Stress Plate Optical Modulator for Circular Dichroism Measurements

L. F. Mollenauer, D. Downie, H. Engstrom, and W. B. Grant

The fused silica stress plate modulator described below offers several advantages over the other known

electrooptic modulation devices: primarily, high transmission over a broad wavelength range, and large

aperture. When operated at its electromechanical resonance frequency of 16.7 kHz, the modulator

requires only low voltage, low power drive to operate as a ±X/4 plate. Complete constructional details

are given, including a model from which resonance frequencies may be calculated. As part of a circular

dichroism apparatus, the modulator has allowed measurement of effects as small as 1 part in 105. The

possibility of extension of the operating range into the vacuum uv is discussed.

1. IntroductionCircular dichromism measurements often involve

only very small differences in absorption coefficient forright- and left-hand circularly polarized light. This isespecially true, for example, in the detection of para-magnetic resonance in solids through monitoring of themagnetic circular dichroism of visible absorption bands,'or in the measurement of the circular dichroism ofcertain organic materials.2 Such measurements aremost easily made by a modulation technique in whichthe light beam is rapidly and symmetrically switchedback and forth between right- and left-hand polariza-tions. Although a number of usable electrooptic modu-lators are known, practically all suffer from one or moreof the following limitations: low transmission, narrowbandwidth of wavelengths transmitted, small aperture,excessive drive requirements with respect to power and/or voltage, and costliness. We describe here a stressplate modulator having essentially none of the abovedisadvantages, and capable of operation at the relativelyhigh modulation frequency of 16.7 kHz. The device issomewhat similar to a shutter described by Hauseret al., 3 but we give important constructional detailsomitted by the authors of Ref. 3, along with analysisof the device operated as a modulator at its lowestelectromechanical resonance.

The modulator is shown in Fig. 1. Two electricallydriven, piezoelectric transducers transmit their strainthrough the two steel end bars to a fused silica plate,alternately stretching and compressing it. The resul-tant induced optical activity makes the quartz a d9\/4plate. As viewed from its electrical terminals, the

device has two closely spaced lowest frequency reson-

The authors are with the Physics Department, University of

California, Berkeley, California 94720.Received 5 September 1968.

ance points, both characterized by a purely resistiveinput impedance. At one point, the impedance is veryhigh (the pole) and at the other, it is very low (thezero). By driving the device at the frequency of itszero, only a few volts are required at an impedancelevel on the order of 50 Q.

The uniaxial stress required to make a plate of fusedsilica into a quarter-wave rotator is given by the for-mula: S = X/4Ct, where X and t are the wavelength andplate thickness in cm, C is the stress-optic constant, andS is in dynes/cm2 . For fused silica, C has the value3.40 X 10-"3 cn/dyne. Thus, for a wavelength of540 mu4 and a plate thickness of 1 cm, the required valueof S is a modest 4 X 107 dynes/cm'; the correspondingvalue of strain, e = 5.4 X 10-'. The above values areat least one order of magnitude less than that requiredto fracture the quartz.

The most suitable transducer material is one of thelead-zirconium-titanium ceramics, such as ClevitePZT-4, PZT-8, or Gulton Industries HDT-31; allfeature large electromechanical coupling coefficients,large Young's modulus, very low thermal expansioncoefficients, and mechanical Q factors in the hundreds.See Table I for numerical values.4 The modulatorbuilt in this laboratory and described below used PZT-8, but PZT-4 or its equivalent, HDT-31, would haveworked just as well or better. To match the essentiallyzero thermal expansion coefficients of both the trans-ducers and the fused silica, the end bars were made ofInvar steel.

II. ConstructionConstruction began with epoxying together of 12.7-

mm (2-in.) diam by 2.54-mm (0.10-in.) thick trans-ducer disks into two stacks of eight transducers each;two end caps of 12.7-mm diam by about 1-mm thickInvar were included on each stack. For the epoxy, weused 10 parts by weight of Shell Epon 828 to 1 part ofShell curing agent D; this combination requires a curing

March 1969 / Vol. 8, No. 3 / APPLIED OPTICS 661

DISCS22 mm

25.4 mm

I 50.8 mm

Fig. 1. Stress plate modulator. Quartz element is stretchedand compressed along a vertical axis; light path is normal to

plane of paper.

Table I. Piezoelectric and Other Materials ConstantsPertinent to Modulator Design

Thermal S33Dexpansion or 1/Ycoefficient 10-12

Material a3, 10-60 C 112/N e33S/E k33 Q

PZT-8 -1? 8.5 616 0.62 1000PZT-4 or 0-1.7 7.90 663 0.70 500HDT-31Fused silica 0.5 13.9 - - -

cycle of 2 h at 60'C followed immediately by 30 min at150'C. After curing, the expoxied parts should beallowed to cool slowly to room temperature. At sometime during the oven curing cycle, the Epon flows veryfreely, such that the resultant bond, which is verystrong, contains only a thin layer of epoxy. Thus, theextent to which the joints between disks detract fromthe stiffness and mechanical Q of the completed trans-ducer is minimized.

To make electrical contact with the silver-plated endsof the transducer disks, small grooves were cut into thesides of the stacks with a diamond saw, as illustrated inFig. 2. The groove was then filled with conductiveepoxy and a copper wire set down into it. A suitableepoxy can be mixed from 100 parts by weight of Wald-man 3022 to 8 parts of 18 hardener; this epoxy cures ina few hours at 60'C.

We would like to underscore the significance of theabove method of joining transducer disks by citing ourexperience with a design that did not work well. Inthat preliminary design, the transducers were built upin sandwich fashion from alternate layers of disks, con-ductive epoxy, brass electrode, conductive epoxy, disk,etc. The resultant modulator required excessive drive,by about one order of magnitude, and the resonancefrequencies were much lower than they should havebeen, by a factor on the order of two. The only

explanation consistent with the above is that the con-ductive epoxy joints contributed the major part of theelastic compliance of the completed transducer, andthey were furthermore quite lossy.

The two transducer stacks and the quartz plate werethen epoxied to the lower Invar bar, again with theShell Epon. A jig held the pieces together as the epoxywent through the oven curing cycle. Prior to epoxying,the mating surfaces of both the Invar bar and the quartzhad been ground flat to assure maximum and uniformstrength over the whole area of contact.

It was then necessary to grind the unmated ends ofthe transducer stacks and the quartz to a commonplane. This most delicate operation was carried out ona precision grinding machine with a diamond wheel; thewheel was allowed to descend by no more than 0.013-mm (mil) per pass. It was then possible to epoxythe second Invar bar (also with its mating surfaceground flat) into place with not a trace of gap showinganywhere.

The completed modulator was suspended in an alumi-num holder from two loops of radio dial cord, see Fig. 3.This mounting method is very efficient and quiet; otherattempts at mounting the modulator by metal leafsprings have proven noisy and unstable.

INVAR END CAP

EDGE EXPOSI

CONDUCTIVE X

EPOXY---,

COPPER WIRE

OF SILVER:D BY SAW CUT

N CINVAR END CAP"

5Fig. 2. Completed transducer. Details of contact with silver-

plated electrodes of transducer disks.

RADIO DIAL CORD

- - [ _ 1--LIGHT PATH

Fig. 3. Method for mounting modulator.views are identical.

Top and bottom

662 APPLIED OPTICS / Vol. 8, No. 3 / March 1969

C. -C~ Cm C.

ELECTRICAL C, MECHANICAL

C =-3800 pF C, = 452 pF -'go t Ox fffLf-10 mH

,, C,

Cm ,1370 pF 870 pF

Fig. 4. (Top) electrical analog of transducer. (Bottom) elec-trical analog of modulator. See text for details.

Ill. Analysis of Electromechanical Properties

Analysis of a coupled electromechanical system suchas the modulator is greatly facilitated by reduction ofthe mechanical elements to suitable electrical analogelements.' The most convenient correspondence re-places force with voltage and displacement with charge.To avoid confusion, MKS units should be adhered tothroughout. Thus, for example, a mass of m kg isreplaced with an inductance of m henrys, a force of nnewtons corresponds to n volts, etc.

We have made several simplifying assumptions in theprocess of constructing an equivalent circuit: (1) theend bars are treated as lumped masses; (2) the distri-buted masses of the transducer stacks and quartz arereplaced by lumped masses one third as large; (3) weassume that the modulator will vibrate only in itsfundamental mode when driven at or near the corre-sponding resonance frequency. Since the center ofmass of the modulator does not move for vibration inthe fundamental mode, half the modulator can be re-placed by a support of infinite mass; one must simplykeep in mind that the resultant equivalent circuit, inrepresenting only half the modulator, will display twicethe impedance at its electrical terminals as the modula-tor itself.

The upper half of Fig. 4 shows an equivalent circuit'for the transducers alone; the values given are for twohalf stacks in parallel electrically and mechanically.Co is calculated in a straightforward way from E33S, thedielectric constant for a mechanically clamped trans-ducer. The value of C, in farads is numerically equalto the compliance of the transducers in meters/newton,and is calculated from S33D, the elastic compliance atconstant charge, i.e., the value is that obtained with theelectrical terminals open. The mutual capacitance Cmis calculated from C0, C, and k33, through the relation:k332 = CoCe/Cm'. (In the characterization of piezoelec-tric ceramics, the subscript 3 refers to the directionparallel to the axis of poling; 1 refers to any axis perpen-dicular to that direction.) For numerical values of theconstants mentioned above, see Table I.

Figure 4 also shows an equivalent circuit for half themodulator. L represents a suitable value for the mass(largely that of the Invar bar) and C, is the complianceof the quartz. C is simply the series equivalent of Coand Cm; in like manner, C, is the series equivalent of

Ce and Cm. Cd represents the essentially incalculablecombined elastic compliances of the steel end bars andthe epoxy joints, and is treated as an adjustable param-eter. Strictly speaking, the circuit should contain aresistance to account for dissipative losses, but since thedevice has a Q factor much greater than unity, omissionof the resistance does not materially affect calculationof the resonance frequencies.

The pole and zero frequencies are calculated in astraightforward manner from a simple expression forthe complex impedance at the electrical terminals.For Cd = 0, the computed values are, respectively,22.2 kHz and 18.8 kHz. These are to be compared withthe experimentally measured pole and zero frequenciesof 18.10 kHz and 16.71 kHz. A much better fit isobtained with Cd set equal to 300 pF; the computedfrequencies are then 18.08 kHz and 16.71 kHz. Withsuch a close fit to both frequencies simultaneously, wemay be fairly confident that the model is essentiallycorrect. Also, the fairly large value of Cd requiredindicates rather clearly that the combined complianceof the epoxy joints and the steel end bars is not entirelynegligible.

The resonance at the pole has an experimentallymeasured width between half power points of 0.063 kHz;this corresponds to a Q factor of about 290. Since theQ factors of the individual components are all muchhigher than this value, we conclude that the major lossstems from the epoxy joints and from radiated acousticpower.

IV. Operation and Performance

A suitable drive circuit is shown in Fig. 5. The smallde voltage supply allows one to compensate for anyresidual strain in the quartz plate, such that modulationcan be perfectly symmetric about zero activity. At thered end of the spectrum, about 1 W of power is requiredto drive the modulator as a tX/4 plate; of course, driverequirements for shorter wavelengths are less. If themodulator is to be driven from a generator containingits own power amplifier, an attenuator must be used toisolate the modulator from the negative feedback loopof the amplifier; otherwise, the amplifier may burst intooscillation and the modulator overdriven to the pointof fracture of the quartz. Alternatively, a low power,single stage, transistor amplifier would make an excel-lent buffer between generator and modulator. The

STANCOR1400 Q P8150

120 V60 Hz

70VZENERS 33 Q 330 1 LF

33 Q T

Fig. 5. Drive circuit and dc bias supply for modulator.

March 1969 / Vol. 8, No. 3 / APPLIED OPTICS 663

SAMPLE

MODULATOR

LIGHT FROMSPECTROMETERSLIT

Fig. 6. Measurement of circular dichroism.

most efficient drive is obtained with a source impedanceon the order of 50 U2.

A typical setup for the measurement of circular di-chromism is shown in Fig. 6. Parallel light from amonochromator is polarized with a Glan-Thompsonprism or other suitable device and presented to themodulator with its E vector at 450 to the strain axis.Upon passage of the beam through the sample, thealternate right- and left-hand polarizations are differen-tially absorbed, thereby producing an intensity varia-tion at the detector surface. The resultant dichroismsignal can then be amplified and measured with a lock-in system.

A very simple and direct test for correct operation ofthe modulator can be made by substituting a circularanalyzer for the sample in Fig. 6. One of the in-expensive plastic circular polarizers, such as PolaroidHTNCP37, is satisfactory for this purpose, as long asthe wavelength used is in the middle of the visiblespectrum. Output of the detector should be a nearlyperfect sine wave whose minima correspond to essen-tially zero detector current. Incorrect adjustment ofthe modulator dc bias will produce even harmonics ofthe modulator drive frequency in the detector output;when the resultant asymmetry is combined with suffi-cient drive, the detector output waveform will appeardoubled over at either the sine wave maxima or minima.Symmetric overdrive of the modulator will produce oddharmonics; this time both maxima and minima will bedoubled over.

A more sensitive test and one applicable to a muchgreater range of wavelength can be made through useof a linear polarizer alone as the analyzer. One firstadjusts the dc bias for symmetry with the axis of theanalyzer at 450 to the modulator strain axis; the resul-tant signal should contain nothing but second harmonic.With the modulator driven to be an exact X/4 plate atthe extremes of its cycle, the detector current shouldvary between zero and Io/2 for one of the 450 orienta-tions of the analyzer axis; for the other 450 orientation,the current should vary between Io/2 and Io. As afinal check, essentially no ac signal should be seen withthe analyzer axes either parallel or perpendicular to themodulator strain axis.

By stopping the beam down to about 3-mm diam, itwas possible to test the uniformity of rotation achievedfor various points across the modulator aperture. Bothof the tests described above were applied. Beginning

with correct adjustment of the modulator drive andbias for the beam passing through the plate center, nochange was detectable in either test as the beam wasmoved horizontally across the full 19-mm width. Forthe corresponding test in the vertical direction, nodetectable change occurred until one edge of the testbeam was almost grazing the Invar at either the top orbottom of the plate. Thus, a working aperture ofabout 18-19-mm diam is implied.

In the experiments of Ref. 1, we were able to measurecircular dichroism effects as small as one part in 100,000when the lock-in detector integration time was 1 sec;this performance corresponded rather closely to thefundamental limit imposed by the statistics of countinga flux of about 1010-1011 photoelectrons per second. Toachieve such sensitivity, one must be very careful toeliminate anything in the light path between modulatorand detector that might favor one linear polarizationover another. The combination of such a partial polar-izer with a small amount of activity in another opticalelement may result in a residual signal which masks thesmall dichroism of the sample itself.

The modulator described above has provided hun-dreds of hours of trouble free service, and shows no signsof failure to date. If properly constructed and operated,similar devices should show essentially limitless servicelife. It may be advisable for those wishing to duplicatethe modulator to change its dimensions slightly, suchthat the operating frequency is raised above the limit ofaudibility. However, most experimenters have notfound the rather faint sound emitted by the modulatoroperating at 16.7 kHz to be objectionable.

V. Extension of Operating Range into theVacuum Ultraviolet

With the best grade fused silica, the modulatordescribed above should be useful down to about 180 mu.However, there is considerable need for a device whoseoperating range extends as far as possible into thevacuum uv. The high transmission and large aperture

BRASS(19 mm THICK)

Al CAl, APZT 4 \ lo(10 mm THICK) 2 8

- 19mm - 1 -19 mm--DIAM

Fig. 7. Suggested adaptation for use with CaF2.

664 APPLIED OPTICS / Vol. 8, No. 3 / March 1969

ffi mm

of the stress plate modulator would make it especiallyuseful in this range where light sources are rather feeble.In particular, replacement of the fused silica withcalcium fluoride would allow operation down to about130 mt. Although the large thermal expansion coeffi-cient of calcium fluoride (18 X 10-6/C) (Ref. 6) pre-vents a direct substitution into the above design, anadaptation should be possible.

Figure 7 shows one such possible adaptation. Theend bars are of brass, whose expansion coefficientmatches that of calcium fluoride almost exactly. Theindicated length of the aluminum compensator slugs iscalculated to yield a total thermal expansion of thecolumns (aluminum plus PZT), which matches that ofthe calcium fluoride blank in the vertical direction.The calculation was based upon an expansion coefficientof 22.1 X 10-6/C for type 2024 aluminum alloy. Fromthe photoelastic tensor for CaF2 (Ref. 7), we calculate astress optic constant of 1.49 X 10-13 cm'/dyne for stressin the 100 direction. When this value is combined withthe larger Young's modulus for CaF2 , the level of strainrequired for a given wavelength is comparable with thatfor quartz. Since the wavelengths involved are on theorder of four times less than the maximum wavelengths(at least 800 mu) handled by the quartz modulator, onlytwo transducer disks per stack should be able to providesufficient drive.

Calculation of resonance frequencies can be made bythe method of Sec. III. For calcium fluoride, the con-stants necessary for the calculation are: Young's mod-ulus for stress in the 100 direction, 14.4 X 1010 N/m2 ,and mass density, 3.18 g/cm. Elastic compliance ofthe aluminum compensator slugs will be represented

by a rather large value of Cd in the equivalent circuitof Fig. 4, somewhat in contrast to the situation obtain-ing for the quartz modulator.

It has been pointed out to us by M. Klein that thestress plate modulator has one further advantage thatis particularly pertinent to its use in the ultraviolet:namely, that it does not produce luminescence or fluor-escence of its own, as long as the optical material is freeof rare earth or other contaminants. By way of con-trast, it has been found' that a KDP modulator emitsa strong and unavoidable electroluminescence at around327 mp.

The authors would like to thank M. Klein for muchuseful discussion and information about application ofthe modulator to the uv.

This work was supported in part by the U.S. AtomicEnergy Commission.

References1. L. F. Mollenauer, W. B. Grant, and C. D. Jeffries, Phys. Rev.

Lett. 20, 488 (1968).2. E. A. Dratz, Ph. D. Thesis, U. C. Berkeley UCRL 17200, to

be published.3. S. M. Hauser, L. S. Smith, D. G. Marlowe, and P. R. Yoder,

Jr., Appl. Opt. 2, 1175 (1963). Also, see the Hauser articlefor a reference to the earlier but unpublished work of HansMueller.

4. Clevite Corp., 232 Forbes Road, Bedford, Ohio, PiezoelectricTechnology for Designers (1965).

5. W. P. Mason, Proc. Inst. Radio Eng. 23, 1252 (1935).6. S. S. Sharma, Proc. Ind. Acad. Sci. A31, 261 (1950).7. R. S. Krishnan, Progress in Crystal Physics (Interscience

Publishers, New York, 1958), Vol. 1.8. D. Downie and M. Klein, Appl. Opt. 7, 1245 (1968).

Molecular Spectroscopy Symposium

2-6 September 1969

Columbus

The 24th annual Symposium on Molecular Structure and Spectroscopy will be held in the Department ofPhysics, The Ohio State University, 2-6 September 1969. G. Herzberg (National Research Council ofCanada) will be one of the principal speakers during the plenary sessions. The invited papers programwill also include Robin M. Hochstrasser (Univ. of Pennsylvania) speaking on electronic spectra of largemolecules, and T. Oka (NRCC) discussing microwave studies of collision-induced transitions betweenrotational levels. Seminars on special topics will also be featured. Some instrument companies willexhibit their latest products during the Symposium. Air-conditioned dormitory accommodations willbe available for individuals as well as married couples. Write to K. Narahari Rao, Molecular Spectros-copy Symposium, Department of Physics, The Ohio State University, 174 West 18th Avenue, Columbus,

Ohio, 43210, for further information

March 1969 / Vol. 8, No. 3 / APPLIED OPTICS 665

Meetings Calendar continued from page 648

25-28 52nd Canadian Chemical Conf. and Exhibition,Queen Elizabeth Hotel, Montreal Chem. Inst.of Canada, 151 Slater St., Ottawa 4, Ont., Canada

26-28 IEEE Conf. on Laser Engineering and Applications,Wash., D.C. W. B. Bridges, Hughes ResearchLabs., 3011 Malibu Canyon Rd., Malibu, Calif.90265

26-30 Internatl. Spectroscopy Colloq., Madrid

June2-6 Fundamentals of Infrared Technology course, U. of

Mich. Eng. Summer Confs., U. of Mich., ChryslerCtr., Dept. 127, Ann Arbor, Mich. 48105

2-13 X-Ray Diffraction course, Polytechnic Inst. ofBklyn. D. Cattell, PIB, 333 Jay St., Bklyn., N.Y.

112013-5 1969 Conf. on Microelectronics, Eastbourne, Sussex

Conf. Dept., EE, Savoy P., Victoria Embank-ment, London W.C.2, England

8-27 Digital Computers in Chemical Instrumentationcourse, Purdue U. Div. of Confs. and ContinuationServices, Purdue U., Lafayette, Ind. 47907

9-10 Holography Seminar, NYC H. F. Sander, SPIE,216 Avenida Del Norte, Redondo Beach, Calif. 90277

9-11 IEEE Internat. Communications Conf., Boulder,Colo. IEEE, 345 E. 47 St., New York, N.Y. 10017

9-13 1st Internat. Color Assoc. Mtg., Sweden G. T. J.Tonnquist, Radjursstigen 44, Solna, Sweden

9-13 Advanced Infrared Technology course, U. of Mich.Eng. Summer Confs., U. of Mich., Chrysler Ctr.,Dept. 127, Ann Arbor, Mich. 48105

9-13 Laser Interaction and Related Plasma PhenomenaWorkshop, RPI H. J. Schwarz, Rensselaer Poly-technic Inst.-Hartford Grad. Center, E. WindsorHill, Conn. 06028

9-13 Laser Raman Inst. and Workshop, U. of Md. E. R.Lippincott, Ctr. of Mater. Res., U. of Md., CollegePk., Md. 20742

16-20 Infrared Radiometry-Instrument Calibrations andPrecision Measurements course, U. of Mich. Eng.Summer Confs., U. of Mich., Chrysler Ctr., Dept. 127,Ann Arbor, Mich. 48105

16-20 Gordon Res. Conf. on Lasers in Medicine and Biology,Kimball Union Acad., Meriden, N.H. Director,Gordon Res. Confs., U. of R.I., Kingston, R.I. 02881

16-20 Gordon Res. Conf. on Molecular Energy Transfer,Proctor Acad., Andover, N.H. Director, GordonRes. Confs., U. of R.I., Kingston, R.I. 02881

16-20 Summer Inst. in Advanced NMR and Advanced MassSpectroscopy, SIT E. R. Malinowski, Dept. ofChem. and Chem. Eng., Stevens Inst. of Technol.,Hoboken, N.J. 07030

16-21 Automation Analysis in Chemistry course, Washing-ton U. Inst. for Cont. Educ. in Eng. and Appl.Sci., Washington U., St. Louis, Mo. 63130

16-21 Theory and Interpretation of Massbauer Spectracourse, Catholic U. L. May, Dept. of Chem.,The Catholic U. of Amer., Washington, D.C. 20017

17-20 AAS Mtg., Denver G. W. Morgenthaler, Dept. 1600,Martin-Marietta Corp., Denver, Colo. 80201

17-21 Technique of Infrared Spectroscopy course, MITR. C. Lord, Spectrosc. Lab., Mass. Inst. of Technol.,Cambridge, Mass. 02139

17-28 Physics of Quantum Electronics course, FlagstaffS. F. Jacobs, Optical Sci. Center, U. of Ariz., Tucson,Ariz. 85721

18-20 APS Mtg., Rochester W. W. Havens, Jr., 33S E. 46thSt., New York, N.Y. 10017

18-20 Quantum Optics Symp., Rochester E. Wolf, Dept.of Phys. and Astron., U. of Rochester, River CampusStation, Rochester, N.Y. 14627

22-27 ASTM 72nd Ann. Mtg., Atlantic City ASTM HQ,1916 Race St., Philadelphia, Pa. 19103

23-25 7th Internatl. Shock Tube Symp., Toronto I. I.Glass, Inst. for Aerospace Studies, Toronto U.,Toronto 6, Canada

23-27 Applications of Infrared Spectroscopy course, MITR. C. Lord, Spectrosc. Lab., Mass. Inst. of Technol.,Cambridge, Mass. 02139

23-27 Gordon Res. Conf. on Glass, Proctor Acad., Andover,N.H. Director, Gordon Res. Confs., U. of R.I.,Kingston, R.I. 02881

23-27 Gordon Res. Conf. on Plasma Physics, ProvidenceHgts. Coll., Issaquah, Wash. Director, Gordon Res.Confs., U. of R.I., Kingston, R.I. 02881

25-28 Can. Assoc. of Physicists, ann. mtg., U. of WaterlooJ.-L. Meunier, CAP, 151 Slater St., Suite 903,Ottawa 4, Ont., Canada

Summer AAS Convention Mtg., Albany 211 FitzRandolphRd., Princeton, N.J. 08540

July3-8 10th Automatic Control Conf., Boulder IEEE,

345 E. 47th St., New York, N.Y. 100177-11 Infrared and Raman Spectroscopy: Techniques,

Theory, and Interpretation course, UCLA Eng.and Phys. Sci. Ext., U. of Calif., Los Angeles, Calif.90024

7-11 X-ray Techniques in the Industrial Laboratorycourse, London M. L. Fallert, McCrone Res.Inst., 451 E. 31 St., Chicago, l. 60616

7-12 Optical Data Processing course, Orsay SummerSchool Office, Inst. d'Optique, 8, blvd. Pasteur, Paris1ie, France

7-18 Probability and Random Processes for Engineersand Scientists course, U. of Mich. Eng. SummerConfs., U. of Mich., Chrysler Ctr., Dept. 127, AnnArbor, Mich. 48105

8-10 Measurement Education Conf., U. of Warwick,Warwickshire IEE, Savoy Pl., London W.C.2,England

8-11 IEEE Ann. Conf. on Nuclear and Space RadiationEffects, Penn. State U. D. K. Wilson, Bell Tele-phone Labs., Whippany, N.J.

13-25 Infrared Spectroscopy and Gas and Liquid Chroma-tography, summer course, Pye Unicam, CambridgeA. Evans, Pye Unicam, York St., Cambridge,England

14-17 Fundamentals of Remote Sensing course, U. of Mich.Eng. Summer Confs., U. of Mich., Chrysler Ctr.,Dept. 127, Ann Arbor, Mich. 48105

14-18 Reflection Spectroscopy: Theory and Applicationscourse, UCLA Eng. and Phys. Sci. Ext., U. ofCalif., Los Angeles, Calif. 90024

14-18 Industrial Use of the Polarizing Microscope course,London M. L. Fallert, McCrone Res. Inst. 451E. 31 St., Chicago, Ill. 60616

14-18 Gordon Res. Conf. on Radiation Chemistry, NewHampton School, New Hampton, N.H. DirectorGordon Res. Confs., U. of R.I., Kingston, R.I.02881

14-18 Internatl. Atmos. Absorption Spectroscopy Conf.,Sheffield AAS Conf. Sec., Soc. for AnalyticalChemistry, 9 Savile Row, London, W.1, U.K.

14-19 Optical Instruments and Techniques Conf., ReadingA. Thetford, The University, Reading, Berks., U.K.

16, 18 ICO, 8th Gen. Assembly Optical Instruments,Reading H. H. Hopkins, The University, Reading,U.K.

16-18 4th Natl. Conf. on Electron Microprobe Analysis,Huntington-Sheraton Hotel, Pasadena

21-25 Internat. Symp. on Analytical Chemistry, Birming-ham D. M. Peake, 61 Lodge Rd., Walsall, Staffg.,England

22-26 Techniques of Infrared Spectroscopy course, U. ofMinn. Dept. of Confs. and Insts., Nolte Ctr. f orCont. Educ., U. of Minnesota, Minneapolis, Minn.55455

26-29 Electron Microscopy Soc. of Am., St. Paul E. C.Shaffer, Central Res., 3M Co., 2301 Hudson Rd.,St. Paul, Minn. 55119

28-August 1 1969 Research Conf. on Instrumentation Science,Hobart and Wm. Smith Coll., Geneva, N.Y. '.E. Tremellen, ISA, 530 Wm. Penn Pl., Pittsburah,Pa. 15219

28-August 1 Chemical Interpretation of Infrared Spectracourse, U. of Minn. Dept. of Confs. and Insts.,Nolte Ctr. for Cont. Educ., U. of Minn., Min-neapolis, Minn. 55455

28-August 2 6th Internat. Conf. on the Physics of Electronicand Atomic Collisions, MIT I. Amdur, Dept.of Chem., MIT, Cambridge, Mass. 02138

continued on page 676

666 APPLIED OPTICS / Vol. 8, No. 3 / March 1969