Scanning interferometer and method of using same providing for rapid, reliable detection of chemical compounds that are readily implemented in low-cost, portable configurations for application in a variety of monitoring and detection applications. A scanning double-beam interferometer, particularly a Michelson interferometer, in which the length of at least one of the optical paths (or arms) of the interferometer is selectively adjustable by use of an actuator in which rotational displacement of a rotatable element is converted into linear displacement of at least one reflective surface which forms an end of an optical path of the interferometer is employed to obtain interferograms of electromagnetic radiation attenuated, emitted, scattered or reflected from a sample. The length of the optical path that is adjusted is determined using an optical detection scheme, particularly where marking on the rotatable element are detected to determine linear displacement of the reflective surface.