CARS thermometry in fuel-rich combustion zones

Robert J. Hall and Laurence R. Boedeker

Experimental and theoretical investigations of N2 coherent anti-Stokes Raman scattering (CARS) ther-mometry in laboratory ethylene-air diffusion flames have revealed significant nonresonant susceptibilityeffects in fuel-rich regions of the flames. The effects appear to be due to the size of the nonresonant suscep-tibility for typical hydrocarbon fuels and can give rise to significant temperature errors if not accounted for.An efficient theoretical algorithm for reducing spectra affected by nonresonant interference is presented andshown to give excellent agreement with experiment. It is shown that uncertainty about mixture composi-tion or the values of nonresonant susceptibilities of individual constituents need not have a significant effecton CARS temperature measurement.

I. Introduction

Laser Raman diagnostic techniques are an active areaof research today because they offer the promise of re-mote nonperturbing measurements of medium condi-tions with high spatial and temporal resolution. Incombustion research, in particular, such optical diag-nostics are well suited to probe the high interferenceenvironments characteristic of practical combustiondevices. The use of physical probes for temperatureand species concentration measurement can be ques-tionable in many circumstances; they may disturb themedium they seek to measure; their measurements maybe subject to corrections that are difficult to specify (asin radiation corrections for thermocouples), and theymay not even survive especially hostile environments.The spontaneous Raman effect has been widely appliedas a means of avoiding these problems, but its relativeweakness and spatial incoherence (its signal is scatteredinto 47r sr) have restricted its utility to environments inwhich the background interferences are relatively weak.Coherent anti-Stokes Raman scattering (CARS), on theother hand, is a spatially coherent process with a muchhigher signal conversion efficiency; it thus makes pos-sible better discrimination against unwanted interfer-ences and has largely supplanted spontaneous Ramanscattering for diagnostic probing of practical combus-tion media. Reviews of the basic theory of CARS andits applications have been provided by several au-thors. 1-4

The authors are with United Technologies Research Center, EastHartford, Connecticut 06108.

Received 27 December 1983.0003-6935/84/091340-07$02.00/0.© 1984 Optical Society of America.

It is well known that the CARS signature will consistof a resonant frequency-dependent contribution fromthe probed molecule of interest plus a nonresonant,sensibly frequency-independent background contri-bution that arises mainly from virtual (nonresonant)one- and two-photon absorptions in all species that maybe present. In air-fed combustion, N2 is usually thedominant constituent and will be present nearly ev-erywhere in large concentration. Consequently, itsCARS signature will be dominated by the resonantcontribution, reflecting the temperature of the gas, andthe distortions of the spectrum due to the nonresonantbackground susceptibility will normally be minimized.Nitrogen has, therefore, been the molecule of choice forCARS thermometry, and high confidence can be placedin these measurements because the basic Raman spec-troscopic parameters such as line positions and Ramanlinewidths needed for interpretation of the experi-mental signatures are much better known than those ofany other molecule. One problem in N2 thermometrythat has not received much attention, however, is theeffect of the nonresonant susceptibility in regions wherethe latter may have a relatively large value. In thispaper, we report significant nonresonant susceptibilityeffects observed in fuel-rich regions of laminar, sootydiffusion flames, and show how these effects can bereadily handled in the data reduction process.

11. Theory

CARS temperature measurements are carried outusing the shape of the spectrum (the variation withfrequency); a unique feature of the technique is thatconcentration measurements can also be carried out incertain ranges from the spectral shape by using thenonresonant susceptibility as an in-situ referencestandard 5 thus avoiding the complications associatedwith absolute intensity measurements. The CARS

1340 APPLIED OPTICS / Vol. 23, No. 9 / 1 May 1984

intensity is proportional to I X 2, where the third-orderelectric susceptibility X(3) relates the lowest-ordernonlinear polarization term (P) in isotropic media(gases, liquids, centrosymmetric crystals) to the incidentelectric field amplitudes (E) through the relation-shipl-4

P = XME + X(3)E3 +., (1)

where the first-order susceptibility governs the ordinaryabsorption and dispersion of light. The CARS signalarises from the third-order component P( 3 ) modulatedat the frequency W3 = 2 1 - w2, with the sources atfrequencies 1 and w02 termed the pump and Stokes,respectively. The third-order electric susceptibility canalso give rise to other frequency components corre-sponding to such processes as tripling, two-photon ab-sorption, and field-induced second harmonic genera-tion. If the frequency difference w1 - w2 between theincident sources coincides with the frequencies oj of acollection of Raman-active vibrational modes, thethird-order electric susceptibility in the ordinarypressure- or Lorentz-broadened regime may be repre-sented as

X(3) = E (X] + iX)) + XNR,

where the complex resonant contribution of esRaman transition is given by

X + 2Np c4 (aUz)jAp3 )

xi ' h 2 [j-(L1 -0 2 )]-i rj

In Eq. (3) Np is the probed molecule number densi(o,)j is the spontaneous Raman cross section (alignpump and Stokes polarizations assumed); Ap(°) is tunperturbed Boltzmann population difference betwethe initial and final states in the transition, and tlinewidth rj is a coherence dephasing rate that is pected in the gas phase to arise mainly from rotatioirelaxation. It has been assumed in Eq. (3) that nonethe field frequencies W1 , 2, or 3 coincides with oiphoton absorptions in the probed molecule, that tpressure is not so high that collisional narrowing effeneed to be considered, that no saturation of the mediaoccurs, and that the laser pulse durations are longthan any dephasing time (7 1 ). If one- and two-photabsorptions are avoided in all the molecules presenta mixture, the nonresonant susceptibility term XNR vbe a real dispersionless number given by a mole-fractiweighted sum of contributions from all the specpresent. Values of XNR for various pure species habeen reported by Rado,6 DeMartini et al. 7 and HEchecorne et al.8 ; these measurements are generaconsistent with one other, but the actual numbers hebeen normalized to an assumed susceptibility value]the Q(1) vibrational transition in H2 on exact resonanIt is now generally accepted that the H2 Q(1) suscepbility can be more accurately specified and that th(nonresonant susceptibility values should be scaledby a factor of 2.-2.5.5,9 10 There is reason to belie,based on the size of the values for CH4 and C2H6, tlthe nonresonant susceptibilities for other hydrocarb(

might be quite large; a reasonable guess might be thatthey will increase monotonically with the number ofmethyl groups. This would suggest that caution beexercised in performing N 2 thermometry in fuel-richregions. Away from fuel-rich zones, the backgroundsusceptibility can reasonably be assigned a valueranging from 1.0 to -1.2 times the N2 nonresonant valueitself, which reflects the range of values expected as oneproceeds from unburned air to typical stoichiometriccombustion products. While it is never a good ap-proximation to ignore the background susceptibilityentirely in N2 thermometry, inferred temperatures infuel-free regions will not be very sensitive to variationsin this expected range. The issue of the nonresonantbackground can be avoided entirely by employing thepolarization orientation approach to background can-cellation,5 11 -13 but because this technique entails a verylarge reduction in signal strength, there will be manyexperimental situations in which it is not possible to doso.

The CARS intensity I3 for monochromatic sourcesmay thus be generally represented in the form

I3(W3) (a xi) + ( x;)2 + 2 XNR (a X + XNR,(2)

(4)

or, introducing per molecule contributions X,, X- andXNR to the various susceptibility components, in theform

(3) W -13(3) 1 + 2 (X-NRI I X XjiI2 ) I) (5)

where x is the mole fraction of the probed molecule.Finite laser bandwidths can be included by introducingthe convolution operator ( ), where14

(F) = (If1I2)' S dAl(W 3 - A)F(A) f dcolI(wl) I2(W1 - A), (6)

and A1 and 2 are the integrated source intensities.Equation (5) thus becomes

NC0@3) (1) + 2 - 8/ \ 3XNRJ\

(X ) ((E_,) + (z~) j (7)

The Raman linewidths rj which appear in the resonantsusceptibility expressions will in general be functionsof composition, but there is evidence that this depen-dence may not be extreme,151 6 particularly when themasses of the radiating molecule and its collision part-ners are roughly comparable. The issue of linewidthsensitivity has been addressed in Refs. 4 and 17.Doppler-broadening effects can also be included but aresmall for the peak temperatures encountered in thisstudy. In this approximation, the resonant suscepti-bility terms are functions of temperature alone, so thatEq. (7) may be expressed as

I(w3) - e(W3) + 2C(cv3,T) + C2g(w3,T), (8)

where C = x/xNR; e = ();f = (j ); andg = ((Yjyj)2 + (j x,)2 ). The aim in representing the CARS

1 May 1984/ Vol. 23, No. 9 / APPLIED OPTICS 1341

intensity distribution in this form has been to separatethe factors which are functions of composition fromthose which are functions of temperature; -NR shouldnot have a significant temperature dependence. Thereare thus two independent variables or fit parametersthat will be involved in fitting synthetic spectral shapesto experimental signatures: the gas temperature andthe ratio C of probed species mole fraction to the aver-age per molecule background susceptibility, which willbe a function of mixture composition. If the latterquantity is not known precisely because of uncertaintyabout the overall composition or the particular contri-bution of any of the bath gases, the inferred species molefraction will be uncertain to the same degree. However,because temperature and this concentration ratio areindependent variables, thermometry and concentrationdetermination can be performed simultaneously; theinferred temperature from a least-squares fit will beunaffected by the initial values assumed for the speciesconcentration or background susceptibility as long asthere is sufficient resonant contribution to the signal.If one's primary concern is thermometry, lack of infor-mation about these other parameters will not stand inthe way of a temperature measurement as long as thebackground contribution does not obscure that of theprobed molecule. In the limit of small C, one has thefamiliar situation in which the CARS intensity is de-termined by the modulation of XNR by the real part ofthe resonant susceptibility

I3(0)3) - e(w3) + 2Cf (w3,T). (9)

It is in this regime that concentration predictions willbe most accurate if assumptions about XNR are made.In the limit C - 0, the resonant modulation will dis-appear, and the lower detectivity limit will have beenreached. In the limit of larger C, the CARS intensitywill be mainly determined by the squared modulus ofthe resonant susceptibility

I3(0)3) C2 g(w3,T), (10)

and C will just be a multiplicative factor that will notaffect the overall band shape. Concentration fits areexpected to be much less accurate in this regime becausethe spectral shape loses sensitivity to C.

The laser profile convolution Eq. (6) can be special-ized14 to the two ways of generating the CARS signa-ture: either a tunable, narrowband, or a broadbandStokes source can be employed. The use of a tunableStokes laser makes possible higher resolution spectraand much stronger CARS intensities but also requiresmuch longer data acquisition times. Consequently,most practical investigations employ a broadband dyelaser as the Stokes source. The acquisition times in thiscase are much shorter, with single-pulse spectrumgeneration routinely performed,18 but a significant re-duction in CARS intensity occurs because the Stokesintensity is distributed over a relatively large frequencyinterval. In many cases, then, the overall count levelsin broadband CARS are such that it is not possible toemploy the previously mentioned polarization orien-tation approach to background susceptibility cancel-

lation; this is particularly a problem in very hotgases.

Equation (8) provides the basis for an efficient datareduction algorithm in which not only the temperaturebut also the ratio C are fit parameters. In any iterativeleast-squares fitting procedure, it will be required toprovide a synthetic spectrum for specified values of thefitting parameters. To have to calculate such a spec-trum from first principles for each iteration will ordi-narily be too time-consuming, particularly if the datareduction is being carried out on a minicomputer. If,however, jj ,and i + iy)I 2 are stored in ad-vance in a temperature library, it will be possible toretrieve susceptibility components from the library byinterpolation and generate a spectrum from Eq. (8).This should be many orders of magnitude faster, andit will be exact if the increments in the temperature li-brary are sufficiently small and/or if the interpolationalgorithm is sufficiently precise. For broadband CARSwith the Stokes bandwidth very much larger than thatof the pump,. a convolution of the pump profile alonewith the susceptibility components can be performedin advance for the library, which will then be applicableto all experiments performed with the same pumpbandwidth and pressure. The library can be generatedduring periods of low computer utilization and usedindefinitely. Correction of the CARS signature for theStokes intensity profile can be performed in the fittingprogram itself after retrieval of the pump-convolvedsusceptibility components from the library. [Forbroadband CARS, e = 1, f and g are corrected by thefactor exp(-4 n21co3 - [2wP) - WT)]12/1W2), where AW 2

is the dye bandwidth FWHM, and AW2 >>Awl.] Asimilar concept has been developed by Greenhalgh andPorter.19 A nonlinear least-squares fitting program hasbeen developed to extract temperature informationfrom experimental signatures. In addition to thetemperature T and concentration parameter C, the baseline count level, a calibration frequency, and a stretchingfactor for the theoretical spectrum have been includedas fit parameters. The program uses the Levenberg-Marquardt algorithm,20 producing a fit in -5 min CPUon a VAX 11-750. The fit program user has the optionof dropping the concentration ratio C as a fitting pa-rameter, leaving temperature as the only physical fitparameter. Sensitivity studies have shown that theStokes laser profile generally has an important influenceon the inferred temperature.

The foregoing discussion has been motivated by someunexpected nonresonant background susceptibilityeffects which were observed in an investigation of N2CARS thermometry in laboratory diffusion flamesburning ethylene. It was found that accurate ther-mometry in regions of the flame where significant un-burned ethylene or its pyrolysis products could be ex-pected required inclusion of the parameter C as aleast-squares fitting parameter in the manner justoutlined. Very large temperature errors and very poortheory-experiment fits were observed in these regionswhen the fits were carried out using the temperaturealone as a fitting parameter. The experiments and

1342 APPLIED OPTICS / Vol. 23, No. 9 / 1 May 1984

Fig. 1. Ethylene-air diffusion flame. Burner tube radius = 5 mm;air flow diameter = 105 mm; flow rates = 917 cm3 /sec (air), 3.37

cm3 /sec (ethylene).

results will now be discussed; it is expected that the ef-fect will have to be taken into account in other com-bustion environments as well and thus has an impor-tance that goes beyond laboratory flames.

Ill. Experimental

Experimental N2 CARS spectra have been obtainedas part of an investigation of soot formation in laminardiffusion flames, where measurement of the tempera-ture distribution in small axisymmetric flames is animportant part of the study. Ethylene (C2H4/air) dif-fusion flames are important reference cases in sootformation studies,21 and the experimental spectra to bereported here have been taken in one such flame asdepicted in Fig. 1. The flame is seen to emit intenseradiation from soot particles, and an annular sootbackground band can be observed as wings of sootcentered about the flame tip. The present measure-ments were obtained as part of a study of the role oftemperature in soot breakthrough as the height of sucha flame is increased. The results of CARS theory-experiment fits to be presented here are intended onlyto illustrate the previously discussed influence of non-resonant susceptibility on temperature measurement;the aim is not to present the results of a complete flameinvestigation or to draw any conclusions about flamestructure or soot formation. These questions will beaddressed in a later publication.

The spectra to be reported here were obtained in ra-dial scans at heights of h = 3.8,7.6, and 15.2 mm abovethe burner tube lip as indicated in Fig. 1. As such thespectra encompass the lower blue zone of the flame (thedark space in Fig. 1), where little soot has formed, as wellas more intense soot zones at the larger two heights.The results are representative of those obtained at allheights up to the flame tip at 76 mm. A hexagonalchimney with flat glass windows (not shown in Fig. 1)provided stabilization of the flame and optical accessfor the CARS beams. The need for high spatial reso-lution led to the use of folded BOXCARS2 2 to satisfy theCARS phase-matching requirement; the spatial reso-lution achieved was -200 X 700 m. A frequency-doubled Nd:YAG laser provided the two pump com-ponents, and a portion of the Nd:YAG laser output wasused to excite a broadband (bandwidth 120-cm-1FWHM) dye laser centered near 16,500 cm-1 . The N2CARS spectra in the vicinity of 21,100 cm-1 were dis-persed with a holographic grating and detected with a500-channel PAR optical multichannel analyzer (OMA2). The signals were averaged over 500 laser pulses (500sec) at each location, and the resulting spectra togetherwith their experimental parameters were stored on aPDP 11/34 computer; the experimental files were latertransferred to a VAX 11-750 for analysis using theleast-squares fitting program discussed earlier. Be-cause the dye center frequency and bandwidth are veryimportant input parameters in the least-squares fittingprogram, particular care was exercised to ensure thatthese parameters were known as accurately as possible.CARS spectra of pure CO2 or of ethylene with traceamounts of N2 were taken befor'e and after each radialscan; these spectra were essentially due to the nonre-sonant background and thus provided a representationof the dye laser profile. The base lines of all experi-mental signatures were corrected for OMA dark currentby subtracting the count levels obtained over the sameaveraging time when one of the two pump componentswas blocked. In sooting regions, a small C2 (formed bylaser vaporization of soot particles) Swan band contri-bution also contributes to the background count; thisis primarily an incoherent effect generated by the si-multaneous presence of the pump and Stokes sourcesand is corrected for by the above experimental proce-dure.2 3

IV. Discussion of Results

The most widely employed data reduction procedurein N2 CARS thermometry has been to perform one-parameter fits with the temperature as the main fittingparameter and the background susceptibility assigneda value representative of stoichiometric combustion(a 1.2 times the pure N2 value). At all the heights in-vestigated, this procedure was found to yield very pre-cise fits at all radial locations greater than a value givenapproximately by the luminous flame surface (Fig. 1).In this outer region, use of the two-parameter fit pro-cedure (T and C) gave inferred temperatures essentiallythe same. The best-fit C values in this relativelybackground-free region were consistent with alarge N2

1 May 1984 / Vol. 23, No. 9 / APPLIED OPTICS 1343

uS

u-

Li

u-

H

RAD AL

2400- b) h = 7.6 mm

2000 A

1600-

1200-

800-

400

2400 * A c) h 3.8 mm

2000- L

1600-

1200

800-

400 BURNER TUBE ADIABATIC- RADIUS--i FLAME00 AU- TEMPERATURE

0 1 2 3 4 5 6 7 8 9 10

DISTANCE FROM CENTERLINE, mm

Fig. 2. Radial temperature profiles at (a) h = 15.2 mm, (b) 7.6 mm,and (c) 3.8 mm. A denotes prediction of one-parameter (T) fit; 0prediction of two-parameter (T and C) fit. Dashed vertical lines

indicate approximate boundary of luminous zone.

mole fraction (70-80%) and the above backgroundsusceptibility, although, as expected, the standard de-viation in C is very large in this region. The one-pa-rameter fitting procedure is thus felt to be quite validin this region.

At radial locations closer to the center line, an abrupttransition is made to an inner region in which the one-parameter fitting procedure breaks down. The fitsobtained in this region are seen to be deficient by visualexamination and also in the sense that large, obviouslyerroneous, local temperature maxima can be predictedwell inside the known flame reaction zone and peaktemperature locations.24 In this region there is clearevidence of interference between the resonant andnonresonant susceptibility components as will be seen,and use of the two-parameter approach results in fitsthat are generally excellent. The differences betweenthe one- and two-parameter approaches are shown inFig. 2 for radial scans at three heights just above theburner tube lip. In the outer regions there are no sub-stantive differences between the two procedures, butat a radial location close to the luminous flame surfaceand reaction zone location, a significant difference

abruptly occurs. At this location, which becomes pro-gressively smaller as the height is increased, the fittingparameter undergoes a similarly abrupt or discontin-uous transition from the large N2 concentration/back-ground-free values to much smaller values indicativeof small N2 concentrations and/or large backgroundsusceptibility. This discontinuity in C may mark thelocation of the fuel diffusion layer. It can be seen thatcontinued use of the one-parameter model in the innerregion can lead to serious temperature errors.

Inclusion of C as a fitting parameter results in fitsthat are generally excellent as exhibited in Figs. 3-5,where theory-experiment comparisons with associatedinferred temperatures are presented at three locations.The inadequacy of the one-parameter approach is re-vealed by a general failure to reproduce the modulationdip near the fundamental bandhead and by substantialdiscrepancies in the spectral vicinity of the vibrationalhot bands. These deficiencies are resolved by thetwo-parameter fitting approach as can be seen. Sig-nificant temperature errors can result even if thebackground interference effects are relatively small asin Fig. 4. At larger values of h, the same effects areobserved with the radius of demarcation between theinner and outer zones decreasing as the visual flame tipis approached; only beyond the flame tip is the one-parameter fit everywhere valid. In the intense sootingannulus, whose location is revealed by the distinct humpon the one-parameter fit results at the larger height h= 15.2 mm, the two-parameter fits are somewhat lesssatisfactory than those shown in Figs. 3-5. There maybe additional physics or experimental artifacts to con-sider in this zone, but at any rate the inferred temper-atures here are close to those which would be obtainedby interpolation between the inner and outer solu-tions.

The importance of C inside the reaction zone is mostlikely due to the size of the nonresonant backgroundsusceptibility for ethylene or its pyrolysis products,although at low heights the smallness of the N2 spec-trum is also a factor. Figure 6 shows a highly modu-lated spectrum on the center line (y = 0) for h = 3.8 mm.The very precise fit shown results in the temperaturegiven and a value of C = 0.04, where XNR has been ex-pressed in cgs units of (1017 L) (L = 2.46 X 1019 cm- 3 ).To infer an N2 concentration x from C, it is necessaryto make some assumptions about the relative compo-sition of the mixture and the pure background suscep-tibilities of the individual constituents. As an example,if in the case of Fig. 6 one assumes a two-componentmixture N2 and C2H4 and further assumes that XNR forethylene is the same as that for ethane (-5 times thatof N2),5 6 one has from x/[x + 5(1-x)] = 0.04 that x =0.17. This level of N2 concentration on the center lineis consistent with available theory and mass spec-trometer sampling results in diffusion flames.24 Ingeneral, however, such simplified assumptions aboutthe fuel-rich mixture will not apply even if one had thepure background susceptibilities available, so that N2concentration information may not be reliable. Thepoint of this paper is, however, that such uncertainties

1344 APPLIED OPTICS / Vol. 23, No. 9 / 1 May 1984

a)

U)

LU

U)

0LU

-J,LU

1.0-

0.8-

0.6-

0.4-

0.2-

0-

2220 2260 2300 2340 2380

RAMAN SHIFT, cm- 1

Fig. 3. Fits of N2 signature at h = 7.6 mm, r = 1.91 mm; (a) one-parameter fit, (b) two-parameter fit, ... experiment, -theory.

a)

1.0- T =2060 K

0.8-

0.6-

0.4-

u0.2-LU

Ern6

0.4-

0.2-

0-

2220 2260 2300 2340 2380RAMAN SHIFT, cm-

Fig. 4. Fits of N2 signature at h = 7.6 mm, r = 4.76 mm; (a) one-parameter fit, (b) two-parameter fit, ... experiment, - theory.

CU)Er b)

u 1.;O T 1526 K

< 0.8--Li

0.4-

0.2-

0

2220 2260 2300 2340 2380RAMAN SHIFT, cm- 1

Fig. 5. Fits of N 2 signature at h = 15.2 mm, r = 1.27 mm; (a) one-parameter fit, (b) two-parameter fit, ... experiment, - theory.

1.0-0.9-

,0.8-

LU 0.7-

Z 0.6-U)

cr0.5

0.Liz 0.4

tJ 0.2Er

0.1

0

2220

I . . .I

2260 2300

RAMAN SHIFT,

Ir Z-2340

cm-1

2380

Fig. 6. Fit of N2 signature with large background interference at h= 3.8 mm, r = 0. Best fit C = 0.04.

do not stand in the way of temperature measure-ment.

V. Conclusions

Theory-experiment fits in fuel-rich regions ofC2H4 /air-diffusion flames have shown that the probedmolecule mole fraction and overall nonlinear back-ground susceptibility need to be considered for accurateN2 thermometry; this effect evidently results from thesize of the nonresonant susceptibility for typical hy-drocarbon fuels. It has been shown that this can be

1 May 1984 / Vol. 23, No. 9 / APPLIED OPTICS 1345

b)

T= 1227 K

T=894 K

a)

I

done without unduly complicating the data reductionprocedures, however, and that, therefore, the presenceof nonresonant background effects in practical com-bustion media need not be considered a drawback to theapplication of CARS in these environments.

A significant note of appreciation is due Gregory M.Dobbs for computerization of the experiment, which hasbeen essential for the acquisition, storage, and efficientprocessing of CARS spectral data. The experimentalcontributions of Sandro Gomez and Alan C. Eckbrethare also gratefully acknowledged.

The experimental portions of this research weresponsored by the Office of Naval Research, under con-tract N00014-81-C-0046.

References1. S. Druet and J. P. E. Taran, "Coherent Anti-Stokes Raman

Spectroscopy," in Chemical and Biological Applications of La-sers, C. B. Moore, Ed. (Academic, New York, 1979).

2. J. W. Nibler and G. V. Knighten, "Coherent Anti-Stokes RamanSpectroscopy," in Topics in Current Physics, Vol. 2, A. Weber,Ed. (Springer, Heidelberg, 1979).

3. J. W. Nibler, W. M. Shaub, J. R. McDonald, and A. B. Harvey,"Coherent Anti-Stokes Raman Spectroscopy," in VibrationalSpectra and Structure, Vol. 6, J. R. Durig, Ed. (Elsevier, Am-sterdam, 1977).

4. R. J. Hall and A. C. Eckbreth, "Coherent Anti-Stokes RamanSpectroscopy (CARS): Application to Combustion Diagnostics,"in Laser Applications, Vol. 5, R. K. Erf, Ed. (Academic, SanDiego, 1984).

5. A. C. Eckbreth and R. J. Hall, Combust. Sci. Technol. 25, 175(1981).

6. W. G. Rado, Appl. Phys. Lett. 11, 123 (1967).7. F. DeMartini, F. Simoni, and E. Santomato, Opt. Commun. 9,176

(1973).8. G. Havchecorne, F. Kerherve, and G. Mayer, J. Phys. Paris 32,

47 (1971).9. R. L. Farrow, paper presented at Lasers '82 International Con-

ference (Dec. 1982).10. G. S. Rosasco, National Bureau of Standards; private commu-

nication (July 1983).11. J. L. Oudar, R. W. Smith, and Y. R. Shen, Appl. Phys. Lett. 34,

758 (1979).12. A. F. Bunkin, S. G. Ivanov, and N. I. Koroteev, Sov. Tech. Phys.

Lett. 3, 182 (1977).13. L. A. Rahn, P. L. Mattern, and R. L. Farrow, Opt. Commun. 39,

249 (1979).14. M. A. Yuratich, Mol. Phys. 38, 625 (1979).15. R. J. Hall, Appl. Spectrosc. 34, 700 (1980).16. P. L. Varghese and R. K. Hanson, J. Quant. Spectrosc. Radiat.

Transfer 26, 339 (1981).17. R. J. Hall, Combust. Flame 35, 47 (1979).18. A. C. Eckbreth, G. M. Dobbs, J. H. Stufflebeam, and P. A. Tellex,

AIAA Paper No. 83-1294 (1983).19. D. A. Greenhalgh and F. M. Porter, (reference is not available);

to be published.20. D. W. Marquardt, J. Soc. Ind. Appl. Math. 11, 431 (1963); K.

Levenberg, Q. Appl. Math. 2, 164 (1944).21. I. Glassman and P. Yaccarino, Proceedings, Eighteenth Inter-

national Symposium on Combustion (The Combustion Institute,Philadelphia, 1981), p. 1175.

22. J. A. Shirley, R. J. Hall, and A. C. Eckbreth, Opt. Lett. 5, 380(1980).

23. A. C. Eckbreth and R. J. Hall, Combust. Flame 36, 87 (1979).24. R. E. Mitchell, A. F. Sarofin, and L. A. Clomburg, Combust. Flame

37, 227 (1980).

1346 APPLIED OPTICS / Vol. 23, No. 9 / 1 May 1984

OSA Medals continued from page 1339

NEW HONORARY MEMBER Nicolaas

BloembergenNicolaas Bloembergen of the Department of Applied

Physics at Harvard University has been named an honorarymember of the Optical Society of America. The bylaws of theOptical Society specify that any person may be elected tohonorary membership who has rendered preeminent servicein the advancement of optics. The number of honorarymembers in the Society is limited to eight. Bloembergen iscited for pioneering contributions to the fields of nonlinearoptics and laser spectroscopy.

Born in The Netherlands, Nicolaas Bloembergen receivedhis B.A. and M.A. degrees from the University of Utrecht andhis Ph.D. from the University of Leiden in 1948. Since 1949he has been on the faculty of Harvard University. In 1957 hebecame Gordon McKay Professor of Applied Physics, and in1975 he was named Rumford Professor of Physics. He hasbeen a visiting professor at the Universities of Paris (1957),Berkeley (1965), and Leiden (1973). Recipient of the 1981Nobel Prize in Physics, Bloembergen has also been honoredwith the Oliver E. Buckley prize of the American PhysicalSociety (1958), the Morris Liebman Memorial Award of theIRE (1959), the Stuart Ballantine Medal of the Franklin In-stitute (1961), the National Medal of Science, awarded by thePresident of the United States (1974), and the 1979 FredericIves Medal of the Optical Society.

NEWPORT RESEARCH AWARDSRecognizing that the future well-being of this nation rests

on the development of new technology and the effective useof that technology, the Newport Corp. has endowed theNewport Research Awards. Their purpose is to encourageand support university research in the advancement of laserand electrooptics technology. Milton Chang, president ofNewport, anticipates funding of up to $500,000 over a five-yearperiod. Awardees will be doctoral candidates who are pursuingthesis projects in lasers and electrooptics, or who are makingtechnological advances in other fields through the applicationof lasers and electrooptics.

The selection of the candidates and administration of theprogram will be the responsibility of the Optical Society ofAmerica. Awards of up to $12,000 each will be made. Theywill include a maximum stipend of $8000 and additionalfunding of $4000 for expenses related to the recipient's re-search and other academic requirements.

Applications should be submitted by 15 May 1984, for anaward to begin with the 1984 fall term. Awardees will benotified in July 1984. Each award will be for a period of onecalendar year and will be once renewable, assuming reasonableprogress with the research project.

For applications and further details concerning the awards,contact the Optical Society of America, 1816 Jefferson Place,N.W., Washington, D.C. 20036, 202-223-8130.

The Optical Society of America, founded in 1916 to increaseand diffuse the knowledge of optics in all its branches, topromote mutual interests, and to encourage cooperation inthe field, has a membership of some 8500, of whom nearly 2000are overseas. OSA is one of nine member societies of theAmerican Institute of Physics.