An Optical Null Double-Beam Far Infrared Spectrophotometer

An Optical Null Double-Beam

Far Infrared Spectrophotometer

Hiroshi Yoshinaga, Shigeo Minami, Isao Makino,

Isao Iwahashi, Masao Inaba, and Koichi Matsumoto

The design, construction, and performance of a compact double-beam far infrared spectrophotometerare described. An optical null system which minimizes the loss of energy is used as the photometric

system. Efficient filter combinations not involving a crystal chopper are used for eliminating unwantedradiation. All optical components are mounted in a vacuum tank to eliminate the energy loss due to

water vapor absorption. Accordingly, high resolution can be obtained through the entire spectral regionfrom 500 cm-' to 60 cm'. In the instrument, provision for fully automatic performance is made through

the control system which includes a variety of mechanisms. Ease of change from double-beam to single-beam operation is an additional feature.

Introduction

Far infrared spectroscopy has become of increasingimportance during the past ten years. A number of in-struments and accessories have been individually de-veloped in research laboratories.'- However, only afew of them have recently been developed to the pointwhere they are available commercially.9 Many tech-nical difficulties, such as the handling of the extremelysmall amount of radiant energy, elimination of highergrating orders, disturbance caused by water vapor ab-sorption, etc., must be overcome to meet the user's re-quirements. The authors have designed and con-structed a compact double-beam far infrared spectro-photometer using the optical null principle for thespectral region from 500 cm-' to 60 cm-'.

According to mathematical analysis, the optical nullmethod is one of the best of the various kinds of double-beam photometric systems, as far as the signal-to-noiseratio is concerned.'" Taking advantage of its efficientuse of energy, the authors adopted the optical nullprinciple in the photometer system, in spite of certaindifficulties encountered by this system, in making lowor high temperature measurements.

The design was developed, taking into considerationthe desirability of compact construction and convenientoperation for laboratory and industrial uses. Sinceevacuation is the most perfect way to eliminate water

Hiroshi Yoshinaga and Shigeo Minami are with the Depart-ment of Applied Physics, Osaka University, Osaka, Japan; andIsao Makino, Isao Iwahashi, Masao Inaba, and Koichi Mat-sumoto are with Naka Works of Hitachi Ltd., Ibaraki, Japan.

Received 30 March 1964.

vapor absorption which greatly attenuates the energyin this spectral region, the optical system was assembledin a vacuum tank. Ease of change from double-beamto single-beam operation is also one of the features.Single-beam operation is used in the measurement ofsamples at high or low temperatures.

The instrument makes it possible to complete thespectrogram of any predetermined range with fullyautomatic operation after pushing the start button.

Optical System

The optical layout of the instrument is illustrated inFig. 1. Since a crystal chopper for screening out theshorter wavelength radiation cannot be used with aconventional beam switch in a double-beam system,provision is made in the filter arrangement for efficientelimination of the energy from higher grating orders.

Two radiation sources, that is, a globar, Li, for themeasurements down to 125 cm-' and a high pressuremercury lamp, L2, below 125 cm-', are used, and radia-tion from either one can be directed to mirror M12 bysliding a plane mirror, Ml, between its two positions.The radiation reflected by spherical mirror M2 andplane mirrors M3 and M4 is directed to reststrahlenfiltering assembly R. This filtering system is com-prised of two filter wheels in which six kinds of rest-strahlen crystals (LiF, NaF, BaF2 , KCl, KBr, andTJCl) are held. In set positions, two crystal surfacesin a pair are kept in crossed positions at the polarizingangle." This arrangement provides a sharp cutofffilter for shorter wavelength radiation in comparisonwith the conventional use of a single reststrahlen plate.After reflection from a scatter plate F1 which is an

December 1964 / Vol. 3, No. 12 / APPLIED OPTICS 1425

Fig. 1. Optical layout of spectrophotonieter.

Fig. 2. Front view of spectrophotometer.

aluminized roughened mirror, the beam is directed to aswitching system and through the sample space.

As a beam switching system, two rotating sectors,CH-1 and CH-2, are placed one on either side of thesample space. One is a so-called beam splitter and theother is a beam combiner. This switching system,which is sometimes used in conventional infraredspectrophotometers, has also the advantage of eliminat-ing the trouble caused by the minute fluctuations andthe nonuniformity of radiance of the source. Besides,it simplifies insertion of a prefiltering section betweenthe source and the sample space. This is especiallydesirable in the far infrared region. The use of thebeam combining sector behind the sample space mayrestrict the flexibility of the instrument in making highor low temperature measurements. However, theefficient use of energy in the optical null system is asignificant advantage in far infrared instruments.

Mirrors M8 and M9 and scatter plate F2, which isthe same as F1, send the beam from the combiner to amonochromator slit. A filter wheel, T, for transinis-sion filters, some of which are powder filters developed

in our own laboratory,2 is located in front of the en-trance slit.

A conventional Littrow-type arrangement is usedfor the monochromator optics. The height of the slitsis 12 mm, and the maximum opening is 10 mm. A 200off-axis paraboloidal mirror of 290-mm focal length isused as a collimator mirror, M11. Three gratings ofwhich the ruled area is 64 mm X 64 mm are mountedon a trigonal-prism shaped holder, G. To obtain first-order spectra throughout the entire wavenumber rangewith these, the grating constants 30 lines/mm, 20 lines/mm and 8 lines/mm are selected, respectively. After a5X image reduction, the exit beam is converged by a600 off-axis ellipsoidal mirror, M12, on a Golay cellhaving a 3-mm diam target.

A comb-shaped beam attenuator, A, is used at theconjugate point of the entrance slit. This type ofattenuator introduces only minor effects on the linearityand accuracy of transmission measurements even in thefar infrared region.

ConstructionA front view of the spectrophotometer is shown in

Fig. 2. All optical components and a part of the driv-ing mechanisms are mounted on the vacuum tank base.The inside of the vacuum tank is kept at about 0.1 mmHg during the operation. The evacuation process iscompleted within 30 min after starting the pump. Inpractice, evacuation is the preferable way to removewater vapor in such a unit body construction. An air-tight compartment which can be inserted at the samplespace is also provided for introducing samples withoutdisturbing the vacuum. The compartment is alsoevacuable individually if desired.

With the exception of the motor for exchanging thegratings, all motors are mounted outside the tank andmechanically connected to the mechanisms located inthe tank with 0-ring seals through the base. A num-ber of mechanical features are provided to assureaccurate exchange of gratings and reststrahlen filters.The smooth rotation of the optical attenuator shaftthrough the tank wall is accomplished by means of aspecial vacuum tight bearing made of Teflon. A grat-ing and slit cam assembly and most of the control mech-anisms are placed below the base plate of the vacuumtank. Amplifiers, control electronics, and power sup-plies for radiation sources are located under the tankand are readily operated from a position in front of theinstrument. The recording part is placed in front ofthe tank and is easily handled from the operator'sposition. Pilot lamps, wavenumber, and slit-width in-dicator beside the recorder show the successive proc-esses of the operations.

Electronics and Control SystemFigure 3 is a block diagram of the electronics and the

control system.The 10-cps output signal from the Golay cell is

amplified by a linear amplifier and then fed to a phase-sensitive rectifier which is driven by the reference sig-nal from a generator connected to the beam switch. To

1426 APPLIED OPTICS / Vol. 3, No. 12 / December 1964

SLIT SERVOMOTOR

RESTSTRAHLEN P RE - SLIT

FILTER WHEEL E AMPLIFIE POTA GOLAY -E SLAVE POT._

iLAM f - EL- GRATING

I ~ ~ ~ -~DL - SETTING

~I _ TRANSMISSION MOTORIGWNAR - -~~~~~~ o ~ FILTER WHEEL

SLIT -- - WAVENAM9ER SLIT

W;I - AMPLIFIER

IS CPS

AMPLIFIER I WAVENU ER

LDY i jbjTER MATE CONTROL

PHASE I PENIl_ SENSITIVENIS

RENCTIFtIER__, POT

- MICRO CONTROL MOTOR

FILTER CONTROL t SW. AM SCANNING _IDAN D RE LAlSERVO

APLIFIE RANK

PEN SERVOMOTOR RECORSER

Fig. 3. Block diagram of electronics and control system.

provide for high accuracy, the main amplifier was de-

signed with a wide range of linearity. After passingthrough the phase-sensitive rectifier, the signal ismodulated with line frequency ahead of a power am-

plifier for driving a servomotor. The servomotor is

mechanically coupled to the recording pen and theoptical attenuator shaft.

By turning switch knobs, either single-beam or

double-beam records can be easily displayed on a

built-in recorder. For double-beam operation, the

conventional optical null principle in which the outputof the servomotor is used for completing the servo loop

through the beam attenuator is utilized. For single-beam operation, a multiturn helical potentiometer in

the pen-driving mechanism, which provides a dc signalproportional to the pen motion, is switched into the in-

put terminal of the servo-amplifier such that the feed-

back is electrically applied. It means that the servo-amplifier and the pen-drive systems work as a conven-tional electronic recorder.

The control cam assembly located under the vacuum

tank comprises a grating cam, a slit cam, and a programcam. These are placed on a common shaft which isprecisely rotated with a worm and a worm wheel. A

synchronous motor for wavenumber scanning is con-nected to the worm and a chart paper driving mech-

anism through gear trains. Two star-shaped cams

are used in accomplishing the scanning with a linearwavenumber scale and making the slit program so as to

keep the reference beam energy constant, respectively.The program cam which actuates microswitches located

around the cam edge permits the fully automatic opera-tion of the instrument.

The significant features in automatic operation are as

follows. At the changing points of the reststrahlenfilters, the succeeding pair of crystals is brought into

position during the interruption of scanning. At the

same time, the transmission filter wheel and a controlcam for adjusting a beam trimmer is also rotated to the

next stop. Provision is made for the overlapping ofrecords in the vicinity of the changing points of the

gratings. The changing process is started at the end

of the wavenumber cam contour for the correspondinggrating. When the grating- and the filter-changing

mechanisms start operating, both the grating and slitcam followers are lifted by an auxiliary mechanism.After the cams are rotated a certain angle in the for-ward direction, the followers are returned to the camcontour for the next grating, and then these are ro-tated in the backward direction as far as the startingpoint of the next contour. From the new starting pointthe regular scanning operation is resumed. During thewhole changing process, the recording pen is lifted and ahigher rate of rotation is automatically provided to thecam shaft by means of an electromagnetic clutch. Inparallel with this operation, a beam shutter is auto-matically inserted in front of the entrance slit in orderto protect the Golay cell from intense unexpected radia-tion.

The combination of the star cams and the specialchanging mechanisms mentioned above makes it pos-sible to permit the endless operation of wavenumberscanning in conjunction with a disk-type wavenumberdial. Consequently, prompt reset from the lowest tothe highest wavenumber region, or to an intermediateposition, is accomplished with ease. Either type ofscanning system, one of which is the endless and theother the conventional one with a revolution counterdisplay, is optionally available in the instrument. Theschedule of the wavenumber range to be scanned isreadily provided by using a scanning programmer on thepanel, which is operated with the scanning gear shaft.

The mechanical clutches in the scanning gear trainspermit selection of scanning speed in six steps from0.12-3.86 cm-'/min. Extremely slow scanning speedranges are also available with manual change of thegears. The time constant of the servo recording systemcan be mechanically changed from 15 see to 60 see bymeans of a change gear selector. For single-beamoperation, time constants of the system of from 5 see to50 see are electrically provided by selecting the ap-propriate RC filter in the output circuit of the phase-sensitive rectifier.

Performance

The desired results have been obtained in the wave-number region from 500 cm-' to 60 cm-' both insingle-beam and double-beam operation. The combi-nations of the dispersion gratings, reststrahlen crystals,scatter plates, and transmission filters in each spectralrange are listed in Table I. These filter combinationswere finally chosen after precise checking of the un-wanted higher-order radiation in each range. In care-fully made transmission measurements of crystalsamples, such as NaCl, NaF, KC1, KRS-5, etc., theaverage unwanted radiation in most wavenumberregions proved to be less than 2% of the effective signal.

Figure 4 shows a series of typical double-beam watervapor spectrograms. Performance as shown by resolu-tion in the water vapor absorption bands is also shownin Fig. 5. These curves demonstrate that the best

resolution obtained was close to 0.5 cm-'.The reproducibility of the instrument is illustrated by

the two superimposed Teflon spectra shown in Fig. 6.


Table I. Combination of Optical Elements for Each Spectral Range

Spectral Grating Reststrahlen Scatter Lightrange (cm-') (lines/mm) filter Transmission plate source500 410 30 LiF - Two 800-mesh Globar

roughenedmirror

410 - 260 30 NaF -"267.5 180 20 BaF 2 (BeO + ZnO)

powder filter180 - 142.5 20 KC1 Quartz plate

142.5 117.5 20 KBr (LiF + SrF2)powder filter

125 - 80 8 TlCI Quartz + sooted Hg lamppolyethylene

80 - 60 8 TICI Quartz + sootedpolyethylene+ (BeO + ZnO+ NaF + KCI)powder filter

dinSCANSPEED 84 c m rtJ 4,

TIME CONST:60 sec r4It~

400 ~nI I ~ _ _ _ _ _ _ _ _ _

7<11 S1 .X

I GAIN 3- 9SCAN.SPEED:0.42 cmminTIME CONST60 sec

140-_, 180 i1o cmr'

Fig. 4. Typical double-beam

Conclusion

The introduction of the optical null principle to adouble-beam far infrared instrument was achieved withsuccess by using an efficient combination of reflectionand transmission filters, excluding the crystal chopperfilter. Consequently, satisfactory performance was ob-

z20 150 cm-'

-10'^ 1 . t } 1' ' I '''' ! . :..... .. ;. .t t ,,{ ,-,

GAIN :39SCAN SPEED: 0 c^ min TIME CONST:60 se r

90 70 s 60 0c,spectra of water vapor.

tained, considering especially the effective use ofenergy. MWoreover, the double-beam feature with fullyautomatic operation makes the instrument very usefulin chemical research and related fields, since the fre-quent change of the grating and filter combinationsnecessary in the far infrared region usually makes thework in this region tedious. The evacuation of the


: :::ff 0p

: - +:# ~ :tir 4C:.

t: :^ ¢ ig 4 S X # sft #

nfh l .i - 0 Ob .B : . i}:

o O'f i i+w e

L i ::D~ 0 : h>.4 rw k^ i .f S?: iS ne ;oi

'"an

0 ' t <? 8 tN Y > - 8iY 9 9^; y'� � 0 >0 8i t +' ̂ t i 0

*- _ E *: v - + k <- :e i s e 4: :8 > ^>o

. y:: > 8: : -YY __8oh

, ,^.. <. y v ^y.; iztsi 8 f- tt v +M y .. .§ :+ tr i . y . ;> S +

a...v.�ia,*Y8 .2;'j^F > Yh8 ' 8iBo fi . o=_4===-e eY� -8.<t>^- i . . .C:. t;

i>.>..s.>s..;..h<....vv:_+8:e +.v.E>e>:<.is>tlh .N ....:; 4 ssa :+ < t h* f s V § X �> Y X Yex9T v

# i s 8 < aSI<t *; h 8 C 8 * . .8

:, t: >0. i R 0Xi>i. Y h: t t 8 h. Y t X s e #

;< < . 8[ o: >- < i h . §4 y s . .

__W.. i . � . *::i v - } 4--Y Y h'9 '^ r a

: . . : 8 . < h Yv Ji vY: i +r Y :y ^ o f 8:8 *. - s< e S Y S s ao thit-8*>-aa'*5 ftl0^ 5 Le

.Y O; H1:a... X s . +/;.sYaswT8s}v.^�.

v * P-e *-_-by8tt**ly:[+stty*ti i* o w

.Z..i .� 4 < ^ :>-giY�} i f f tt t * h + S < v * f

_e-rr _: v v e a r h t 8 y - t t t { e ° h f> h; i i t t y Yii*tht.Y4t 1; X i q; .

iYhese h h Q th f* > > ; t *;;X8> set - e f . t >: ee bY 5 Y r} t Ptte-w^§T^a |

, <^ 9 > w * t Y � + w Yllr''- 9 X

, Y Y

o::; j : . h .: . Y 8 ^ S h, . ^: .. .. Yewk t t X Vhh:f Y8 ^: t f

t i8Y8y a 8gy f > - pY. h.<;v>;.:; Y * :� w (fi:^ Y :: e h y frt

' lE z '0 ', ' . f 8 #< 0 y7e:0 ' i '02s r S i ¢ b } e r < s

; * * ¢S < y E P f o w

¢ < as sr rZ ; Y:

0 ;, , _ t*|04 h . . ,gh ;MiA ho ;+ " uJ 1 at 8 pt t-o Yt

. v . v i: ^ :h $ N :> ^ ^ t ' P ^ ^

. w _ . h.... Y + oxY w i zo e +..<. )_* 8 f; :; ;, fb,, +::,::>: gh v . kr 0. ^ ... *SaiiiS^Y * -- ? ^ t ! * - f

< . .:: > > y: <: ye: E o; y <

X t h-o § < ;:. + + kii i t C h- i t * 3.x i ° :h oE . < S y e k t ^ ' ' ' t ' ' 0

,, r Q 8 * * f s ^: i ': ::

t.Cii.:: t:: Y ,::,:j:X:+:S::,:,,v, j*yi

$ U > i o w i t4 > e t z e< i S / i 0 ̂ S§ + 2tR 9 054> tt fi5' Nt -5- tB

¢ P y w 1 e ; + 8 x Q g h P

^r * to - - - y t f ^ '' 0 C^ f 1 XYza Yt z .<>a:Y:h t Y.yso yzy! of ys X

0 igh F 0 (t Shk t i90 f ukf 0 Vi, ff ilt 0+0 ,0 0^

. :> ;.:o S h R e B : E : },,y* ,yhywyR +i iiY8Y

B . tY: - < B Y hY k -

i * y 6, *f s o h y < _ :. > f < -; e N w . i h Y <: j o; F ,; h; . ^+ hy� '

: i ai.° Y -0 +Y¢q8 ktto a4. haw i h B: ..

a .: . C l k - i t S

i: > v < f > Sk :> 0; 0 0 YB: r: k Y 'hS ......... ' ' §: ' Y ........... f

__s8h+** *'�' v 8 s <� t . s e:: . . g

¢ * * : S * t * * * e A; S v A C

i . i g 0 h > < ' ';, � y :, ,, : j : ; w� .§ § .. � i f k X � _ h ii . f > i

S : r t C

k: P : ^

* § ? ' S - i

f -e f fSU;

a-AiGuN ; X 8 39 I

000020 SCAN SP£D t o . 447 ¢.f.f. / m:itu;; L1T kSJ0i, w (J; w

TIMg OONST.. 60 s4ee

.~~~ -.s.,:;.0tt 4.:4th~ *vhYz ~>4 >11i hYt34#

Ct0 - 0 t

'6'!>*tt- ,,

; h Y t -ht^hihhh: ih g ~i;ri-y Y 8

C ' y0a -fM wQ< :X

SIT GAIN : 9SCAN.SPELD 0.42 cmr1/in 1

- SLIT WIDYT 2.0 mmTIE CONST. 60 see

Ii1P Y

Fig. 5. Resolution perform-ance for water vapor bands.

T

0 ; f 0 0 % 3._^ .. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.. .. ...,Ma ; TILOJCI X L V -7

GAIN .......

: 9:M cmAoin A

S8CALE 1o6.mu-5L

TIE CONST 0 nec ____=_=_,______

50 400 I -. 0 4 200 100 0 0

APE DATE B Y TEST N. SMPLE DATE aBYTETN, SML

optical section is the most profitable way of removing Referencesthe disturbance of the atmosphere in such an auto- 1. R. A. Oei

matically operated instrument. H. E. Sc]Several prototypes of this instrument, which have 559 (1952

minor differences in control mechanisms from one to 2. L. Genze

another, have been constructed and are now in routine 3. R. C. Loioperation.

jen, W. H. Haynie, W. M. Ward, R. C. Hansler,ihauwecker, and E. E. Bell, J. Opt. Soc. Am. 42,

* and W. Eckhardt, Z. Physik 139, 578 (1954).

rd and T. K. McCubbin, Jr., J. Opt. Soc. Am. 47,


.... _11- 111.1.11.- � .1�,�-�1-1" -:,:�,.:��:.-:�-�-" "-.,.,.I ... - +1 1. _ .. ", _::'_= �_� I 1- ... 1+11'.."

. 1

11 y I'yk h

1 YY1~f3lo 2 1hs~~

Fig. 6 Two superimposed spectra of Tetion tilm.

689 (1575

[4. H. Yoshinaga, S. Fujita, S. Minami, A. Mitsuishi, R. A.Oetjen, and Y. Yamada, J. Opt. Soc. Am. 48, 315 (1958).

5. N. G. Yaroslavski and A. E. Stanevich, Opt. i Spektro-skopiya 5, 384 (1958).

6. A. Hadni, Spectrochim. Acta 19, 793 (1963).7. P. J. Hendra, R. D. G. Lane, and B. Smethurst, J. Sci.

Instr. 40, 457 (1963).

8. L. R. Blaine, J. Res. NatI. Bur. Std. C67, 207 (1963).9. C. C. Helms, H. W. Jones, A. J. Russo, and E. H. Siegler,

Jr., Spectrochim. Acta 19, 819 (1963).10. M. J. E. Golay, J. Opt. Soc. Am. 46, 422 (1956).11. M. Czerny, Z. Physik 16, 321 (1923).12. Y. Yamada, A. Mitsuishi, and H. Yoshinaga, J. Opt. Soc.

Am. 52, 17 (1962).

Me:etings Calendar,December2 OSA Pittsburgh Sect. Mtg., Jt. mtg. with local library

and computer grps., speaker W. Lewis Hyde, U. ofRochester

3 OSA San Diego Sect. Mtg., What on earth can anastronaut see? by S. Q. Duntley

3-4 R. Photog. Soc. Symp. on Optimum Results fromColor Photography, Inst. of Elect. Eng., London, C.Roberts, Res. Lab., Kodak Ltd., Harrow Middlesex,U. K.

9 ARPA Lecture "Space Astronomy" by Lyman Spitzer,Jr., The Pentagon, Wash., D.C., Room 5A 1070,2:30 p.m. Samuel Koslov, ARP, Wash., D.C. 2030121-23 APS, Winter Mtg. in the West, Berkeley, Calif.K. K. Darrow, Secretary, Columbia Univ., New York27, N.Y.

26-31 AAAS, 131st ann. mtg., Montreal, Canada. R. L.Taylor, AAAS, 1515 Mass. Ave. N.W., Wash. 5, D.C.

1965

January5-7 Symp. on Glass Formation, Phase Equilibria,

Nucleation, and Crystal Growth, SheffieldD. Hawksworth, Soc. of Glass Technology,Thornton, 20 Hallam Gate Rd., Sheffield 10, U. K.

14 OSA San Diego Sect. Mtg., Uses of shock waves aslight sources by Jim Missinan of General Dynamicsand tour General Atomics Division

20 OSA Chicago Sect. Mtg., Plant tour of the RaulandCorp. Anton Weigandt, 1434 W. Catalpa Ave.,Chicago 40

27-30 APS, Ann. Mtg., New York CityFebruary

3 OSA Pittsburgh Sect. Mtg., Spectrometer Design byCharles H. Church, Westinghouse Electric Corp.

11 OSA San Diego Sect. Mtg.17 OSA Chicago Sect. Mtg., Optical Staining by Walter

McCrone of McCrone Assoc. Anton Weigandt, 1434W. Catalpa Ave., Chicago 40

26-27 APS, K. K. Darrow, Columbia U., New York City 27March1-5 16th Pittsburgh Conf. on Anal. Chemistry and Appl.

Spectroscopy, Pittsburgh, Pennsylvania W. G.Fateley, Mellon Inst., 4400 Forbes Ave., Pittsburgh,Pa.

3 OSA Pittsburgh Sect. Mtg., speaker Thomas M.Donahue, U. of Pittsburgh

11 OSA San Diego Sect. Mtg., Information retrieval byW. Lewis Hyde

20 OSA Chicago Sect. Mtg., Optical Metrology, all dayseminar at 1IT Anton Weigandt, 1434 W. CatalpaAve., Chicago 40

28-Apr. 2 ASP Ann. Mtg., Amer. Cong. on Surveying andMapping, Wash., D.C.

31-Apr. 2 Optical Society of America Spring Meeting, Statler-Hilton Hotel, Dallas, Tex. M. E. Warga, OSA,1155 16th St. N.W., Wash., D.C. 20086

April- Symp. on Inhomogeneity in Glass, Sheffield D. Hawks-

worth, Soc. of Glass Technology, Thornton, 20 HallamGate Rd., Sheffield 10, U. K.

- 14th Pugwash Conf. on Science and World Affairs,Italy J. Rotblat, 8 Asmara Rd., London, N.W. 2,U. K.

7 OSA Pittsburgh Sect. Mtg., What can a fish see? byS. Q. Duntley

7 OSA San Diego Sect. Mtg., An Astronautics spacesystem simulator by Robert Ackley of Astronautics20-22 Internatl. Symp. on System Theory, PolytechnicInst. of Brooklyn Symp. Comm., Polytechnic Inst.of Brooklyn, 333 Jay St., Brooklyn, N.Y. 1120121 OSA Chicago Sect. Mtg., Projection TV Systems byJohn R. Miles of John R. Miles Corp. AntonWeigandt, 1434 W. Catalpa Ave., Chicago 4021-23 IEEE Conf. on Non-Linear Magnetics, Wash., D.C.E. W. Pugh. IBM Components Div., Poughkeepsie,N. Y. 12602

May5 OSA Pittsburgh Sect. Mtg., Interference Filters and

Thin Optical Films by R. J. Pegis, St. John FisherCollege, Rochester, N.Y.

5 OSA San Diego Sect. Mtg., Transformation of irbackgrounds to electrical noise by George Car-michael of Astronautics

5-7 1965 Microwave Theory & Techniques Symp., JackTar Harrison Hotel, Clearwater J. E. Pippin,Sperry Microwave Electronics Co., Box 1828, Clear-water, Fla.

13-14 Symp. on Signal Transmission & Processing, Colum-bia U., New York City Omar Wing, Dept. Elec.Engr., Columbia U., New York City 10027

15-21 SPSE Annual Conference, Cleveland, Ohio SPSE,P.O. Box 1609, Wash., D.C.

19 OSA Chicago Sect. Mtg., Discussion of some papersgiven at ICO, Japan, by Philip N. Slater of IITAnton Weigandt, 1434 W. Catalpa Ave., Chicago 4023-27 IFIPS, 3rd Congress, N.Y.C. I. L. Auerbach, Auer-bach Corp., 1635 Arch St., Phila., Pa. 19103

24-June 1 IAMA Internatl. Conf. on Cloud Physics, Tokyo andSapporo, Japan H. Weickmann, Meteorological Br.,Signal Corps Engr. Labs., Ft. Monmouth, N.J.07701

31-June 2 5th Australian Spectroscopy Conf., Perth A. J.Parker, Dept. of Chem., U. of Western Australia,Nedlands, Australia

June- 8th Internatl. Color Mtg., Lucerne, Switzerland

Centre d'Information de la Couleur, 23, rue Notre-Dame-des-Victoires, Paris, France

- 20th Ann. Cong., Canadian Assoc. of Physicists,Vancouver, B.C.

2 OSA San Diego Sect. Mtg., annual address by out-going president, John M. Hood, Jr. of U.S.N.Electronics Lab.

6-10 Internatl. Symp. on Photographic Optics, Amateurand Professional Film Technics, and Sensitometry,Prague Jiri Moravek, Perm. Comm. of INTER-KAMERA and Press Service, Plzenska 66, Smichov,Czech.

9-11 MISFITS Conf. (Mellon Inst. Symp. on Far InfraredTranspose Spectroscopy), Pittsburgh W. G. Fateley,Mellon Institute, Pittsburgh, Pa.

13-18 ASTM 68th Ann. Mtg., Purdue Univ., Lafayette,Indiana

14-18 Symp. Molecular Structure and Spectroscopy, OhioState U. H. H. Nielsen, Dept. Physics, OSU, 174W. 18 St., Columbus, Ohio 43210

16 OSA Chicago Sect. Mtg., Activities and Responsibili-ties of Sears Color Control Lab. by N. R. Pugh ofSears Roebuck Anton Weigandt, 1434 W. CatalpaAve., Chicago 40

21-23 Physics of Quantum Electronics Conf., San Juan,Pue.-to Rico P. L. Kelley, M.I.T. Lincoln Lab., Lex-ington, Mass. 02172

21-25 Program on Principles of Color Technology by FredW. Billmeyer, Jr., Rensselaer Polytechnic Inst.A. A. K. Booth, Rensselaer Polytechnic Inst., Troy,N.Y. 12181


Documents

An Optical Null Double-Beam Far Infrared Spectrophotometer