Interferometer, Liquid, Irregular (Historical)
Saturday, September 09, 2006
A Liquid Interferometers has been designed and developed to measure homogeneity of index of refraction in irregularly shaped or very oversized samples requiring full aperture measurements.
The Interferometer used a large cavity, which is filled with oil. The Immersion liquids require a liquid to match the index of refraction of the test sample. At the bottom of the cavity is a supported optical flat. This optical flat defines the maximum aperture of the cavity.
A collimated beam is folded downward into the cavity. A 24” diameter parabolic mirror, a Newtonian telescope with a HeNe Laser and pinhole at the mirror focus can be used. The two-axis tilt assembly allows manipulation of the test sample and allows orientation of the interference fringe.
Interference occurs between the mirror at the bottom of the cavity and the top surface of the oil, which is very flat and level (with a 4000 mile earth radius). The return image forms at the focus of the collimator and is directed into a camera to record the interferograms. A slight de-centering of the light source will allow the return image to be directed into the camera.
Thermalsensitivity: Immersion oils are very thermally sensitive. If the test sample and the immersion oil are not at the same temperature, eddy currents will occur and could affect the interferograms.
Vibration: A Liquid reference surface flat requires good vibration isolation.
Reactivity: Immersion oils come in a variety of chemical compositions. Immersion oil can react with the test sample or cavity container.
Source: Steve M. Miller, Optical Fabrication Consultant, 274 Kettering Circle, Gibsonia, PA 15044
Reference: Cargille Labs, New Jersey
Industrial Products
posted by JD52 @ 1:47 PM,
