NBSIR 75-639

Optical Materials Characterization

Albert Feldman, Deane Horowitz, and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Irving Malitson and Marilyn J. Dodge

Optical Physics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20 2 34

January 1975

Semi-Annual Technical Report

Period Covered: July 1, 1974, to December 31, 1974

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 22209

NBSIR 75-639

OPTICAL MATERIALS CHARACTERIZATION

Albert Feldman, Deane Horowitz, and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Irving Malitson and Marilyn J. Dodge

Optical Ptiysics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

January 1975

Semi-Annual Technical Report

Period Covered: July 1, 1974, to December 31, 1974

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 22209

" Co.

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Seaetary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

OPTICAL MATERIALS CHARACTERIZATION

Albert Feldman, Deane Horowitz, and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Irving Malitson and Marilyn J. Dodge

Optical Physics Division

Institute for Basic Standards

ARPA Order No 2620

Program Code Nimber . .4D10

Effective Date of Contract January 1, 1974

Contract Expiration Date December 31, 1975

Principal Investigator Albert Feldman

(301) 921-2840

The views and conclusions contained in this dociament are those

of the authors and should not be interpreted as necessarily representing

the official policies, either express or implied, of the Advanced Research

Projects Agency or the U. S. Government.

OPTICAL MATERIALS CHARACTERIZATION

Abstract

We have measured the following parameters of chemical vapor deposited

polycrystalline ZnSe (CVD ZnSe) : Refractive index and change of index of

refraction with temperature (dn/dT) over the wavelength range 0.5 ym to 18

using the method of minimum deviation; the coefficient of linear thermal

expansion and dn/dT at 10.6 ym using Fizeau interferometry; and the elastic

moduli and photoelastic moduli using Fizeau and Twyman-Green interferometry

A sensitive technique has been developed for measuring stress-optical constants of materials that exhibit a small stress-optical effect.

Table of Contents Page

1 . Technical Report Suininary 1

1.1 Technical Problem 1

1.2 General Methodology . 1

1.3 Technical Results 2

1.4 Department of Defense Implications 2

1.5 Implications for Further Research 2

2. Technical Report - Some Properties of Polycrystalline Zinc Selenide. ... 3

2.1 Introduction 3

2.2 Refractive Index and Change of Index with Temperature by the

Method of Minimum Deviation 4

2.3 Interferometric Measurement of Thermal Expansion and Change of

Refractive Index with Temperature 6

2.4 Measurement of Stress-Optical Constants and Elastic Constants 8

2.5 Acknowledgements 10

2.5 References 12

OPTICAL MATERIALS CHARACTERIZATION

1. Technical Report Summary

1.1 Technical Problem

Windows siabjected to high average power laser radiation will

undergo optical and mechanical distortion due to absorptive heating. If

the distortion becomes sufficiently severe, the windows become unusable.

Theoretical calculations of optical distortion in laser windows depend

on the following material parameters: absorption coefficient, refractive

index, change of index with temperature, thermal expansion coefficient,

stress-optical constants, elastic compliances, specific heat, thermal

conductivity and density. Our' program has been established to measure

refractive indices, changes of index with temperature, stress-optical

constants, elastic compliances, and thermal expansion coefficients of

candidate infrared laser window materials.

1 . 2 General Methodology

Laboratory experiments are conducted for measuring refractive

indices, changes of index with temperature, stress-optical constants,

elastic compliances, and thermal expansion coefficients.

The refractive indices of prismatic specimens are measured on precision spectrometers by using the method of minimum deviation. Two

spectrometers are used. One instrument, which uses glass optics, is used

for measuring refractive indices in the Visible with an accuracy of

several parts in 10^. The other instrument, which uses mirror optics,

is used for measuring refractive indices in the ultraviolet and the

infrared to an accuracy of several parts in 10^. Using both spectrometers

we can measure refractive indices over the spectral region 0.2 ym to 50 ym.

We measure the coefficient of linear thermal expansion, a, by a method of Fizeau interferome try. The interferometer consists of a specially

prepared specimen which separates two flat plates. Interference fringes

are observed due to reflections from the plate surfaces in contact with

the specimen. We obtain a by measuring the shift of these interference

fringes as a function of temperature.

The change of refractive index with temperature, dn/dT, is measured

by two methods. In the first method, we measure the refractive index with

the precision spectrometers at two temperatures, 20 °C and 30 °C, by

varying the temperature of the laboratory. This provides us with a measure

of dn/dT at room temperature. The second method may be used for measuring

dn/dT up to a temperature of 800 °C. We obtain dn/dT from a knowledge of

the expansion coefficient and by measuring the shift of Fizeau fringes in

a heated specimen as a function of temperatiire . The Fizeau fringes are due to interferences between reflections from the front and back surfaces

of the specimens.

1,
We measure stress-optical coefficients and elastic compliances

using a combination of Twyman-Green and Fizeau interferometers. From the

shift of fringes in specimens subjected to uniaxial or hydrostatic compression, we obtain the necessary data for determining all the stress-optical constants

and elastic compliances. In materials with small stress-optical constants

or in materials that cannot withstand large stress, we measure the stressoptical effect with a modified Twyman-Green interferometer, which has a sensitivity of about O.OIA at 10.6 pm.

1.3 Technical Results

The following measurements have been made on polycrystalline ZnSe

that has been grown by the chemical vapor deposition technique: a) the

refractive index was measured at 20 °C for 30 wavelengths and at 30 °C for

20 wavelengths in the range from 0.51 ym to 18.2 ym. From these data we obtained a dispersion curve of the change of index with temperature, b) An

equation for the change of thickness as a function of temperature was

obtained, c) The change of index with temperature was measured

interferometrically at 0.6328 ym and at 10.6 ym. At 10.6 ym we made a total of six measurements on three specimens. Our results were highly

reproducible, however, they differed significantly from data reported by

AFCRL. . The discrepancy may be due to specimen differences, d) We measured the

stress-optical constants q-^-^ and q]^2 10.6 ym. These data, which are presented together with earlier data at 0.6328 ym and 1.15 ym, suggest

that the dispersion in the coefficients from 1.15 ym to 10.6 ym is small,

e) We calculated the elastic compliance component s-j^-j^ from interferometric

measurements on a specimen under hydrostratic pressure and from previously

reported values of s^2' '^^^ ^^'^ "312 obtained at 0.6328 ym.

We built a specially modified Twyman-Green interferometer for

the stress-optic measurements at 10.6 ym. This was necessary because

the change in optic path at 10.6 ym for the maximum permissible applied

stress is less than A. The estimated resistivity of the interferometer

is 0.01 X at 10.6 ym.

1.4 Department of Defense Implications

The Department of Defense is currently constructing high-power

infrared laser systems. Criteria are needed for determining the suitability

of different materials for use as windows in these systems. The measurements

we are performing provide data that laser system designers can use for

deteirmining the optical performance of candidate window materials.

1.5 Implications for Further Research

Measurements of refractive index, change of index with temperature,

thermal expansion, stress-optical coefficients, and elastic compliances will

be continued on candidate laser window materials. More specifically, we plan

measurements on polycrystalline KCl, reactive atmosphere process (RAP) grown

KCl, doped KCl, and other materials supplied by manufacturers under contract

to the Advanced Research Projects Agency and other Department of Defense

agencies. An important preliminary to the actual measurements will be the

preparation of test specimens. This will require cutting, grinding, and

polishing of samples.

2.
In using the data we have obtained on CVD ZnSe, some caution

must be applied. For example, we have treated the ZnSe as an isotropic

material, whereas other workers indicate that the material is not

isotropic. We are, therefore, measuring the stress-optical constants

and elastic compliance on new material to ascertain whether one can expect significant differences in the coefficients of different specimens.

Preliminary results indicate that these coefficients may differ in

specimens obtained from different batches.

2. Technical Report - Some Properties of Polycrystalline Zinc Selenide

2.1 INTRODUCTION

This report will discuss the measurement of refractive index,

change of index with temperature, thermal expansion coefficient, stressoptical constants and elastic compliances in high power laser window

materials. These parameters are needed for calculations that predict the

optical distortion that occurs in windows subjected to high energy laser

radiation [1-5] . In particular, we are investigating these properties

in polycrystalline ZnSe that has been grown by the chemical vapor

deposition (CVD) technique.

We have measured the refractive index, n, of CVD ZnSe on a prism

spectrometer using the classical minimum deviation method. Data were obtained

at 20 °C for 30 wavelengths and at 30 °C for 22 wavelengths in the range

from 0.51 ym to 18.2 ym. At 10.6 ym, n = 2.4027 at 20 °C.

The change of refractive index with temperature, dn/dT, was measured

by two methods. In the first method we measured n by the method of minimum

deviation at both 20 °C and 30 °C. This method permitted us to calculate

dn/dT at room temperature. At 10.6 ym this value was 7.9 x 10~^/°C. In the

second method we measured the shift of Fizeau fringes in a parallel plate

at discrete wavelengths as a function of temperature from 25 °C to 200 °C.

With these data, together with our measured value of the thermal expansion

coefficient we calculated dn/dT. From a linear least squares fits to the

data we obtain dn/dT = 6.4 x 10~^/°C at 10.6 ym. The differences between

the values obtained by the two methods and the differences of both these

values with measurements at other laboratories is, as yet, unexplained.

The value of the coefficient of linear thermal expansion, a, has

been obtained using Fizeau interferometry . We find that at 25 °C, a - 7.79 x 10~^/°C. An air correction term was used in the calculation.
In our previous report we reported measurements of the absolute stressoptical constants, and q^^' °^ "^^"^ ^^^^ 0.6328 ym and 1.15 um. These

measurements were made with conventional Twyman-Green and Fizeau interferometers. We have now developed a more sensitive technique for measuring absolute stress-optical constants at 10.6 ym. The technique makes it possible

for us to detect the shift of 0.01 fringe in a Twyman-Green interferometer.

This precision is necessary because the stress-optical effect in ZnSe is

very small at 10.6 ym. Preliminary measurements suggest that the absolute

stress-optical constants of polycrystalline ZnSe at 10.6 ym do not differ

greatly from the coefficients at 1.15 ym.

•In addition, values are presented for the elastic compliance components,

s and s , for polycrystalline ZnSe. In the past, we have obtained the

component by measuring the shift in fringes of Twyman-Green and Fizeau

interferometers as a function of uniaxial stress applied to a specimen. We

have now measured the shift of Fizeau fringes of a specimen under hydrostatic

compression. From this measurement together with the stress-optical constants

and 32^2 ^® calculate and the other related elastic moduli.

2.2 Refractive I ndex and Change of Index with Temperature by the Method

of Minimum Deviation

The refractive index of a prism of CVD ZnSe was measured at 30 wavelengths from 0.51 ym to 18.2 ym at a controlled temperature near 20 °C. The

apparatus has been described in earlier work [6-8] . In the visible and nearinfrared regions, n, was measured at known wavelengths of mercury, cadmium

and helium lamps. At longer infrared wavelengths, measurements were made at

known absorption bands of H20,C02, polystyrene and 1 , 2 ,4-trichlorobenzene

We also used a series of narrow-band filters between 3.5 and 10.7 ym. A

globar was the infrared source and a thermocouple with a Csl window was the

detector.

The experimentally determined index values at 20 °C are represented by

the solid curve in Fig. 1. The index decreases from a value of 2.7270 at

0.51 ym to 2.3278 at 18.16 ym, an overall change of 0.4. At 10.6 ym, n = 2.4027. The dispersion data are in the process of being fitted by

computer to a Sellmeier-type dispersion equation. A preliminary computer

run, suggests that the errors in the raw data are probably less than

5 X 10-5.

Of the six previously reported investigations of the refractive index

of ZnSe between 0.5 ym and 14 ym, four have used deviation methods that

employ prismatic specimens. Because deviation methods are considered to be

the most accurate, we compare the results of these four workers with our

results. Marple [9] has measiired n for single crystal ZnSe between 0.48 ym

euid 2.5 ym with a claimed accuracy of 4 x lO'^. His values are about 0.01

less than our values. Rambauske [10] studied both single crystal and polycrystalline ZnSe in the visible region. He found the index of the polycry4.
2.80

2.70

2.60

2.50

2.40

2.30

ZINC SELENIDE —NBS - (CHEMICAL VAPOR DEPOSITION) o MARPLE - SINGLE CRYSTAL ^ RAMBAUSKE - SINGLE CRYSTAL

I KODAK - IRTRAN 4

HILTON - IRTRAN 4

0.1 0.5 1.0 5.0 10.0 50.0 WAVELENGTH, /xm

Figure 1, Refractive index of CVD ZnSe at 20 °C as a function of wavelength,

CVD ZnSe

0.1 0.5 1.0 5.0 10.0

WAVELENGTH, Atm

50.0

Figure 2. Thermal coefficient of index of CVD ZnSe at 25 °C as a function

of wavelength.

5
stalline material to be generally 1% larger than the index of the single

crystal material. Kodak has published values of index for IRTRAN 4 [11]

which is a hot-pressed polycrystalline ZnSe material. Hilton's measurements

on IRTRAN 4 [12] generally agree with Kodak's values to within 1 x 10"3,

but are about 0.2% larger than the indices we measured in CVD ZnSe. To

the best of our knowledge, these are the first measurements of n in CVD ZnSe

over its practical transmission range on a single instrument.

Measurements of n were repeated at 22 selected wavelengths at a controlled

room temperature near 30 °C. These values together with the values at 20 °C were used to calculate dn/dT. Fig. 2 shows dn/dT as a function of wavelength.

The value of dn/dT varies from 18.5 x 10-5/°C at 0.5461 pm to 5.5 x 10" /°C

at 18.2 ym. At 10.6 um, dn/dT = (7.9+1.0) x 10-5/°C. The fact that dn/dT

is positive indicates that the temperature dependence of the electronic polarizabilities predominates over the density effect.

2 . 3 Interferometric Measurement of Thermal Expansion and Change of

Refractive Index with Temperature

In some earlier work [8] we discussed the measurement of the linear

coefficient of thermal expansion by the method of Fizeau interferometry

The expression for a is

1 dt ...

.

°' = I

^

where T is the temperature in °C, and t is the specimen thickness. We have

measured the thermal expansion of a specimen of CVD ZnSe over the temperature

range 25 °C - 200 °C and have fitted the data to a quadratic expansion in

the temperature. A correction for air was taken into account in the calculation. We then obtained

. t = t [l+a(T-25) + b(T-25)^] (2) o —6

where t is the specimen thickness at 25 °C, a = 7.79 x 10 /°C, and

b = 2.1°x 10-10 (°C)~2. At 25 °C, a = a. Data obtained at Raytheon [13]

from dilatometer measurements are in good agreement with our data.

In that same earlier work [8] we discussed our method for measuring

dn/dT in the visible using Fizeau interferometry . The method has been

modified to make use of laser sources. Fig. 3 is a schematic diagram of

the system as used at 10.6 um. A special feature of the system is an As^S^

glass plate which acts as a Fizeau interferometer to monitor the mode

stability of the laser.

The experimental procedure consisted of heating the specimen, which acts

as a Fizeau interferometer, so that the temperature rise was about one degree

per minute from room temperature to 200 °C. We counted the fringe minima

as a function of the temperatiire , and then fit the data by a computer to a power expansion in the temperature. We then calculated dn/dT taking into

account the thermal expansion of the specimen. At 0.6328 um we found

dn/dT = 1.08 X 10~V°C at 25 °C. In Table I we present values of dn/dT at

25 **C for several runs at 10.6 um. Runs #1 and 2 were repeated measurements

6
C02 Laser

Beam

Expander

Mirror

Ge Beam

Splitter

Specimen Located

Within Furnace "

Asz S3 Plate

Figure 3. Apparatus to measure change of refractive index with temperature

at 10.6 micrometers.

OSCILLOSCOPE

PYROELECTRIC

DETECTOR

LOCK-IN AMPLIFIER A C AMPLIFIER

MIRROR ON

PZT DRIVE

CO2 LASER

RADIATION

Figure 4, .Modified Twyman-Green interferometer for measuring fractional

wavelength changes of optic path at 10.6 micrometers

7
on the same specimen. Runs #3 and 4 were made on another specimen but in

different directions; in Run #3 the radiation was propagated parallel to the

specimen growth direction while in Run #4 the radiation was propagated perpendicular to the specimen growth direction. Runs #5 and 6 were repeated

interferometric measurements on the same prism that was used in the refractive

index measurements.

The first column in the table was obtained by fitting the thermal expansion data to a linear curve; the second column was obtained by fitting the

data to a quadratic curve. The data within a given column are quite reproducible although mean values of the two columns differ by about 7%. The

values in both columns appear to differ significantly from the value obtained

from the refractive index data. Additionally, values in the literature of

dn/dT in polycrystalline ZnSe prepared by different methods vary from

5 X 10~V°C to 1.0 x 10"V°C [14]. The origin of these discrepancies is

not yet known. We originally thought that a difference in dn/dT might be

observed between light propagating parallel to the specimen growth direction

and light propagating perpendicular to the specimen growth direction; however,

the reproducibility of the data for runs #3 and 4 suggests that this assumption would not explain the discrepancy. The discrepancies might be due to

sample variability; however, the consistency of our data for the three different specimens casts doubt on this assumption.

• 2.4 Measurement of Stress-Optical Constants and Elastic Constants

Previously [8,15] we discussed a method for determining the absolute

stress-optical constants and the elastic compliance component S]^2 °^ ^ material and data were presented for several materials including CVD ZnSe [8]

Values of and q2_2 10.6 ym could not be obtained for the ZnSe because

the fringe shift at this wavelength was too small to measure with any accuracy. We have now developed a technique for measuring small fringe shifts

and have obtained preliminary values for q-^^-j^ and q-]_2 at 10.6 ym. These

values agree quite well with values obtained at 1.15 ym which suggests that

the dispersion of the coefficients in the intervening wavelength range is

small.

The apparatus used in this measurement is a Twyman-Green interferometer that has been modified so that fringe location can be determined

electronically to a precision of 0.01 A at 10.6 ym. Figure 4 shows a schematic of the apparatus. The two arms of the interferometer are in close

proximity, in order to minimize instabilities due to air currents and vibrations. The effects of vibration are also minimized by mounting the diagonal

mirror on the same base as the germanium beam splitter and by mounting the

two end mirrors on a common base. The end mirror in the specimen arm is

mounted on a piezoelectric translator and undergoes a sinusoidal translation

along the axis of the interferometer thus modulating the output intensity of

the interferometer in the following manner

where I is the intensity at a fringe maximiam, A is the maximum excursion of

I

4TTA sincot

X + 4-)] , (3)

o

8
Table I. Interferometric Measurements of dn/dT in CVD ZnSe at 10,6 ym and

at 25 °C

Run Linear Fit Quadratic Fit

#1 6.36 X 10"^/°C 5.86 x 10~V°C

#2 6.35 6.03

#3 6.42 5.95

#4 6.42 5.92

#5 6.34 6.03

#6 6.36 . 5.91

Average 6.38 + .04 5.95 + .07

Value from Refractive Index Measurements 7.9 x 10 ^/°C

Table II. Photoelastic Properties of CVD ZnSe

X(um) 0.6328 1.15 10.6

n 2.590 2.473 2.403

q^11 (10""''^m^/N) -1.32 -1.36 -1.39

q^2^10~"''^mVN) 0.28 0.62 0.58

q^^-q^^aO~'^'^m^/U) -1.60 -1.96 -1.97

p^^ -0.10 -0.08 -0.08

Pj^2 -0.01 0.03 0.02

9
the modulated mirror about its average position, and (j) is a phase related to

the mean optic path difference of the two arms of the interferometer. The

reference specimen, which is placed in the other arm of the interferometer,

is a device which is made to produce a known optic path change. In our case we use a reference specimen of Ge in a compression apparatus. The Ge is

self-calibrating because a shift of many fringes can be produced as a function of stress. Fractional fringes are then obtained by linear interpolation.

In operation, the Ge is stressed until the interferometer is at a null which

is determined by observing that the first harmonic of the output intensity is zero and the second harmonic is maximum. A given stress is then applied to

the unknown specimen, which shifts the interferometer away from null, but

which is compensated by applying an incremental stress to the reference

specimen. From these data we obtain the change of optic path in the unknown

specimen as a function of stress and combined with a knowledge of the: elastic

compliance component ^® obtain the stress-optical constant.

In Table II we sijmmarize all our stress-optic data for a specimen of CVD

ZnSe. We have slightly modified our previously reported values because of

the improved values of refractive index we have obtained. Our new procedure

was used to obtain q^^^. ^'^ 10.5 pm. We obtain 10.6 um using the birefringence data (<3ii~q]_2^ * interesting to note the small differences

between the values at 10.6 ym and 1.15 ym.

We have also measured the shift of Fizeau fringes in a specimen of CVD

ZnSe as a function of hydrostatic pressure [8] using a HeNe laser source. This data, combined with the known stress-optical constants and the value of

^12' PS^itted us to calculate s-^-^. In Table III we summarize all the elastic moduli we have measured and derived for CVD ZnSe. These moduli have

permitted us to calculate the photoelastic constants p^j, which are shown

in Table II [16]

In using the data we have obtained, some caution must be applied.

Because we have treated the ZnSe as an isotropic material, future measurements are planned on several other specimens in order to ascertain whether

one can expect significant differences in the coefficients of different

specimens

2.5 Acknowledgements

We would like to thank Dr. Carl Pitha of ARCRL, John Fenter of AFML and

Dr. Perry Miles of Raytheon for specimens of CVD ZnSe. We also thank William

McKean for help in the design and building of a new stressing apparatus.

10
Table III. Elastic Properties of CVD ZnSe

Elastic Compliances:

Elastic Constants;

Poisson's Ratio:

Young ' s Modulus

Rigidity Modulus:

Bulk Modulus:

s^^ = 14.5 X 10

-12

-12

s = -4.0 X 10

„ „ ,^10 N

^11 = 8.8 X 10 "2

m

^ , ^10 N

°12 = ^ ^° -2

m

V = 0.28

E = 6.9 X 10 "2

m

G = 2.70 X

10"'"° m

K = 5.20 X

10"""° m

11
2.6 References

1. M. Sparks, J. Appl. Phys. 42, 5029 (1971).

2. J. R. Jasperse and P. D. Gianino, J. Appl. Phys. £3, 1686 (1972).

3. B. Bendow, J. R. Jasperse, and P. D. Gianino, Optics Coinmun. 5^, 98 (1972)

4. B. Bendow, P. D. Gianino, A. Hordvik, and L. H. Skolnik, Optics Commun.

1_, 219 (1973) .

5. B. Bendow and P. D. Gianino, Appl. Phys. 2^, 1 (1973) .

6. C. Weir, S. Spinner, I. H. Malitson, and W. J. Rodney, J. Res. Nat. Bur.

Stds. (U.S.), 58, 189 (1957) RP 2751.

7. L. W. Tilton, J. Res. Nat. Bur. Stds. (U.S.), 2_, 909 (1929) RP 64.

-8. A. Feldman, I. Malitson, D. Horowitz, R. M. Waxier and M. J. Dodge,

in Proceedings of Conference on Damage in Laser Materials, June 1974.

To be published as a Special NBS Publication; A. Feldman, D. Horowitz,

R. M. Waxier, I. Malitson and M. Dodge, Optical Material Characteriza-

• tion, NBS Report # NBS-IR 74-525, July 1974.

9. D. T. F. Marple, J. Appl. Phys. 25^, (3), Pt. 1, 539 (1964).

10. W. R. Rambauske, J. Appl. Phys. 25_, (10) 2958 (1964) .

11. Kodak Irtran Infrared Optical Materials (Kodak Publication U-72, Eastman Kodak Co., 1971).

12. A. R. Hilton and C. E. Jones, Appl. Opt. 1513 (1967).

13. Private Communication.

14. L. H. Skolnik and O. M. Clark, Appl. Opt. 13^, 1999 (1974).

15. A. Feldman, D. Horowitz and R. M. Waxier, "Stress Optic Measurements

in the Infrared" , in the Proceedings of the Third Conference on High

Power Infrared Laser Window Materials, Nov. 1973, Edited by C. A. Pitha

and B. Bendow, ARCRL-TR-74-0085 (1), Special Reports, No. 174, p. 403,

February 1974.

16. J. F. Nye, Physical Properties of Crystals , (Oxford University Press,

London 1957) , p. 249.

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1. PUBLICATION OR REPORT NO.

NBSIR 75-639

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Optical Materials Characterization

5. Publication Date

.T;^ nn^1 yT7 1 Q 7 R

6. Performing Organization Code

7. AUTHOR(S) Albert Feldman, Deane Horowitz, Roy M. Waxier,

T>-T7i nq Malitsnn anrJ Marilyn .T . Dodge

8. Performing Organ. Report No. NBSIR 75-639

9. PERFORMING OllGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11, Contract/Grant No. 2620/4D10

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Advanced Research Projects Agency

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Semi—Annual Tech. Report

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15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

We have measured the following parameters of chemical vapor deposited

polycrystalline ZnSe (CVD ZnSe) : Refractive index and change of index of

refraction with temperature (dn/dT) over the wavelength range 0.5 ym to 18 ym

using the method of minimum deviation; the coefficient of linear thermal

expansion and dn/dT at 10.6 ym using Fizeau interferometry; and the elastic

moduli and photoelastic moduli using Fizeau and Twyman-Green interferometry.

A sensitive technique has been developed for measuring stress-optical

constants of materials that exhibit a small stress-optical effect.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Coefficient of thermal expansion; elastic constants; infrared laser window materials;

photoelasticity ; polycrystalline ZnSe; refractive index; stress-optical constants;

thermal coefficient of refractive index.

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