Fourier transform infrared imaging: Theory and practice

The signal-to-noise ratio (SNR) of spectral data obtained from a microimagi ng Fourier transform infrared (FT-IR) spectrometer assembly, employing a st ep-scan interferometer and focal plane array detector, is analyzed. Based o n the methodology of data collection, a theoretical description for the per formance characteristics is proposed and quantitative effects of the acquis ition parameters on the SNR are explained theoretically and compared to exp eriment. To obtain the best strategy for achieving either the highest SNR i n a given time interval or for attaining a given SNR in the shortest time p eriod, the concept of characteristic plots is introduced. The theoretical a nalysis is extended to Fr-IR microimaging employing continuous scan interfe rometers in which the advantages of fast image collection are enumerated, w hile SNR limitations arising from mirror positioning errors are discussed. A step-scan method is suggested for faster data collection in which an opti mal detector response and SNR benefits are retained. Theoretically obtained SNRs based upon the expressions proposed in this paper predict experimenta lly determined values quite well and can be used to obtain an understanding of the required developments for improved performance. Finally, SNRs for b oth microimaging systems and conventional microspectroscopic instrumentatio n are compared.