ . .
, . . . ... . .
.. . ~ .. ... .
- . .. ~ . :`
~038953
Further, another a6pect of this invention encompasses apparatus
for carrying out, inter alia the processes described herein. Accordingly,
there is provided a continuous wave chemicsl laser comprising:(l) a channel
defining a confined flow path, said channel being adapted to contain, in use,
a gaseous mixture consisting of the reactant gases hydrogen halide, nitric
oxide and chlorine dioxide; (2) an optical resonator cavity disposed in the
flow path; (3) supply means for supplying the reactant gases hydrogen halide,
nitric oxide and chlorine dioxide, the halide being selected from the group
consisting of hydrogen bromide and hydrogen iodide, the gases being respectively
contained in the supply means; (4) generating means for generating an excited
gaseous lasing medium, the generating means consisting of first injecting means
for injecting the nitric oxide into the channel flow path upstream of the
: optical cavity, and second separate injecting means for separately injecting
the hydrogen halide and the chlorine dioxide into the channel flow path up-
stream of the optical cavity, wherein the nitric oxide reacts with the chlorine
dioxide to produce chlorine atoms, which atoms in turn react with the hydrogen
halide to form hydrogen chloride, the hydrogen chloride being at a sufficiently
elevated energy level that the population of some of the energy states are
inverted, wherein the resulting gaseous medium is laseable and the sequence
20 of injection of the hydrogen halide is such that the reaction of the hydrogen
halide with the chlorine atoms is in a time period which is less than the time
period for 63% 1088 of the chlorine atoms by recombining into chlorine molecu-
les and (5) exhaust means for exhausting gases from the flow path downstream
of the optical cavity.
In the first process, chloride dioxide is generated and reactedwith nitric oxide to yield the required chlorine atoms. This may be
accomplished either by mixing two volumes of nitric oxide with one of
chlorine dioxide in a single stage, or by "splitting~ the reaction by first
reacting one volume of nitric oxide with one volume of chlorine dioxide to
30 form chlorine monoxide and then reacting a second volume of nitric oxide
~ - 9a -
MR/.~'I
- , '
~0389~3
with the chlorine monoxide thus formed to generate chlorine atoms. The
split reaction is likely to be found suitable for use in supersonic trans-
verse flow laser apparatus.
The atomic chlorine thus liberated may be reacted with
hydrogen iodide to form hydrogen chloride at elevated energy levels for
use in direct lasing activity of the hydrogen chloride, or the vibrational
energy of the hydrogen chloride may be transferred to another substance
such as carbon dioxide for lasing of the latter material in a hybrid laser.
In longitudinal flow lasers, the hydrid mode is more suitable, because of
the longer lifetime of excited CO2 molecules, whereas lasing of the hydrogen
chloride is to be preferred in transverse flow lasers because of the superior
efficiency obtained by lasing the hyd~ogen chloride itself.
In the second process, chlorine dioxide is generated and
mixed with hydrogen iodide. Into this mixture nitric oxide is injected.
The result is the production of excited hydrogen chloride.
!
; The second process might at first sight appear to be im-
practicable because since atomic chlorine is liberated by the reactions
C12 + NO 2 ClO + NO2
ClO + NO > Cl + NO2,
it mlght be expected that the at = ic chlorine would react
.' ' ,~
,
.. - ~'' .
_ 9b -
:
MR/V~
, . . ~ .~.-
1038953
preferentially with the hydrogen iodide, thus preventing the
third reaction in the chain, viz.
Cl + ClO2 3 ---~ 2ClO
from generating the additional amounts of ClO required to sustain
the chain reactions. However, it has been found that the
reactions will proceed at an acceptable rate if the C1O2 and NO
concentrations are sufficiently high relative to the HI con-
centration. The second process affords the advantage that a single
injection of nitric oxide into the HI-C1O2 mixture is sufficient
to initiate the reaction.
For either the first or second process above, the
required chlorine dioxide is suitably supplied in admixture with
an appropriate inert gas, such as helium.
The chlorine dioxide may be obtained utilizing known
techniques, such as flushing sodium chloride with chlorine and
such suitable inert gas, or by flowing such suitable inert gas
through chlorine dioxide dissolved in water.
It is important to recognize, at least in a qualitative
sense, the inter-relationship between the significant parameters
which govern the construction of chemical lasers making use of the
aforementioned reactions. Pressures, flow rates, concentrations,
and physical dimensions must be correlated so that the required
chemical reactions occur in the right place at the right time.
Because of loss reactions of reactive species and so-called
"relaxation" phenomena associated with excited vibrational states
of molecules, it is necesaary in the interests of relatively
efficient laser operation to utilize the available reactive species
before they are depleted. Furthermore, it must be recognized that
certain chemical reactions occur at certain definite rates, and
therefore in a flowing gas system require a certain minimum path
- 10 -
:, . .
1038953
length for a reasonable level of completion of the reaction (for
a given flow rate concentration, etc). Accordingly the
governing parameters must be adjusted to permit the necessary
reactions to be completed, but once they have been completed,
use must be made of the reaction products before their useful
energy becomes dissipated by relaxation phonomena.
The chlorine dioxide required in the chemical laser
according to the invention is an unstable and explosive material
and therefore should be used as quickly as possible after it is
generated. However, given that direction, it is not necessary
to specify precisely the concentration level, pressure, or -
average linear flow velocity associated with the supply of
chlorine dioxide, nor to specify the dimensions of its passageway,
provided that it is understood that it should be consumed
expeditiously and that its concentration, pressure and average
linear flow velocity should be chosen to accommodate the governing
parameters or the later reactions occuring in the apparatus.
In the first process, the supplied chlorine dioxide is
reacted with nitric oxide to produce atomic chlorine. First
assuming that the nitric oxide is supplied in a single stage and
that no split reaction (to be described further below) is
arranged, calculations based upon the above reactions 1, 2 and 3
indicate that the time required for 90 percent completion of the
NO-ClO2 reaction is given by the following equation:
T = D = S x 1011
r V [C1O2] (6)
where
Tr is the reaction time in seconds for 90 percent
completion of the reaction;
D is the distance along the flow line following the
-- 11 -- :
., : . . . .
~0~8953
introduction of the nitric oxide into the chlorine
dioxide flow, required for 90 percent completion
: of the reaction;
- V is the linear velocity of flow of the reagents;
and
[ClO2] is the initial concentration of chlorine dioxide
in molecules per cubic centimeter,
Once the chlorine atoms are obtained, it is necessary
to react them with the hydrogen iodide before the free chlorine
10 atoms recombine into chlorine molecules. A useful working -
time period may be taken as one in which the required reaction
time is appreciably less than the tlme required for 63 percent
loss of chlorine atoms (a 63 percent loss corresponds to a
remaining concentration which is 1 times the initial concentration,
where e is the base of natural logarithms~. The time for 63
percent loss of chlorine atoms has been calculated from the rate
constants for the loss processes to be given by the following
relationship:
[C102 ] P
20 where
TCl is the time for 63 percent loss of chlorine atoms;
[ClO2] is the initial concentration of chlorine dioxide in
molecules per cubic centimeter; and
P is the total pressure prevailing in the reaction
chamber, in torr.
Optimally, the following relationship should prevail:
Tr ~ Tf <TCl (8)
where
Tr is the time for 90 percent completion of the
reaction of nitric oxide with chlorine dioxide;
- 12 -
,. . . ~ - .
- . ...
1038953
Tf is the actual flow time of NO with ClO2
permitted in the apparatus before the Cl
atoms are utilized; and
TCl is the time for 63 percent loss of chlorine ~ -~
atoms.
(In practice, a flow time Tf about equal to or just greater than
Tr and less than one-fifth of the time for 63 percent loss has
been considered to be reasonably satisfactory).
While the foregoing relationships have been determined
on theoretical grounds, such empirical investigations as have
been made to date to indicate that they are reasonably
accurate. However, it is possible that further empirical studies
will reveal that the above equations and relationships have to -
be adjusted to a limited extent for optimum laser performance. -
The next significant reaction in the first process is
that of the chlorine atoms with the hydrogen iodide. The hydrogen
iodide should, according to the above governing considerations,
be introduced at the end of the indicated flow time before any
appreciable loss of chlorine atoms has occured. In practice, it
has been found that the optical cavity should follow the point
of introduction of the hydrogen iodide as immediately adjacent
as dimensional and structural limitations permit. The reaction
of the hydrogen iodide with the atomic chlorine is very fast,
and therefore the governing consideration is not the reaction
speed but the mixing time, and the relaxation time of the HClt.
In other words, it is necessary to make use of the excited
hydrogen chloride produced before its vibrational energy is
dissipated.
From the limited available data on the relaxation of
HClt, it has been estimated that self relaxation of excited hydrogen
. ~
- 13 -
.
1038953
chloride can be considered to be substantially complete (i.e. at
least about 2/3 complete) within a time THClt given, approx-
imately, by the following relationship:
HCl~ 12 t
6 x 10 [HCl ] ~9)
- where [HClt] is the concentration of excited hydrogen chloride,
and 6 x 10 12cm3s 1 is the estimated relaxation rate constant.
Since we require the actual flow time between the
introduction of hydrogen iodide and the arrival of the gas at
the optical centre of the laser cavity to be substantially less
(say 1/5 or less) than the above-identified relaxation time
THCl, we can derive an upper limit to the actual flow time between
the source of the hydrogen iodide and the optical axis. This
flow time of course is equal to the distance between the hydrogen
iodide injector and the optical axis of the cavity, divided by
the average linear flow velocity. Since this flow velocity
however has been previously established in relation to the dis-
tance between the nitric oxide injector and the hydrogen iodide
injector, it is possible to derive, for a given concentration of
reagents, the relationship between the distance of the nitric oxide
injector from the hydrogen iodide injector on the one hand and the
distance of the hydrogen iodide injector from the laser optical
axis on the other hand. The actual relationship will depend upon
the relationship chosen between the actual flow times and the
times required for 63 percent loss of relevant constituents.
In a longitudinal flow laser utilizing subsonic linear
velocities, the above relationships indicate that the dwell time
required in a practical longitudinal flow laser construction is too
long in relation to the available useful life-time of excited
hydrogen chloride molecules to permit a practical lasing of the
hydrogen chloride. Accordingly, in such longitudinal flow lasers
the vibrational energy of the hydrogen chloride is transferred to
- 14 -
~038953
some other suitable molecule, such as carbon dioxide, havinga longer life-time at excited levels.
In order to utilize the more efficient hydrogen chloride
lasing operation, a transverse flow laser may be constructed in
which the governing parameters are given according to the above
relationships. At subsonic flow rates, no additional parameters
require special consideration. However, in order to maximize
the available power output for a given size of apparatus, it -
would be desirable to increase both HClt concentration and velocity.
It will be appreciated that higher power can be derived from ~ -
higher concentrations, but since higher concentrations give rise
to more rapid relaxation, it is necessary to increase the linear
flow velocity substantially in order to reduce or accommodate
such higher concentrations. This can be done by increasing the
linear flow velocities into the supersonic range. However, such
supersonic operation requires equipment modification in order to
accommodate the supersonic phenomena. According to a further
proposal to be described, such supersonic phenomena are accommo-
dated both chemically and structurally.
First, from a chemical point of view, a "split nitric
oxide" reaction may be employed so that one volume of nitric oxide
; is first of all reacted with the chlorine dioxide to form chlorine
; monoxide, and then the chlorine monoxide is subsequently reacted
with a second volume of nitric oxide to liberate chlorine atoms.
In principle the hydrogen iodide can be injected into the reaction
chamber along with the second volume of nitric oxide, since the
` reactions associated with the two reagents are non-chain reactions
which occur very rapidly.
In practice, a slow reaction between HI and NO necessi-
tates a careful design of the NO/HI injection.
Structurally, the proposed apparatus is designed so
that the first chlorine dioxide - nitric oxide reaction occurs at
- 15 -
iO38953
high pressure at subsonic flow rates. A nozzle immediately
follows this reaction chamber to cause the high pressure gases
to acquire supersonic velocity. While the gases are flowing at
supersonic velocity, the remaining nitric oxide and the hydrogen
iodide are injected together, and the laser cavity immediately
follows. The reacted gases continue to flow at supersonic
velocity through the laser cavity. It may be possible to provide
a diffuser beyond the laser cavity to permit the gases to re-
acquire a somewhat higher pressure, which would facilitate the
exhaustion of the gases by pumping.
The use of the second process described above avoids
the need for analysis of some of the operating conditions appli-
cable to the reactions in question, because the reactions in
accordance with the second process are initiated by a single
injection (of nitric oxide), whereas in the first process, a
first set of reactions initiàted by the nitric oxide injection is
followed by a second set of reactions initiated by a subsequent
hydrogen iodide injection. On the other hand, it is necessary
when practising the second process to recognize the desirability
of maintaining a slight excess of chlorine dioxide and a consi-
derable excess of nitric oxide, for a given hydrogen iodide con-
centration, over that which would have been required by the first
process to produce sufficient chlorine atoms to react with the
hydrogen iodide. A NO concentration at least of the order of
four times the ClO2 concentration is preferred.
The second process may also prove to be useful in super-
sonic operation, in which case the split N~ reaction would be
unnecessary.
Hydrogen bromide may be substituted for hydrogen iodide
in the split NO reaction or using the second process described
above, with appropriate changes in system parameters.
- 16 -
'
" .: ''
. - - - . -: - . . - ,. . , .: .. . - ... ..
10389S3
SUMMARY OF THE DRAWINGS
Figure 1 is a transverse section of an embodiment of
longitudinal flow laser apparatus constructed in accordance with
the present invention;
Figure 2 is a transverse section of an embodiment of a
~` chlorine dioxide generator for use with laser apparatus constructed
in aeeordanee with the present invention;
Figure 3 is a perspective view of an embodiment of a
transverse flow laser apparatus constructed in accordance with the ~
present invention; -
Figure 4 is a plan view of the laser apparatus of
Figure 3;
Figure 5 is a detail fragment view in section of a gas ~-
injeetor array for use in the apparatus of Figure 3; and
Figure 6 is a sehematie longitudinal elevation seetion
view of a supersonie transverse flow laser apparatus eonstructed
in aecordance with an extrapolation of the teaehings of the
present invention.
Referring to Figure 1, an embodiment of a eontinuous- -
wave (CW) HCl/CO2 hybrid longitudinal-flow laser pursuant to
the present invention ineludes a laser tube 10 having a first
inlet 11, a seeond inlet 12, and a third inlet 13. An exhaust
tube 14 is eonneeted to the laser tube 10 and communicates with
appropriate eooling traps and pumping apparatus (known pex se in
- the art) via valve 15 eapable of achieving near-sonic flow at
the end of laser tube 10. The laser tube 10 is provided at opposite
ends with a pair of laser mirrors 16 and 17, known per se in the
art. Mirror 16, whieh may be, for example, a spherical front-
surfaee totally reflecting laser mirror of the type known as a -
proteeted metal germanium mirror (i.e., the germanium is
impervious to ehemical contamination by the atmosphere), is
- 17 -
., . . :-, ' : , ~ ' , .
- - . ~
-:' . . : .
~038953
mounted in a vacuum tight bellows 18 provided with conventional
alignment screws 19 as is known in the laser art. Similarly,
mirror 17 which may be, for example, a spherical front-surface
or planar front-surface partially transmitting laser mirror of, for
example, 2~ transmission, and may be a dielectric-coated germanium
mirror, is mounted in a bellows 20 provided with adjusting screws
21 for adjusting the alignment of the mirror.
Inlet 11 is connected to a suitable chlorine dioxide
generator, for example that described in relation to Figure 2
below, through a needle valve 22 to control the chlorine dioxide/
helium flow from the chlorine dioxide generator. Since ClO2 is
unstable, the ClO2 generator should be connected as closely as
possible to the laser apparatus, and the ClO2 consumed as
expeditiously as possible. Inlet 12 is connected to a source of
nitric oxide and connects to an injector 23 which for example may
consist of twelve holes 0.75 millimeters diameter equally spaced
around the circumference of laser tube 10. Laser tube 10 may
typically consist of a Teflon* tube 1 centimeter inside diameter
by 30 centimeters in length. Inlet 13 is connected to a similar
injector 24 which is spaced far enough for a given rate of flow,
from the injector 23 to allow substantial completion of the
chemical reaction
ClO2 + 2NO > Cl + 2NO2
(It will be recalled from the preceding discussion that 90
completion occurs in about 8 x 1011 seconds, where [C1O2]
[C102 ]
is the concentration of chlorine dioxide in molecules/cm3).
Inlet 13 may be connected to a source of hydrogen iodide ' -
(HI) and carbon dioxide (CO2) so that hybrid lasing action may be
obtained. A mixture of C1O2 and He is admitted through the inlet
11 and reacts with NO admitted through the injector 23 to provide
*Trade mark
- 18 -
: ~ '
- ~038953 :
atomic chlorine in the laser tube. The chlorine then reacts
with HI in the reaction
Cl + HI 10 ~ HCl~
which results in the production of the HCl molecule in an upper ~ ~ -
excited state. The HCl vibrational energy is then transferred
to the CO2 molecules, which emit light in dropping to a lower
energy level. The result is that hybrid chemical laser action
; occurs, with lasing of the CO2 molecule at 10.6 microns.
A prototype of the structure illustrated in Figure 1
has been successfully operated with a power of 7 mW using the
following flows expressed in standard cubic centimeters per
- minute of gases:
- chlorine dioxide 100
helium (mixed with the
chlorine dioxide) 3500
carbon dioxide 1540
hydrogen iodide 100
nitric oxide 200
The total pressure in the laser was 7.5 torr.
Figure 2 illustrates a chlorine-dioxide generator
suitable for use in supplying chlorine-dioxide and helium to
the laser apparatus of Figure 1. Molecular chlorine from a
source 30 is fed via tubing 31, T-connection 32, and tubing 33
to a reactor column 34. Similarly, helium from a source 35 is
fed via tubing 36 to the T-connection 32 and into the reactor 34.
The reactor 34 as illustrated in Figure 2 consists of two columns
45 and 46 connected by a cross-connection 37 at the bottom and
provided with lead rupture discs 33, Teflon* closures 39, and
an outlet 40. The two columns 45 and 46 are packed with sodium
30 chlorite (NaClO2~)~ flake packing. Glass wool packing is provided -
*Trade mark
-- - . . .. .
. . ~ .
- . - . . . . - .
. . . . . .
1~038953
in a Section 37 and at the top and bottom of each of the columns
45 and 46.
The ClO2 generator tube 34 may be constructed of
Corning "Double Tough" Pyrex* glass plumbing with a 4 in, inside
diameter. The entry and exit to the columns may be sealed by
means of 3/4 in. thick Teflon* plates 39 sealed to the glass
surface by means of a perfluorocarbon putty. This putty may
be made by heating fine Teflon* powder and fluorocarbon wax
together in methylene chloride to form a heavy, malleable paste.
This paste h~sbeen found to be generally useful for sealing
joints of relatively smooth mating surfaces that are to be
exposed to highly reactive halogen compounds.
All the glass sections are held together with the
standard bolts and collars, the seals preferably being made
with Teflon* gaskets. The bottoms of the vertical columns 45
and 46 on each side may be closed with sheets of 1/16 in. thick
lead 38 which can be sealed with the putty. These lead sheets
serve as rupture discs in the case of explosion or overpressure
in the column.
The feed of gas to the column may consist of a
stainless steel gas handling system, employing 1/4 in. OD
stainless steel tubing and stainless steel 1/4 in. "Swagelok"*
fittings. Bottled He and C12 may be employed. The He can be ;~
handled in the usual way with standard regulators and pressure
gauges. The flow can be measured with a flowmeter at a pressure ;~
of 1200 torr absolute. The C12 can be measured at 1200 torr `~
absolute pressure using a flowmeter made of Monel*. The two
flows are combined and fed directly into the column which is
controlled at the desired operating pressure shown on gauge 41 ~-
by means of a glass and Teflon* needle valve (22, Figure 1) at
*Trade mark
- 20 -
:: :
: - ~ - - . .
1038953
the effluent end. The flowmeters may be calibrated from
measured filling times of a known volume.
The reactor 34 is filled with (say) about 20 lbs.
reagent grade "flaked" sodium chlorite (NaClO2). With this
- packing no measurable pressure drop within + 5 torr has been
detected in prototype apparatus when a helium flow rate of 7000
standard cm3 per minute (SCCM) was passed through the column.
In the prototype apparatus, the C1O2 column supplied
a flow of ClO2, highly diluted in He gas (~4~) at a flow rate
of about 100 SCCM of C1O2. The column itself was always run
at a pressure of 970 torr and the flow was regulated by the
needle valve at the effluent end of the column. By means of ~-
this needle valve, the gas pressure was reduced to that required
in the laser; about 10 torr.
, _ . /
/ - 21 -
' .
.: .
~038953
To establish the flow, the desired feeds of He and C12
- were set up in the gas feed system to the column, and the
operating pressure was maintained at 970 torr with the needle
valve. In this way, a steady feed of ClO2/He to the laser could
easily be maintained.
Typical flow rates of He plus C12 were on the order
of 3500 SCCM; the total volume of the empty column was 27 litres.
If the free volume of the column packed with NaClO2 is 3 litres,
then the residence time of the gas in the column is on the
order of 50 s. The free ~olume was not measured.
With a fresh charge of NaClO2 in the column, a flow
of 121 SCCM of C12 and 5000 SCCM He was admitted continuously
to the column. The column was found to yield approximately ~`
240 SCCM ClO2.
There is generally insufficient C12 evolved from the
column to permit reliable measurement with the C12 optical
absorption tube described above. With an extinction coefficient -
of 25 M lcm 1, the minimum reliably detectable pressure of C1
is about 0.4 torr in the total effluent gas pressure of 970 torr.
After verifying the low C12 pressure in the effluent gas, use of
the optical absorption tube was abandoned in order to eliminate
the possibility of loss of ClO2 by photolysis with the probe ~ ;
beam~ ~
A~ embodiment of a transverse flow laser constructed ~-
according to the invention is depicted in Figures 3 to 5 inclusive.
The laser generally comprises a rectangular houslng 50 pro~ided
with spaced input conduits 52, 54, 56 for the introduction of
the required gaseous reagents. The laser cavity section of the
apparatus, generally indicated by reference numeral 58, is
provided between two mutually opposed inclined windows 83, 84.
.
- 22 -
~038953
These windows are inclined at the Brewster angle with respect
to the parallel top and bottom surfaces of the housing 50 in
order to minimize the reflection of light by the windows 83 and
84. The windows 83 and 84 are sealed to the housing by
conventional O-ring type seals, as is known per se in the art.
The housing 50 continues beyond the downstream end 54 of the laser
cavity section of the apparatus into a conventional cold trap
and a suitable pumping facility, neither of which is illustrated.
Opposed laser mirrors 66, 68 are coaxially mounted on either
}~ side of the opposed windows 60, 62. The conventional mo~unting
and adjustment structures for the mirrors 66, 68 are not
illustrated.
The operation of the apparatus in accordance with the ,
first process will now be described. A flow of ClO2 mixed with
He enters the laser housing 50 from a suitable C1O2 generator
through the supply tube 52. The mixture enters a plenum 70 at a ;~
suitable pressure (say about 50 torr), then escapes through
a perforated baffle plate 72 into flow channel 74 in which the
, pressure is much lower, say 2 torr. The baffle plate may be
made of Teflon* drilled with an array of small holes of, say,
1 mm diameter. This serves to constrict the flow prior to
entry into the flow channel 74 in order to produce an even
flow pattern in the channel.
Nitric oxide gas is then metered into the flow
channel through feed-tube 54, plenum 76 and series of Teflon*
gas injection needles 77. Each of these needles 77 is drilled
with small holes 78 (e.g. 0.3 mm diameter) disposed such that
the injected gas is directed across the flow substantially at
right angles to the main gas stream in the flow channel 74. The
scale of the needles 77 and holes 78 is exaggerated in the drawings
*Trade mark
- 23 -
:. : ,
- -
1038953
for ease of illustration. The N0 pressure in the plenum 76
is preferably maintained sufficiently high that the gas flows
through the holes in the injector needles at near sonic velocity
to promote efficient gas penetration and mixing in the flow
channel.
After passing the location of the N0 injector needles,
the gases flow a further distance down the rectangular s~ction
flow channel until the reaction
2 N0 + C102 4 ~ Cl + 2N02
has reached a satisfactory state of completion. This distance
is designed having regard to equations (6), (7), and (8) above.
The hydrogen iodide is then introduced via inlet conduit 56, `
plenum 80 and Teflon* injector needles 82. This HI injector
array is essentially identical to the N0 injector array.
After passing the location of the HI injector array,
the gases immediately flow into laser cavity section 58 of the -
flow channel between the optical windows 83, 84 mounted on the ~ -~
.~ ,~ . ,
shorter side (upright as seen in Figure 3) of the flow channel.
The dead gas space on each side of the laser cavity between
the windows and the projection of the upright edge 86 of the
flow channel is purged out with helium which enters through
slots 88 running the length of the lower edge of the windows
and fed by supply tube 90. This serves to prevent spent gases ;
from the reaction from accumulating in the dead gas space and
contributing to the cavity optical losses. The flow of helium
across the window face also serves to keep the window surface
free from particulate matter and other deposits that might
otherwise lodge there.
The CaF2 windows 83, 84 are installed in such a way
that the optical axis passes through the gas mixture immediately
; *Trade mark ;
- 24 -
1038953
downstream of the HI injector array. The axis of the optical
cavity is defined by the line joining the centres of the mirrors
66, 68 which are installed facing one another through the
- windows. It is conceivable that in certain circumstances the
laser cavity 58 would be placed further downstream,but at
sonic flow velocity it has been indicated empirically that the
cavity should be located immediately downstream of the HI
injector, e.g. less that one centimeter downstream.
The spent gases, after passing through the optical
cavity, flow into a liquid nitrogen-cooled cold trap (not
shown) of conventional design. This serves to remove the larger
part of the condensible gases from the mixture. Thereafter,
the remaining gases (mostly helium) flow into a conventional
pump, also not shown. -
A prototype embodiment of a subsonic transverse flow
laser constructed according to the invention was adapted from
a previous design of K. D. Foster and G. H. Kimbell, described ~ ~ -
in Fourteenth Symposium (International) on Combustion,Aug. 20-
25, 1972, pp. 203-210. It consists generally of a rectangular
cross-section flow channel 50 milled out of aluminum. The
channel dimensions selected for the prototype were 1.5 cm in
height by 14 cm across the flow, and the channel had a total
length of 30 cm from the conduit 52 for introduction of the
ClO2-He m~xture at the head end to the downstream end of the
laser cavity. The distance from NO injector 54 to HI injector -
56 was about 12 cm, at a prevailing pressure of about 2 torr
and a flow rate of about 160 ms 1 This gave an available
reaction time of about 750 ~s for a ClO2 concentration of about
1015 molecules/cm3. There was no valve between the laser and the
cold trap, as this would have been difficult to install and,
- 25 -
* ~ - .
4' .
;. ~
.
1(~3B953
in any event, the laser operated best with no attempt to limit
the pumping speed. The pump used was a 1200 c.f.m. Kinney*
pump-blower combination.
The ClO2-He supply to the transverse flow laser
conveniently can be generated by a ClO2 generator of the type
described with reference to Figure 2. A series of tests was
made to verify that the ClO2 generating column was capable of ~ -
supplying the increased quantities of ClO2 needed for a
subsonic transverse flow laser. The C1O2 absorption band at -
4.9~ was used to monitor the ClO2. The ClO2 generator was
found to be adequate. The moisture content of the effluent
gas flow was measured using the infrared water absorption band
near 2.6 ~ in the same series of experiments. An infrared
spectrometer was calibrated using gases containing known ~
concentrations of water vapour. In this way it was found that t' ~ '
the gases issuing from the column contained from 0.7 to 0.9%
water vapour. A supplementary drying column (not shown) was
inserted between the ClO~ column and the needle-valve leading ~-~
to the laser. This was effective in reducing the water to less
than 0.1~. The drying column had no effect on the ClO2 content
of the effluent gases as was verified by infrared absorption
spectroscopy, using the absorption band of ClO2 near 4.9~.
To provide for the possible requirement of even i-
greater ClO2 flows, additional ClO2 generators could be
installed in parallel with the first.
Where the metering of reagent gases is required, as --
- in the case of the NO and HI flows, and also for the He and
C12 for the ClO2 generator, Hastings* mass flow-meters were
employed. Commercially available bottled gases were drawn from
the cylinder at a regulated pressure and the flow was
*Trade mark ~
- 26 -
:~
- 1038953
measured at that pressure, generally about 1.5 atmospheres
; absolute. The flow was then admitted to the laser apparatus
through a Nupro* Fine Metering needle-valve. For HI, however,
regulators are not available and the gas was bled from the
cylinder into the flow meter using another needle-valve.
Because of this, the pressure varied somewhat in the flow
meter depending on the balance of flows through the two needle-
valves. The pressure-independent properties of the flow meter
ensured accurate measurement of the HI reagents.
The flow lines, gauges, valves and flow meters were
constructed of Monel* or stainless steel for corrosion
resistance, depending on the gas used.
The laser cavity portion 58 of the flow channel was
5 cm long fit with CaF2 optical windows mounted on the 1.5 cm
side of the flow channel at the Brewster angle.
In the prototype apparatus, one mirror 66 was flat
and the other 68 was curved with a radius of curvature of 10 m.
They were mounted with a distance of separation of 65 cm between
them. The flat mirror was a CaF2 optical flat coated with a
dielectric multilayer reflective coating (for 3.82~m wave-
length) that was partially transmitting at the HCl 3.8~m ~ -
wavelength band. Transmissions of 1, 2, 4 and 6 percent were
used in the experiments, with greatest power being extracted
using the 4% transmission mirror. The curved mirror was a
protected metal on Ge totally reflecting (i.e. greater than
99.5% reflecting) mirror.
In the first successful experiments with the prototype
transverse flow laser, only about 3-4 mW of light energy was
extracted from the apparatus. This was principally due to the
fact that a very high reflectively mirror was installed as output
*Trade mark
- 27 -
- \
1038g53
coupler in the laser cavity in order to maximize the optical
quality of the cavity for a low oscillation threshold. Thus
the reflectivity of the output coupler in these experiments
was greater than 99~, causing most of the power generated in
the cavity to be dissipated internally. The conditions in the
cavity for the first observation of lasing were:
He 16860 SCCM (cm /mi~
through the
Cl 335 SCCM ~ C12
2 generator
NO 1700 SCCM ~ into the
HI 680 SCCM J optical cavity
cavity pressure 0.9 torr
Under these conditiDns~ a power of 3-4 mW was measured using
an Eppley* thermopile.
Higher power of about 4 watts was extracted from the
laser by increasing the percentage output coupling (percentage
of light transmitted) to 4% and optimizing the reagent gas
flows. The C12 flow, however, was maintained at 335 SCCM to
provide a theoretical Cl atom flow of 670 SCCM, or 0.5 mmol s 1,
The cavity conditions during this experiment were: ;
He18300 SCCM ~ ,
1 through C1O2
C12335 SCCM J generator
NO 1800 SCCM
HI1000 SCCM ¦ into laser ~
- He50900 SCCM J
total pressure 2.43 torr
It is conceivable that it will be possible to increase
the power output in the future. Higher C12 flows can be used
*Trade mark
- 28 ~
r
1038953
by bringing additional ClO2 generators on line in parallel with
the first. Further, it is expected that more power can be
extracted for given ClO2 flow by empirically optimizing the
optical cavity and flow conditions. At higher gas flows some
over-addition of NO and HI may be helpful to improve reaction
- completion under relatively poor mixing conditions.
In accordance with the second process, the hydrogen
iodide is mixed with the chlorine dioxide prior to the
injection of nitric oxide into the flow path. Again referring
to Figures 3 and 4, the ClO2-He mixture can be supplied as
before via inlet pipe 52 and plenum 70. The hydrogen iodide
is then injected via inlet pipe 54 and plenum 76 thence to
- the flowpath via injector needles 77. The reactions are then
initiated by injecting nitric oxide into the flowpath via
inlet pipe 56, plenum 80 and injector needles 82. The relative
spacing of the injector needle arrays with respect to one -~
another are not critical if this process is used, provided that ~ -
sufficient mixing of the reagents occurs. Also, the optical
cavity should as before be located immediately downstream of
the injector needles 82. ;~
As an example of representative operating conditions
applicable to the second process, flow rates for the gases were
as follows:
He15000 SCCM through the
Cl 700 SCCM C1O2 generator
HI 1000 SCCM through injector
needles 77
NO 5000 SCCM through injector
needles 82
Total pressure in the flowpath in the vicinity of the
optical cavity was approximately 4 torr. The power obtained was
slightly more than half a watt with 4% output coupling.
.
29
.
.
10389S3
The power realized from the prototype subsonic
embodiment of the HCl transverse flow laser is not necessarily
the maximum that can be obtained, for given laser dimensions.
It may be possible, in all likelihood, to increase the partial
pressures of active species in the laser and obtain higher power ~ -
performance. However, as the laser is scaled to higher pressure, -
vibrational-vibrational exchange processes between HClt molecules
decrease the inverted population. The effect of these processes
can be minimized by operating at higher (i.e. supersonic) linear
velocity and, hence, shorter residence times in the laser
cavity. ~ -
Some of the factors which are likely to influence
the design and operation of a supersonic transverse flow laser
are considered below.
A subsonic pre-reactor for production of Cl atoms
at moderate pressures could be employed. Subsequent expansion
to supersonic velocities of the resultant gas could then be
performed before injecting the HI into this expanded, lower-
pressure flow. The lasing could then be carried out in this
low pressure expanded flow and a diffuser could conceivably
be added, downstream of the laser cavity, to return the flow `~
to a higher pressure. This would provide pumping at higher
pressure, and this minimizes the volume pumping rate required
for a given mass throughout. -~
When the population of Cl in the gases flowing through
the pre-reactor reached a maximum, the gases would be expanded
through a nozzle of a convenient geometry into an optical
cavity region defined by suitable laser mirrors. In this
region, the pressure of the gases would fall and their linear
velocity would rise rapidly to supersonic values. Into this
- ~30 - ,:
. , ~ ., , , , :
`: 1038953
expanding gas, the HI would be injected just upstream of the
optical axis, where the reaction:
Cl + HI > HClt + 1 -
would occur.
The supersonic expansion proposed above would require
the production of Cl atoms in a high pressure environment.
However, another possibility for the production of the Cl atoms
exists. If we consider the system of reactions 1 - 3 (page 7 above)
it can be seen that, if a volume of NO equal to instead of double
that of the ClO2 is added, the ClO2 is just converted to ClO with
the formation of an equal volume of NO2 by:
12 NO ~ ClO + NO2
ClO molecules are known to be lost in the process: ,
ClO + ClO + M ~ C12 + 2 + M Kll = 1.0 x 10 cm s
ClO molecules may perhaps also be lost by the process:
12
ClO + ClO ) 2 2 K12 = 5 x 10 (350K)
This process should never compete with reaction 11 for ClO loss
as long as the pressure is greater than about 15 torr; in
general, it should not be a serious loss for the time scales
involved in the transverse flow laser.
The loss rate for ClO molecules by reaction 11 has been
estimated from existing kineticdata to be about 14 times slower
than that for Cl atoms by the relaxation processes previously
described. Therefore, by using ClO molecules as the intermediate
rather than Cl atoms, it is possible to scale to higher pressures
before being limited by pressure-dependent losses of the
intermediate becoming comparable to the rate of formation of the
intermediate.
Furthermore, ClO molecules are a potentially useful
possibility as the intermediate species since they can be very
rapidly converted into Cl atoms by the reaction
NO + ClO ) NO2 + Cl
- 31 -
- ~
1~38953
in a non-chain process. Since this reaction is not a chain
process, the HI necessary for the generation of HClt molecules
could be added at the same injector as the final volume of NO.
- Then the Cl atoms would be consumed immediately as they are ~-
formed, and the two reactions could be carried out at a position
immediately upstream of the optical cavity. This is the basis
for the "split NO flow" proposal for scaling ClO production to
higher pressures than is possible for Cl production. (Since
the pressure-induced rate of loss of ClO is theoretically about
14 times slower than that of Cl, the generation of ClO could be ;
carried out at correspondingly higher pressures. This permits
scaling to pressures in excess of 100 torr, according to
presently available rate data.)
The supersonic HCl transverse flow laser would there-
fore optimally include a subsonic pre reactor, operating at -
relatively high pressure (e.g. 50 to 100 torr), where ClO molecules
would be produced. The gases would be expanded as proposed above
and a mixture of NO and HI would be injected just upstream of
the optical axis, where the reactions:
NO + ClO ) NO2 + Cl
and Cl + HI 10 ~ Hclt + I
would occur sequentially.
Such an arrangement would incorporate several desirable
features:
.. ~ ~, .
- 1. The generation of active ClO molecules would be carried
~ out rapidly at high pressures.
- 2. The generation of Cl atoms and their reaction with
HI to produce HClt could be carried out simultaneously rather
than in two steps, thus requiring only a single gas injection
array for both HI and the second influx of NO in the expanded
- 32 -
.''' ''.
. , .
- ~ . : . . .
":- . . :' ; '': . ,, ..... ; . : "
~ .. ~ - . : . ,~
1~38953
supersonic flow. Since it has been found that NO and HI tend to
react slowly at higher pressures it may be necessary to design
injectors to avoid prolonged contact of NO and HI at these high
- pressures.
3. The energy flux carried into the cavity as HClt is
high because of the great velocity of the gas, but static
pressures are maintained low, preventing loss of population ~ -
inversion by vibrational exchange processes.
4. By adding a diffuser downstream of the cavity, an
increase in pressure (up to several times the cavity pressure)
should be capable of attainment. This latter feature would allow
the pumping to be conducted as higher pressure and, hence, smaller
vacuum pumps would be needed for a given mass throughout.
5. The ambient Cl concentration in the laser cavity would
be kept low, preventing deactivation by the process:
Cl + HClv ) Cl ~ HClV_l
A schematic model to implement the foregoing proposal
is illustrated in Figure 6. A mixture of C102 in He flows
from a C102 generator (not shown in Figure 6) into subsonic duct
91 until it encounters an NO injector 92. At this point the
pressure is high, say 50-lOG torr, and the reaction
NO + C102 ~ N02 + C10
produces a mixture of He, N02 and C10 before reaching the nozzle
93. (This is important, since the chemistry might "freeze out"
in a strong expansion, feeding unreacted C102 into the supersonic
region). As the gases expand to pressures where the concentration
of C10 is of the order 1015cm 3 downstream of the nozzle 93, more
NO and HI is injected through injectors 94, where the reactions
NO + C10 > N2 +Cl
Cl + HI 10 ) HClt + I
takes place rapidly. Lasing of HClt occurs as the rarified
- 33 -
'~
1~38953
gases pass through the axis of the optical cavity 95. A diffuser
96 in the form of a constriction is shown for the purpose of
permitting possible recovery of some of the plenum pressure
to reduce pumping requirements from exhaust duct region 97.
The technique of split flowNO addition has been
verified in the subsonic apparatus illustrated in Figures 3 and
4.
For the split flow NO addition the final downstream in-
jection elements 56, 80, 82 were replaced by a dual injector
with the two sets of injector needles approximately 2 cm apart.
This was four.d necessary since if the hydrogen iodide and
nitric oxide were injected together in the plenum 80 they
partially reacted and formed iodine which gradually blocked the
injection needes 82. Although this reaction occurred in the
., - .. ..
high pressure low flow velocity region of the plenum, it was
not significant at the much lower pressuresand higher flow
velocities of the laser flow tube 50 and thus did not interfere
- with the laser cavity chemistry. The experimental conditions
during this verification were:
He 15,000 SCCM
through ClO2 generator
C12 700 SCCM
NO 4,000 SCCM constant total flow
through all injectors -
NO 1,000 SCCM through injector
needles 77
NO 3,000 SCCM through second set of
final downstream
injector needles
HI 1,000 SCCM through first set of
final downstream
- injector needles 82A
e total pressure was approximately 4 torr.
Using a 4~ output coupling mirror, the power obtained
was l watt with th~ optical axis located 1 cm downstreamof the
~ .
- 34 -
. .': .. :. ; ~ . ~'- , ~ ,
.. -,: : -., :.. ,
1~)38953
second final downstream injector row and 1.45W with the
optical axis located 1.8 cm downstream of the said row. The
higher power at the further downstream location of the optical
axis no doubt reflects the slower rate of HClt build up, since
the latter is controlled by the rate of Cl atoms release by
reaction 2 rather than by the very much faster rate of Cl atoms
with HI. The total nitric oxide flow was in excess of that
required to convert the chlorine dioxide to chlorin~ atoms and
it appeared that the laser was more efficient with this higher
nitric oxide flow. This may occur because the excess nitric
oxide increases the rate of chlorine atom release in reaction 2.
In the construction of a supersonic laser it may be
advantageous to initiate all the chemistry in the expanded
(supersonic)-flow. Accordingly, the second process, in which
the hydrogen iodide is injected before the reactions are
initiated by the nitric oxide injection, may be preferred.
Variations and modifiaations of the above-described
structures and operations will occur to those skilled in the
art. For example, it may be useful to mount various injectors
adjustably with respect to the flowstream, so that the distances
between them and their distance from the optical cavity could
be varied to obtain optimum operating conditions for given
pressures, concentrations and flow rates of the various reagents.
Internally mounted mirrors rather than externally mounted mirrors
could be used at the optical cavity. The scope of the invention
is not to be limited to the specific embodiments and processes
described above, but is to be ascertained by the appended
claims.
- 35 -
- ~
