NBSIR 74-525

Optical Materials Characterization

Albert Feldman, Dean 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. 20234

July 1974

Semi-Annual Technical Report

Period Covered: January 1, 1974, to June 30, 1974

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 22209

NBSIR 74-525

OPTICAL MATERIALS CHARACTERIZATION

Albert Feldman, Deane Horowitz, and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Irving Malitson ar:d Marilyn J. Dodge

Optical Physics Division

Institute for 3£sic Standards

National Bureau of Standards

Washington, 3. C. 20234

July 1974

Semi-Annual Technical Report

Period Covered: January 1, 1974, to June 30, 1974

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 22209

U. S. OEPARTMEIMT OF COMMERCE, Frederick B. Dent. Secretary

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 Number 4D10

Effective Date of Contract January 1, 1974

The views and conclusions contained in this document 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

,

Contract Expiration Date September 30, 1974

Principal Investigator Albert Feldman

(301) 921-2840

Table of Contents

1. Technical Report Summary . .". . . . . . . . . . . . 1

1.1 Technical Problem 1

1.2 General Methodology 1

1.3 Technical Results . . ... i .... 1

1.4 Department of Defense Implications . . . , .. . . 2

1.5 Implications for Further Research 2

2, Technical Report 2

2 . 1 Introduction 2

2.2 Refractive Index and Change of Index with

Temperature 3

2.2.1 Index Data 3

2.2.2 Thermal Coefficient of Index 6

2.3 Thermal Expansion and Change in Refractive Index

Temperature 6

2.4 Measurement of Stress-Optical Coefficients and

Elastic Constants 6

2.4.1 Apparatus 9

2.4.2 Experimental Procedure 9

2.4.3 Results 12

2.5 Summary 14

2.6 Acknowledgments 14

2.7 References 15

i
OPTICAL MATERIALS CHARACTERIZATION

Abstract

A program has been established for measuring refractive index, n, stress-optical constants,

q^j, change of index with temperature, dn/dT, thermail expansion coefficient, a, and elastic

compliances, s^^, of infrared laser window materials. These parameters are necessary for

determining the optical distortion that occurs in windows due to heating by the absorption of

high power laser radiation, n and dn/dT are measured over a spectral range 0.2 to 50 ym by the

method of minimum deviation on precision spectrometers. Twyman-Green cind Fizeau interferometers,

which operate at 0.6328 \im, 1,15 ym, and 10.6 ym, are used for measuring dn/dT and s^^.

Materials currently under study are polycrystalline ZnSe, AS2S3 glass, chalcogenide glass

(Ge 33%, As 12%, Se 55%), and KCl . Results are given for n and dn/dT in KCl, and q^^ and S12 in

ZnSe, AS2S3 glass, and chalcogenide glass.
OPTICAL MATERIALS CHARACTERIZATION

1. Technical Report Summary

1.1 Technical Problem " '

Windows subjected 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, stressoptical 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 [Section 2.2], Two spectrometers are used. One

instr\mient, 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 \im to 50 ym.

We measure the coefficient of linear thermal expansion, a, by a method of Fizeau

interferometry [Section 2.3]. 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 [Section 2.2.2],

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 [Section 2.3]. We obtain dn/dT from

from a knowledge of the expansion coefficient and by measuring the shift of Fizeau fringes

in a heated specimen as a function of temperature. The Fizeau fringes are due to interferences

between reflections from the front and back surfaces of the specimen.

Stress-optical coefficients and elastic compliances are measured using a combination of Twyman-Green and Fizeau interferometers [Section 2.4]. From the shift of

fringes in specimens subjected to uniaxial or hydrostatic compression, we obtain the

necessary data for determining all the stress-optical coefficients and elastic compliances.

1.3 Technical Results

Measurements of refractive index have been made on a crystal of KCl from

220 nm to 14.3 ym. This is the first time that measurements of refractive index have been

made on a single sample of KCl over this wide a spectral range on a single instrument.

The data compared favorably with earlier compilations of refractive index [see Section 2.2.1].

The refractive index measurements were made at 20°C and 30°C. From these data we obtained

dn/dT. [Section 2.2.2].

1
The thermal expansion coefficient of polycrystalline ZnSe was measured interferometrically. Data obtained at Raytheon using a dilatometer was in agreement with our data

[Section 2.3]

Techniques were developed for measuring stress-optical constants q. . and elastic

compliances S12 [Section 2.4]. The techniques use Twyman -Green and Fizeau rferometers

operating at 10.6 ym, 1.15 ym, and 0.6328 pm. We have measured the stress-optical constants

of AS2S3 glass at 10.6 ym, 1.15 ym, and 0.6328 ym, of a chalcogenide glass (33% Ge, 12% As,

55% Se) at 1.15 ym and 0.6328 ym, and of polycrystalline ZnSe at 1.15 ym and 0.6328 ym. In ZnSe we have measured the stress- induced birefringence at 10.6 ym as well. We have also

measured S12 in AS2S3 glass, the chalcogenide glass, and polycrystalline ZnSe. In AS2S3

glass and the chalcogenide glass, the values of S12 agreed with the values obtained by other

workers. We have been unable to find measurements of S12 in polycrystalline ZnSe by other

workers

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 determining 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, polycrystalline ZnSe, 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.

The measurement of stress-optical coefficients in materials that possess very small

stress-optical coefficients, or in materials that connot withstand large stresses, requires

a very sensitive interferometric technique. Such an interferometer is currently under development .

2. Technical Report

2.1 Introduction

Laser systems of high average power are currently under development. As the output power

increases, the optical components in these systems undergo optical and mechanical distortion due

to absorptive heating. If the distortion is sufficiently severe, the optical elements become

unusable. The parameters necessary for determining this optical distortion [1,2]^ are absorption

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

stress-optical coefficients, elastic compliances, specific heat, thermal conductivity, and density.

The temperature change that occurs in a laser window due to absorptive heating will produce

three effects: (1) an expansion, (2) a direct change of refractive index, and (3) a system of

internal stresses due to thermal gradients, which changes the refractive index through the stress- optical effect.

Although some information is available [3,4] on thermal expansion and change of index with

temperature of laser window materials, there is very little data on the stress-optical effect [5]. In the past stress-optical coefficients have been measured in the visible region of the spectrum

Figures in brackets indicate the literature references at the end of this paper.

2
using interference methods [6,7] . We have now constructed Twyman-Green and Fizeau interferometers

for making these measurements at 1.15 um and 10.6 ym as well as a:t 0.6328 pm. This is the first

time that interferometers have been used for measuring stress-optical coefficients in the infrared.

These interferometers are also useful for measuring thermal expansion, change of index with

temperature, and elastic compliance coefficients.

In this paper we present the methods used for measuring refractive index, n, change of index

with temperature, dn/dT, linear thermal expansion, coefficient, a, d:ress-optical coefficients, q. ., and elastic con^Jliances , s. .. We also report on results obtained on AS2S3 glass, a chalcogenide-^

glass (Ge 33%, As 12%, Se 55%), polycrystalline ZnSe, and single crystal KCl.

We discuss measurements of n and dn/dT by using precision refractometry methods in Section 2.2.

The quantity dn/dT is obtained near room ten^erature by measuring n at 20°C and at 30°C. Results

are reported for KCl

In Section 2.3 we discuss the measurement of thermal expansion and dn/dT up to a temperature

of eoCC. These measurements involve the use of Fizeau fringes.

In Section 2.4 we discuss the measurement of stress-optical coefficients and elastic compliances

In isotropic materials there axe two independent elastic constants and two independent stress-optical

coefficients. The use of Twyman-Green and Fizeau interferometers in conjunction with samples under

uniaxial and hydrostatic compression supplies us with sufficient data for obtaining all the constants

In Section 2.5 we present the results of measuring q^. and S12 on the chalcogenide glass, AS2S3

glass, and polycrystalline ZnSe.

2.2 Refractive Index and Change of Index with Temperature

In the search for potential window and auxiliary optical component materials for high-power

lasers, KCl appears to be one of the most promising candidates. It has useful transparency from

'^' 0.2 to 20 iim (with 90% transmittance between 0.45 and 14 ym) . This covers window utilization in

both the ultraviolet and infrared.

2.2.1 Index Data

A KCl prism cut from a commercially grown crystal was used in this study. The prism faces are

10 X 10 mm and the refracting amgle near 60'. The refractive index was measured by means of the

classical minimum deviation method with two precision spectrometers. The spectrometer schematic

shown in figure la is designed for visible region refractometry and is capable of accuracy of several

paurts in 10^ . The spectrometer schematic shown in figure lb employs mirror optics and is used in the

non-visible spectral regions. It is capable of accuracy of several parts in 10^. Both instruments

and procedures for high-precision refractive index measurements have been described in previous

pi^blications [8,9].

Refractive index measurements were made at controlled room temperatures near 20 °C at 60 wavelengths from 0.22 ym in the ultraviolet to 14.3 ym in the infrared. The wavelengths were selected

from the spectra of emission sources of Hg, Cd, He, Cs and Zn, and from calibrated absorption bands

of H2O, polystyrene, and methylcyclohexane . A series of calibrated narrow-band filters was also used

in the infrared in the 3.5 to 10.6 ym region.

The experimentally determined index values at 20°C for KCl are represented by the solid curve in

figure 2. The refractive index decreases from a value of 1.6360 at 0.224 ym to 1.4374 at 14.3 ym, an over-all change of 2 x 10~^. At 10.6 ym the value of the refractive index is 1.4542 at 20°C.

The refractive index measurement program is being supplemented with a compilation of critically

evaluated refractive indices of key laser materials. A literature search has turned up fourteen

published papers dealing with refractive index of KCl. The data cover the wavelength range from

'V' 0.16 to 220 ym and were obtained by a variety of experimental techniques. It is interesting

to note that in the spectral regions of interest to laser designers, the most accurate measurements

were made in 1901 [10], 1908 [11], and 1927 [5]. The crystals measured were natural salt, and

the minimim deviation method was employed with the sample in prism form. The excellent agreement

between the NBS and the early data is shown in figure 2. The NBS values are lower in index by

an average value of 2 x 10"**.

3
(b)

Figure 1. (a) Schematic of spectrometer used for visible-region

refractometry . A. source; B. divided circle; C. prism table; D. collimator;

E. telescope, (b) Schematic of spectrometer used for nonvisible-region

refractometry . A. source; B. divided circle; C. prism table; F. collimating mirror (fixed); G, movable mirror; H. detector.
1.63 — REFRACTIVE INDEX

OF

1.61 POTASSIUM CHLORIDE

1.59

1.57

1.55

I - MALITSON

1.53 1 • SMAKULA

1.51

149 —

1.47 —

1 45

1.43

. 1 .1 .1 -

0.1 1.0 10.0 100.0

WAVELENGTH, fjm

Figure 2. Refractive index of KCl at 20°C.
2.2.2 Thermal Coefficient of Index

Refractive index measurements in KCl were repeated at; 22 selected wavelengths at a controlled room

temperature near SO'C. The refractive index values at 20''G; and SCC were used to calculate the thermal

coefficient of index, dn/dT. The dependence on wavelength is shown in figure 3. The value of dn/dT

varies from -2.1 x 10"^ K"'^ at 0.27 ym to -2.5 x 10"^ at 14.3 ym; dn/dT remains relatively constant at about -3.0 X 10"^ in the infrared between 3 ym and 6.0 ym. The fact that dn/dT is negative indicates

that the variation in index with temperature is essentially due to the change in density of the

crystal. At the extremes, where dn/dT is less negative, the influence of temperature suggests a shift

of the ultraviolet and infrared absorption edges to longer wavelengths.

The dn/dT values of Gyulai [12] and Paschen [13] are shown in figure 3 for comparison. Gyulai's

values for a mean temperature of 33°C cover the wavelength range 0.20 to 0.51 ym. Paschen's data,

for which the mean temperature is unknown, covers the wavelength range 0.59 to 17.7 ym. It can be seen that the absolute values of the earlier work are generally higher than those of NBS . It has

been observed in halide crystals that the absolute value of dn/dT increases with increasing temperature.

2.3 Thermal Expansion and Change in Refractive Index with Temperature

The thermal expansion and change of refractive index with temperature dn/dT may be measured up

to a temperature of 800°C by an interferometric method that uses Fizeau type fringes [14] . In the

visible part of the spectrum these measurements can be made simultaneously.

The interferometer assembly as used in the visible is shown in figure 4. The set of fringes

on the left is obtained between the top and bottom surfaces of the lower fused silica plate, T, and is calibrated in terms of temperature so that the fringes serve as an optical thermometer. The center set of fringes is obtained between the top and bottom surfaces of the index sample, R, and

is used to calculate the change in refractive index. Beneath this sample is a frosted area on the,

lower plate so that no fringes are formed at the interface. The third set of fringes is formed by

the slight wedge introduced between the upper plate, E, and the lower plate, T, when these fring-es are separated by the expansion sample, S, which is cut from the same material as the index sample, R. These fringes are used to obtain the thermal expansion. The assembly is heated by a vertical tube

furnace and the shifts in the three sets of fringes are recorded simultaneously on a single strip

of 35 mm film as a function of temperature.

The interference pattern generated by the sample of thickness, t, &d refractive index, n, is

expressed by the equation,

"

' NX = 2nt, 4" (1)

which relates the optical path, nt, and the fringe number, N, when monochromatic light of wavelength,

X, passes twice through the sample at normal incidence. By differentiating with respect to temperature, T, and rearranging, it is found that

dn ^ X_ AN ndt

dT 2t AT " dT ''

'

We calculate the change of refractive index as a function of temperature from the number of fringes

that pass a point of reference and from the change of thickness obtained from the thermal expansion

sample [15]

.

Using a modification of the above method, we intend to extend the measurement of dn/dT to the

infrared. „ \

The expansion coefficient of polycrystalline ZnSe was measured by the above method. Data obtained at Raytheon using a dilatometer was in agreement with our data. We obtained a = 7.9 x 10~^/K.

2.4 Measurement of Stress-Optical Coefficients and Elastic Constants

The importance of measuring all the stress-optical coefficients in the infrared is not always

well understood. Several laboratories have been measuring stress-induced birefringence at 10.6 ym. However, these data are not sufficient for determining the optical wavefront distortion due to thermal

6
cOL X Oo/lP

^ up

Figure 3. Temperature coefficient of refractive index of KCl,
Figure 4. Interferometer assembly for the measurement of thermal

expansion and thermal change in refractive index. E. an interferometer plate;

S. thermal expansion specimen; R. refractive index specimen; T. interference thermometer; Mg, Mj^, and Hp, reference lines for the interference

fringes of thermal expansion, refractive index change and temperature

change

.
stresses, because they measure only the relative stress-optical coefficients [(qn - qia) ^""^ ^44

cubic materials]. We know of only one paper which presents measurements of qjj and qj2 separately at 10.6 um [5] , and these measurements, which were done on Ge, did not give the sign of the coefficients.

Both qj^ and qi2» combination with the elastic constants, are necessary for calculating the optical

distortion due to stresses from thermal gradients in optical materials [1,2]. Index changes due to these stresses can be even greater than changes in index due to a rise in temperature. For example,

in a material tailored to have dn/dT = 0, the changes of index will be due solely to the stressoptical effect.

2.4.1 Apparatus

Conventional Twyman-Green interferometers are used [16] . The Twyman-Green interferometer at

.6328 and 1.15 pm uses helium-neon lasers as sources. The fringes are observed with a silicon matrix

vidicon camera.

The Twyman-Green interferometer at 10.6 ym uses a CO2 laser source, a germanium beam expander,

and a germanium beam splitter. The fringes are viewed either on a liquid crystal detector or on a commercial thermal image plate.

For uniaxial loading, the specimen, in the form of a rectangular parallelepiped is compressed in a rectangular frame screw clamp equipped with a calibrated load cell and a digital readout voltmeter.

A photograph of the stressing apparatus with the voltmeter is shown in figure 5.

2.4.2 Experimental Procedure

The sample is placed within one arm of the Twyman-Green interferometer. The fringe shift per unit

of applied stress is measiured for stress parallel to the polarization of the radiation, ANj/AP, and

for stress perpendicular to the polarization of the radiation, AN2/AP.

The sample, itself, functions as a Fizeau interferometer if the faces are properly polished;

interference fringes are obtained from reflections from the sample surfaces. The fringe shifts

obtained for stresses parallel and perpendicular to the polarization of the radiation are, respectively,

ANj/AP and AN2/AP.

For an isotropic material we obtain

si2 =

ANi ANi 1 X AP~

~ aF", 2t

ANi

^11 ~ ^ AP

+ [-]

\ AN2 r2 S2 ~ 7^ AP

+

AN2 AN2

AP AP~

(3)

(n - 1) (4)

(n - 1) ^ (5.)

Additional experimental data can be obtained by measuring the stress-induced birefringence.

The experimental arrangement is shown in figure 6. The stress is applied 45° with respect to the

plane of polarization. The analyzer is oriented parallel to the incident polarization. The uniaxial

load applied to the sample is increased until extinction is obtained. The loaded specimen then acts effectively as a half-waveplate, and considering the double passage of the light through the specimen,

the load is that which creates a single pass quarter wave retardation in the sample. The relative

stress-optic coefficient is

^11 ~ '^12 = X/(2n3pt). (6)

The value of q^^ ~ *^12 measurement of birefringence is more precise than the value of qj j - obtained from eqs (4) and (5). Thus, we calculate q^^ and q^2 ^^om the sum q^^ + qi2' obtained by

adding eqs (4) and (5), and the difference q^j - qj2 from eq (6). This assures us that the birefringence calculated from the numerical values of q^j and equals the measured value.

9
Figure 5. Stressing apparatus with specimen, load cell, and digital

voltmeter readout.

Equation (3) gives the value for Sj,, , In order to obtain s^j, we use a method similar to the

method for measuring dn/dT. The sample which acts as a Fizeau interferometer is compressed in a pressure vessel. Figure 7 shows the pressure vessel. Hydrostatic pressure is generated by compressing

a fluid. From the shift in fringes per unit pressure, AN/AP, we obtain for an isotropic material

Using Sj2 obtained from eq (3) together with eq (7), we can solve for s^j.

The procedures described in this section are for measuring stress-optical constants and elastic

constants of isotropic materials. These constants can be measured with the same procedures on crystalline materials. Because stresses must be applied along several crystal lographic axes, more

samples are required for measurements on crystalline materials than for measurements on isotropic

materials.

2.4.3 Results

Measurements of absolute and relative stress-optical coefficients have been made on chalcogenide

glass, AS2S3 glass, and polycrystalline ZnSe. The results are given in Table 1. The data for AS2S3

are presented for three wavelengths, 0.6328 ym, 1.15 ym, and 10.6 ym. Data for the same wavelengths

are presented for polycrystalline ZnSe although absolute values are lacking at 10.6 ym. We have

assumed the ZnSe to be an isotropic material. Data for the chalcogenide glass are presented at the

infrared wavelengths.

Table 1. Stress-optical constants, q^j and qi2' ^^'^ elastic compliance, s^j/ units of 10"^^ m^/Hl.

AS2S3

0.6328 ym

1.15 ym

10.6 ym

2.606

2.452

2.354

In

7,63

7.64

8.23

6.36

6.54

6.95

- 1.27

- 1.10

-1.28

, ^12

- 18.6, - 18.8*^

Chalcogenide Glass

(Ge 33%, As 12%, Se 55%)

1.15 ym

10.6 ym

Polycrystalline ZnSe

0.6328 ym

1.15 ym

10.6 ym

2.5704

2.4919

2.578

2.465

2,408

5.32. 5.42

- 1.34

- 1.37

4.89

4.94

0.29

0.62

- 0.43

- 0.48

1.62

1.98

1.96

12.0, - 12.2*^, - 11.5®

-• 4.0

These values were not measured in this work, but are given because they were used to calculate the q^ _, The values for ZnSe are from single crystal data.

^Estimated accuracy of numbers from this work is ± 2%.

'F. W. Glaze, D. H. Blackburn, J. S. Osmalov, D. Hubbard, and Mason H. Black, J. Res. Natl. Bur. Std.

59, 83-92 (1957)

.

^Ray Hilton, private communication — value for Texas Instrxnnents. 'Ray Hilton, private communication — value for Bell Laboratories.

12
TO PRESSURE

WINDOW EACH

SIDE

Figure 7. Pressure vessel.
The birefringence of the above infrared glasses is of opposite sign to most optical glasses [17],

The is greater than the q^j of most optical glasses by a factor of ten, and q^j is greater

than the q^j of most optical glasses by a factor of three [18].

From the theory of photoelasticity and from the data, we expect that the refractive index of the

ZnSe will decrease under hydrostatic pressure. This behavior has been observed previously in single

crystal ZnS [19] . Since dn/dT for ZnS is positive [20] , it would be of interest to observe whether

the same is true for ZnSe. In addition, for ZnSe there is a large dispersion in <li2- Also included in Table 1 are the values we have obtained for Si2' Agreement with the values

of other workers is very good.

2 . 5 Summary

We have outlined the program of optical materials characterization at the National Bureau of

Standards. The properties that we are measuring are refractive index, change of index with temperature,

thermal expansion, stress-optical coefficients, and elastic constants. At the present time, primary

interest is in laser window materials at 10.6 urn. Data have been presented on chalcogenide glass,

AS2S3, polycrystalline ZnSe, and crystalline KCl. Measurements on these materials and on other infrared

laser window materials are in progress. In addition, we are developing more sensitive techniques

for measuring the stress-optical coefficients in materials that exhibit a small stress-optical effect.

A similar need exists for optical materials characterization in the ultraviolet. Techniques

similar to those we have used in the infrared can be employed in the ultraviolet should the need

arise

.

2.6 Acknowledgments

We would like to acknowledge the receipt of samples from Carl Pitha of AFCRL, Bennett Sherman of

the Servo Corporation, Ray Hilton of Texas Instruments, Phillip Klein of NRL, and Colonel William

Goldberg of AFML. We would like to thank W. J. McKean for his technical assistance.

14
2 . 7 References

[1] B. Bendow, P. D. Gianino, A. Hordvik, and L. H. Skoln:':, Optics Commun. 2.' ^1- .

[2] B. Bendow and P. D. Gianino, Appl. Phys. 2_, 1 (1973).

[3] C. S. Sahagian and C. A. Pitha, AFCRL72-0170 , 9 March 1972, Special Reports No. 135.

[4] C. A. Pitha, AFCRL-TR-73-0372 (1) , 19 June 1973, Special Reports No. 162, Vols. I and II.

[5] R. L. Abrams and D. A. Pinnow, J. Appl. Phys. 41, 2765 (1970).

[6] F. Twyman and J'. W. Perry, Proc. Phys. Soc. London 34_, 151 (1922).

[7] K. Vedaiti and S. Ramaseshan, in Progress in Crystal Physics , Vol. I, edited by R. S. Krishnan (Interscience Publishers, New York, London, 1958), pp. 102-138.

[8] C. Weir, 8. Spinner, I. H. Malitson, and W. J. Rodney, J. Res. Natl. Bur. Std. 58_, 189 (April 1957), RP2751.

[9] L. W. Tilton, J. Res. Natl. Bur. Std. 2_, 909 (1929), RP64.

[10] F. F. Martens, Ann. d. Phys. 6_, 603 (1901).

[11] A. Smakula, Office of Technical Services, U. S. Department of Commerce (October 1952), p. 81.

[12] Z. Gyulai, Z. Phys. 46, 80 (1927).

[13] Reference 11, page 66.

[14] J. B. Saunders, J. Res. Natl. Std. 35_, 157 (1945), RP1668.

[15] R. S. Krishnan, in Progress in Crystal Physics , Vol. I (Interscience Publishers, New York and

London, 1958)

[16] N. Bom and E. Wolf, Principles of Optics , (Pergamon Press, 1970), p. 303.

[17] R. M. Waxier and A. Napolitano, J. Res. Natl. Bur. Std. 69A , 325 (1965).

[18] K. Vedam, Proc. Indian Acad. Sci. [A] 31_, 450 (1950).

[19] R. M. Waxier, IEEE J. Quant. Electron. QE-7 ,' 166 (1971)

[20] Reference 15, page 146.

15
NBS-l 14A (REV. 7-73)

U.S. DtPT. OF COMM. ]. PUIil.K, A 1 K).\ OK KI.PcJKT BIBLIOGRAPHIC DATA

SHEf^T NBSIR 74-525

2. Gov't Accession

No.

3. Recipient's Accession No.

4, TITLl: AND SUBTITLt

Optical Materials Chciracterization

5. Publication Date

.Till \r T Q7d

6. Performing Organization Code

7. AUTHOR(S) Albert Feldman, Deane Horowitz, Roy M. Waxier, 8. Performing Organ. Report No. NBSIR 74-525

9. PERFOKMir^G ORGANIZAYION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Vt'ork Unit No. 3130442

11. Contract/Grant N'o. 2620/4D10

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

Advanced Research Projects Agency

Arlington, Virgiiiia 22209

13. Type of Report & Period Covered

Semi-Annual Tech. Report

1_1_74 to fi-.'.n-74

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less (actual sunmiary of most significant information. If document include.-^ n significant

bibliography or literature survey, mention it here.)

A program has been established for meastiring refractive index, n, stressoptical constants, q.^, change of index with temperature, dn/dT, thermal expansior.

coefficient, a, and elastic compliances, s.., of infrared laser window materials.

These parameters are necessary for determining the optical distortion that

occurs in windows due to heating by the absorption of high power laser radiation,

n and dn/dT are measured over a spectral range 0.2 to 50 ym by the method of

minimum deviation on precision spectrometers. Twyman-Green and Fizeau interferometei

s

which operate at 0.6328 ym, 1.15 ym, and 10.6 ym, are used for measuring g. ., a,

dn/dT and s. .. Materials cvirrently xmder study are polycrystalline ZnSe, i32S3

glass, chalcigenide glass (Ge 33%, As 12%, Se 55%) , and KCl. Results are given

for n and dn/dT in KCl, and q, . and 3^2 in ZnSe, AS2S3 glass, and chalcogenide glass.

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)

AS2S3; chalcogenide glass; coefficient of thermal expansion; elastic constants;

infrared laser window materials; KCl; photoelasticity; polycrystalline ZnSe; refractive index; stress-optical constants; thg^-rmaT rnf>ffi ripnl- nf y-pf-rptr.tAvf^ index.

18. AVAILABILITY Unlimited

I For Official Distribution. Do Not Release to NTIS

I

' Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CH

I

^ Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SEC:UR!TY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

15

22. Price

USCOMM-DC 29042-P74