NBSIR 77-1304 (ARPA)

Optical Materials Characterization

Albert Feldman, Deane Horowitz and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Marilyn J. Dodge and Warren K. Gladden

Optical Physics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

August 1 977

Semi-Annual Technical Report

Period Covered: February 1, 1977 to July 31, 1977

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 22209

NBSIR 77-1304 (ARPA)

OPTICAL MATERIALS CHARACTERIZATION

Albert Feldman, Deane Horowitz and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

and

Marilyn J. Dodge and Warren K. Gladden

Optical Physics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

August 1977

Semi-Annual Technical Report

Period Covered: February 1, 1977 to July 31, 1977

ARPA Order No. 2620

Prepared for Advanced Research Projects Agency

Arlington, Virginia 2209

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Director
V

>

.

. 1 •, B

i

••

• :
OPTICAL MATERIALS CHARACTERIZATION

Albert Feldman, Deane Horowitz and Roy M. Waxier

Inorganic Materials Division

Institute for Materials Research

Marilyn J. Dodge and Warren K. Gladden

Optical Physics Division

Institute for Basic Standards

ARPA Order No

Program Code Number. . . .

Effective Date of Contract

Contract Expiration Date .

Principal Investigator . .

2620

4D10

January 1, 1974

December 31, 1977

Albert Feldman

(301) 921-2840

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 expressed or implied, of the Advanced

Research Projects Agency or the U.S. Government.
OPTICAL MATERIALS CHARACTERIZATION

Abstract

The refractive index of fusion cast CaF

2 was measured at room temperature over the wavelength range 0.2144 ym to 8.662 ym and the data were

fitted to a Selmeier type equation. Measurements of refractive index of

hot forged CaF

2

were extended to the wavelength range 0.2024 ym to

0.2483 ym. Data are presented for dn/dT of single crystal specimens of

CaF

2

, BaF

2

, reactive atmosphere processed (RAP) KC1 and KBr, LiF, NaF,

and^SrF

2

, and polycrystalline chemical vapor deposited (CVD) ZnSe and

ZnS. Tne measurements were done by the method of Fizeau interferometry

over the temperature range -180° to 200 °C at the wavelengths 0.6328 ym,

1.15 ym, 3.39 ym and 10.6 ym. Data are presented for the refractive

indices, the linear thermal expansion and dn/dT of Lexan and Plexiglas 55.
1

Table of Contents

1. Technical Report Summary 1

1.1 Technical Problem 1

1.2 General Methodology 1

1.3 Technical Results 2

1.4 Department of Defense Implications 3

1.5 Implications for Further Research 3

2. Technical Report 4

2.1 Refractive Index of Fusion-Case Calcium Fluoride - Marilyn J. Dodge and Warren K. Gladden 4

2.1.1 Introduction 4

2.1.2 Experimental Technique 4

2.1.3 Index Data 5

2.1.4 Conclusions 7

2.1.5 References 8

2.2 Temperature Derivative of Refractive Index of Infrared

Window Materials - Albert Feldman, Deane Horowitz and

Roy M. Waxier 11

2.2.1 Introduction 11

2.2.2 Experimental Method 11

2.2.3 Results and Discussion 12

2.2.4 References 12

3. Acknowledgments 37
/i
1

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 Darameters; 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 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 th^ 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 y

m

to 50 ym.

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

a from -180 °C to 800 °C.

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 from -180 °C to 800 °C. We obtain dn/dT from a knowledge of the expansion coefficient and by measuring the shift of Fizeau
- 2 -

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 specimens.

We measure piezo-optic 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 con- stants and elastic compliances.

In materials with small piezo-optic constants or in materials that

cannot withstand large stresses, we use interferometers designed to

measure fractional fringe shifts. At 10.6 ym we use a modified TwymanGreen interferometer which has a sensitivity of 0.01 A. At 632.8 nm, we

use a modified Dyson interferometer which has a sensitivity of 0.002 a. When using these interferometers to measure piezo-optic constants we must know the elastic constants of the material under test.

1.3 Technical Results

The refractive index of fusion cast CaF~ was measured from 0.2144 urn to 8.662 ym at room temperature and the results were fitted to a Selmeier

type equation. These results agreed well with earlier measurements on single crystal CaF~. In an extension of previously reported measurements,

the refractive index of hot forged CaF

? was measured from 0.2024 ym to

0.2483 ym.

We present data of dn/dT that we have obtained for the following

materials at the specified wavelengths:

.6328 ym 1.15 ym 3.39 ym 10.6 ym

BaF^ x CaF^ x KBr (RAP)* x

KC1 (RAP)* x

Li F x

x

x

X

X

X

X

X

X

X

X NaF X X X SrF^ x ZnS (CVD)

+

ZnSe (CVD)

+

x

x x

x

x

x

x

x

x

x

x

x

x

reactive atmosphere processed

+ chemical vapor deposited.
3

The measurements were made by the method of Fizeau interferometry

over the temperature range -180° to 200 °C. All the measurements on

ZnS (CVD) and the measurements at 1.15 ym and 10.6 ym on the other

materials are new. The other numbers were included in our previous

report but are included here for completeness.

In addition to the above measurements on potential laser window

materials, we have measured the refractive index, the linear thermal

expansion coefficient and dn/dT of Plexiglas 55 and Lexan, materials

used in the construction of aircraft windows. This work was done at the

request of Captain Hurst of the Air Force Materials Laboratory at WrightPatterson Air Force Base. The thermal expansion coefficient and dn/dT

of Plexiglas 55 had been presented in our previous report, but the

values for dn/dT were found to have a small error so we present the

corrected values in this report.

1 .4 Department of Defense Implications

The Department of Defense is currently constructing high-power

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

We plan to comDlete the interferometric measurements of dn/dT and

photoelastic constants in the infrared. We plan to measure dn/dT of

NaCl and MgF

2 at .6328 ym, 1.15 ym, 3.39 ym, and 10.6 ym. We plan to

measure the photoelastic constants of CaF^, BaF^, and SrF^ at 3.39 ym.

Measurements of refractive index will be completed on ZnS (CVD)

through the infrared. Refractive index measurements on MgF

2 will be

started.

Apparatus will be assembled for measuring photoelastic constants

and dn/dT in the ultraviolet. We are awaiting the arrival of an argon

ion laser for measurements at 351 nm. We have procured a frequency

doubler for producing 257 nm radiation from the argon ion laser line at

514 nm. After the system is assembled we plan to start measuring dn/dT

and photoelastic constants on fused Si0

2

, Al^, and CaF

2

.
2.2.1 Technical Report

Refractive Index of Fusion-Cast Calcium Fluoride

2.1.1 Marilyn J. Dodge and Warren K. Gladden

Introduction

The search for improved transparent optical component materials to be

used in large, high-resolution systems i ncorporating high-power lasers has

resulted in the development of new techniques for material fabrication.

Hot-forging and fusion-casting [1 are two techniques developed for the

fabrication pf alkaline-earth fluorides including calcium fluoride. Refractive index measurements from 0.25 pm to 8.0 ym have been previously

reported [2] for a sample of Harshaw2 hot-forged CaF 2

- Since that report,

the wavelength range of index determinations on this sample have been extended

to 0.2 ym.

A large prismatic sample of Raytheon developed fusion-cast CaF

2 was provided by Raytheon Corporation for refractive index measurement. The

prism has a refracting angle of approximately 70° and two polished faces

about 2.5 cm x 4 cm. Measurements have been made on this specimen from

0.2144 ym to 8.662 ym.

2.1.2

Experimental Technique

A precision spectrometer , shown schematically in figure 1 [3], was used

to determine refractive index by means of the minimum-deviation method. From

the ultraviolet to 2.0 ym, the index was determined at known emission wavelengths of mercury, cadmium, helium, and zinc. Beyond 2 ym, a glo-bar was

used for the radiant-energy source and measurements were made at known absorption bands of water, carbon dioxide, polystyrene and 1,2-4 trichlorobenzene.

A series of narrow-band interference filters was also used between 3.5 ym and

6.5 ym. A thermocouple with a cesium iodide window was used for signal detection in the visible and infrared and a photo-multiplier tube was used for

the detector in the ultraviolet. The scale of this Spectrometer can be read

to 1.0 second of arc. The accuracy of this scale permits the determination

of the refractive index of good optical quality material to within 2 x 10"5

over a wide wavelength range.

1. Figures in brackets indicate the literature references at the end of

this paper.

2. The use of company and brand names in this paper are for identification

purposes only and in no case does it imply recommendation or endorsement by

the National Bureau of Standards and it does not imply that the materials

used in this study are necessarily the best available.
- 5

-

The index of the cast CaF 2 was determined from 0.214438 to 8.662 pm

at an average controlled room temperature near 21.7°C. Additional index

data were obtained for the hot-forged CaF 2 from 0.202458 ym to .25 ym at

21 .0°C.

The experimental data for the fusion-cast specimen was fitted to a threerterm Sel lmeier-type dispersion equation [4] of the form n^-l = E[A • XV (X2-X . ) ] , and a new fit was obtained for the hot-forged CaF 2

- TheJ index o-r refraction is represented by n, A is the wavelength of

interest in ym, the Aj's are the calculated wavelengths of maximum

absorption and the Aj's are the calculated oscillator strengths corre- sponding to the absorption bands. The X

j

1 s and Aj's are not intended to

have any physical significance. Primary emphasis is given to procuring

a mathematical fit of the measured data useful for interpolation.

2.1.3 Index Data

The constants calculated for each disperson equation, the number of

wavelengths fitted and the average absolute residual (the average

difference between the experimental values and the calculated values)

are given in table 1

.

Table 1: Constants for Dispersion Equations for CaF

2 Constant Hot-Forged 20.8°C Fusion-Cast 21 .7°C

A

i 0.36648840 0.3439319

A

2

0.6724568 0.6948269

A

3

4.9928893 3.8902192

A

1 0.0167162 0.0127821

A 2 0.0946259 0.0936663

A 3

39.2563990 34.82590

No . of wavelengths 75 60

Wavelength range

of fit 0.2267-8.03 ym 0.2144-8.662 ym

Average absolute

residual of index

x 10 5 2.8 2.1

The average absolute residual is an indication of the overall accuracy

of the experimental data. Generally, the largest residuals were in the

IR beyond 5 ym, where 35 strong atmospheric absorption bands existed

between 5.0 and 7.3 ym. Because of the large size of the prisms and the

apparent excellent quality of both samples, these bands were sharp and
- 6

-

their minima were easily determined. Therefore, the index determinations

are not considered to be any less accurate than in the UV or near IR.

The wavelengths of these atmospheric bands were assigned from values in

the 1 i terature[5,6]. The uncertainties in the wavelength values would

be difficult to define due to differences in the laboratory conditions

and the existence of many weak bands which could effect the wavelengths

of nearby strong bands. An error of 0.1 °l in wavelength would result in an index residual of 9 x 10"^ in this particular material.

The constants given in table 1 refer only to these two samples at

the given temperature. Since the refractive index of samples of similar

materials fabricated at different times can vary from one sample to

another, caution should be used when either of these parameter sets is

used to interpolate an index value at a specific wavelength for the

purpose of describing another specimen. When using these parameters to

obtain index values, interpolation should only be attempted within the

wavelength range of the experimental data.

Although the hot-forged sample was measured at 0.202459 pm, a mean

of two Hg lines, a satisfactory fit could not be accomplished below

0.226747 pm. When any of the 3 measured values at wavelengths below

.226746 pm were included in the fit, the A-| and A 2 values increased to

0.077 and 0.192 respectively, which resulted in changes in the calculated index of the order of -1 x 10" 4 at wavelengths up to 0.27 pm with

large residuals in this region. This fitting-phenomena is characteristic when an attempt is made to fit experimental data close to a region

of strong absorption to a Sellmeier-type equation. Although the absorption properties of this sample are not known in the spectral region

around .2 pm, it appears that there could be an absorption in this area large enough to affect the refractive index to an extent that it can not

be fitted. The final fit which was obtained resulted in A], A 2 , A] and

Ao values which are close to those obtained for the fusion-cast sample,

which would be expected. The A 2 values are also close but below the

known sharp ultraviolet cutoff of .125 pm for single crystal Ca [ 7]

.

The refractive index of each specimen was calculated at regular

wavelength intervals by using the appropriate fitted parameters. The

results for the fusion-cast material are plotted as a function of wavelength in figure 2.

The index values obtained for both types of material are compared

in figure 3 with those obtained by I. H. Malitson on single crystal

CAF 2 [8]. The single crystal data, corrected to 20.8°C is represented by

the "zero" line. The difference in index between the single crystal and

both the hot-forged CaFo and cast CaF 2 reaches a maximum close to 0.3 pm.

This index variance could be evidence of a weak absorption band near

0.3 pm. The Flarshaw catalog [7] shows transmission runs for two grades

of CaF 2

, the UV grade in which this band does not appear, and the optical

grade, sold for use in IR components, in which the band does exist. Assuming this band did not exist in the single crystal studied previously.
the difference in index would become more negative, reaching the maximum

An, then receeding as the index of the new CaF0 anoroaches that of the

single crystal in the red region of the soectrbm. The refractive index

of the fusion cast sample is within 1 x 1C) of the index for the single

crystal material between 1 and 8 ym, which is well within the exDerimental

error of both sets of data. The refractive indexes of the cast material,

measured at 21.7 °C, were not corrected for temperature. However, since

the accepted dn/dT (°C)~ of CaF^ is about -1 x 10~ b (°C)~ [8], the

effect on An of the cast sample caused by the temperature difference

would be within the experimental error. The dip in the An curve for the

forged sample was discussed in the earlier report [1]. Since this

phenomenon is not exhibited by the cast material, it appears to be a property peculiar to the forged specimen.

2.1.4 Conclusions

The refractive index of hot-forged CaF~ and fusion-cast CaF~ are

in good agreement from .3 ym to about 1.5 ym. The index of the fusioncast material does not seem to be affected quite as much by the absorption

in the IJV as is the index of the forged specimen. Between 1 and 8 ym

the fusion-cast sample has an index very close to the sinqle crystal

index, whereas the forqed sample shows a change in index in the 5 ym

region which might be related to an absorption effect. Without further

study on other samples of hot-forged CaF^, it is not possible to determine if this phenomenon is peculiar to tne particular sample in this

study, or if it is the result of something in the fabrication technioue.
- 8 -

2.1.5 References

1. Newberg, R. and Pappis, J., Fifth Annual Conference on Infrared

Laser Window Materials, P. 1065, UDRI (Feb. 1976).

2. Dodge, M. J., "Laser Induced Damage in Optical Materials: 1976,"

P. 64, NBS Special Publication 462, U. S. Govt. Printing Office,

Wash. (1976).

3. Rodney, William S. and SDindler, Robert J., J. Res. Nat'l. Bur.

Stds . (US), 5]_, 123, (1953).

4. Sutton, Loyd E. and Stavroudis, Orestes N., J. Opt. Soc. Am. 5^,

901 (1961 ).

5. Downie, A. R. , Magoon, M. C. , Purcell, Thomasine and Crawford,

Bryce Jr., J. Opt. Soc. Am. 43, 941 (1953),

6. Benedict, W. S,, Claassen, H. H. and Shaw, J. H., Res, MBS

49, 91 (1952).

7. Harshaw Optical Crystals, the Harshaw Chemical Co., 22, (1967).

8. Malitson, I. H., Applied Optics 2^, 1103 (1963).
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COMPARISON OF REFRACTIVE

INDEX OF CaFrt

• • ••

• V

.*•

_L

• • •

> : i

0.1 0.5 1.0

WAVELENGTH (^m)

5.0 10.0

Fig. 3 The differences in the refractive index of hot-forged CaF2 and

fusion-cast CaF 2 from single crystal CaF£ near 21 °C as a function of wavelength (logarithmic scale). The index of the

single crystal is represented by the zero line, data for the

hot-forged by the and data for the fusion-cast by *.
11

2.2 Temperature Derivative of Refractive Index of Infrared Window

Materials

Albert Feldman, Deane Horowitz and Roy M. Waxier

2.2.1 Introduction

When high-power radiation propogates through a laser window, the

residual absorption causes a temperature rise in the window. The temperature distribution is, in general, nonuniform and hence, will distort

the wavefront of the beam. The distortion arises from: the change of

refractive index with temperature; the change of thickness with temperature; the change of refractive index and thickness caused by stresses

produced by thermal gradients. In order to predict the distortion of a laser beam wavefront from the laser energy deposited in a window, one requires certain material parameters. These include the absorption

coefficient, the refractive index n, the change of index with temperature dn/dT, the piezo-optic constants q.., the thermal expansion coefficient a, and the elastic constants s . • or c... It is the purpose of the

Optical Materials Characterization Program at the National Bureau of

Standards to measure n, dn/dT, q. . and if necessary, a and s^.

In this report we present data of dn/dT on CaF

?

, BaF

?

, KBr (RAP),

KC1 (RAP), LiF, NaF, S^, ZnS (CVD), and ZnSe (CVDj. The measurements

were made over the temperature range -180 °C to 200 °C at the wavelengths

0.6328 um, 1.15 ym, 3.39 ym and 10.6 ym, except that ZnS was not measured

at 0.6328 ym due to excessive light scattering and CaF^, LiF, and NaF,

were not measured at 10.6 ym because of absorption in the specimens.

Some of the data were presented in our previous report, but are included

here for completeness.

In addition, we present data on refractive index, the linear thermal expansion coefficient, and dn/dT of Plexiglas 55 and Lexan. The

measurements were made at the request of Captain Hurst of the Air Force

Materials Laboratory for determining the effect of heating caused by a nuclear explosion on the optical properties of aircraft windows. These

measurements were supported in part by funds provided by the Air Force

Materials Laboratory.

2.2.2 Experimental Method

We measured dn/dT and linear thermal expansion by the method of

Fizeau interferometry , which has been described in detail in our previous

report [1]. The refractive indices of Plexiglas 55 and Lexan were measured on a V-block refractometer [2].
12

2.2.3 Results and Discussion

In figures 4-12, we plot dn/dT as a function of temperature for

BaF

2

, KBr (RAP), KC1 (RAP), LiF, NaF, SrF

2

, ZnS (CVD) and ZnSe

. ATI of the specimens used were from single crystal material

except for the ZnS and ZnSe which were polycrystalline. The points in

each of the figures are the measured values. The data were fitted to a third degree polynominal in the temperature by the method of least

squares and the results of the fit are tabulated in tables 2-10. The errors in the table are the standard deviation of the experimental data

to the least squares fit. The refractive indices, the specimen thicknesses and references to the thermal expansion coefficient all of which

were used in the computation of the results, are given in Table 11.

In figure 13 we show the linear thermal expansion coefficient of

Lexan as a function of temperature. Figure 14 is a plot of dn/dT of

Lexan as a function of temperature. In figure 15, we present a cor- rected plot of dn/dT as a function of temperature for Plexiglas 55. For

completeness, we also give the linear thermal expansion coefficient of

Plexiglas 55 as a function of temperature in figure 16. The refractive

indices of Lexan and Plexiglas 55 at four wavelengths in the visible are presented in Table 12.

As discussed in our previous report, R. J. Harris, et al . [3] in a recent paper, presented dn/dT data on a series of materials including

BaF

2

, CaF

2

, KC1 , ZnS, and ZnSe. After correcting for their input parameters of refractive index and thermal expansion, we find good agreement

between our values of dn/dT and their values for BaF^, CaFp, and KC1.

However, there is disagreement in the values for ZnS and ZnSe. In a measurement on ZnSe at 0.6328 ym using an immersion technique similar

to the technique used by Harris et al . , we find that our newly measured

values agree with our earlier measurement and disagree with the values

of Harris et al

.

2.2.4 References

[1] A. Feldman, D. Horowitz, R. M. Waxier, M. J. Dodge, and W. K. Gladden, Optical Materials Characterization , National Bureau of

Standards Internal Report, NBSIR 77-1219 (March 1977).

[2] A. Feldman and D. Horowitz, J. Opt. Soc. Amer. 59, 1406 (1969).

[3] R. J. Harris, G. T. Johnston, G. A. Kepple, P. C. Krok, and H.

Mukai, Appl . Optics 1_6, 436 (1977).
13 -

Table 2. dn/dT of BaF^ (10'V 1

)

Temperature

(°C)

Wavelength (ym)

0.6328a 1.15

b

3. 39

b

10.

6

b

-180 - .86 - .81 - .81 - .73

-160 - .98 - .96 - .95 - .85

-140 -1.09 -1 .08 -1.07 - .96

-120 -1.19 -1.19 -1.17 -1.05

-100 -1.27 -1.29 -1.26 -1.13

- 80 -1.35 -1.37 -1.34 -1 .21

- 60 -1.41 -1.44 -1 .41 -1.27

- 40 -1.47 -1.50 -1.47 -1.32

- 20 -1.52 -1.55 -1.51 -1.37

0 -1.56 -1.59 -1.56 -1.41

20 -1.60 -1.62 -1.59 -1.45

40 -1.63 -1.66 -1.62 -1 .48

60 -1.66 -1.69 -1 .66 -1.51

80 -1.70 -1.71 -1.68 -1.54

100 -1.73 -1.74 -1.71 -1.57

120 -1.76 -1.77 -1.75 -1.60

140 -1.79 -1 .80 -1.78 -1.63

160 -1.83 -1.84 -1.82 -1.66

180 -1.87 -1.88 -1.87 -1.70

200 -1.92 -1.93 -1.92 -1 .75

a Standard deviation from a third degree polynomial fit is 0.02

^Standard deviation from a third degree polynomial fit is 0.03
- 14 -

Table 3. dn/dT of CaF

2 (lCfV 1

)

Temperature

(°C)

Wavelength (pm)

0.6328a 1.1

5

a

3. 39

b

-180 - .40 - .41 - .40

-160 - .54 - .56 - .52

-140 - .66 - .68 - .63

-120 - .77 - .78 - .73

-100 - .85 - .87 - .82

- 80 - .93 - .95 - .89

- 60 - .99 -1.01 - .95

- 40 -1.03 -1.06 -1 .00

- 20 -1.07 -1.10 -1 .05

0 -1.10 -1.13 -1.09

20 -1.13 -1.15 -1.12

40 -1.15 -1.18 -1 .14

60 -1.17 -1.20 -1.17

80 -1.19 -1.22 -1.19

100 -1.21 -1.24 -1 .21

120 -1.23 -1.26 -1 .23

140 -1.26 -1.29 -1.25

160 -1.30 -1.32 -1.27

180 -1.34 -1.36 -1.30

200 -1.40 -1.41 -1 .34

a Standard deviation from a third degree polynomial fit is 0.02

Standard deviation from a third degree polynomial fit is 0.03
- 15 -

Table 4. dn/dT of KBr (10“ 5 K

_1

)

Wavelength (yin)

Temperature

(° C ) 0 . 6328a

1 . 1

5

a

3 . 39

a 10 . 6

b

-180 - 2.95 - 3.05 - 3.05 - 3.06

-160 - 3.17 - 3.26 - 3.26 - 3.24

-140 - 3.36 - 3.44 - 3.44 - 3.40

-120 - 3.53 - 3.59 - 3.60 - 3.54

-100 - 3.67 - 3.73 - 3.74 - 3.66

- 80 - 3.78 - 3.84 - 3.85 - 3.77

- 60 - 3.88 - 3.94 - 3.95 - 3.86

- 40 - 3.96 - 4.02 - 4.03 - 3.93

- 20 - 4.02 - 4.09 - 4.10 - 4.00

0

- 4.08 - 4.14 - 4.16 - 4.06

20 - 4.12 - 4.19 - 4.21 - 4.11

40 - 4.16 - 4.23 - 4.25 - 4.16

60 - 4.19 - 4.27 - 4.29 - 4.20

80 - 4.23 - 4.31 - 4.33 - 4.25

100 - 4.27 - 4.35 - 4.36 - 4.29

120 - 4.31 - 4.39 - 4.40 - 4.33

140 - 4.36 - 4.44 - 4.44 - 4.38

160 - 4.42 - 4.49 - 4.49 - 4.43

180 - 4.49 - 4.56 - 4.55 - 4.49

200 - 4.58 - 4.63 - 4.62 - 4.56

a Standard deviation from a third degree Dolynomial fit is 0.03

^Standard deviation from a third degree polynomial fit is 0.06
16 -

Table 5. dn/dT of KC1 (lO'V 1

)

Temperature

(°c)

Wavelength (ym)

0. 6328a 1.1

5

a 3. 39

a 10.

6

b

-180 -2.32 -2.35 -2.39 -2.33

-160 -2.52 -2.55 -2.58 -2.50

-140 -2.70 -2.74 -2.75 -2.65

-120 -2.86 -2.90 -2.91 -2.80

-100 -3.00 -3.05 -3.05 -2.93

- 80 -3.13 -3.17 -3.17 -3.04

- 60 -3.24 -3.29 -3.28 -3.15

- 40 -3.35 -3.39 -3.38 -3.24

- 20 -3.43 -3.48 -3.47 -3.33

0 -3.51 -3.55 -3.55 -3.41

20 -3.58 -3.62 -3.62 -3.48

40 -3.65 -3.68 -3.69 -3.54

60 -3.70 -3.74 -3.75 -3.60

80 -3.76 -3.79 -3.80 -3.65

100 -3.81 -3.84 -3.85 -3.70

120 -3.86 -3.89 -3.90 -3.74

140 -3.91 -3.94 -3.94 -3.79

160 -3.96 -4.00 -3.99 -3.83

180 -4.02 -4.05 -4.04 -3.87

200 -4.08 -4.11 -4.09 -3.91

a Standard deviation from a third degree polynomial fit is 0.02

^Standard deviation from a third degree polynomial fit is 0.04
17 -

Table 6. dn/dT of LiF (lO'V 1

)

Temperature

(°C)

Wavelength (ym)

0. 6328

a

1 . 1

5

b

3. 39

b

-180 - .36 - .38 - .40

-160 - .63 - .64 - .60

-140 - .86 - .86 - .78

-120 -1.05 -1.05 - .93

-100 -1.21 -1.21 -1.06

- 80 -1.34 -1.34 -1.16

- 60 -1.44 -1 .45 -1.25

- 40 -1.52 -1.53 -1.32

- 20 -1.59 -1.60 -1.37

0 -1.63 -1.65 -1.42

20 -1.67 -1.69 -1.45

40 -1.70 -1.73 -1 .48

60 -1.72 -1.75 -1.51

80 -1.75 -1.77 -1.53

100 -1.78 -1.79 -1.56

120 -1.81 -1.81 -1.59

140 -1.85 -1 .84 -1.63

160 -1.91 -1.88 -1.67

180 -1.99 -1.92 -1.73

200 -2.09 -1 .99 -1 .80

a Standard deviation from a third degree polynomial fit is 0.02

Standard deviation from a third degree polynomial fit is 0.04
18 -

Table 7. dn/dT of NaF (lCfV 1

)

Temperature

(°c)

Wavelength (ym)

0. 6328a1 . 1

5

a

3. 39

a

-180 - .51 - .53 - .55

-160 - .67 - .71 - .69

-140 - .81 - .85 - .82

-120 - .92 - .96 - .92

-100 i oo -1 .06 -1.00

- 80 -1.07 -1.13 -1.06

- 60 -1.12 -1.18 -1.11

- 40 -1.16 -1.21 -1.14

- 20 -1.19 -1.24 -1.17

0 -1.20 -1.25 -1.18

20 -1.21 -1.26 -1.19

40 -1.21 -1.26 -1.19

60 -1.22 -1.26 -1.19

80 -1.22 -1.26 -1.20

100 -1.22 -1.26 -1.20

120 -1.24 -1.27 -1.21

140 -1.26 -1.30 -1.23

160 -1.29 -1.33 -1.26

180 -1.33 -1.39 -1.30

200 -1.39 -1.46 -1.35

a Standard deviation from a third degree polynomial fit is 0.05
- 19 -

Table 8. dn/dT of SrF

2

(10‘

5 K

-1

)

Temperature

(°c)

Wavelength (ym)

0. 6328a 1.15

b

3.39° 10.

6

d

-180 - .56 - .55 - .56 - .38

-160 - .69 - .69 - .68 - .51

-140 - .81 - .81 - .80 - .63

-120 - .90 - .91 - .89 - .72

-100 - .98 -1.00 - .97 - .80

- 80 -1.05 -1.07 -1 .04 - .86

- 60 -1.11 -1.13 -1.10 - .91

- 40 -1.15 -1.17 -1.15 - .95

- 20 -1.19 -1.21 -1.19 - .98

0 -1.22 -1.24 -1.22 -1 .00

20 -1.24 -1.26 -1.24 -1.02

40 -1.25 -1.28 -1.26 -1.03

60 -1.27 -1.29 -1.27 -1.03

80 -1.28 -1.30 -1 .28 -1.03

100 -1.29 -1.31 -1.29 -1.04

120 -1.30 -1.32 -1.29 -1 .04

140 -1.32 -1.33 -1.30 -1.05

160 -1.34 -1.35 -1.31 -1.06

180 -1.36 -1.37 -1.32 -1.08

200 -1.39 -1 .40 -1.33 -1.10

a Standard deviation from a third degree polynomial fit is 0.02

Standard deviation from a third degree polynomial fit is 0.01

r Standard deviation from a third degree polynomial fit is 0.03

^Standard deviation from a third degree polynomial fit is 0.05
- 20 -

Table 9. dn/dT of CVD ZnS

Temperature

(°c)

Wavelength (pm)

1 . 1

a

3. 39

a 10.

a

-180 3.5 2.8 2.7

-160 3.7 3.1 3.0

-140 3.8 3.3 3.3

-120 4.0 3.5 3.5

-100 4.1 3.7 3.7

- 80 4.2 3.9 3.8

- 60 4.3 4.0 3.9

- 40 4.4 4.1 4.0

- 20 4.5 4.1 4.0

0 4.5 4.2 4.1

20 4.6 4.2 4.1

40 4.6 4.3 4.1

60 4.7 4.3 4.1

80 4.7 4.3 4.1

100 4.7 4.3 4.2

120 4.8 4.4 4.2

140 4.8 4.4 4.3

160 4.9 4.4 4.4

180 4.9 4.5 4.5

200 5.0 4.6 4.7

Standard deviation from a third degree polynomial fit is 0.2
I - 21 -

Table 10. dn/dT of CVD ZnSe (lO'V 1

)

Temperature

(°C)

Wavelength (um)

0. 6328

a

1 . 1

5

a

3. 39

a 10.

6

a

-180 7.6 5.4 5.0 4.9

-160 8.2 5.7 5.2 5.1

-140 8.7 6.0 5.4 5.4

-120 9.1 6.3 5.6 5.5

-100 9.4 6.5 5.8 5.7

- 80 9.7 6.6 5.9 5.8

- 60 10.0 6.7 6.0 5.9

- 40 10.2 6.8 6.1 6.0

- 20 10.3 6.9 6.1 6.0

0 10.5 7.0 6.2 6.1

20 10.6 7.0 6.2 6.1

40 10.7 7.0 6.2 6.1

60 10.8 7.1 6.3 6.1

80 10.9 7.1 6.3 6.2

100 11.0 7.2 6.3 6.2

120 11.1 7.2 6.4 6.3

140 11.3 7.3 6.4 6.3

160 11.5 7.4 6.5 6.4

180 11.8 7.6 6.6 6.6

200 12.1 7.8 6.7 6.7

a Standard deviation from a third degree polynomial fit is 0.1
22 -

Table 11. Data Used in Computation of dn/dT

Material

Refractive

632.8 nm 1 . 1 5 ym

Index, n 0

3.39 ym 10.6 ym

4 o (mm)

a

BaF^ 1 . 47 3 a

1 . 47

a 1.460a

1 .393

a 13.16 b

CaF^ 1 . 433 C

1 .43

C 1.416 c

- 13.41 b,d,e,f

KBr(RAP) 1 . 57

g

1 .542 g1 .536 g 1.525 q 11.83 h KC1 (RAP) 1 . 488J

1 . 478"* 1 . 473 J

1 . 454 J 11.87 h

Li F 1 .392

k

1 . 386

k

1 . 360

k

- 5.59 h NaF 1 .325

1

1 . 321

1

1 . 31

1 - 12.21 h

SrF

2

1 . 436

m

1 . 43

n

1 . 425

n

1 . 31

n 13.15 b

ZnS(CVD) - 2. 28 p 2.25° 2. 21 p 4.47 q,r

ZnSe(CVD) 2 .590

s 2.47 s 2.436 s 2.403 s 17.49 q,r

a I.H. Malitson, J. Opt. Soc. ^A.C. Bailey & B. Yates, Proc. Phys.

Amer. 54, 628 (1964). Soc. 9]_, 390 (1967).

C I.H. Malitson, Appl . Opt. 2,

1103 (1963).

e S.S. Sharma, Proc. Indian Acad.

Sci. A31_, 261 (1950).

g R.E. Stephens, E.K. Plyler,

W.S. Rodney A R.J. Spindler,

J. Opt. Soc. Amer. 43^ 111

(1953).

g A. Feldman, D. Horowitz, R.M.

Waxier, I.H. Malitson & M.J.

Dodge, Optical Materials

Characteri zation, NBSIR 76-1010

(Feb. 1976).

^S.S. Ballard, J.S. Browder & J.F. Ebersole, in American

Insti tute of Physics Handbook , Dwight E. Gray Ed. (McGrawHill Book Co., 1972) pp. 6-12

to 6-57.

n Estimated

^D.N. Batchelder A R.0. Simmons, J. Chem. Phys. 411, 2324 (1964).

f

S. Valentiner & J. Wallot, Ann. Phys.,

Lpz 46, 837 (1915).

^R.K. Kirby, T.A. Hahn, K B.D. Rothrock,

American Insti tute of Physics Handbook , Dwight E. Gray ed. {McGraw-Hill Book

Co., 1972) pp 4-119 to 4-142.

k L.W. Tilton & E.K. Plyler, J. Res. NBS

47, 25 (1951). m

D.C. Stockbarger, 0SRD Report No. 4690,

Dec. 31, 1944.

Reference [3].

rData to be published in the next

report.

S A. Feldman, D. Horowitz, R.M. Waxier,

I. Malitson & M.J. Dodge, Optical

Materials Characterization, NBSIR 75-781

(Aug. 19751:

g J.S. Browder & S.S. Ballard,

Appl. Optics 8, 793 (1969).
- 23 -

Table 12. Refractive Index of Lexan and Plexiglas 55

Lexan

n (486.1 nm) 1.5995

n (589.3 nm) 1.5854

n (632.8 nm) 1 . 5816

n (656.3 nm)

Plexiglas 55

1 .5014

1.4950

1.4934

1.5800 1 .4928
- 24 -

I c

TEMPERATURE

(°C)
- 25 -

CM

i

cn

TEMPERATURE

(°C)
- 26 -

Fig. 6. dn/dT of KBr (RAP) as a function of

temperature.
- 27 -

Fig. 7. dn/dT of KC1 (RAP) as a function of

temperature.
- 28 -

(^g.OOlP/uP

TEMPERATURE

(°C)
29 -

(

* 01) Ji/iP

CT>

TEMPERATURE

(°C)
- 30 -

( M

g

.0l) 1P/“P

Ij

I

TEMPERATURE

(°C)
- 31 -

cn

TEMPERATURE

(°C)
- 32 -

Fig. 12. dn/dT of ZnSe (CVD) as a function of

temperature.
LEXAN

01) D

Linear

thermal

expansion

coefficient

of

Lexan

as

a

function

of

temDerature.
34 -

CM

O

o

C71

( l.)I s

- 0L) iP/“P

)(

dn/dT

of

Lexan

at

0.6328

gm.
- 35 -

-200

-100

0

TEMPERATURE

(°C)
36

(,-X9

-0l) D

Fiq.

16.

Linear

thermal

expansion

coefficient

of

Plexiglas

55.

Triangles

are

from

the

manufacturer's

literature.
- 37 -

3. Acknowledgments

We thank Dr. Phillip Klein of the Naval Research Laboratory for

supplying the KC1 (RAP) and KBr (RAP). The ZnS (CVD) was supplied by

Raytheon. ZnSe (CVD)was provided both by Dr. Perry Miles of Raytheon

and Dr. Carl Pitha of RADC. Polycrystalline CaF~ was suDplied by

R. J. Harris of the University of Dayton Researcn Institute.
NBS-1 ?4A in t v /- /si

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC A 1 ION OR REPORT NO. NBSIR-77-1304

2. Ciov’t Acc ession

No.

3. Rer ipu-nt *s Accession No.

. 4. TITLE AND SUBTITLE

OPTICAL MATERIALS CHARACTERIZATION

5. Publication Date

6. Performing Organization Code

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

Marilvn J. Dodge, and Warren K. Gladden

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NA'foE AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3130442

11. Contract/Grant No.

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

Advanced Research Projects Agency

Arlington, Virginia 22209

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of moat significant information. If document includes a significant

bibliography or literature survey, mention it here.)

The refractive index of fusion cast CaFo was measured at room temperature over the wavelength range 0.2144 urn to 8.662 -pm and the data were

fitted to a Selmeier type equation. Measurements of refractive index of

hot forged CaFp were extended to the wavelength range 0.2024 to

0.2483 pm. Data are presented for dn/dT of single crystal specimens of

CaF

2

, BaF

2

, reactive atmosphere processed (RAP) KC1 and KBr, Li F, NaF,

and SrF

2

, and polycrystalline chemical vapor deposited tCVDl ZnSe and

ZnS. The measurements were done by the method of Fizeau interferometry

over the temperature range -180° to 200 °C at the wavelengths 0.6328 pm,

1.15 pm, 3.39 pm and 10.6 pm. Data are presented for the refractive

indices, the linear thermal expansion and dn/dT of Lexan and Plexiglas 55.

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) BaF

2

; CaF

2

; KBr; KC1 ; Lexan ; LiF; NaF; Plexiglas 55;

refractive index; SrF

2

; thermal coefficient of refractive index; ZnS; ZnSe.

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