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Extension of Complex Refractive Index Measurements to the Near-Infrared for Liquids: Methodology and Uncertainty Analysis.

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Title: Extension of Complex Refractive Index Measurements to the Near-Infrared for Liquids: Methodology and Uncertainty Analysis.
Authors: Primera-Pedrozo, Oliva M.1 (AUTHOR), Tonkyn, Russell G.1 (AUTHOR), Baker, Tracy J.1 (AUTHOR), Lockwood, Schuyler P.1 (AUTHOR), Bradley, Ashley M.1 (AUTHOR), Johnson, Timothy J.1 (AUTHOR), Myers, Tanya L.1 (AUTHOR) Tanya.Myers@pnnl.gov
Source: Applied Spectroscopy. Mar2026, Vol. 80 Issue 3, p259-271. 13p.
Subjects: Refractive index, Near infrared spectroscopy, Aerosols, Liquids, Error analysis in mathematics, Absorption spectra, Chemical fingerprinting
Abstract: Optical identification of liquid droplets, aerosols, or thin films is critical for many applications. While reference spectra are sometimes available for such measurements, they are not always applicable to the observed spectrum or the given sample morphology. Reference spectra for many forms can be modeled, however, if the n / k vectors (real and imaginary refractive indices) are available. In previous work we have reported protocols to determine the n / k vectors for dozens of liquids, primarily in the mid-infrared (MIR) spectral range from 7500 to 400 cm–1. In this work we extend the spectral range into the near-infrared (NIR) region, demonstrating a method to measure and merge the data sets to create composite n / k data ranging from 10 000 to 400 cm–1 (1.0 to 25 µm) with absorbance fidelity spanning over four orders of magnitude, and vastly improved signal-to-noise in the NIR. The precision of the composite data is evaluated for three different liquids, focusing primarily on the steps for converting the raw absorbance spectra to k values. The variability in both MIR and NIR data as well as in the final n/k vectors is also investigated for several liquids. For typical liquids, the overall variability (reported as 2σ) in the final n and k -vectors is determined to be ∼0.4% and 3%, respectively. Finally, the derived n / k data are used to calculate absorbance spectra for aerosol droplets, showing marginal variability due to the typical measurement errors in the final n / k vectors. [ABSTRACT FROM AUTHOR]
Copyright of Applied Spectroscopy is the property of Sage Publications Inc. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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  Data: Extension of Complex Refractive Index Measurements to the Near-Infrared for Liquids: Methodology and Uncertainty Analysis.
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  Data: <searchLink fieldCode="JN" term="%22Applied+Spectroscopy%22">Applied Spectroscopy</searchLink>. Mar2026, Vol. 80 Issue 3, p259-271. 13p.
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– Name: Abstract
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  Data: Optical identification of liquid droplets, aerosols, or thin films is critical for many applications. While reference spectra are sometimes available for such measurements, they are not always applicable to the observed spectrum or the given sample morphology. Reference spectra for many forms can be modeled, however, if the n / k vectors (real and imaginary refractive indices) are available. In previous work we have reported protocols to determine the n / k vectors for dozens of liquids, primarily in the mid-infrared (MIR) spectral range from 7500 to 400 cm–1. In this work we extend the spectral range into the near-infrared (NIR) region, demonstrating a method to measure and merge the data sets to create composite n / k data ranging from 10 000 to 400 cm–1 (1.0 to 25 µm) with absorbance fidelity spanning over four orders of magnitude, and vastly improved signal-to-noise in the NIR. The precision of the composite data is evaluated for three different liquids, focusing primarily on the steps for converting the raw absorbance spectra to k values. The variability in both MIR and NIR data as well as in the final n/k vectors is also investigated for several liquids. For typical liquids, the overall variability (reported as 2σ) in the final n and k -vectors is determined to be ∼0.4% and 3%, respectively. Finally, the derived n / k data are used to calculate absorbance spectra for aerosol droplets, showing marginal variability due to the typical measurement errors in the final n / k vectors. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Applied Spectroscopy is the property of Sage Publications Inc. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1177/00037028251399225
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        Text: English
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        PageCount: 13
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      – SubjectFull: Refractive index
        Type: general
      – SubjectFull: Near infrared spectroscopy
        Type: general
      – SubjectFull: Aerosols
        Type: general
      – SubjectFull: Liquids
        Type: general
      – SubjectFull: Error analysis in mathematics
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      – SubjectFull: Absorption spectra
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      – SubjectFull: Chemical fingerprinting
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      – TitleFull: Extension of Complex Refractive Index Measurements to the Near-Infrared for Liquids: Methodology and Uncertainty Analysis.
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              Text: Mar2026
              Type: published
              Y: 2026
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