Applications Of Step-Scan Interferometry

Manning, Christopher J.; Widder, Jeffrey M.; Palmer, Richard A.; Ji, Chao

doi:10.1117/12.969609

SPIE Proceedings

1989

DOI: 10.1117/12.969609

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Applications Of Step-Scan Interferometry

Christopher J. Manning

Jeffrey M. Widder

Richard A. Palmer

et al.

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Cited by 5 publications

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“…The use of S 2 FT-IR PAS for spectral depth profiling has been developed during the past 8 years. − Since the step-scan mode allows the interferogram to be measured point-by-point, while the optical path difference is held constant, the time dependence of the interferogram is eliminated. This allows a single modulation frequency to be applied to all wavelengths, in contrast to the wavelength-dependent Fourier frequencies of the conventional continuous-scan FT-IR method.…”

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“…There are two basic approaches to PA spectral depth profiling: (1) variation of the modulation frequency and (2) analysis of the signal phase. Application of the modulation frequency variation method (by use of path difference, or phase, modulation) in S 2 FT-IR PA depth profiling of both continuously heterogeneous and discretely heterogeneous materials has been widely demonstrated. − , However, with this method, the depth resolution is limited by the phase modulation frequency range and frequency selection of the instrument. Furthermore, with sine wave phase modulation, each frequency requires a separate scan.…”

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Comparison of Phase Rotation, Phase Spectrum, and Two-Dimensional Correlation Methods in Step-Scan Fourier Transform Infrared Photoacoustic Spectral Depth Profiling

Jiang

Palmer

1997

Anal. Chem.

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This paper compares three photoacoustic phase-related analytical approaches for spectral depth profiling of heterogeneous materials, particularly in conjunction with step-scan Fourier transform infrared spectroscopy. The three approaches compared are (1) the phase rotation method, (2) the direct analysis of the phase spectrum, and (3) the calculation of two-dimensional (2D) frequency correlation maps. The experimental data for a representative two-layer sample consisting of a 12-µm-thick layer of ethylene-vinyl acetate on a 60-µm-thick polypropylene substrate are compared for the three approaches. Similar/ identical phase difference information can be obtained from either the continuous phase rotation plot or the phase spectrum. However, the phase spectrum method provides more accurate, direct, and efficient results with a higher depth resolution than does the phase rotation method. Qualitative agreement between the 2D correlation analysis and the photoacoustic phase analysis is observed, although the 2D approach does not clearly distinguish between spectral bands with similar response phase, limiting it to qualitative use.

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mentioning

confidence: 99%

mentioning

confidence: 99%

Comparison of Phase Rotation, Phase Spectrum, and Two-Dimensional Correlation Methods in Step-Scan Fourier Transform Infrared Photoacoustic Spectral Depth Profiling

Jiang

Palmer

1997

Anal. Chem.

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Step-scan Fourier-transform infrared spectrometer

Manning¹,

Palmer²,

Ji³

1991

Review of Scientific Instruments

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This article describes the modification of a commercial Fourier-transform infrared (FT-IR) spectrometer for step-scan operation. Step-scan operation decouples the FT-IR spectral multiplexing from time and is therefore applicable to a variety of time-dependent spectroscopic experiments, including, particularly, photoacoustic and photothermal spectroscopy. The step-scan instrument described controls the retardation (moving mirror position) with a feedback loop. The loop uses path difference, or phase, modulation of the reference laser intensity, together with lock-in amplifiers to detect the mirror position. Since the interferogram can be sampled at intervals as small as 1/4 λHeNe, the maximum free-spectral range is 31 600 cm−1. For initial positioning of the mirror, stepping can be as rapid as 100 Hz. The current software will allow data collection at ∼1.6 Hz, although the mirror settling time of ≤20 ms would allow data to be collected at 20–30 Hz stepping frequency with more efficient software. The mirror control phase modulation (PM) can also be used for efficient modulation of the infrared beam by use of a PM amplitude on the order of 1–2 λHeNe. The stability of the retardation, which imposes an upper limit on the SNR of the measured spectra, is ∼±15 nm. Data collection times on the order of 20 min are typical for 8 cm−1 resolution. Examples of dynamic spectroscopic data obtained using the step-scan mode of operation are presented. Future improvements to the instrument are briefly discussed.

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Investigation of Time-Dependent Phenomena by Use of Step-Scan FT-IR

et al. 1993

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The development, during the last decade, of modern step-scan interferometry instrumentation has allowed FT-IR to be applied to the study of time-dependent phenomena in ways not previously possible, because of the problems of uncoupling the spectral multiplexing from the temporal domain in the continuous-scan FT-IR mode. Specifically, the time regime from tens of nanoseconds to tens of milliseconds has been accessible to time-domain measurements to only a very limited degree with continuous-scan instrumentation and not at all for modulation-demodulation (frequency-domain) experiments in this time range. The step-scan technique not only works very well in this time regime and for slower phenomena, but is only prevented from application to faster processes by the signal strength, the speed of available detectors, the intensity of sources, and the speed and sophistication of the electronics. This paper surveys the various types of experiments which are either enhanced by use of step-scan FT-IR methods or are only possible by use of these techniques. The principles of step-scan instrumentation are reviewed, particularly those of retardation control, signal generation, and data acquisition, as well as the place of step-scan FT-IR relative to other techniques of dynamic vibrational spectroscopy. The importance of path difference (phase) modulation, particularly in frequency-domain measurements, the extraction and use of the signal phase, the creation of 2D FT-IR spectra, and the strategies for acquisition of both time- and frequency-domain data in the step-scan mode are discussed and illustrated.

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Applications Of Step-Scan Interferometry

Cited by 5 publications

References 0 publications

Comparison of Phase Rotation, Phase Spectrum, and Two-Dimensional Correlation Methods in Step-Scan Fourier Transform Infrared Photoacoustic Spectral Depth Profiling

Comparison of Phase Rotation, Phase Spectrum, and Two-Dimensional Correlation Methods in Step-Scan Fourier Transform Infrared Photoacoustic Spectral Depth Profiling

Step-scan Fourier-transform infrared spectrometer

Investigation of Time-Dependent Phenomena by Use of Step-Scan FT-IR

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