Tilt compensated interferometers

Abstract

A novel variation of Michelson's interferometer uses tilt- and shear-compensation optics together with a beamsplitter and parallel reflector assembly to allow various mirror motions to produce variation of path difference. The tilt-compensation mechanism consists of two complementary reflections from a single plane mirror to produce a beam having a constant angle of propagation, typically the same as the input beam. Using a retroreflector to invert the image of the single plane mirror before the second reflection produces the complementary reflections. A particularly efficient embodiment of the present invention uses a balanced disk-shaped mirror to effect very rapid variation of path difference by nutation or precession. Other advantages of tilt-compensation include photometric stability. This interferometer has applications in spectrometry, spectral imaging and metrology.

1 . A spectrometer, comprising: 
 a source of a primary beam of radiant energy;    a beamsplitter with parallel reflector assembly, fixed in position relative to the primary beam of radiant energy, for dividing the primary beam of radiant energy into at least first and second energy beams which are parallel;    a single moving mirror that receives the first and second energy beams from the beamsplitter and parallel reflector assembly, the moving mirror having a planar optical surface mounted so as to reflect the first and second energy beams, the single moving mirror also being mounted to move the planar optical surface relative to the primary beam of radiant energy;    a retroreflector, fixed in position relative to the primary beam of radiant energy, positioned to receive the first energy beam after it is reflected by the optical surface of the moving mirror;    a second retroreflector, fixed in position relative to the primary beam of radiant energy, positioned to receive the second energy beam after it is reflected by the optical surface of the moving mirror;    
   
   
       2 . A spectrometer as claimed in  claim 1 , wherein the retroreflector is a cube-corner reflector.  
   
   
       3 . A spectrometer as claimed in  claim 1 , wherein the retroreflector is a lateral-transfer retroreflector.  
   
   
       4 . A spectrometer as claimed in  claim 1 , wherein a retroreflector inverts the energy beam from the moving mirror.  
   
   
       5 . A spectrometer as claimed in  claim 1 , wherein the mounting of the moving mirror rotates it about an axis of rotation.  
   
   
       6 . A spectrometer as claimed in  claim 6 , wherein the moving mirror has a disk shape and the optical surface is one side of the disk.  
   
   
       7 . A spectrometer as claimed in  claim 7 , wherein the disk-shape of the moving mirror has a thickness that varies sinusoidally with angle about the axis of rotation.  
   
   
       8 . A spectrometer as claimed in  claim 7 , wherein the side of the disk opposite the optical surface is contoured to compensate for deformation of the disk caused by rotation of the disk about the axis of rotation.  
   
   
       9 . A spectrometer as claimed in  claim 7 , wherein the disk is balanced for rotation about the axis of rotation.  
   
   
       10 . A spectrometer as claimed in  claim 7 , wherein the disk is compensated for stretching distortion to provide a flat surface when rotated about the axis of rotation.  
   
   
       11 . A spectrometer as claimed in  claim 1 , wherein the mounting of the moving mirror pivots it about a pivot axis.  
   
   
       12 . A spectrometer as claimed in  claim 1 , wherein the mounting of the moving disk mirror translates it along a translation axis where a portion of the translation is parallel to the optical surface of the parallel reflector.