Enhanced Sensitivity for Internal Reflection Spectroscopy

Abstract

A standing wave with an evanescent electromagnetic field in the rarer medium is established normal to the reflecting surface for total internal reflection. Optical spectra of materials can be obtained by measuring the interaction of this evanescent field with an absorbing rarer medium. This spectroscopy technique, called Internal Reflection Spectroscopy, can be employed in many instances where conventional either fail or cannot easily be employed. Examples of these are the recording of the spectra of monomolecular films and powdered samples. By placing appropriate resonant thin films (optical cavities) on the reflecting surface, strongly amplified fields, analogous to that obtained in microwave cavities are established, and enhanced absorptions are obtained. In addition to a brief review of Internal Reflection Spectroscopy, the principles and applications of these optical cavities will be discussed as well as other methods for enhancing the sensitivity.