Polarization based interferometric detector

Abstract

A sensor and method for determining the optical properties of a sample material is disclosed. The sensor comprises a light source that generates a linearly polarized light beam having a predetermined polarization orientation with respect to the plane of incidence. The linearly polarized light beam is reflected off the sample and is split into second and third light beams where the second and third light beam consist of the combined projections of mutually orthogonal components of the first light beam. A signal processor measures the intensity difference between the second and third light beams to calculate the phase difference induced by the sample material.

1 - 73 . (canceled) 
     
     
         74 . A device for detecting a sample material, comprising:
 a. an optical element that comprises or is adjacent to an interface having a surface configured to come in contact with said sample material;   b. a light source that generates a first tight beam for application to said optical element and towards said interface, wherein said first light beam comprises a first polarization component and a second polarization component, and wherein upon application of said first light beam to said optical element, ent, said first light beam is reflected away from said interface with a phase shift in said first tight beam having a sensitivity to surface refractive index change of at least about 5×10 −8  Refractive Index Units (RIU) to permit detection of at least about 50 femtograms of said sample;   c. at least one optical retarder that provides substantially circular polarization in said first tight beam;   d. a beam splitter downstream of said interface that splits said first tight beam into a second light beam and a third light beam after said first light beam is reflected away from said interface;   e. a detector module downstream of said polarizing beam splitter, wherein said detector module accepts and generates signals from said second tight beam and said third light beam; and   f. a processor programmed to calculate a phase shift between said first and second polarization components based on said signals generated from said second and third light beams, to permit the detection of at least about 50 femtograms of said sample.   
     
     
         75 . The device of  claim 74 , wherein said first polarization component and second polarization component are substantially in phase relative to each other. 
     
     
         76 . The device of  claim 74 , wherein said first polarization component and said second polarization component are substantially orthogonal to each other. 
     
     
         77 . The device of  claim 74 , wherein said optical element comprises an optically dense material. 
     
     
         78 . The device of  claim 74 , wherein said phase shift is a variable phase shift between said first polarization component and said second polarization component. 
     
     
         79 . The device of  claim 74 , wherein said light source comprises a linearly polarized coherent light. 
     
     
         80 . The device of  claim 79 , wherein said linearly polarized coherent light has a wavelength in the range of about 500 nanometers to 700 nanometers. 
     
     
         81 . The device of  claim 79 , wherein said linearly polarized coherent light is oriented at a predetermined angle with respect to the plane of incidence of said interface. 
     
     
         82 . The device of  claim 81 , wherein said predetermined angle is based on the maximum phase shift between said first and second polarization components due to a change adjacent to said surface. 
     
     
         83 . The device of  claim 74 , wherein said surface comprises a material that has a higher index of refraction than said sample. 
     
     
         84 . The device of  claim 74 , wherein said surface comprises a material including glass, plastic, silicon or ceramic. 
     
     
         85 . The device of  claim 74 , wherein said detector module comprises (i) a first detector that measures an intensity of said second light beam and (ii) a second detector that measures an intensity of said third light beam. 
     
     
         86 . A method for detecting a sample material, comprising:
 a directing a first light beam comprising a first polarization component and a second polarization component towards an optical element that comprises or is adjacent to an interface having a surface configured to come in contact with said sample material;   b. reflecting said first light beam away from said interface with a phase shift in the first light beam having a sensitivity to surface refractive index change of at least about 5×10 8  Refractive Index Units (RIU) to permit detection of at least about 50 femtograms of said sample, which first light beam has substantially circular polarization;   c. splitting said first light beam into a second light beam and third light beam after said first light beam is reflected away from said interface;   d. generating signals from said second and third light beams; and   e. calculating a phase shift between said first and second polarization components based on said signals generated from said second and third light beams, thereby detecting at least about 50 femtograms of said sample.   
     
     
         87 . The method of  claim 86 , wherein said sample material comprises nucleic acid, viral particles, bacteria or organic molecules. 
     
     
         88 . The method of  claim 86 , wherein signals from said second and third light beams are generated separately. 
     
     
         89 . The method of  claim 86 , wherein said first polarization component and said second polarization component are substantially in phase and orthogonal relative to each other. 
     
     
         90 . The method of  claim 86 , wherein said phase shift is a variable phase shift between said first polarization component and said second polarization component. 
     
     
         91 . The method of  claim 86 , wherein said first light beam is a linearly polarized coherent light beam that is rotated at a predetermined angle with respect to a plane of incidence of said interface. 
     
     
         92 . The method of  claim 91 , wherein said linearly polarized coherent light beam has a wavelength in the range of about 500 nanometers-700 nanometers. 
     
     
         93 . The method of  claim 91 , wherein said predetermined angle is based on a maximum phase shift between said first and second polarization components due to a change adjacent to said surface. 
     
     
         94 . The method of  claim 86 , wherein said first light beam has substantially circular polarization downstream of said interface.