STEP SCAN INTERFEROMETRY IN THE MID-INFRARED WITH PHOTOTHERMAL DETECTION

A medium resolution mid-infrared FT-IR instrument has been modified to do step scanning; this has been done with the use of concepts previously applied to both near- and far-infrared instruments. The authors illustrate the method used for driving the mirror in the step scan mode and present some preliminary results from using the instrument with photothermal detection. At the current state of development, results obtained with the use of phase modulation indicate that this method produces significantly higher signal-to-noise ratios than does the use of amplitude (chopper) modulation to generate the photothermal signal.