Interferometric vibration and thermal expansion compensator

Abstract

A refractive index variability measuring system using a configuration of ical interferometers, mirrors, windows and receivers is desirable. The system provides an improved and a distinctive method for vibration and thermal expansion cancellation. Additionally, an improved matching of optical paths by using this system allows for growth of several measurement paths without additional mismatch of measurement and vibration canceling paths.

What is claimed is: 
     
       1. An interferometric vibration and thermal expansion compensator for a system to study changes in the refractive index of a medium in a test tank full of the medium using a two-frequency orthogonally polarized laser beam having a first horizontally polarized component and a second vertically polarized component, said compensator comprises: means for allowing second vertically polarized component of said laser beam to pass through the medium in said tank;   means for providing different optical paths for the first horizontally polarized component and the second vertically polarized component of said two-frequency and orthogonally polarized laser beam;   means for recombining the first horizontally polarized component and the second vertically polarized component of said two-frequency and orthogonally polarized laser beam so as to cause interference; and   means for subtracting the changes in the refractive index measurements resulting from vibration and thermal expansion effects.   
     
     
       2. The compensator of claim 1 wherein the means for allowing the second vertically polarized component of said two-frequency and orthogonally polarized beam to pass through the medium includes at least a pair of optical windows, a first one for the incoming and a second one for outgoing of the vertically polarized component of said laser beam through the medium. 
     
     
       3. The compensator of claim 2 wherein said means for providing different optical paths includes a first beamsplitters-reflectors-receiver arrangement for said two components of said two-frequency and orthogonally polarized laser beam to be allowed to interfere after reflection at the first of said pair of optical windows of the tank. 
     
     
       4. The compensator of claim 3 wherein said means for providing different optical paths includes a second beamsplitters reflectors-receiver arrangement for the two polarized components of said two-frequency, orthogonally polarized laser beam to be allowed to interfere after reflection at the second of said pair of optical windows of the tank. 
     
     
       5. The compensator of claim 4 which includes at least a third beamsplitters-reflectors-receiver arrangement for the two components of said two-frequency orthogonally polarized laser beam to be allowed to interfere after traveling of the two components of said laser beam through the medium in the tank. 
     
     
       6. The compensator of claim 5 wherein said medium is water. 
     
     
       7. The compensator of claim 6 wherein said tank is configured to use ocean water as the medium.