Demodulation of multimodulation artifacts in Fourier-transform infrared spectroscopy

Abstract

Fourier-transform infrared (FTIR) spectra can show artifacts, for example, in the vicinity of the overtone when light is doubly modulated. Technical approaches, i.e., modifications to the spectrometer setup, have been devised in order to reduce those artifacts. Elimination of the artifacts was achieved only partly but at the expense of a loss of intensity or an increase in the noise level. We devised a computational demodulation scheme that is capable of almost fully reducing the artifacts with neither a loss of spectroscopic information nor an increase in the noise level. This has been demonstrated for the FTIR absorption spectra in the overtone regions of HCl(g) and CH(g).

Potential Second-Harmonic Ghost Bands in Fourier Transform Infrared (FT-IR) Difference Spectroscopy of Proteins

“…All these features strongly indicate that the above commented bands do not originate from overtones of retinal vibrations but rather from second harmonic bands originated from double-modulation artifacts. 39…”

“…28 Reports on inter-reflection artifacts are scarce, mostly limited to our knowledge to highresolution FT-IR of gases, where artifactual harmonics from fundamental vibrations overlap and distort overtone vibrations. 39,40 Here, we show that light-induced FT-IR difference spectra of the proton-pump bacteriorhodopsin (BR) measured with a commercial spectrometer shows artificial bands in the 2800-1800 cm À1 region. We show that these ghost bands are second harmonics from genuine bands in the 1400-900 cm À1 region, originated from double-modulation artifacts.…”

“…Inter-reflection artifacts can be even more troublesome than detector nonlinearity, being less obvious to diagnose and to correct for. 38,39 They arise from back-reflections of the IR beam into the interferometer, where further modulation occurs before reaching the detector. 28 Back-reflections can occur at any surface present in the optical path, before or after the interferometer.…”

“…harmonic in a single-beam spectrum. 39 Although some optical designs are able to impede back-reflected light reaching the interferometer to be redirected to the detector, they go with at the cost of a reduced photon throughput. 28 Reports on inter-reflection artifacts are scarce, mostly limited to our knowledge to high-resolution FT-IR of gases, where artifactual harmonics from fundamental vibrations overlap and distort overtone vibrations.…”

“…28 Reports on inter-reflection artifacts are scarce, mostly limited to our knowledge to high-resolution FT-IR of gases, where artifactual harmonics from fundamental vibrations overlap and distort overtone vibrations. 39,40…”