Spectrophotometry : accurate measurement of optical properties of materials

538 Pages·2014·26.41 MB·English

by  Germer

Experimental Methods in the
Physical Sciences
Thomas Lucatorto, Albert C. Parr and Kenneth
Baldwin
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Spectrophotometry:accuratemeasurementofopticalpropertiesofmaterials/editedby
ThomasA.Germer,JoanneC.Zwinkels,BenjaminK.Tsai.
pagescm—(Experimentalmethodsinthephysicalsciences;volume46)
Includesbibliographicalreferencesandindex.
ISBN978-0-12-386022-4
1. Spectrophotometry.I. Germer,ThomasA.,editorofcompilation.II. Zwinkels,JoanneC.,
1955-editorofcompilation.III. Tsai,BenjaminK.,editorofcompilation.IV. Series:
Experimentalmethodsinthephysicalsciences;v.46.
QD117.S64S642014
5430.55–dc23
2014015452
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ISBN:978-0-12-386022-4
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Contributors
NumbersinParenthesesindicatethepagesonwhichtheauthor’scontributionsbegin.
CarolJ.Bruegge(457),JetPropulsionLaboratory,CaliforniaInstituteofTechnology,
Pasadena, California, USA
Roger Davies (457), Department of Physics, University of Auckland, Auckland,
New Zealand
PaulC.DeRose(221),NationalInstituteofStandardsandTechnology(NIST),NIST,
Material Measurement Laboratory,Gaithersburg, Maryland,USA
Michael B. Eyring (489), Micro Forensics, Ltd., and Arizona Department of Public
Safety Crime Laboratory,Phoenix,Arizona, USA
Arnold A. Gaertner (67), National Research Council Canada, Ottawa, Ontario,
Canada
ThomasA.Germer(1,11,67,291),NationalInstituteofStandardsandTechnology,
Gaithersburg, Maryland,USA
JohnP.Hammond(409),StarnaScientificLimited,Hainault,Essex,UnitedKingdom
LeonardHanssen(333),NationalInstituteofStandardsandTechnology,Gaithersburg,
Maryland,USA
Andreas Ho¨pe (179), Physikalisch-Technische Bundesanstalt, Braunschweig,
Germany
JuntaroIshii (333),National MetrologyInstituteof Japan, AIST,Tsukuba,Japan
SimonG.Kaplan(97),NationalInstituteofStandardsandTechnology,Gaithersburg,
Maryland, USA
Tomoyuki Kumano(333),KobeCity Collegeof Technology, Kobe, Japan
James E.Leland (221),Copia LLC,Goshen, New Hampshire,USA
Paul C.Martin (489),CRAICTechnologies, San Dimas, California,USA
MariaE.Nadal(367),NationalInstituteofStandardsandTechnology,Gaithersburg,
Maryland, USA
ManuelA.Quijada(97),NASAGoddardSpaceFlightCenter,Code551,Greenbelt,
Maryland, USA
Sven Schro¨der (291), Fraunhofer Institute for Applied Optics and Precision
Engineering, Jena, Germany
Florian M. Schwandner (457), Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California, USA
Felix C. Seidel (457), Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, California, USA
xv
xvi Contributors
JohnC.Stover(291),The Scatter Works, Inc.,Tucson, Arizona, USA
Benjamin K. Tsai (1, 11), National Institute of Standards and Technology,
Gaithersburg, Maryland,USA
Peter A.vanNijnatten(143),OMT SolutionsBV,Eindhoven, Netherlands
HidenobuWakabayashi (333),KyotoUniversity, Kyoto,Japan
Hiromichi Watanabe (333), National Metrology Institute of Japan, AIST, Tsukuba,
Japan
DaveWyble(367),Avian Rochester,LLC,Webster, New York, USA
HowardW.Yoon(67),NationalInstituteofStandardsandTechnology,Gaithersburg,
Maryland,USA
Clarence J. Zarobila (367), National Institute of Standards and Technology,
Gaithersburg, Maryland,USA
Joanne C. Zwinkels (1, 11, 221), National Research Council Canada, NRC,
MeasurementScience and Standards,Ottawa, Ontario,Canada
Volumes in Series
Experimental Methods in the Physical Sciences
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Volume 45. Single-Photon Generation and Detection
Edited by Alan Migdall, Sergey Polyakov, Jingyun Fan, and Joshua Bienfang
Volume46.Spectrophotometry:AccurateMeasurementofOpticalProperties
of Materials
Edited by Thomas A. Germer, Joanne C. Zwinkels, and Benjamin K. Tsai
Preface
Spectrophotometryisthequantitativemeasurementoftheopticalpropertiesof
materialsoverawidewavelengthrangeencompassingtheultraviolet,visible,
andinfraredspectralregions.Thesespectralmeasurementsincludereflectance,
transmittance, absorptance/emittance, scattering, and fluorescence, and their
accuratemeasurementhasanimpactonawidefieldofscienceandtechnology.
Thedesignandperformanceofopticalinstruments,rangingfromlowcostcell-
phonecamerastohighcostmicrolithographyprojectiontoolsandsatellitetele-
scopes,requiresknowledgeoftheopticalpropertiesofthecomponents,suchas
their refractive index, roughness, subsurface scatter, and contamination. The
pharmaceuticalandchemicalindustriesuseopticalabsorptionandfluorescence
measurementstoquantifyconcentrationwhichisrequiredforaccuratedosing
and elimination of contaminants. Global climate change simulations require
accurate knowledge of the optical properties of materials, gases, and aerosols
tocalculatethenetenergybalanceofourplanet.Thepropertiesofthinfilms,
even when they are not intended for optical applications, are often related to
their optical reflection, transmission, and scattering properties. Commercial
productsareoftenselectedbyconsumersbasedupontheirappearance,acom-
plex attribute that encompasses more specific attributes, such as color, gloss,
andtexture.Renewedinterestinsolarenergyhasdriventheneedtomaximize
thelightcaptureefficiencyofsolarcollectors.
This book is intended to be a hands-on text for those seeking to perform
precise and accurate spectrophotometry of the optical properties of materials.
Based on teaching experiences at our respective institutes, it is our aim to
presentmaterialthathelpsthepractitionertosetupandoptimizethespectro-
photometer to perform these various measurements, validate the instrument
performance, and be aware of the various sources of errors that can impact
the results. A number of our students have been from institutes interested in
developing an independent capability for realizing spectrophotometric scales,
and it isour intentionto also provide the researcher the necessary framework
for designing and characterizing reference instruments for traceable measure-
ments of these optical quantities.
Chapter1introducesthetopicofspectrophotometryandashorthistoryof
itsdevelopmentandpresent-daychallenges.Itincludesasectionoutliningthe
standard methods and terminology used for evaluating and expressing uncer-
tainty in any measurement. This will provide the reader the background
needed to follow the examples of uncertainty analysis that are given for spe-
cific spectrophotometric measurements in some of the following chapters.
xxi
xxii Preface
Chapter 2 describes some theoretical concepts underlying spectrophotom-
etryandtheoptical propertiesofmaterials.Itbeginsbydefiningthedifferent
radiometric quantities of radiance, irradiance, and intensity. These quantities
are then related to the corresponding electromagnetic field quantities. This
theoretical foundation allows the definition of the spectrophotometric quanti-
ties: reflectance, transmittance, emittance, diffuse reflectance, diffuse trans-
mittance, and the bidirectional reflectance distribution function (BRDF).
Relationships between these quantities are derived and explained. A review
of the Fresnel relations is given, including expressions appropriate for thin
films and thick films. The Kirchhoff relationship between the reflectance
and emittance is derived. While the topic of BRDF modeling is beyond the
scopeofthistext,Chapter2describesthetheoryofKubelkaandMunk,which
isapplicable to highly diffuse materials and used widely in color formulation
and for determining molecular optical properties (absorption and scattering
coefficients). Chapter 2 also describes two theories for scattering from rough
surfaces,oneappropriateforveryroughsurfacesandoneappropriateforvery
smooth surfaces.
Chapters 3 and 4 discuss the means of obtaining wavelength separation
andspectralresolutioninspectrophotometry.Chapter3providesanoverview
of the use of grating and prism spectrometers in spectrophotometry, while
Chapter 4 discusses the use of Fourier transform interferometric methods.
Eachofthesemethodshasitsadvantagesanddisadvantages.Includedinthese
chaptersarediscussionsofhowmeasurementnoiseispropagated,hownonli-
nearities affect results, how stray light or interreflections produce artifacts,
andwhatdeterminesthespectralresolutionorbandpassofthemeasuredspec-
trophotometric quantities. Methods to identify and alleviate these problems
are described.
Chapter5coversthetopicofspecularreflectanceofnonscatteringsamples
such as mirrors and other samples with mirror-like reflection, and of regular
transmittanceoftransparentsamplessuchasglassfilters.Theinstrumentation
and procedures for measuring these properties via both absolute and relative
methods are discussed and practical methods are given for improving the
measurement accuracy. Sources of error are treated and representative uncer-
taintybudgetsaregivenforvariousexamples.Asaspecialtopic,methodsfor
accurate reflectance measurement at oblique incidence of very high reflec-
tance materials like reference mirrors and laser mirrors are discussed. Exam-
ples are given for both Fourier transform infrared (FTIR) and ultraviolet,
visible, and near-infrared (UV/Vis/NIR) spectrophotometry.
Chapter 6 describes the basic principles of diffuse reflectance and trans-
mission measurements. Unlikethe measurement ofspecularreflection, where
the angle of incidence equals the angle of reflection, in the case of diffuse
reflection, the incomingradiationisspreadover thehalf-spaceabove thesur-
face, with a certain distribution specific to the surface or material under test.
The integrating sphere with its ability to collect all or the diffuse-only