Refractive scanning interferometer

Abstract

Embodiments are disclosed relating to a refractively-scanning interferometer comprising an aperture that receives an incident light beam at a receiving angle, a beam splitter configured to split the incident light beam into a first beam and a second beam, a first and a second reflector arranged to reflect the first beam and second beam, respectively, towards a combining optical element, and a refractive Optical Path Difference (rOPD) assembly interposed between the beam splitter and the first reflector, wherein the rOPD Assembly refracts the first light beam an even number of times with induced phase discrepancy being a vector sum of a first phase discrepancy induced by a first refraction and a second phase discrepancy induced by a second refraction, the rOPD Assembly being configured such that the first phase discrepancy is substantially opposite in direction to the second phase discrepancy, a portion of the first and second phase discrepancies cancelling one another out to decrease magnitude of the phase discrepancy.

1 . A scanning interferometric system comprising:
 an aperture that receives an incident light beam at a receiving angle;   a beam splitter configured to split the incident light beam into a first beam and a second beam;   a first and a second reflector arranged to reflect the first beam and second beam, respectively, towards a combining optical element; and   a refractive Optical Path Difference (rOPD) assembly interposed between the beam splitter and the first reflector;   wherein the rOPD Assembly comprises a pivotable refractor able to pivot about an axis extending substantially perpendicular to a direction of travel of the first beam in order to induce and alter a difference in path length between the first beam and the second beam, thereby phase-shifting the first beam relative to the second beam; and   the combining optical element is configured to emit an output beam having an interference pattern induced by the phase-shifted first beam and the second beam interfering with one another;   further wherein the interference pattern contains a phase discrepancy with a magnitude dependent upon the receiving angle of the incident light beam, the phase discrepancy being induced during refraction of the first light beam;   the aperture has a critical receiving angle, such that incident light having a receiving angle greater than the critical receiving angle subsequently results in the phase discrepancy in the interference pattern of the output beam having magnitude sufficient to render a produced interference pattern illegible, invisible or otherwise undetectable; and   the rOPD Assembly refracts the first light beam an even number of times with the phase discrepancy being a vector sum of a first phase discrepancy induced by a first refraction and a second phase discrepancy induced by a second refraction;   the rOPD Assembly being configured such that the first phase discrepancy is substantially opposite in direction to the second phase discrepancy, a portion of the first and second phase discrepancies cancelling one another out to decrease magnitude of the phase discrepancy.   
     
     
         2 . The system of  claim 1 , wherein the pivotable refractor refracts the first light beam an even number of times; and
 the rOPD Assembly comprises a light-rotating element arranged to rotate the first light beam by approximately 90° about the direction of travel thereof, the first light beam being rotated after a first refraction and before a second refraction.   
     
     
         3 . The system of  claim 1  wherein the pivotable refractor is an X-axis pivotable refractor, the rOPD Assembly further comprising a Y-axis pivotable refractor, the first light beam refracting through each in sequence; and
 the Y-axis pivotable refractor has a pivot axis optically perpendicular to the pivot axis of the X-axis pivotable refractor and to the direction of travel of the first beam. 
 
     
     
         4 . The system of  claim 3  wherein the first light beam passes through the light-rotating element an even number of times, each time rotating by approximately 45°. 
     
     
         5 . The system of  claim 3  wherein the X-axis pivotable refractor and y-axis pivotable refractor have pivot axes that are not physically perpendicular to one another; and
 the rOPD Assembly further comprises a light-rotating element between the X-axis pivotable refractor and y-axis pivotable refractor, such that, through rotating the first light beam about the direction of travel, the X-axis pivotable refractor and y-axis pivotable refractor have pivot axes that are optically perpendicular to one another. 
 
     
     
         6 . The system of  claim 1  wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly. 
     
     
         7 . The system of  claim 2 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly and the pivotable refractor of the rOPD Assembly comprises a dual-beam pivotable refractor that is configured to refract each of the first and second beams an even number of times, the dual-beam pivotable refractor having a pivot axis perpendicular to the direction of travel of both of the first beam and the second beam; and
 the light-rotating element is configured to rotate the first light beam by approximately 90° about the direction of travel thereof and the second light beam by approximately 90° about the direction of travel thereof.   
     
     
         8 . The system of  claim 2 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly and the pivotable refractor of the rOPD Assembly comprises a first pivotable refractor arranged to refract the first light beam and a second pivotable refractor arranged to refract the second light beam; and
 the light-rotating element is configured to rotate the first light beam by approximately 90° about the direction of travel thereof and the second light beam by approximately 90° about the direction of travel thereof.   
     
     
         9 . The system of  claim 7 , wherein the light-rotating element comprises:
 a first light-rotating element arranged to rotate the first light beam by approximately 90° about the direction of travel thereof; and   a second light-rotating element arranged to rotate the second light beam by approximately 90° about the direction of travel thereof.   
     
     
         10 . The system of  claim 8 , wherein the light-rotating element comprises:
 a first light-rotating element arranged to rotate the first light beam by approximately 90° about the direction of travel thereof; and   a second light-rotating element arranged to rotate the second light beam by approximately 90° about the direction of travel thereof.   
     
     
         11 . The system of  claim 3 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly and at least one of the X-axis pivotable refractor and Y-axis pivotable refractor is a dual-beam pivotable refractor configured to refract both the first beam and the second beam. 
     
     
         12 . The system of  claim 3 , wherein both the first beam and the second beam are refracted an even number of times by the rOPD Assembly and wherein either:
 the X-axis pivotable refractor comprises a first X-axis pivotable refractor pivotable about the X-axis of the first beam, and a second X-axis pivotable refractor pivotable about the X-axis of the second beam;   the Y-axis pivotable refractor comprises a first Y-axis pivotable refractor pivotable about the Y-axis of the first beam, and a second Y-axis pivotable refractor pivotable about the Y-axis of the second beam; or   the X-axis pivotable refractor comprises a first and second X-axis pivotable refractor, and the Y-axis pivotable refractor comprises a first and second Y-axis pivotable refractor.   
     
     
         13 . The system of  claim 1 , wherein the combining optical element is the beam splitter, such that the system is a Michelson-type interferometric system. 
     
     
         14 . The system of  claim 3 , wherein the combining optical element is the beam splitter, such that the system is a Michelson-type interferometric system. 
     
     
         15 . The system of  claim 8 , wherein the combining optical element is the beam splitter, such that the system is a Michelson-type interferometric system. 
     
     
         16 . The system of  claim 1 , wherein the combining optical element is a second beam splitter, such that the system is a Mach-Zehnder-type interferometric system. 
     
     
         17 . The system of  claim 3 , wherein the combining optical element is a second beam splitter, such that the system is a Mach-Zehnder-type interferometric system. 
     
     
         18 . An interferometer comprising at least a first and second rOPD assembly interposing between a beamsplitter and a first and second reflector,
 the rOPD assemblies being configured for sequential path length modulation of a first and second light beam and being concatenated such that their respective pathlength modulation effect is mutually reinforced by the concatenation, in that a total path length modulation is a sum of the path length modulation of the first rOPD assembly and the second rOPD assembly;   wherein the second rOPD assembly is further configured so that its associated pathlength discrepancy function at least partially cancels an associated pathlength discrepancy function of the first rOPD assembly.   
     
     
         19 . An interferometer comprising two or more rOPD assemblies interposing between the beamsplitter and retro reflecting mirrors and concatenated such that a pathlength modulation effect of both is mutually reinforced by the concatenation; and
 a beam redistribution element between the concatenated elements which bijectively reassigns directions within the beam, such that directions which undergo a positive pathlength discrepancy in the first rOPD assembly are mapped to directions which undergo a negative pathlength discrepancy in the second rOPD assembly, thereby providing at least a partial cancellation of an overall pathlength discrepancy function of the system.   
     
     
         20 . An interferometer as per  claim 19 , wherein the second rOPD assembly is further configured so that its associated pathlength discrepancy function at least partially cancels an associated pathlength discrepancy function of the first rOPD assembly; and
 cancellation of the path length discrepancy function of the system is provided through a combination of cancellation by the beam redistribution element and cancellation by the configuration of the second rOPD assembly.