5.1 Introduction

Thermoptometry (also referred to as thermo-optical analysis, TOA) is a group of techniques in which optical properties of a sample are measured as a function of temperature ^[1]. Under this heading, the major technique is thermomicroscopy, i.e. direct observation of the sample. Other techniques involve measurement of total light reflected or transmitted (thermophotometry), light of specific wavelength(s) (thermospectrometry), refractive index (thermorefractometry), or emitted light (thermoluminescence). Wiedemann and Felder-Casagrande ^[2] have recently reviewed these techniques and also dealt with their historical development, including the important role of W.J. McCrone ^[3] in the development and popularisation of thermomicroscopy. Wendlandt's book ^[4] contains an excellent chapter and there is also useful information in references ^[5], ^[6]. Gallagher's chapter in reference ^[7] contains much recent information.

To the above techniques must now be added the more recent developments of scanning tunnelling microscopy and atomic force microscopy that have led to the new field of Micro Thermal Analysis described in section 5.10 below.