k UNITED ST/| AlllDt. 3b0335

dEPARTMENT „ bOMMERCE

PUBLICATION

U.S.

PARTMENT

OF

COMMERCE

National

Bureau

of

Standards

NBS SPECIAL PUBLICATION 260-38

Standard Reference Materials:

PREPARATION AND CALIBRATION

OF STANDARDS OF

SPECTRAL SPECULAR REFLECTANCE
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards^ was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau consists of the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac

Radiation-—Nuclear Radiation-—Applied Radiation^—Quantum Electronics-'

Electromagnetics-^—Time and Frequency''—Laboratory Astrophysics^—Cryogenics^.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes

and methods of test; and provides technical advice and services to Government agencies

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THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

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and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

- Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
Addendum to NBS Special Publication 260-38

Preparation and Calibration of Standards of

Spectral Specular Reflectance

Polarization effects were believed to be negligible, and

hence were ignored in the calibration of the standards of specular

spectral reflectance. This belief was based on (1) the small angle

of incidence on the test sample, about 9° from normal, and (2) the

use of an averaging sphere in front of the entrance slit of the

monochromator , which eliminated errors due to polarization effects

in the monochromator

.

It has since been brought to our attention—'^ that, with gold,

polarization errors are not negligible in the ultraviolet at angles

of 15° or more from the normal, such as are used in many reflectometers , and may not be negligible even at the incidence angle of 9°.

Computations by Luedke— using the published values of n= 1.40 and

K= 1.88 for gold at 0.45 ym, showed that for a plane polarized

incident beam at 10° from normal R = 0.4038, R = 0.3915 and R= 0.3976

s p

The angle of incidence on mirror Ml (figure 3) , which was of

aluminum, was about 10°, and that on mirror M6 , which was also of

aluminum, was about 40° from normal. The mercury arc source used

for these measurements should be free from any significant polarization introduced by mirrors Ml, M3 , or M4 and M6 would be in the

direction normal to the plane of incidence , and hence would tend

to give values that are slightly higher than would be obtained with

a completely unpolarized incident beam.

Luedke— found the discrepancies to exist only at wavelengths

shorter than 0.5 ym, where the reflectance of gold falls off rapidly

to fibout 0.35. Good checks were obtained at longer wavelengths,

which suggests that the polarization errors are absent at the

longer wavelengths.

- Personal communications from E. E. Luekde, Head, Thermophysics

Section, Systems Group of TRW, Inc.
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Similar discrepancies were noted by Champetier— , who ascribed

the errors to scattering. Scattering becomes much more pronounced

at short wavelengths than at longer wavelengths.

Because of the discrepancies noted above, anyone using the

spectral specular reflectance standards under conditions other

than those used in the calibration is cautioned to be aware that

polarization effects and scattering can cause significant errors,

particularly in the ultraviolet portion of the spectrum.

Personal communication from R. J. Champetier, The Aerospace Corp.

^974 2 3 DEC 19F4

, ^ ^ standard Reference Materials:

^^40-^2 Preparation and Calibration

ioa of Standards of

Spectral Specular Reflectance

J. C. Richmond and J. J. Hsia

Institute for Basic Standards

(J » S • National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Peter G. Peterson, Secretary

NATIONAL BUREAU OF STANDARDS, Lawrence M. Kushner, Acting Director

Issued May 1972
Library of Congress Catalog Card Number: 72-600063

National Bureau of Standards Special Publication 260-38

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-38, 57 pages (May 1972) CODEN: XNBSAV

Issued May 1972

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:260-38). Price 60 cents.
PREFACE

Standard Reference Materials (SRM's) as defined by the

National Bureau of Standards are "well-characterized materials, produced in quantity, that calibrate a measurement

system to assure compatability of measurement in the nation."

SRM's are widely used as primary standards in many diverse

fields in science, industry, and technology, both within the

United States and throughout the world. In many industries

traceability of their quality control process to the national

measurement system is carried out through the mechanism and

use of SRM's. For many of the nation's scientists and technologists it is therefore of more than passing interest to

know the details of the measurements made at NBS in arriving

at the certified values of the SRM's produced. An NBS series

of papers, of which this publication is a member, called the

NBS Special Publication - 260 Series is reserved for this

purpose

.

This 260 Series is dedicated to the dissemination of

information on all phases of the preparation, measurement,

and certification of NBS-SRM's. In general, much more detail will be found in these papers than is generally allowed,

or desirable, in scientific journal articles. This enables

the user to assess the validity and accuracy of the measurement processes employed, to judge the statistical analysis,

and to learn details of techniques and methods utilized for

work entailing the greatest care and accuracy. It is also

hoped that these papers will provide sufficient additional

information not found on the certificate so that new applications in diverse fields not foreseen at the time the SRM

was originally issued will be sought and found.

Inquiries concerning the technical content of this

paper should be directed to the author (s). Other questions

concerned with the availability, delivery, price, and so

forth will receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

J. Paul Call, Chief

Office of Standard Reference Materials
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iv
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vi
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Preparation and Calibration of Standards of Spectral

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vii
TABLE OF CONTENTS

PAGE

1 . INTRODUCTION 1

2. PREPARATION OF STANDARDS 3

3. DESCRIPTION OF APPARATUS 4

1. Sample Mount 4

2. Focusing Optics 6

3 . Monochromators 7

4 . Sources 9

5. Detector-Amplif ier-Recorder Systems 10

6. Atmospheric Absorption H

4. OPTICAL ALIGNMENT 13

5. TEST PROCEDURE 17

1. Recording Data 17

2. Reducing Data 18

6. REFERENCES 25

7. APPENDIX 37

LIST OF TABLES

TABLE NO.

I. Ultraviolet Range 26

II. Visible and Near Infrared

III. Near Infrared

IV. Infrared 27

LIST OF FIGURES

FIGURE NO.

1. Range of reflectance values obtained in the

ultraviolet on different sized samples of

aluminum mirrors 28

2. Sketch of the sample mount assembly. The base

plate has been moved back from its normal

position in order to show the leveling

screws 29

viii
3. Schematic diagram of the equipment used for

reflectance measurements in the wavelength

range of 0.25 to 0.58 ]im, together with a

block diagram of the source power supply

and recording circuit 30

4. Schematic diagram of the equipment used for

reflectance measurements in the range of

0.6 to 1.2 ym, together with a block diagram

of the source power supply and recording

circuit 31

5. Schematic diagram of the equipment used for

reflectance measurements in the 1.2 to 4.0 ym

range, together with a block diagram of the

source power supply and recording circuit...

6. Schematic diagram of the equipment used for

reflectance measurements in the 5 to 30 ym

range 33

7. Block diagram of the control circuits for the

interferometer spectrometer

8. Size and location of the areas irradiated on

samples of each size during reflectance measurements 35

9. Average spectral specular reflectance of gold

and aluminum reflectance standards 36

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PREPARATION AND CALIBRATION OF STANDARDS OF

SPECTRAL SPECULAR REFLECTANCE

J. C. Richmond and J. J. Hsia

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

This report describes in detail the preparation and calibration of Standard Reference

Materials 2001 through 2008. These standards

of spectral specular reflectance were prepared

commercially by vacuum depositing opaque coatings of gold and aluminum, respectively, onto

polished substrates of fine-annealed borosilicate

glass. The near-normal (9° from normal) spectral

specular reflectance, was measured by the multiplereflection technique. Four different combinations

of source, spectrometer, and detector were used

to cover the wavelength range from about 0.25

to 30 ym and beyond.

Key words: Aluminum; gold; infrared reflectance;

interferometer spectrometer; mirrors; reflectance;

reflectance standards; spectral reflectance;

spectral specular reflectance; specular reflectance; standards; ultraviolet reflectance.

1. INTRODUCTION

There has been a greatly increased interest in absolute

reflectance measurements since the advent of Sputnik I. Much

of the interest has been in the aerospace industry, where

absolute spectral reflectances are required for radiant heat

transfer analysis in computing heat transfer rates to and

from satellites and space vehicles in space, where radiation

is the only mode of heat transfer that does not also involve

mass transfer. Such computations are an essential part of

the thermal design of such vehicles. The wavelength range

of interest extends from the lower limit of the solar range

(about 0.25 ym for heat transfer purposes) out to at least

30 ym. Other applications include remote sensing, where

the wavelengths involved are primarily in the infrared

1
out to about 15 ym, solar energy conversion, industrial

radiant heat transfer and appearance measurement. Standards

are required primarily for calibration of ref lectometers

.

Absolute spectral reflectance is defined as the ratio

of all the radiant flux reflected by a sample to that incident upon it, the incident flux being limited to a narrow

wavelength band about a known wavelength. This definition

at least implies that the incident and reflected radiant

fluxes are separately evaluated. The incident radiant

flux is rarely evaluated directly, particularly with commercial ref lectometers

.

The absolute reflectance of a good mirror is comparatively easy to measure. In this case nearly all of the

reflected radiant flux is confined to directions near the

direction of specular reflection, and only a small solid

angle of collection need be used, hence flux losses from

the reflected beam are largely eliminated. The classical

method of measuring reflectance of good mirrors is the

multiple reflection technique described by Strong [1] and

later perfected by Bennett and Koehler [2] . A modification

of this method was used in calibrating the standards of

spectral specular reflectance.

All of the above discussion has been in terms of radiant

fluxes . The response of a detector may or may not be proportional to the flux incident upon it. All of the detectors

used in this study were checked for linearity by use of calibrated filters and rotating disc attenuators, and no detectable departures from linearity were found.

2
2. PREPARATION OF STANDARDS

The standards were prepared by a commercial optical

company. The blanks were of fine-annealed borosilicate

glass, in nominal sizes of 76 x 102 x 16 mm (3 x 4 x 5/8 in)

,

38 X 38 X 12.7 mm (1 1/2 x 1 1/2 x 1/2 in), and discs 28.6

mm (1 1/8 in) diameter by 9.6 mm (3/8 in) thick and 23.7 mm

(7/8 in) diameter by 6.4 mm (1/4 in) thick. The surface to

be coated was polished to a nominal finish of 0.05 wavelength

(about 27 nm or 1.0 yin)

.

The coating, of pure gold or aluminum, was applied to

the center 51 x 76 mm (2x3 in) area of the 76 x 102 mm

blanks, and the center 25.4 x 25.4 (1 x 1 in) of the 3 8 x

38 mm blanks, and to the entire face of the discs. Leaving

the edges of the larger blanks uncoated reduces the danger

of contamination of the edges from fingerprints. The smaller

disc samples are easier to handle, and hence are less likely

to be contaminated.

The purchase specifications called for metallic coatings

to be applied at a thickness sufficient to be opaque, by fast

(1 or 2 second) vacuum deposition at a pressure not to exceed

1 X 10 ^ torr. These conditions have been shown [3] , [4] , [5]

to produce coatings of relatively high reflectances in the

ultraviolet.

Unfortunately, the samples supplied were evidently prepared under conditions that were not optimum. This was not

discovered until actual measurements were made of the spectral

specular reflectance in the ultraviolet. The reduced reflectance of aluminum films in the ultraviolet has been shown

[5] , [6] , [7] , to be due to an oxide layer on the surface

of the aluminum. It has also been shown [7] that the films

with lower initial reflectance show a greater reduction in

reflectance with time. The reduction in reflectance in the

ultraviolet is logarithmic and reaches essentially a

steady condition after about one year of ageing [4]

.

3
The primary requirements of a standard of specular

spectral reflectance are that its reflectance (1) be accurately known, and (2) be stable with time. There is no

significant advantage to having the highest possible reflectance, provided the other criteria are met.

The samples were received during the transfer of the

NBS laboratories from Washington to Gaithersburg , and this

factor, combined with the press of other work, resulted in

a delay of about two and one-half years between receipt of

the samples and the first calibration measurements. This

was ample time for the reflectance of the aluminum coatings

to stabilize.

The range of values obtained in the ultraviolet and visible on samples of the different sizes is shown in figure 1.

3. DESCRIPTION OF APPARATUS

The complete apparatus used in calibration of the standards of spectral specular reflectance consisted of a source,

a sample mount, focusing optics, a monochromator , a detector

and an amplifier-recorder system. A sketch of the sample

mount assembly is shown in figure 2, and schematic diagrams

of the equipment used in each wavelength range, together with

block diagrams of the source power supply and detectorrecorder-amplifier system, in figures 3, 4, 5, 6, and 7. The

sample mount and focusing optics were used in all wavelength ranges, and will be described first. Different combinations of source, monochromator and detector-amplifierrecorder systems were used in the different ranges.

1. Sample Mount

In order to more easily describe the optical system,

which comprised primarily the sample mount and focusing optics,

the position of various components will be described relative

to the axis of the system which is defined as a horizontal

line normal to the plane of the front surface of the sample

and passing through the center of the two reference mirrors.
The sample mount assembly formed an important feature

of the optical system. It was designed—^ and built at the

National Bureau of Standards. The assembly consisted of a

sample holder, two reference mirror mounts, a base plate and

a mounting plate. Two reference mirrors having identical

specular spectral reflectance over the wavelength range of

measurements, or whose reflectance ratio is precisely known

over this wavelength range, are required in this method.

This point is discussed further in Part 2 of the Test

Procedure. (See page 2 3)

.

The sample holder permitted one large or two small

samples to be rigidly mounted so that their front surfaces

were parallel to, and at a fixed distance from, the plane of

the front surface of the holder. The holder fitted into a

key slot in the base plate, with the plane of its front surface normal to the axis. The sample holder could be moved

horizontally in the slot into or out of the optical path. A

movable stop in the slot could be adjusted so that the sample was centered laterally on the axis when the holder was

in contact with the stop, or if two samples were being measured, they were centered in the respective beams. Several

front plates for the holder were provided to accommodate

the samples of different sizes. A sketch of the sample

mount assembly is shown in figure 2.

The base plate rested on two horizontal slides or

ways, which were attached to the mounting plate. These

slides were parallel to the axis, and permitted the base

plate to be moved in a direction parallel to the axis.

The top of the base plate was 8 cm below the axis. A locking device, attached to the mounting plate, was provided to

hold the base plate in any desired position. Leveling screws

were provided near the four corners of the mounting plate

.

—'^By Lawrence J . Nivert

5
Two mounts held the reference mirrors. Each mount

consisted of a base, a rod, and a mirror holder. The reference mirrors were 7 x 20 mm in size. The mirror holder held

the mirror firmly in position, but was pivoted about a horizontal line normal to and intersecting the axis , and its

degree of tilt could be controlled by means of adjusting

screws . The mount was attached at the top of a vertical rod

that fitted into a hole in the base, and could be rotated.

It was held in position by a set screw. There were two dowel

pins in the base of each mount, centered 25.4 mm apart, that

fitted into holes in the base plate. The mount was held in

place by a screw through the base that fitted into a tapped

hole in the base plate. A set of mounting holes in the base

plate consisted of two holes for the dowels, centered 12.7 mm

on either side of a vertical plane through the axis, and a tapped hole centered in that plane and 9.5 mm farther from

the key slot than the dowel holes. There were 33 sets of

such mounting holes on each side of the key slot, spaced

6.35 mm apart, with the dowel holes of the set nearest the

key slot 46.04 mm from the plane of the front surface of the

sample, so that the plane of the reference mirror when mounted

in these holes was 38.1 mm from the plane of the sample mirror.

Both reference mirrors were coated with vacuum-deposited aluminum.

2. Focusing Optics

The focusing optics included (1) two spherical mirrors, 16 cm in diameter, with a 71 cm radius of curvature,

(2) two plane mirrors, (3) circular apertures 10, 7.5 and

5.0 cm in diameter, cut in cardboard covered with black velvet. The position of these components will be described in

the section on alignment.
3 . Monochromators—

Three different monochromators were used in different spectral ranges: (1) a Leiss quartz double-prism monochromator, used in the spectral range 0.25 to 0.58 ym, (2) a Perkin-Elmer model 98 monochromator with a lithium fluoride

prism for use in the spectral ranges of 0.58 to 1.2 ym and

1.2 to 4.0 ym, and (3) a Block model 200 interferometer spectrometer for use in the spectral range of 5.0 to 30 ym.

All detectors vary in response over their sensitive

areas. A major source of error in the multiple reflection

method of measuring specular reflectance is due to slight

differences in the position of the reflected beam on the

detector or on the entrance slit of a monochromator when

the sample is moved into or out of the beam. Such shifts

may result in a change in the fraction of the energy in

the beam reaching the detector when the detector or entrance slit is overfilled, or in change in apparent gain

of the detector when the slit or detector is underfilled.

Such errors can be avoided in either of two ways: (a) by

use of a very elaborate optical system to eliminate such

shifts of the reflected beam, as was reported in reference

[2] , or (b) by use of an optical averaging device in the

system to eliminate the effects of slight shifts of the

beam on detector output. The latter approach was used in

this work.

An averaging sphere [8] was used to uniformily

irradiate the entrance slit of the prism monochromators.

With an averaging sphere having an entrance aperture that

is large compared to the cross-sectional area of the beam.

— The manufacturer and model number of certain equipment is given for identification only, and does not

constitute an endorsement by the National Bureau of

Standards, and does not imply that such equipment

was necessarily the best available for the purpose.

7
the detector output will remain constant as the beam is

moved provided only that the entire beam is always contained within the aperture. For the Leiss monochromator

used in the range 0.25 to 0.58 ym, the averaging sphere

was 76 mm in diameter and had a circular entrance port

19 mm in diameter and a rectangular exit port 19 by 6.3 mm.

The ports were centered 135° apart on a plane through the

center of the sphere. The long dimension of the exit port

was noirmal to this plane. The inside of the sphere was

coated with smoked magnesium oxide. The averaging sphere

was placed with its exit port immediately in front of the

entrance slit of the monochromator so that the slit was

always completely filled, regardless of its width.

The same MgO coated sphere was also used with the PerkinElmer model 9 8 monochromator in the wavelength range of 0.5 8

to 1.2 ym. In this case the averaging sphere was located

with its exit port in the position normally occupied by the

source for the monochromator. The source optics, consisting

of a short focal length spherical mirror and a small plane

mirror, formed an image of the exit port of the sphere on

the entrance slit of the monochromator. When the averaging

sphere was placed immediately in front of the entrance slit,

the off -axis paraboloid mirror in the monochromator, used

to collimate the beam and reflect it onto the prism and then

to refocus the dispersed beam onto the exit slit, was overfilled, and some of the undispersed radiant energy reached

the detector, causing a significant error. With the image

of the exit port of the sphere focused onto the entrance

slit, the paraboloid mirror was slightly underfilled, and

the scattered light error was eliminated. The customary checks

for errors due to stray light, using auxiliary filters,

showed in these measurements that the remaining errors were

negligible. Errors due to overfilling the off-axis paraboloid

may be expected with single-dispersion monochromators , but

8
should be absent with double-dispersion systems because the

stray light scattered within the monochromator is blocked

by the center slit of a double prism instrument, or is not

chopped and hence not detected in a double-pass instrument.

A second averaging sphere, 50.8 mm in diameter, with

ports of the same sizes and in the same relative positions

as those of the 76 ram sphere, was used in a similar position

for use in the wavelength range of 1.2 to 4.0 ym. This

sphere was coated with sprayed sodium chloride [9] , which

has much higher reflectance than MgO in the infrared beyond

about 2 ym.

In the wavelength range of 5 to 30 ym, where the interferometer spectrometer was used to disperse the reflected

radiant energy, the reflected beam was focused onto an aperture 3 mm wide by 12 mm high, placed approximately 25 cm in

front of the entrance window of the spectrometer. The radiant

energy passing through the aperture irradiated uniformly an

area with a diameter appreciably larger than that of the

entrance window of the spectrometer. The image on the aperture plate was approximately 4.5 mm wide by 6 mm high, hence

could be moved over a range of at least 1 mm horizontally

and still cover the entire width of the aperture, and at

least 4 mm vertically and still all be within the aperture.

lnIo movement of the beam was observed as the test mirror was

moved into or out of the optical path.

4. Sources

Three different sources were used in the different

spectral ranges. An Osram mercury arc lamp model Hg3, with

accompanying power supply, was used in the wavelength range

0.25 to 0.58 ym. This lamp is a limited-pressure arc, and

as such is much more stable than other types. The arc is

confined to a sealed quartz tube with inside dimensions of

2 mm diameter by 20 mm long. The outer glass envelope of

the lamp has an opening through which the ultraviolet radiant

energy passes. An aperture 4 mm wide by 6.35 mm high was

9
placed immediately in front of the lamp. Selected lines of

the mercury spectrum from this source were used in the

calibration, as indicated in Table I. A tungsten lamp

with a strip filament 3 x 15 mm in size was used in the 0.58

to 1.2 y wavelength range. The filament was viewed by the

optical system through a plane quartz window. The lamp was

enclosed in a shield having a circular aperture 17.5 mm in

diameter, directly in front of the quartz window. The power

to the lamp was regulated by a regulated d.c. power supply.

A Globar source, nominally 6.35 mm in diameter and 51 mm

long, was used at wavelengths beyond 1.2 ym. The power to

the Globar was regulated by a controller. The source was

enclosed in a water-cooled mount, to reduce convection,

and a water-cooled aperture, 4.5 mm wide and 6 mm high,

was placed immediately in front of the aperture in the

enclosure.

5. Detector-Amplifier-Recorder Systems

In the 0.24 to 0.58 ym wavelength range the incident

beam was chopped near the source at 33 Hz. The detector was

an EMI type 9558 QA photomultiplier tube, used at a potential

of 450V. The signal from the detector was amplified by a preamplifier, then fed to a synchronous amplifier where it

was further amplified and rectified. The output of the synchronous amplifier was a d.c. potential, which was fed to a digital voltmeter. The signal from the voltmeter was read

by a TWX coupler, converted into ASCII code and typed in

printed form and on punched paper tape by a Teletype machine.

The same system was used in the 0.5 8 to 1.2 ym range,

except that an EMI photomultiplier tube, type 96 84B with a S-1 cathode was used as the detector, at a potential of 760V.

10
In the 1.2 to 4.0 ym range a similar system was used, but in

this case the chopper frequency was 11.3 Hz, and a liquidnitrogen-cooled lead sulfide detector, at a bias potential of

180V, was used. The preamplifier and amplifier were different units of the same model number as before, but peaked at

the lower chopper frequency.

The detector-amplifier-recorder system used with the

interferometer spectrometer was quite complex, and will be

described only in general terms. The interferometer recorded

the interf erograms for the wavelength range of 4 to 4 0 ym at

the rate of one sweep per second. The signal was amplified,

and sampled at 520 time increments, equally spaced from the

beginning of the sweep. The potentials at each of the 520

points were digitized, and stored in separate memory banks of

a miniature computer that was part of the interferometer, in

the form of a 16-bit binary word, of which the first bit was

a sign bit. The signals for 300 sweeps were coherently added

in the memory. The instrument provided for addition and

subtraction of interferograms in the memory, hence background

corrections were made directly, before the interferograms

were reduced. After the complete interferogram had been

stored, and background corrections made, it was read out

of the memory one point at a time by the TWX coupler, which

converted each 16-bit binary word into a 6-bit octal word

with negative numbers in 7 's complement, of which the first

bit was again a sign bit, and fed it, in ASCII code to a Teletype machine, where it was recorded on punched paper

tape and in typed form.

6. Atmospheric Absorption

Absorption due to water vapor and carbon dioxide

in the atmosphere is significant at certain wavelengths in

the 0.25 to 30 ym range, and variations in such absorption

could cause significant errors if ignored.

11
Major absorption bands of occur at 1.87, 2.70

and 6.22 \im, and minor bands at 0.94, 1.1, 1.38 and 3.2 ym.

Major absorption bands of occur at 2.7, 4.3 and 15.0 ym,

and generally in the region between 11.4 and 20 ym. Weaker

bands are present at 1.4, 1.6, 2.4, 4.8, 5.2, 9.4 and 10.4 ym.

The wavelengths shorter than 4.0 ym at which measurements were made were selected to avoid the atmospheric

absorption bands, and hence errors due to such absorption.

The measurements at wavelengths longer than 4.0 ym

V7ere made in a water-free, C02-free atmosphere. The entire

optical path, including the source, spectrometer and detector,

was enclosed with sheet plastic, and C02-free dry air was

fed into the enclosure at a rate of about 0.75 liter per

second. The atmospheric purification train is described in

reference [10] . A minor modification was made in the purification train, in order to increase the efficiency in

removing CO^ . The order of absorbing towers now is (numbers

refer to figure 14 in reference [10]) 10. Ascarite

absorber, 11. Ascarite, 12. Silica gel. All other components are as shown in the figure. After the entire system

had been exposed to the laboratory atmosphere for several

days , continuous purging for 24 hours was required to reduce

atmospheric absorption to a point where it could not be detected. This long purging time is believed to be due to the

time required to remove adsorbed films from optical elements,

particularly the window to the spectrometer, because the

water vapor bands could be detected long after a hygrometer

showed the atmosphere to have a relative humidity of less

than one percent. After the system had been purged for 24

hours, only about 30 minutes of purging were required after

opening the cover to remove one sample and insert another

to restore the system to a condition where the atmospheric

absorption could not be detected.

12
4. OPTICAL ALIGNMENT

Very careful optical alignment was required in order

to assure proper operation of the equipment. Two special

pieces of equipment were used to aid in this alignment, a machinists level with a sensitivity of about 0.0025'', and

a small helium-neon laser.

The equipment was mounted on an optical table that was

nominally level. The first step was to locate the sample

mount assembly on the table, level the base plate by means

of the leveling screws in the mounting plate, and clamp the

mounting plate in position. A sample was mounted in the

sample holder, and the holder positioned in the key slot

so that the sample intersected the axis. The laser was

then positioned so that its beam was centered on the axis,

which was 8 cm above the top of the base plate and normal

to the sample. The two reference mirrors were then mounted

in their holders, the sample holder was moved out of the

beam, and each reference mirror in turn was mounted in the

base plate and adjusted to be noraial to the laser beam.

The two spherical mirrors were in adjustable mounts

which permitted them to be tilted about horizontal and

vertical axes. The two mounts were placed side by side on

an aluminum plate, in a position such that they were about

65 cm from the slot in the sample holder assembly, and

equally spaced on either side of the axis. The aluminum

plate was then raised until the centers of the mirrors were

in the horizontal plane through the axis, leveled, and

clamped in position. The laser was then moved to a position where its beam was in the horizontal plane through the

axis, and passed through the position of the source. The

laser was left in this position for checking alignment when

changing from one size of sample to another, or when changing

system components in going from one spectral range to another.

A plane mirror with its surface vertical was placed in posi13
tion to reflect the laser beam to the center of the first

spherical mirror. The sample holder was then removed from

the beam, and a reference mirror mounted in the base plate

facing the spherical mirrors. The base plate was then

moved on the slides until the reference mirror was 71 cm

from the spherical mirror. The tilt of the first spherical

mirror about a horizontal axis was then adjusted until the

reflected laser beam was level, and the position of the

plane mirror was adjusted, if necessary, to bring the laser

beam to the center of the reference mirror. The beam reflected by the reference mirror was then incident on the

center of the second spherical mirror. Its tilt was adjusted to keep the laser beam level when reflected. The

sample holder with a sample in place was then placed in

the beam, and the second reference mirror was mounted with

its surface in a position such that the two reference mirrors were equidistant from the front surface of the sample.

The tilt of the second reference mirror was adjusted, if

necessary, to make the positions of the laser beam on the

second spherical mirror coincide when the sample was in or

out of the beam. The spectrometer was then placed in position, its height adjusted until the horizontal plane through

the axis passed through the center of its entrance slit,

and clamped in position. The averaging sphere (or aperture

plate) was then placed in position, and a second plane mirror with its surface vertical was used to reflect the laser

beam to the center of the entrance aperture.

The source was then placed in position, with the aperture in front of the source centered on the horizontal plane

through the axis, and the position of the source behind the

aperture was adjusted until the first spherical mirror was

well centered in the beam. The sample holder was removed

from the optical path, and the base plate was moved forward

or back until a sharp image of the aperture was formed on
the reference mirror. The second spherical mirror was

checked to see that it was uniformly irradiated, the second

plane mirror to see that none of the beam missed the mirror,

and the entrance aperture of the averaging sphere to see that

all of the beam was within the aperture when the sample was

in and out of the beam. When satisfactory alignment had

been achieved, the 10 cm diameter aperture was centered on

the second spherical mirror, and the 7.5 cm aperture was centered on the first spherical mirror. This formed the limiting aperture for the system. When the 38 mm square samples

were being measured, the 7.5 cm aperture was replaced by the

5.0 cm aperture. The felt-covered baffles were then put in

position to prevent scattered light from the source from

reaching the detector.

Two positions of the reference mirrors were required,

25.4 ram from the sample face for the 38 x 38 mm samples,

and 95.25 mm from the sample face for all other samples.

The location and size of the irradiated areas on the samples are shown in figure 8.

The axial ray from the spherical mirror was incident

on the sample from an angle of 8.91° from the normal. When

the 7.5 cm aperture was used in front of the spherical mirror, the angle of incidence of the cone of incident rays

varied over the beam from 5.85° to 11.97° and when the 5.0

cm aperture was used, from 6.87° to 10.95°. The reflectance

of metal surfaces varies only slightly with angle of incidence in this range.

A shutter was provided in front of the source in each

case, which was closed when the background reading was taken.

Immediately before making a reflectance measurement, a sample was mounted in the sample holder, and the sample holder inserted into the key slot in the base plate, but out

of the optical path. The reference mirrors were placed in

the proper position for the sample to be measured. The base

15
plate was moved foirward or back as required to obtain a sharp

image of the source on the rear reference mirror. The position of the beam was checked on each mirror and the entrance

aperture of the averaging device. Minor adjustments in alignment were made, if required, although this was rarely the

case

.

In the case of the disc samples, which were too small

to be measured individually, two samples were mounted in

the sample holder, side by side. In this case each sample

was measured at least twice, in combination with a different

sample each time so that the reflectance of each sample

could be determined separately. (See equation 3).
5. TEST PROCEDURE

1. Recording Data

After the optical alignment had been checked, the

raw data from which the reflectance was computed was recorded. Three different procedures were used, in the ranges

of 0.25 to 1.2 ym, 1.2 to 4.0 ym, and 5 to 35 ym.

In the 0.25 to 1.2 ym range, the wavelength drum

and slit drive of the monochromator were set to give the

desired wavelength and slit width. The room lights were

turned off, and the measurements were made in a darkened

room. The shutter in front of the source was closed, and

the background signal was recorded for 32 successive data

points. The shutter in front of the source was then opened,

and, with the sample out of the beam, the one reflection

signal was recorded for 32 successive data points. The

sample holder was then moved into position where it was in

contact with the stop, and the three reflection signal was

recorded for 64 successive data points. The sample holder

was then removed from the optical path, and the one reflection

signal was again recorded for 32 successive data points.

The shutter in front of the source was then closed, and the

background signal was again recorded for 32 successive data

points . In each case the readings were recorded by the

Teletype on punched paper tape and in typed form. The

wavelength drum and slit drive were then moved to the

settings for the next wavelength, and the process was

repeated until measurements had been completed at all

wavelengths in that range. The wavelengths at which

measurements were made in the 0.25 to 0.58 ym wavelength

range are shown in Table 1 together with the spectral

bandpass at each wavelength. Similar values in the wavelength range of 0.58 to 1.2 ym are shown in Table 2. A

similar procedure was followed in the wavelength range of

1.2 to 4.0 ym, except that the background was recorded

17
for 50 successive data points, the one reflection reading

with the sample out for 50 successive data points, the

three reflection reading with the sample in the beam for

100 successive data points, the one reflection reading again

for 50 successive data points, and finally the background

again for 50 successive data points. The wavelengths at

which measurements were made are shown in Table 3, together

with the spectral bandpass at each wavelength.

The entire optical system used for measurements in the

5 to 30 ym wavelength range was enclosed and maintained in

a water-free, C02-free atmosphere during test. A longsleeved rubber glove attached to the wall of the enclosure

permitted the sample to be moved into or out of the beam

without disturbing the atmosphere. However, it was necessary

to open the enclosure when samples were changed. In this

case the interf erogram for the entire wavelength range from

4 to 40 ym was scanned at once. The procedure was to scan

the background, with the control switch on the console set

to subtract the values from the computer memory, for 150

scans, then change the switch to the add position and record the one reflection data with the sample out of the

beam for 300 scans, then again change the switch to the

subtract position and record background for another 150 scans.

The data were then read out of the computer memory and stored

on punched paper tape and in typed form. The same procedure

was then followed for the three reflection data with the

sample in the beam, again recording negative background for

150 scans, positive reflectance for 300 scans, then negative

background for 150 more scans. This procedure was repeated

six times with each sample.

2. Reducing Data

The data were reduced on the NBS electronic digital

computer. In the 0.25 to 4.0 ym range, the data were recorded

in decimal form in ASCII code on punched paper tape. The

18
data were first transferred from paper tape to magnetic tape,

and then converted from decimal form to binary. The mean

and standard deviation were computed separately for the background, B, the one reflection data, p^^, and the three reflection data, p^. The reflectance, p, was computed as

The standard deviation of the final reflectance, a , was comP puted from the standard deviation of the three reflection

values, and the standard deviation of the one reflection

values , On , as

- B

P =

- B

(1)

Computation of the random error was more complicated.

1/2

(P3 - B)2

+

(Pl

-

(2)

(See reference [11]).

19
In the case of the disc samples, which were measured two at a time, the p in equation (1) represents not the

reflectance of a single sample, but the square root of the

product of the reflectances of the two samples. For samples

A, B and C, three measurements were made, givinq /p p, , /p, n a b be

and /p^p^ . The reflectance of each was then computed as

Pa =

/p, p

3)

and so forth. The inclusion of three measurements in each

reflectance evaluation increased the random error in the

result which was computed by the standard propagation of

error method [11]

.

The precision of measurement of the large (7.6 x 10.2 and 3.8 x 3.8 cm) samples, expressed as the standard

deviation of the mean of six replicate measurements on a single sample, varied from about 0.0002 to 0.0005 in the

wavelength range of 0.257 to 0.577 ym, and from about 0.0010

to 0.0052 in the wavelength range of 0.60 to 4.0 ym.

Corresponding values for the small disc samples were about

0.0004 to 0.0020 at wavelengths from 0.257 to 0.577 ym, and

0.0021 to 0.0095 from 0.60 to 4.0 ym.

The non-random error, or bias, is believed to be less

than the precision of measurement reported above. The four

principal sources of bias are: 1) non-linearity of the

detector-amplifier-recorder system, 2) drift of the response

with time, 3) variations in the atmospheric absorptance with

time, and 4) differences in the spectral reflectances of

the two reference mdrrors. Linearity was checked, and no

non-linearity was found. Non-linearity on the order of

0.002 should be detected. The fact that fluxes of about

equal value were being compared indicates that errors from
this source would be small, except for gold at wavelengths

shorter than about 0.7 ym, even if measurable non-linearity

was present. Drift on order of a few tenths of a percent

per hour has been observed. Such drift is linear with time,

at least to a first approximation. The scheme used in

making the measurements compensates for any linear drift

that my be present. Atmospheric absorption is always present

in the normal laboratory atmosphere, and varies quite

significantly with time when a living person is present.

Human breath contains significantly more carbon dioxide

and water vapor than the noirmal laboratory atmosphere.

Errors due to variations with time in atmospheric absorptions

were avoided by making measurements only at wavelengths

where absorption due to carbon dioxide and water vapor is

essentially absent. The reference mirrors differ in reflectances by as much as 0.001 at some wavelengths. The ratio of

the reflectances was measured at each wavelength at which

the mirrors were calibrated and a correction was made for

the observed ratio. The residual error from this source

should not exceed 0.0001.

The data from the interferometer spectrometer required entirely different treatment. As mentioned previously, the data were recorded for 520 points. The sweep

generator in the controls for the interferometer generated

a pulse at the beginning of each sweep, to serve as a

reference line and start the timer which triggered the recording circuit. This pulse occasionally caused a large

spurious signal to be recorded in the first or second memory

bank, which, if used in reducing the data, would cause errors

in the reduced spectrum. For this reason the first three

data points were discarded in reducing the data.

The data on the punched paper tape were transferred

to magnetic tape for entry into the NBS 110 8 computer. A subroutine picked up the characters from the tape and stored

them in the memory. Only data points from No. 4 to No. 515

21
were used. The computer converted negative numbers from 7's

complement to true negative by subtracting them from 7777 8

in octal, then converted all numbers from octal to binary.

The Fourier coefficients , B^. of the Fourier series

256

YE(X) = A /2 + E (A cos Kx+ sin KX) (4)

K=l ^ ^

where YE(X) is the amplitude of the interferogram at time

. . 3/ or position X were computed— . The YE values are the recorded words, and the X values are the serial numbers from

1 to 512 of the recorded words. The program essentially

solves 512 equations in 512 unknowns.

Next, monochromatic flux values ^jr^^j^ at wavenumbers

(or wavelengths) corresponding to the points K (K = 1 to 256)

were computed as

The proportionality factor in equation (5) is an

instrument calibration factor that is wavenumber dependent,

and is the monochromatic flux at the wavenumber corresponding to K. n is due to the spectral transmittance of

the spectrometer window, the spectral reflectance and transmittance of the beamsplitter in the interferometer, the

spectral response of the detector and polarization effects,

and is constant at any one value of K.

—The computer program for this computation was written

by R. J. Arms, and is designated subroutine FSER

(N,L,Y,YE,A) , and is available at NBS

.

22
There was significant scatter in the riT^^rr values,

Is. is. which appeared to be completely random. In order to reduce

this scatter, the data were smoothed by taking as the value

for each point the mean of five adjacent points centered on

the desired K value. The reflectance, , at each K value

was computed as

where

'^I^^*^K^3

is the smoothed monochromatic flux value at

K for the three-reflection measurements and t]„{^„)^

for the one-reflection measurement.

The wavenumber, W, is related to K by the equation

W = -10.9741 + 10.1522K (7)

for values of K from 25 to 256 from the wavelength calibrations. The wavenumbers corresponding to K less than 25 are

less than 250, or the wavelengths are greater than 40 ym.

The wavenumbers corresponding to K greater than 247 are

greater than 2500, or the wavelengths are less than 4 ym.

The interferometer spectrometer is restricted to wavelengths

in the 4 to 40 ym range, hence only points between K = 25 to

247 were used.

The six values obtained for each K value in the

six replicate measurements on each sample were averaged, and

the standard deviation of the mean was computed, with an

average value of about 0.004. The 223 mean values of p corresponding to K values from 25 to 247 were then plotted as a

function of wavelength, and a smooth curve was drawn through

them. The values reported for each sample were then read off

from this curve.

Our values for the reflectance of the best sample

of aluminum averaged about 0.0035 higher than those of

Bennett, Bennett and Ashley [5] for aged high-vacuum aluminum

23
i -5 deposited at a pressure of about 10 torr , and about 0.0024

lower than those of Bennett, Silver and Ashley [12], for I -9 I fresh aluminum deposited at a pressure of about 10 torr.

Our highest values for the infrared reflectance of gold

| averaged about 0.0018 lower than those of Bennett and Ashley

[13] for gold deposited at a pressure of about 5 x 10 "''^ torr. This is considered reasonable agreement, particularly

in view of the different conditions of application of the

coatings and the reported precision of measurement.

All reflectance values were corrected for differences

in the reflectances of the two reference mirrors. This correction was in most cases less than 0.001.

Figure 9 shows the average spectral specular reflectance of the aluminum and gold coated samples . The individual

values for each sample will be reported in the Certificate

accompanying that sample.

Tables I, II, III and IV show the wavelengths at

which reflectances are measured, together with the slit width

used with the prism monochromators , and the spectral bandpass

at each wavelength. I

i

I

24
6. REFERENCES

;

[1] strong, J. L., Procedures in Experimental Physics^

p, 376 (Prentice Hall, 1938) ,

[2] Bennett, H. E., and Koehler , W. F., Precision measurement of absolute spectral reflectance with minimized

systematic errors ^ J. Opt. Soc „ Am., 50^, pp. 1-6,

1960 .

[3 J Hass , G., and Waylonis , J. E., Optical constants and

reflectance and transmittance of evaporated aluminum

in the visible and ultraviolet, J. Opt. Soc . Am.,

51, [7] pp. 719-722, 1961.

[4] Hass, G. , and Tousey, R. , Reflecting coatings for the

ultraviolet, J. Opt. Soc. Am., £9 [6], pp. 593-602,

1959 .

[5] Bennett, H. E., Bennett, J. M. , and Ashley, E. J.,

Infrared reflectance of evaporated aluminum films,

J. Opt. Soc. Am., 52^ [11], pp. 1245-1250 , 1962.

[6] Madden, R. P., Canfield, L. R. , and Hass, G., On the

vacuum-ultraviolet reflectance of evaporated aluminum

before and during oxidation, J. Opt. Soc. Am., 5_3

[5] , pp. 620-625, 1963.

[7] Hass, G., Filmed surfaces for reflecting optics, J.

Opt. Soc. Am., £5 [11], pp. 945-952, 1955.

[8] Nat. Bur. Stand. (U.S.), Tech. Note 279, (1965).

[9] Nat. Bur. Stand. (U.S.), Tech. Note 439, (1968).

[10] Nat. Bur. Stand. (U.S.), Tech. Note 252, (19 64).

[11] Nat. Bur. Stand. (U.S.), Spec. Publ. 300, Vol. 1,

pp. 331-341 (1969).

[12] Bennett, H. E., Silver, M. and Ashley, E. J., Infrared

reflectance of aluminum evaporated in ultra-high vacuum,

J. Opt. Soc. Am., 53 [9], pp. 1089-1095, 1963.

[13] Bennett, J. M., and Ashley, E. J., Infrared reflectance

and emittance of silver and gold evaporated at ultrahigh vacuum, Appl. Opt. £ [2], pp. 221-224, 1965.

25
TABLE I Ultraviolet Range

Wavelength Slit Width Bandpass

ym mm nm

0.2537 0.1 0.2

0.2650 0.1 0.25

0.2805 0.1 0.3

0.3023 0.1 0.4

0.3340 0.1 0.5

0.3651 0.1 0.6

0.4048 0.1 0.9

0.4358 0.1 1.2

0.5460 0.1 2.6

0.5770 0.1 3.1

TABLE II

Visible and Near Infrared

Wavelength Slit Width Bandpass

ym mm nm

.600 0.1 4.0

.650 0.1 4.5

.700 0.1 5.0

.800 0.1 6.0

.825-/ 0.1 6.0

.850-/ 0.1 6.5

.900 0.1 7.0

1.000 0.1 7.5

1.200 0.17 15.0

-Measurements at these wavelengths for aluminum

mirrors only.

26
TABLE III

Near Infrared

Wavelength Slit Width Bandpass

ym mm nm

1.200 0.17 18

2.000 0.15 13

3.300 0.34 20

4.000 0.80 38

TABLE IV

Infrared

Wavelength Mechanical Travel Resolution

ym ym ym

5 500 0.05

10 500 0.20

15 500 0.40

20 500 0.9

25 500 1.3

30 500 1.8

27
Figure 1. Range of reflectance values obtained in the

ultraviolet on different sized samples of

aluminum itiirrors.

2 8
CO

UJo

-J

UJo

(A

CO

or

UJo

_ioXO

or

a:

UJoz

UJ

q:UJ

UUJ

to

Eh

0}

CDU

H

U

gO

C

•H

iH

03 Q) +J > H Q)

W

Oo o og 43 W

0)^3 0 a > g o

as

ga

u

0) (U o ^ Q) p ^ 0 fO c

•H

C!o

•H 0 (U +J

+J -P -H

0) ITJW

w

a oH o

(0

>-

UJ

29
^2 M5 r 3" Averaging Sphere (MgO Coating)

Hg Arc

Source

Power

Supply

(I.I amp)

A C. Regulator

Model 1001

at Stab. Mode

output llOV

(Sorensen Co.)

Chopper

(33 cps)

Dana Model 5403

Digital Voltmeter

EMI 9558 QA

Photomultiplier

High Voltagt

Power

Supply

Brower

Preamplifier

Brower Model 129

lock- in amplifier

T WX

Cou pier

Teletype

Figure 3. Schematic diagram of the equipment used for

reflectance measurements in the wavelength

range of 0.25 to 0.58 ym, together with a block diagram of the source power supply

and recording circuit.

30
© Tungsten Strip

Lamp (7V,40A.)

© Lamp Shield with

Cicular Aperture

({4"dia)

(D Movable Shutter

(3) Chopper (33cp8)

3" Averaging Sphere ( MgO Coating)

Circular entrance port ( 0.75" dia. ) Exit port (0.75 X 0.25 in. )

Photomultiplier

EMI 9684B (S-1

)

M3 ^Test Mirror

in movable slide ^Single pass Monochromator

Perl(in - Elmer Model 98

(LiF Prism)

Tungsten

Strip Lamp

(7V, 40A)

Kepco

Regulated

DC Power

Supply

Model

KS 18.50 M

Chopper

(33 cps)

Dana Model 5403

Digital Voltmeter

Photomultiplier

EMI 9684B{S-I)

High Voltage

Power

Supply

TWX

Coupler

Brower

Preamplifier

Brower Model 129

lock - in amplifier

Teletype

Figure 4. Schematic diagram of the equipment used for

reflectance measurements in the range of

0.6 to 1.2 ym, together with a block diagram

of the source power supply and recording

circuit.

31
® Globar Source

( 1540 K ) in water cooled enclosure ® Aperture

water cooled

d) Movable Shutter @ Chopper (1 1.3 ops)

2" Averaging Sphere (NaCI Coating)

Entrance port ( 0.75 " dio. ) Exit port ( 0.75 X 0.25 in.

)

Cooled

PbS (78 K)

Quartz lens

focusing window

M Test Mirror

in movable slide ^Single pass Monochromator

Perkin - Elmer Model 98

( Li F Prism )

Globar

(1540 K)

Chopper

(I l.3cps)

L N2 Cooled

PbS Cell (78 K)

Warner

Mod

Source R

Contr

& Swasey

si 10 adiation

oiler

A.C. Regulator

Model 1001

at Stab. Mode

output MOV

(Sorensen Co.)

Dana Model 5403

Digital Voltmeter

180V

( Battery

)

TWX

Coupler

Brower

Preamplifier

Brower Model 129

lock - in amplifier

Teletype

Figure 5. Schematic diagram of the equipment used for

reflectance measurements in the 1.2 to 4.0 ym

range, together with a block diagram of the

source power supply and recording circuit.

32
lO CM

33

U:

bJ
•ao

a> X

Q. o

to

inoO

too

°co

o

CD

-P

}^O

w

•HO

H

O

O }^ ^ 0) C (I) o g

u o

O

0)

S CD

(3 -P

V^ (D

t7> e

o

•H M

CD M U

O CD O -P

CQ -H

5-)

•H

1^4
Figure 8. Size and location of the areas irradiated on

samples of each size during reflectance measurements .

35
REFLECTANCE >
7 . APPENDIX

The following pages are copies of the Certificates

issued with the Specular Spectral Reflectance Standards.

The same first page is used with Numbers 2001, 2002, 2003,

and 2004, and with 2005, 2006, 2007, and 2008, hence only

one copy of each of these first pages is included.

A separate Certificate will be issued with each

standard, and will include in the spaces provided the

actual specular spectral reflectance measured on that

standard at the indicated wavelengths

.

37
U. S. Department' of Commerce Mauric&H. Stans

National Bpr^jf cfi Standards

L. M. Brtn^^pjb; Director

Rational ^mmn of ^tanttarrfs

Ol^rttfttat^

Standard Reference Materials

2001, 2002, 2003, 2004

Aluminum on Glass

(Standard for Specular Spectral Reflectance)

These Standard Reference Materials are for calibrating equipment used in evaluating the thermal

radiation properties of materials. The mirrors were prepared by fast vacuum deposition of

aluminum on fine-annealed borosilicate glass, the surface to be coated being flat to about 27 nm. The mirrors are prepared in four sizes.

SRM No. Size of blank (cm) Coated Area (cm)

2001 7.6 X 10.2 X 1.9 5.1 X 7.6 2002 3.8 X 3.8 X 1.3 2.5 X 2.5 2003 disk: 2.9 diameter X 1.0 thick entire surface 2004 disk: 2.4 diameter X 0.6 thick entire surface

Each mirror is certified for near-normal (9°) specular reflectance at wavelengths ranging from

0.2537 to 30 micrometers and at corresponding resolved bandwidths from 1.0 to 1800 nanometers. The precision measure (Ojn) the standard deviation of the mean of six replicate measurements.

The certified values are given on the attached sheet. Details of experimental techniques used will be

described in an NBS 260 publication.

Measurements of reflectance and other experimental work leading to the certification of these Standard Reference Material were performed by J. C. Richmond, and J. J. Hsia of the Heat

Division, Institute for Basic Standards, National Bureau of Standards.

Washington, D. C. 20234 J. Paul Cah, Chief

April 16, 1971 Office of Standard Reference Materials

38
SRM No. 2001 Specimen material: Aluminum Size: 7.6 X 10.2 X 1.9 cm

Specimen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

0.2537 1.0 0.0008

0.2650 1.0 .0007

0.2805 1.1 .0006

0.3023 1.2 .0005

0.3340 1.3 .0005

0.3651 1.4 .0002

0.4048 1.6 .0004

0.4358 1.7 .0002

0.5460 2.5 .0003

0.5770 2.5 .0003

0.600 4.0 .0030

0.650 4.5 .0020

0.700 5.0 .0018

0.800 6.0 .0015

0.825 6.2 .0014

0.850 6.5 .0013

0.900 7.0 .0010

1.000 7.5 .0009

1.200 15.0 .0038

2.000 13.0 .0035

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

3 20 0.0033

4 32 .0052

5 50 .0040

6 72 .0040

7 98 .0030

8 128 .0030

9 162 .0030

10 200 .0030

11 242 .0030

12 288 .0030

13 338 .0030

14 392 .0030

16 512 .0040

18 648 .0040

20 800 .0040

22 968 .0040

24 1152 .0040

26 1352 .0040

28 1568 .0040

30 1800 .0040

39
SUM No. 2002 Specimen rnnlcrial: Aluminum Size: 3.8 X 3.8 X 1.3 c m

Specimen no.:

iivelcngth Resolved Wavelength Resolved

licrometer) Bandwidth Reflectance am (micrometer) Bandwidth Reflectance am

(nm) (nm)

0.2537 1.0 0.0008 3 20 0.0033

0.2650 1.0 .0014 4 32 .0052

0.2805 1.1 .0008 5 50 .0040

0.3023 1.2 .0003 6 72 .0040

0.3340 1.3 .0005 7 98 .0030

0.3651 1.4 .0002 8 128 .0030

0.4048 1.6 .0003 9 162 .0030

0.4358 1.7 .0002 10 200 .0030

0.5460 2.5 .0002 11 242 .0030

0.5770 2.5 .0002 12 288 .0030

0.600 4.0 .0030 13 338 .0030

0.650 4.5 .0020 14 392 .0030

0.700 5.0 .0018 16 512 .0040

0.800 6.0 .0015 18 648 .0040

0.825 6.2 .0014 20 800 .0040

0.850 6.5 .0013 22 968 .0040

0.900 7.0 .0010 24 1152 .0040

1.000 7.5 .0009 26 1352 .0040

1.200 15.0 .0038 28 1568 .0040

2.000 13.0 .0035 30 1800 .0040

40
SRM No. 2003 Specimen material: Aluminum Size: 2.9 cm diameter

Specimen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

0.2537 1.0 0.0016

0.2650 1.0 .0028

0.2805 1.1 .0016

0.3023 1.2 .0006

0.3340 1.3 .0010

0.3651 1.4 .0004

0.4048 1.6 .0006

0.4358 1.7 .0004

0.5460 2.5 .0004

0.5770 2.5 .0004

0.600 4.0 .0087

0.650 4.5 .0052

0.700 5.0 .0040

0.800 6.0 .0035

0.825 6.2 .0038

0.850 6.5 .0035

0.900 7.0 .0026

1.000 7.5 .0021

1.200 15.0 .0095

2.000 13.0 .0063

Wavenlength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

3 20 0.0058

4 32 .0090

5 50 .0070

6 72 .0070

7 98 .0053

8 128 .0053

9 162 .0053

10 200 .0053

11 242 .0053

12 288 .0053

13 338 .0053

14 392 .0053

16 512 .0070

18 648 .0070

20 800 .0070

22 968 .0070

24 1152 .0070

26 1352 .0070

28 1568 .0070

30 1800 .0070

41
SKM No. 2004 Specimen material: Aluminum Size: 2.4 cm diameter

Specimen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance om

(nm)

0.2537 1.0 0.0016

0.2650 1.0 .0028

0.2805 1.1 .0016

0.3023 1.2 .0006

0.3340 1.3 .0010

0.3651 1.4 .0004

0.4048 1.6 .0006

0.4358 1.7 .0004

0.5460 2.5 .0004

0.5770 2.5 .0004

0.600 4.0 .0087

0.650 4.5 .0052

0.700 5.0 .0040

0.800 6.0 .0035

0.825 6.2 .0038

0.850 6.5 .0035

0.900 7.0 .0026

1.000 7.5 .0021

1.200 15.0 .0095

2.000 13.0 .0063

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

3 20 0.0058

4 32 .0090

5 50 .0070

6 72 .0070

7 98 .0053

8 128 .0053

9 162 .0053

10 200 .0053

11 242 .0053

12 288 .0053

13 338 .0053

14 392 .0053

16 512 .0070

18 648 .0070

20 800 .0070

22 968 .0070

24 1152 .0070

26 1352 .0070

28 1568 .0070

30 1800 .0070

42
U. S. DeparlAfnt' of Commerce

MauriceijjB. Stans

National Bui^IS;! Standards

L. M. BitasobrnK Director Certificate

Standard Reference Materials

2005, 2006, 2007, 2008

Gold on Glass

(Standards for Specular Spectral Reflectance)

These Standard Reference Materials are for calibrating equipment used in evaluating the thermal

radiation properties of materials. The mirrors were prepared by fast vacuum deposition of gold on

fine-annealed borosilicate glass, the surface to be coated being flat to about 27 nm. The mirrors are prepared in four sizes.

SRM No. Size of blank (cm) Coated Area (cm)

2005 7.6 X 10.2 X 1.9 5.1 X 7.6

2006 3.8 X 3.8 X 1.3 2.5 X 2.5

2007 disk: 2.9 diameter X 1.0 thick entire surface

2008 disk: 2.4 diameter X 0.6 thick entire surface

Each mirror is certified for near-normal (9°) specular reflectance at wavelengths ranging from

0.2537 to 30 micrometers and at corresponding resolved bandwidths from 1.0 to 1800 nanometers.

The precision measure (Oj^) is the standard deviation of the mean of six replicate measurements.

The certified values are given on the attached sheet. Details of experimental techniqtfes used will be

described in an NBS 260 publication.

Measurements of reflectance and other experimental work leading to the certification of these

Standard Reference Materials were performed by J. C. Richmond and J.J. Hsia of the Heat

Division, Institute for Basic Standards, National Bureau of Standards.

Washington, D. C. 20234 J. Paul Cali, Chief

April 16, 1971 Office of Standard Reference Materials

43
SRM No. 2005 Specimen material: Gold Size: 7.6 X 10.2 X 1.9 cm

Specimen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

0.2537 1.0 0.0005

0.2650 1.0 .0004

0.2805 1.1 .0005

0.3023 1.2 .0005

0.3340 1.3 .0005

0.3651 1.4 .0002

0.4048 1.6 .0003

0.4358 1.7 .0002

0.5460 2.5 .0003

0.5770 2.5 .0003

0.600 4.0 .0030

0.650 4.5 .0020

0.700 5.0 .0018

0.800 6.0 .0015

0.825 6.2 .0014

0.850 6.5 .0013

0.900 7.0 .0010

1.000 7.5 .0009

1.200 15.0 .0038

2.000 13.0 .0035

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

3 20 0.0033

4 32 .0052

5 50 .0040

6 72 .0040

7 98 .0030

8 128 .0030

9 162 .0030

10 200 .0030

11 242 .D030

12 288 .0030

13 338 .0030

14 392 .0030

16 512 .0040

18 648 .0040

20 800 .0040

22 968 .0040

24 1152 .0040

26 1352 .0040

28 1568 .0040

30 1800 .004(0

44
SRMNo. 2006 Specimen material: Gold Size: 3.8 X 3.8 X 1.3 cm

Specimen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

0.2537 1.0 0.0006

0.2650 1.0 .0010

0.2805 1.1 .0007

0.3023 1.2 .0003

0.3340 1.3 .0005

0.3651 1.4 .0002

0.4048 1.6 .0003

0.4358 1.7 .0002

0.5460 2.5 .0002

0.5770 2.5 .0002

0.600 4.0 .0030

0.650 4.5 .0020

0.700 5.0 .0018

0.800 6.0 .0015

0.825 6.2 .0014

0.850 6.5 .0013

0.900 7.0 .0010

1.000 7.5 .0009

1.200 15.0 .0038

2.000 13.0 .0035

Wavelength Resolved

Bandwidth Reflectance am

(nm)

3 20 0.0033

4 32 .0052

5 50 .0040

6 72 .0040

7 98 .0030

8 128 .0030

9 162 .0030

10 200 .0030

11 242 .0030

12 288 .0030

13 338 .0030

14 392 .0030

16 512 .0040

18 648 .0040

20 800 .0040

22 968 .0040

24 1152 .0040

26 1352 .0040

28 1568 .0040

30 1800 .0040

45
SRM No. 2007 Specimen material: Gold Size: 2.9 cm diameter

Speinmen no.:

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

0.2.537 1.0 0.0012

0.2650 1.0 .0020

0.2805 1.1 .0014

0.3023 1.2 .0006

0.3340 1.3 .0010

0.3651 1.4 .0004

0.4048 1.6 .0006

0.4358 1.7 .0004

0.5460 2.5 .0004

0.5770 2.5 .0004

0.600 4.0 .0087

0.650 4.5 .0052

0.700 5.0 .0040

0.800 6.0 .0035

0.825 6.2 .0038

0.850 6.5 .0035

0.900 7.0 .0026

1.000 7.5 .0021

1.200 15.0 .0095

2.000 13.0 .0063

Wavelength Resolved

(micrometer) Bandwidth Reflectance am

(nm)

3 20 0.0058

4 32 .0090

5 50 .0070

6 72 .0070

7 98 .0053

8 128 .0053

9 162 .0053

10 200 .0053

11 242 .0053

12 288 .0053

13 338 .0053

14 392 .0053

16 512 .0070

18 648 .0070

20 800 .0070

22 968 .0070

24 1152 .0070

26 1352 .0070

28 1568 .0070

30 1800 .0070

46
SRMNo. 2008 Specimen material: Gold Size: 2.4 cm diameter

Specimen no.:

'avelenffth Resolved Wavelenffth Resolved

licrometer) Bandwidth Reflectance am (micrometer) Bandwidth Reflectance am

(nm) (nm)

0.2537 1.0 0.0012 3 20 0.0058

0.2650 1.0 .0020 4 32 .0090

0.2805 1.1 .0014 5 50 .0070

0.3023 1.2 .0006 6 72 .0070

0.3340 1.3 .0010 7 98 .0053

0.3651 1.4 .0004 8 128 .0053

0.4048 1.6 .0006 9 162 .0053

0.4358 1.7 .0004 10 200 .0053

0.5460 2.5 .0004 11 242 .0053

0.5770 2.5 .0004 12 288 .0053

0.600 4.0 .0087 13 338 .0053

0.650 4.5 .0052 14 392 .0053

0.700 .5.0 .0040 16 512 .0070

0.800 6.0 .0035 18 648 .0070

0.825 6.2 .0038 20 800 .0070

0.850 6.5 .0035 22 968 .0070

0.900 7.0 .0026 24 1152 .0070

1.000 7.5 .0021 26 1352 .0070

1.200 15.0 .0095 28 1568 .0070

2.000 13.0 .0063 30 1800 .0070

47
troRM NBS-114A (1-71) U.S. DEPT. OF COMM. 1 . PUBLICATION OR REPORT NO. 2. Gov't Accesslwi BIBLIOGRAPHIC DATA ^ 260-38

3. Recipient's Accession No.

4. TITLE AND SUBTITLE Preparation and Calibration of Standards of Spectral

Specular Reflectance

5. Publication Date May 1972

6. Performing Organization Code

7. AUTHOR(S)

J. C. Richmond, and J. J. Hsia

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 2212726

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same ae No. 9*

13. Type of Report & Period Covered Final

14. sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.)

This report describes in detail the preparation and calibration of Standard

Reference Materials 2001 through 2008. These standards of spectral specular

reflectance were prepared commercially by vacuum depositing opaque coatings

of gold and aluminum, respectively, onto polished substrates of fine-annealed

borosilicate glass. The near-normal (9° from normal) spectral specular

reflectance was measured by the multiple-reflection technique. Four different

combinations of source, spectrometer, and detector were used to cover the

wavelength range from about 0.25 ym to 30 ym and beyond.

17, KEY WORDS (Alphabetical order, separated by semicoions)Aluminum; gold; infrared reflectance; interferometer spectrometer; mirrors; reflectance; reflectance standards; spectral reflectance;

spectral specular reflectance; specular reflectance; standards ;ultravlolet reflectance.

18. AVAILABILITY STATEMENT

UNL IMITED.

I I FOR OFFIQAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

57

22. Price

60 cents

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