Minimum deadpath interferometer and dilatometer

Abstract

An interferometer in which an input beam is divided into two beams, the first of which is incident on a movable first reflecting surface before being recombined in an output beam with the second of the beams. The path for each beam is selected to be as similar as possible to the path for the other beam so that small rotations or translations of elements used to direct the beams affect both beams equally and so that changes in the ambient conditions affect both beams equally. The two beams are directed by reflecting elements, each of which reflects both beams an equal number of times so that small rotations of the elements affect both beams equally. The second beam is incident on a second reflecting surface near the first surface so that the deadpath between the first and second surfaces is as small as possible without interfering with the motion of the first surface. When used as a dilatometer, the first surface is the surface of a specimen and the second surface is the surface of a platen to which the specimen is attached. In this case, the deadpath between the two surfaces is the length of the specimen and therefore is inherently minimized. An etalon can also be combined with the interferometer to enable the detection of the change in the index of refraction of a fluid in the etalon as a function of fluid physical parameters.