A Brief Introduction to Fourier Transform
Infrared Spectrometry

This work was presented at the American Chemical Society
National Meeting in Washington, DC on Aug 22, 2000

Table of contents

A Brief Introduction to Fourier Transform Infrared Spectrometry

A Picture of the Clearwater River

Discovery of Infrared Radiation

Discovery of Interference

Spectroscopy

Molecular Vibrations

Dipole Moments

Correlation between Chemical Structure and Infrared Absorption

Michelson Interferometer

Interferometric Modulation

Rapid-scan Frequency Spectrum

Step-scan vs. Rapid-scan

Step-scan Frequency Spectrum

Fourier Transform

Vector Resolution

Phase modulation

System Block Diagram

The Vision Thing

The Reincarnation of Step-scan FT-IR Spectrometry

A Brief History of Interferometry

Key Enabling Technologies

Conventional Signal Processing

Digital Signal Processing

Time-domain SNR vs. Frequency-domain SNR line spectrum

Phase Modulation Measurement

FT of detector signal single-frequency phase modulation, near zpd

FT of detector signal single-frequency pm, away from zpd

FT of detector signal two-frequency phase modulation

Simultaneous 3-Frequency Phase-modulated Photoacoustic Measurement

Photoacoustic Phase

Double-modulation Frequency Spectra

Double-modulation Measurement

FT of detector signal

Transmission Spectrum of Polypropylene

Dynamic stretching

Comparison of single and multi-frequency stretching results

Effect of Multiplicative Noise

Largest Multiplicative Frequency Mixing Only Adjacent Elements

Possible Instabilities

Refractive Index Variation

100% Line without Insulation

100% Line with Insulation

Block Diagram of DSP-Spectrometer

Instrument Basic Specifications

Picture of the Internal MIR 8000 Arrangement

DSP Specifications PC-32

DSP Specifications M-67

DSP Advantages

Modified Instrument Specifications

Transient Response

Position Stability

Step-scan 100% Line

Schematic of a DSP Based Spectroscopic Imaging System

Picture of the Oriel MIR 8000 Spectrometer Setup

Infrared Brightfield Images of a Bar Target

Infrared Spectra and Images of polymer "Shocktube" Laminate

Cost of Computing

Conclusions

Picture of a Vibrational Spectroscopist on the Clearwater River

Acknowledgements

Contact Information

Author: Chris Manning

E-mail: chris@appl-tech.com

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