This paper proposes an interferometer system for studying transparent objects and describes the results obtained from a sample of the interferometer that has been fabricated. A single optical element is used to separate the initial light wave and to form the interference pattern in this interferometer system. This ensures that the system will be stable with respect to various external effects, especially to vibrations. Results are given for experimental studies of the quality of laser crystals by means of this interferometer. (C) 2001 The Optical Society of America.