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DEUTERIUM FLUORIDE CW CHEMICAL LASERS
Leroy Wilson
To cite this version:
JOURNAL DE PHYSIQUE CoZZoque C9, suppZ6ment au noll, Tome 41, novembre 1980, page ~ 9 - 1
DEUTERIUM FLUORIDE CW CHEMICAL LASERS Leroy E. Wilson
Air Force Weapons Laboratory, KirtZand Air Force Base, New Mexico 120).
Abstract.- This article summarizes the current performance and understanding of deuterium fluoride (DF) cw chemical lasers. The fundamental principles of the laser are explained. The advantages and disadvantages of the laser system are discussed. The characteristics of the DF laser beam, the perfor- mance parameters and operating characteristics are enumerated.
Introduction
Laser emission from a hydrogen chloride chemical laser, the f i r s t chemical laser, was experimentally observed i n 1965 (1). Since that time many vibrational transition and a few elec- tronic transition chemical lasers have been dis- covered and developed. Several recent and general reviews of these em'c lase s are available in the literature. (Sf(3ftH (5)
(8
m e deuterium fluoride (DF) laser has been extensively developed f o r atmospheric pressure recovery and is nearing i t s optimum lasing perfonnance i n t h i s application. This a r t i c l e summarizes the s t a t e of the a r t of cw DF lasers.A chemical laser operates on a population inversion produced
-
directly o r indirectly - i n the course of an exothermic chemical reaction. In t h i s case the excited molecules are produced in five vibrational states by the exothermic reactionwhich takes place a t the e x i t plane of the nozzle bank shown in Figure 1.
OPTICS
LOX '-
--
\ \Figure 1. Schematic of DF Laser
The fluorine atoms, F, are produced in a com- bustor from the reaction of excess NF3 or F2 and C2H4 or; other hydrocarbon fuels with helium (He) diluent t o produce typically 90 percent F-atoms with respect t o the available fluorine for equation
1. Other products, HF, CFq, N2, etc., are also produced depending upon other chemical processes, the heat loss and the combustor gas temperature and pressure. Although the use of NF3 reduces laser power by %IS%, most DF laser applications w i l l require i t s use for safety reasons. Since NF3 i s relatively expensive a t t h i s time, most laboratory experiments have used elemental F2 plus a low molecular weight hydrocarbon t o produce the F-atoms. Laser perfonnance data withNF3 used i n the combustor w i l l be described in t h i s paper. The reaction in equation 1 i s hypergolic and very f a s t . The D2 is added t o the supersonic stream of F atoms a t the e x i t plane of the nozzle bank i n a mixing-limited process t o produce vibrationally excited DF*. This
is
shown schematically i n Figure 2A which shaws the top view of the nozzle bank and the zones of excited DF*. The "trip" holes produce small j e t s of He which create vortex mising increasing the net mixing rate and producing laser power 1.8 times over non- perturbed nozzle banks. The mixing of the oxidiz'er and fuel streams produces a translationally cold temperature flame (nominally 3000K) of products i n which the DF i s vibrational excited to an equivalent vibrational temperature of greater than 10,000oK. The vibrational population i s prodced i n a tri: angula+ peaked distribution with the maximum population in v = 3 and 4. I t i s important t o note again that t h i s nonequilibrium population i s r a t e limited by the mixlng rate of the D2 and F reactants. The excited DF* species are collisionally deacti- vated in the lasing zone by other species. The principal deactivators, in both concentration and f a s t r a t e coefficients, are DF i t s e l f ,HF
products fmm the combustor, excess D2 and F-atoms.
The reaction rates for these interactions and over 100 other possible reactions are given i n reference ( 7 ) .I t i s not the purpose of t h i s paper t o explain the complicated interactions i n the lasing cavity between the fluid mechanics, chemistry and the optical resonator, although what happens can be easily explained i n a global sense. A l l the parti- cles pass by the optical aperture (lasing zone length) i n 20 t o 50 microseconds d e g i i n g upon t h e i r history. In that period of time there i s sufficient reactant mixing and DF* production t o allow the resonator t o extract a specific power of 90 kj for each kg that passes the aperature. During t h i s residence tine the created DF* is de- activated twoards ground s t a t e by lasing and c o l l i - sional processes. In addition, the heat release increases the gas translational temperature from
aperture entrance to e x i t which decreases t h e available inversion.
JOURNAL DE PHYSIQUE "Trip" Holes CAVITY FUEL/DILUENT AND COOLANT LUORINE NOZZLE CAVITY FUEL/ Dl LUENT NOZZLE FLUORINE NOZZLE B
Figure 2. Schematics of DF Laser Nozzle Banks (A) Top V i e w Showing F, D2 and DF*
Supersonic Streams with Nozzle Dimensions i n Inches
(B) Regeneratively Cooled Nozzle
The obvious fundamental advantage of a cw chemical laser compared t o e l e c t r i c a l powered lasers is that it obtains its l a s e r power from combustion. But it is then limited by f i n i t e and practicable reactant tankage f o r long device
run
times. Irreversible chemical processes demand the removal of expended gases from the laser making continuous recirculated flow impossible.
CW
chemical lasers are phenomenologically complex interactions between the chemical kinetics, f l u i d dynamics, optics and laser physics. The devices are simple but highly engineered, and are s t i l l relatively expensive t o manufacture. The nominal 3.8 micron DF wavelength can be focused t o higher f a r f i e l d intensities than the CX)2 laser and propagates well through the atmosphere. (8).
The greatest disadvantage of a cw DF laser i s its i n a b i l i t y t o recover pressure t o one atmosphere without pwrps. The average lasing zone pressure i s 20 t o r r with sufficient momentum i n the
supersonic flow f i e l d t o passively recover t o 200 t o 300 t o r r , depending upon the configuration, which then needs t o be pmped at: high volume flow r a t e s t o atmospheric pressure. Although axial flow pumps are a possibility f o r very long run times, only j e t pumps (ejectors - see Figure 1) and 1-120 mechanical pumps have been used. Although the reactants are easily bottled and handled (including "2
NQ),
which can easily be scrubbed from the effluent the products contain DF which is a mild acidcondensibles by several methods.
Current laser operating fuel costs are $ 2 / h
kw for each second of
run
time with NF3 as the fluorine source. A t industrial usage r a t e s that cost should decrease t o $l.oO/kw per second.DF Beam Characteristics and Optics
The
CW
DF laser beam has a multiline spectrum of P branch transitions between different vibra- tional and rotational levels as s h m i n Figure 3 . Single lines have been extracted by using a diffraction grating as an outcoupling mirror. Single-line output powers are 10 and 20 percent of t o t a l multiline power. (8) Zero power gain measure- ments have been made f o r several of the transitions P2 (4).. .
P2 (8) shown i n Figure 3. Peak gain i sWAVELENGTH (MICRONS)
Figure 3. Representative Simultaneous DF Laser Transitions Showing Relative Power of Lines
typically 10 percent per an a t 1 t o 2 an downstream of the nozzle e x i t plane. (9) The gain f a l l s off rapidly downstream of the peak value due t o a l l of the competing processes deactivating the lasing species, giving r i s e t o asynnnetric gain distribu- tions. The lasing zone length i n the flow direction is typically 5 an. Although the peak zero power gain is high, parasitic oscillations have not been a problem because the resonators are designed t o saturate a l l of the gain medium.
Confocal unstable resonators similar t o Figure 4 extract the DF laser beam. Rectangular scrapers are used t o match the rectangular gain medium with the laser mode volume. The outcoupling generally optimizes f o r near-f i e l d power' between 60 and 75 percent. The mirrors are molybdenum substrate,
t r i p l e pass water cooled, with silver or gold
gas t o prevent absorbing ground s t a t e DF species from circulating i n those cavity spaces.
CONVEX MIRROR c , , , ,
/;p;
INJECTORFigure 4. Typical Chemical Laser Enstable Resonator for Power Extraction
The near-field laser output from the scraper i s similar t o the multiline intensity profile shown in Figure 5A. The near-field intensity dis- tribution has a rectangular hole i n the center which i s a projection of the scraper hole as shown i n Figure 4. The near-field peak intensities a r e several times the average intensity. When the beam i s propagated t o the f a r - f i e l d and squared up with cylindrical optics, the intensity profile i s similar to Figure 5B. A multiline diffraction limited DF beam has been observed on a 2 kw laser. (10) Figures 5A and 5B are computer code predictions (11) which have been qualitatively verified by burn patterns in plexiglass blocks. Chemical lasers have good lasing media quality because of the lower density and small density gradients of the lasing gases. Nozzle banks like-those i n Figure 2 have media quality l e s s than A(DF)/50 over an 8 inch path length. (12)
DF Laser Operating Characteristics
Deuterium fluoride lasers can be characterized by several performance parameters as shown in Figure 6. The specific power, o , expressed in kilowatts of nearfield l a s e r power out of the device divided by the total. mass flow into the laser (excluding the ejector) varies from 45- t o 90 kj/kg. For a given amount of device run time and t o t a l power leve1,this specifies the t o t a l mass of reactants required and the size of the reactant f l u i d supply tanks. The nozzle bank power flux,
6 , i n kilowatts per square inch of nozzle e x i t area 2
varies from 125 t o 225 w/m
.
Hence for a specified power level, 6 gives the required nozzle bank area. Current fabrication techniques produce structurally sound nozzles from 1 to 10 inches i n height. With a chosen height, the length of the nozzle bank and hence the laser size and the fabrication costs are specified. Current nozzle banks cost several hundred dollars per square inch. The t h i r d para- meter i s the passive recovered pressure which varies from 100 t o 300 t o r r . This specifies the necessary mass flow r a t e of the ejector t o recoverto one atmosphere. Experimentally, 80 percent of normal shock t o t a l pressure measured a t the
Figure 5. (A) Calculated Near-Field Intensity Profile f r o m Scraper
(B) Calculated Far-Field Intensity Profile
D2 IN TRIP 100 - SPECIFIC POWER 8 0 - 60 - I I I 100 150 200 250 I POWER FLUX 6 WATTSICM~
C9-4 JOURNAL DE PHYSIQUE
entrance to the diffuser throat i s recovered to s t a t i c pressure. A l l of the parameters a , 6 , and P (recovered) are dependent on the mass flow which i s independently varied i n a given device. The mass flow i s increased by raising the combustor pressure which results i n increased lasing cavity pressure. This increases the deactivation of the lasing species DF and causes the efficiency, a , of the device t o decrease as shown i n Figure 6. In other words, t h e energy extracted from the laser decreases for the mount of F-atoms that are pro- vided by the combustor. In order t o achieve high efficiency and good beam quality i n a chemical laser it is necessary t o use l o w lasing cavity pressure and supersonic flow t o remove the vibra- tionally deactivated DF from the lasing zone a t a high r a t e and t o s t a r t the chemical reaction of Equation 1 a t a low translational temperature.
The combustor's purpose i s t o produce fluorine atoms. This i s accomplished by burning a fluorine source and a l i g h t molemar weight hydrocarbon such as the reactants F2 and C2H4 with He diluent.
The operating conditions can be expressed in
a
general fashion by defining several key molar flow ratios. These r a t i o s provide a s e t of standard operating conditions f o r which the mass flows can be determined by simple thermochemical calculations f o r numerous possible reactant combinations. These are:$, = Total molar combustor d i b e n t r a t i o Moles diluent + Moles combustor
-
-
productsMoles excess fluorine as F2
-
fi = Total l a s e r molar diluent r a t i o Combustor diluent + cavity diluent
+ moles combustor products
-
moles excess fluorine as F2
%
= Laser cavity mixture r a t i o-
Moles cavity fuel =CD21
(4)Moles fluorine as
F2
[F2 + 4 @')ITI = Adiabatic combustor operating temperature Subscripts : c = combustor
L = laser cavity
Using these parameters,conditions for the per- formance curve of figure 6 are:
The combustor products with a specific heat r a t i o of typically 1.62 are expanded i n frozen flow through the fluorine nozzles which have an exit area to throat area r a t i o of 23.- This expansion produces 16S°K products which have a mean flow velocity of 1900 meterslsec a t 9 t o r r . This flow
i s presented t o a parallel supersonic flow of D2 and He (see Figure 2) which i s expanded i n a nozzle of area r a t i o 20 to 8.2 t o r r resulting i n an e x i t mean velocity of 2245 meterslsec and a temperature of 91oK. These two streams, having an oxidizer to fuel r a t i o of 1.67, are then mixed, primarily by diffusion and vortex action from the T1triptl j e t s , producing excited s t a t e DFX (see Equation I ) .
Simplified mixing models for the prediction of chemical laser behavior have been independently developed by road well (13) (14) a t
TRW
and by Mirels(15) a t Aerospace Corporation. As originally ex- pressed the Broadwell formulation was i n the form:
where K = proportionality constant
a = mixing spread angle U = average stream velocity
p = concentration of F atoms
- -
'Gn:
= deactivation r a t e of exciteds t a t e s
L = nozzle e x i t width
M (J,er/T) = functional parameter depen- dent on rotational quantum number, rotational and trans- lational temperature r a t i o
(see Reference 16)
P = laser output power m
F
= atomic fluorine flow r a t e In t h i s simplified f o m l a t i o n , the cavity mixing i s idealized and i s characterized by a single, average stream velocity and the spread angle a. Deactivation of the excited s t a t e species DF* i s assumed t o be dominated by a single collision process involving, i n t h i s case, other DF molemles. The "trip" j e t s are not modeled.Numerous correlations of experimental data have been examined based upon the above mixing model. The correlation which has provided the best f i t t o existing data and i s i n current use i s based on the following modifications of the original formulation:
1) The mixing i s represented by the entrain- ment of D2 into the fluorine stream with
2) A new deactivation parameter, A, i s added t o allow f o r products from the combustor process which effectively de- activate the excited s t a t e DF.
3) The atomic fluorine molar flowrate i s substituted f o r fluorine concentration ,in Equation 1 using the identity
where h = fluorine nozzle height n = t o t a l number of fluorine
nozzles
and the remaining symbols have been defined.
4) A f i n a l revision t o the original formu- l a t i o n allows f o r the incorporation of a rotational temperature term ( q ) B t o account f o r the e f f e c t s of v&i&ions in cavity flow s t a t i c temperature on the p a r t i a l inversion lasing process. Incorporating the above modifications and substitution of i d e n t i t i e s , the equation takes the following form:
where K1 = proportionality constant
-
n = number of fluorine nozzles h = nozzle height
UF = fluorine stream velocity
vD2
= deuterium stream velocity NF = fluorine molar flow r a t eA = experimentally determined constant T = average mixed stream temperature
p r i o r t o heat release i n cavity B = experimentally determined constant Values of the constants have been determined t o be A = B = .5, K 1 = 4.49 x 10-l1 joule/sec/an3
(gm mol/wt)
.
The constant C1, experimentally determined t o be 314.9 wattjgmlsec, i s introduced in order t h a t a s t r a i g h t l i n e f i t of the data over the expected operating range may be u t i l i z e d .Equation 7 suggests t h a t chemical l a s e r cavity injectors should be designed with extremely f i n e scale nozzles (n per unit length should be maxi- mized), t h e stream velocities UF and U D ~ should be maximized, the concentration of combustor produced
HF should be minimized and the cavity s t a t i c temp- erature should be decreased but not below the point where chemical reaction can be sustained.
Figure 7 shows the r e s u l t s of a regression analysis of approximately 80 chemical l a s e r experi- ments. These data were acquired from three chemi- c a l las.er cavity injector configurations, a l l basically of the type shown i n figure 2. The correlation data were acquired d e r the following l i m i t s of operating conditions: Combustor Fuels C2H2
8
C2H4Combus
t o r Oxidizer 'F26
NF3 Combustor Adiabatic 17000F t o 22000K Temperature, TI Combus t o r Diluent 9 t o 21 Ratio $,Total Laser Diluent 28 t o 50 Ratio
Laser Cavity Mixture 3 t o 6 Ratio RL
Variations i n the cavity injector configu- rations included :
Nozzle spacing .I21 inch t o .295
inch
Nozzle area r a t i o A/@,F nozzle 15 t o 25 D2 nozzle 10 t o 20
Figure 7. Chemical Lasing Correlation Analysis Variations in pertinent parameters
of
the
correlation equation were:
JOURNAL DE PHYSIQUE
Average stream tempera- 106 OK to 172 OK
ture before reaction, T
These cavity injectors were tested over a wide range of flow conditions and the data used f o r t h e generation of the performance curves shown by Figure 6. A l l data shown i n Figure 6 were acquired with a D2 plenum stagnation temperature of 600°~. The validity of the U D ~ term i n equation 7 was checked by operating the cavity injector a t two values of the D2 plenum stagnation temperature. This allows for a change of U D ~ and T only, a l l other parameters remaining essentially
unchanged. The fluorine and deuterium nozzles were run a t matched and unmatched pressure con- ditions with no apparent effect on performance. The resultant values of UD and T are given below.
2
ToDly O K T, O K UD9, meters/sec
Figure 8 i l l u s t r a t e s the resulting laser power measurements f o r the two t e s t cases. The per- formance difference measured
is
17%. The perfor- mance improvement calculated by equation 7 is 36%. The simplified model does properly predict the trend but with limited accuracy. Insufficient data currently exist t o upgrade the experimental correlation t o more accurately model the UD effect.2
6 I I I I
4 5 6
LASING ZCNE
mm
((XI
Figure 8. Effect of Increased
D2
Nozzle Plenum TemperatureUsing equation 7 to predict the effect of nozzle s i z e or h e r of nozzles per unit length from the largest nozzle tested (.295 inch) t o the smallest nozzle tested C.121) yields an estimated performance change of 10%. Experimental data over the range of nozzle spacing reveals l i t t l e measurable difference i n performance
.
The theory i s not accounting f o r the "trip" j e t e f f e c t which is a dominate effect. Increasing nozzle spacing t o 0.295 i n has resulted in essen-
t i a l l y constant performance with the increased j e t penetration and mixing countering the "nl' effect i n equation 7. Increased understanding of t r i p j e t s w i l l allow increased nozzle size.
Ultimately chemical laser cavity injectors w i l l be regeneratively cooled as shown by figure 2B. The figure 2B cavity injector converts waste heat energy into increased D2 plenum stagnation temperature by u t i l i z i n g the cavity Hen2 mixture t o cool the cavity injector nozzles. In t h i s configuration, ,the nozzle walls w i l l operate a t %1000oK as opposed to the 5 0 0 ~ ~ normally found i n nozzles such as those of Figure 2.4. This effect has been tested by sub- s t i t u t i o n of N2 coolant for H20 i n the conventional nozzles. Figure 9 shows the effect of hot wall nozzle operation. The increased boundary layer temperature and viscous effects appear t o reduce power by anamountsmall i n relation t o the improve- ments in performance attendant to the U D ~ effect of Figure 8.
8 I I I J
4 5 6
LASING ZONE UNGIH (Of)
Figure 9. Effect of Elevated Nozzle Wall Temperature on Laser Performance Chemical laser cavity designs must be compati- ble with the rapid heat release i n the supersonic flow stream. The top and bottom surfaces of the lasing cavity are gas dynamically contoured t o con- f i n e the flow t o prevent recirculation of ground s t a t e DF and t o turn the flow into the supersonic converging section of a diffuser as shown i n Figure
1. Configuration 2 was the contoured cavity used t o collect the data presented i n Figure 6. Since the flow and heat i s being released by chemical pro- cesses, the s t a t i c pressure rises from 13 to 24 t o r r from 0.5 t o 5 cm downstream respectively. The Mach number decreases from 4.5 t o near 2. The mean velocity i s 2000 meters/sec a t the e x i t of the
lasing cavity. The temperature increase3 from a mixture temperature of near 250°K to 530 K a t cavity e x i t due t o the heat release
From
the chemistry. The average mlecular weight of the gas leaving the cavity i s 6.4 and specific heat r a t i o i s 1.58.VARIABLE CGNTOUR LASER CAVITY HFCLT ICL-XI) TEST GEOMETRIES
1 2
+
I
CL-XI NOZZL BANK CL-
XI hN-
1.375 in. WN-
4.000 in. AN-
6.500 la2Figure 10. Cantoured Lasing Cavities and
q e r s o n i c Diffusen t h a t have been used on Chemical Lasers
Typical chemical laser supersonic diffusers have length t o Yw (height) ratios of 12. The width of the diffuser is expanding t o account f o r thick bound- ary layers & boundary layer enerizers are required.
The pressure recovery of a chemical l a s e r i s a function of the momentum per unit area a t the nozzle bank e x i t plane. For a given l a s e r configuration,
the mean velocity of the flow f i e l d is a function of the specific heat r a t i o , the mean t o t a l tempera- ture, Tte, and molecular weight, W, a t the cavity entrance. The mass r a t e of flow per u n i t area of nozzle bank, fi/A, is increased by raising the com- bustor pressure. The s t a t i c temperature i n the
lasing cavity and the t o t a l temperature i n the com- bustor can only be varied over small ranges f o r an
ANALYTICAL
0 GLAD CALCULATION
EXPERIMENTS
A CLVLll(0.8P ) 1 I N . x 8 I N . t2
CL XI (WITH 1-318 IN. X 4 IN. DIFFUSER)
e f f i c i e n t l a s e r hence the velocity i s relatively fixed. Pressure recovery can be varied from 100 t o 300 t o r r primarily by increasing the Ih/A which increases the pressure correspondingly everywhere i n the laser from combustor t o diffuser e x i t . This higher lasing cavity pressure r e s u l t s i n decreased laser efficiency as shown in Figure 6. The pressure recovery i n chemical lasers can be predicted by Figure 11 which has been correlated t o a t leas* 10 different lasers and many
expyj--,
some of which are shown in Figure 11.The 100 t o 300 t o r r gas a t diffuser e x i t i s then pumped t o atmospheric pressure by adding momentum t o the l a s e r flow with a j e t p w such as shown schematically in Figure 1. The momentum i n the ejector j e t is generated by expanding high temperature hydrazine products from a gas generator through a high Mach number nozzle. Figure 12 shows data from several ejectors. Assuming a diffuser
0 R E F 17
a
REF 180
R E F 19 0 R E F 19-
MASS RATIOFigure 12. Ejector Performance
recovered pres.sure of 230 t o r r the required f j e c t o r pressure r a t i o t o recover t o an atmosphere is 3.3. Figure 12 gives a required ejector mass r a t i o of 3.2 f o r reference 18 data. Hence the ejector requires 3.2 times t h e mass r a t e of flow of the l a s e r effluent. For t h i s example the laser
specific paver from Figure 6 is 49 kw/lb/sec but
the
t o t a l system specific power including the ejector mass flow r a t e is 11.7 kw/lb/sec.
Concluding Remarks
DF lasers are emerging as a strong contender f o r applications requiring high energy radiation w i t h good focusing and propagation characteristics.
The device offers highperformance, goo6 beam quality and s-licity when c q a r e d t o e l e c t r i - cally powered devices. Currently, predictive capabilities f o r performance, pressure recovery, propagation, beam quality, and scaling are reasonably well developed. (20)
Figure 11.
Chemical
LaserPressure
kcawryM e t i o n Gmpared w i t h M a t a n d
JOURNAL DE PHYSIQUE
References
1. Kasper, J.V.V. and Pimentel, C.G.
,
"HC1 Chemical Laser", Phys, Rev. Letters,14,
352 (1965).
2. Dzhidzhoev, M.S.; Platonenko, V.T.;
Khokhlov, R.V., Sov. Phys. Uspekhi,
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247 (1970). 3. Basov, N.G., Igoshin, V. I . , Markin, J. I . , Oraevskii, A.N., Kvantovaja Electronika,2,
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,
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,
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,
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3
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,
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,
TtAtmospheric Gas Absorption a t DF Laser Irlavelengths," Aerospace Corp. TR-0073(3240-10)-9, 1973.
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-
t o be published.(b) Wisner, G.R., Palma, G.
,
and Foster, M., "Laser Beam Quality Study Report", United Aircraft Research Laboratories, UARL M911239-23, Sept. 1973.11. Bullock, D.L., and Lipkis, R., 'Unstable Resonators for Chemical Lasers", Air Force ;Yeapons Laboratory, TR 74-201, July 1975.
1 2 . Hook, D.L., Behrens, H.W., e t a l , "DF Laser Technology Studies" Final Report,
AFWL,
t o be published.13. fqProposal for Aerodynamic Reactive Flow Studies of H /F2 Laser-II", J.E. Broadwell, TKV Report ~ ~ 2 0 9 ~ 7 . 0 0 1 , 22 May 1972.
14. "Effect of Mixing Rate on HP Chemical Laser Performance", H. Mirels, R. Hofland, and W. S. King, AIAA Journal 2 (2) 156, February 1973.
15. "Simplified Model of CW Diffusion Type Chemical Laser",
K.
Mirels, R. Hofland, and W.S. King, AIAA Journal 2 (2) 156, February 1973.16. "Closed Form Solution t o Rate Equations f o r an F + H2 Laser Oscillator", G. Emanuel and J.S. ~Vhigtier, Applied Optics 11, 2047,
September, 1972.
17. Knowles, P.J., Reiner, R . J . , Heckert, B.J., .and Dailey, C.L., "Feasibility Study of High Energ)lr Ejector Systems", Aerospace Research Labo- ratories, ARL-TR-75-0015, May 1975.
18. Teper, R. I . , "Chemical Laser Diffuser/ Ejector Technology", Rocketdyne, t o be published.
19. Kepler, C.E., Zumpano, F.R., Landerman, A.M., Biancard, F.R., Brooks, C.S., and Russel, S., "Pressure Recovery/Scrubber Systems f o r Chemical Lasers", United Aircraft Research Laboratories, TR-R75-911976-8-2, Vol. 11, March 1975.
