Methods for quantitative infrared directional-hemispherical
and diffuse reflectance measurements using an FTIR and a commercial
integrating sphere
Thomas A. Blake, Timothy J. Johnson, Russell G. Tonkyn, Brenda M. Forland, Tanya L. Myers, Carolyn S. Brauer, Yin-Fong Su, Bruce E. Bernacki, Leonard Hanssen, and Gerardo Gonzalez
Thomas A. Blake,1,*
Timothy J. Johnson,1
Russell G. Tonkyn,1
Brenda M. Forland,1,2
Tanya L. Myers,1
Carolyn S. Brauer,1
Yin-Fong Su,1
Bruce E. Bernacki,1
Leonard Hanssen,3
and Gerardo Gonzalez4
1Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99354, USA
2Current address: Red Rocks Community College, 13300 West 6th Avenue, Lakewood, Colorado 80228, USA
3Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
4Alecam FTIR Services and Consulting, The Woodlands, Texas 77381, USA
Thomas A. Blake, Timothy J. Johnson, Russell G. Tonkyn, Brenda M. Forland, Tanya L. Myers, Carolyn S. Brauer, Yin-Fong Su, Bruce E. Bernacki, Leonard Hanssen, and Gerardo Gonzalez, "Methods for quantitative infrared directional-hemispherical and diffuse reflectance measurements using an FTIR and a commercial integrating sphere," Appl. Opt. 57, 432-446 (2018)
We have developed methods to measure the directional-hemispherical
() and diffuse
() reflectances of powders, liquids,
and disks of powders and solid materials using a commercially
available, matte gold-coated integrating sphere and Fourier transform
infrared spectrometer. To determine how well the sphere and protocols
produce quantitative reflectance data, measurements were made of three
diffuse and two specular standards prepared by the National Institute
of Standards and Technology (NIST), LabSphere Infragold and Spectralon
standards, hand-loaded sulfur and talc powder samples, and water.
Relative to the NIST measurements of the NIST standards, our
directional hemispherical reflectance values are within
for four of the standards and within
for a low reflectance diffuse
standard. For the three diffuse reflectance NIST standards, our
diffuse reflectance values are within of the NIST values. For the two
specular NIST standards, our diffuse reflectance values are an order
of magnitude larger than those of NIST, pointing to a systematic error
in the manner in which diffuse reflectance measurements are made for
specular samples using our methods and sphere. Sources of uncertainty
are discussed in the paper.
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Fractional Uncertainties Used for Calculating Systematic
Uncertainties When Using the Bruker Sphere for DHR and Diffuse
Reflectance Measurementsa
Source of Systematic Uncertainty
DHR Configuration
Diffuse Configuration
Knife edges/flat specular port edges
0.0294
0.0135
Curved sample/flat sample
0.0020
0.00106
Detector FOV and baffle position
0.0078
0.0155
FTIR baseline drift
0.0020
0.0020
Fractional uncertainties for the sphere are calculated from
ray trace simulations of the Bruker integrating sphere
assuming a Lambertian wall interior and Lambertian sample
surface both with . For specular samples,
the fractional uncertainty associated with knife edges and
port edges is assumed to be zero.
Table 2.
Average DHR and Diffuse Reflectance and Percent Change Between
PNNL and NIST Measurement of the Five NIST Standardsa
Averages calculated between and
. The values in
parenthesis after the reflectances are the two standard
deviation ( coverage factor) expanded
uncertainties.
Percent change, .
The diffuseness spectrum is defined as
and measured by the
Bruker sphere. is averaged between
and
to give the values
shown.
Table 3.
Average Scaled DHR and Diffuse Reflectance Values for
Infragold, Bruker Diffuse Gold, Spectralon 99% Reflectance
Standard, Hand-Loaded Sulfur, Hand-Loaded Talc, and Watera
Average DHR values for calibration spectra, where
available, and percent change with the PNNL results are
given. Calculated diffuseness values are also given. The
values in parenthesis after the reflectances are the two
standard deviation ( coverage factor) expanded
uncertainties.
Percent change, .
The diffuseness spectrum is defined as
and measured by the
Bruker sphere. is averaged over the
wavenumber ranges noted to give the values shown.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Tables (3)
Table 1.
Fractional Uncertainties Used for Calculating Systematic
Uncertainties When Using the Bruker Sphere for DHR and Diffuse
Reflectance Measurementsa
Source of Systematic Uncertainty
DHR Configuration
Diffuse Configuration
Knife edges/flat specular port edges
0.0294
0.0135
Curved sample/flat sample
0.0020
0.00106
Detector FOV and baffle position
0.0078
0.0155
FTIR baseline drift
0.0020
0.0020
Fractional uncertainties for the sphere are calculated from
ray trace simulations of the Bruker integrating sphere
assuming a Lambertian wall interior and Lambertian sample
surface both with . For specular samples,
the fractional uncertainty associated with knife edges and
port edges is assumed to be zero.
Table 2.
Average DHR and Diffuse Reflectance and Percent Change Between
PNNL and NIST Measurement of the Five NIST Standardsa
Averages calculated between and
. The values in
parenthesis after the reflectances are the two standard
deviation ( coverage factor) expanded
uncertainties.
Percent change, .
The diffuseness spectrum is defined as
and measured by the
Bruker sphere. is averaged between
and
to give the values
shown.
Table 3.
Average Scaled DHR and Diffuse Reflectance Values for
Infragold, Bruker Diffuse Gold, Spectralon 99% Reflectance
Standard, Hand-Loaded Sulfur, Hand-Loaded Talc, and Watera
Average DHR values for calibration spectra, where
available, and percent change with the PNNL results are
given. Calculated diffuseness values are also given. The
values in parenthesis after the reflectances are the two
standard deviation ( coverage factor) expanded
uncertainties.
Percent change, .
The diffuseness spectrum is defined as
and measured by the
Bruker sphere. is averaged over the
wavenumber ranges noted to give the values shown.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
Averaged between and
.
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