Metal matrix composites offer numerous options in materials performance over the more conventional resin matrix composites; consequently, it is necessary to obtain a complete data base on this class of materials. In this report are described methods and results of thermal expansion measurements. Because theoretical predictions indicate that very low expansion values can be achieved, there is an interest in related thermal measurements, such as thermal cycling behavior, the effects of internal stresses, and mircrocracking. In particular, there must be adequate experimental accuracy to measure these quantities as a function of fiber-metal system. The advantages of essentially contactless measurement techniques such as Michelson interferometers are presented, including a lack of restriction on sample size or shape. The special requirements in laser characteristics, optics, gaseous and thermal environments, signal processing, and data reduction needed to describe fully low thermal expansion behavior are outlined. Dimensional changes must be measured with an accuracy on the order of + or - .00000001 m. Since differential thermal strains between fiber and matrix have been found to produce stresses that exceed the transverse strength of resin matrixes, a new acousto-optical technique is employed to study microcracking in metal matrix composites at low temperatures, concurrently with coefficient of thermal expansion (CTE) measurements. The instrumentation required to analyze high-frequency signals in laser interferometers is described. Experimental results are presented for B-A1, graphite-A1, SiC/Al and graphite-Mg composites.