This paper describes the development and operation of two dual-probe interference systems for detection of surface acoustic waves. Both systems operate by comparing the surface displacement under each probe, thus enabling the surface wave velocity to be determined. In the so-called direct interference system the two probe beams are made to interfere with each other whereas in the indirect interference system each probe beam is made to interfere with a common reference. The relative merits of

This paper presents a detailed three-dimensional analysis for the modelling of the photoreflectance effect, in particular the response of layered samples is considered. The dependence of t h e photoreflectance signal on various parameters such as lifetime, surface recombination velocity and carrier diffusion coefficient is discussed. It is shown that the carrier diffusion coefficient and the thermal diffusivity play an important role in determining the signal level from the photoreflectance system. The effects of the wavelength of the pump and probe beams are also discussed. Furthermore, a fast numerical algorithm, allowing for a rapid computational evaluation, has been applied.

A dual beam thermal wave probe has been used to measure the thickness of opaque thin films in a noncontact, nondestructive manner. The method relies on the measurement of the differential phase of two interferometrically determined photodisplacement signals. The technique does not require calibration against standard samples and can be used to determine film thicknesses from a few tens of nanometers up to several micrometers. Alternatively, if the film thickness is known, thermal material properties like diffusivity or conductivity can be determined. The conditions under which the system is expected to give the most accurate results are analyzed.

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Thermal and plasma waves have been simultaneously and independently probed by a novel differential system. This new detection system for characterising and imaging materials such as semiconductors in a noncontacting, nondestructive manner, is based on two parallel, heterodyne interferometers, which probe the specimen on a microscopic scale. These detect changes in sample reflectivity and surface displacement which are induced by a separate laser source. The optical and electronic configuration is described and results showing the measurement and imaging capabilities of the system are presented. New results indicating interference between photodisplacement and photoreflectance effects are discussed.