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Twice-Modulated Light in Fourier Transform Infrared (FT-IR) Spectrometers from Reflective Samples: Avoiding Distorted
Timothy J Johnson1, Tracy J Baker1, Ashley M Bradley1
16865Pacific Northwest National Laboratory, Richland, WA, USA.
Applied Spectroscopy
|February 28, 2022
Summary
A common artifact in Fourier transform spectroscopy arises from sample back-reflection, causing erroneous frequency doubling. Rotating the sample eliminates this artifact, ensuring accurate spectral data for various IR sampling methods.
Area of Science:
- Spectroscopy
- Analytical Chemistry
- Physical Chemistry
Background:
- Fourier transform spectrometers (FTS) are susceptible to artifacts.
- Sample back-reflection can cause erroneous spectral signals.
- This artifact is particularly noticeable with narrow absorption peaks.
Purpose of the Study:
- To identify and characterize an artifact in Fourier transform spectroscopy.
- To explain the origin of the artifact related to sample back-reflection.
- To propose a method for redressing this spectral artifact.
Main Methods:
- Investigating spectral data from Fourier transform spectrometers.
- Analyzing the effect of sample orientation and refractive index on back-reflection.
- Implementing a sample rotation stage to mitigate the artifact.
Main Results:
- Back-reflection from samples oriented normal to the beam causes a secondary modulation.
- This results in spectral signals appearing at twice their true frequency (2f).
- The artifact is effectively eliminated by rotating the sample holder via a rotation stage.
Conclusions:
- Sample back-reflection is a significant artifact in Fourier transform spectroscopy.
- A simple rotation stage effectively corrects this artifact across the spectrum.
- This finding is crucial for accurate spectral analysis in various IR sampling techniques.
Keywords:
FT-IRFourier transform infraredIRInfraredartifactdouble modulationreflectanceretroreflectionMore Related Videos
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