Optical configuration and method for differential refractive index measurements

A method for measuring a difference in refractive index between a first sample and a second sample, said method comprising the steps of:

• A) providing a transparent medium having a sample surface;
• B) contacting a first area of said sample surface with a first sample and a second area of said sample surface with a second sample;
• C) illuminating an interface of said transparent medium and said first sample and an interface of said transparent medium and said second sample with a beam of light having obliquely incident divergent rays to provide a first partial beam defined by the refractive index of said first sample and a second partial beam defined by the refractive index of said second sample;
• D) arranging a first linear scanned array of photoelectric cells to receive said first partial beam and a second linear scanned array of photoelectric cells to receive said second partial beam;
• E) determining a location of a first sample critical angle shadow line on said first linear scanned array and a location of a second sample critical angle shadow line on said second linear scanned array;
• F) calculating said difference in refractive index based on said shadow line locations determined in said step (E).

A method for measuring a difference in refractive index between a first sample and a second sample, said method comprising the steps of:

• A) providing a transparent medium having a metal film adhered thereto;
• B) contacting a first area of said metal film with a first sample and a second area of said metal film with a second sample;
• C) illuminating an interface of said transparent medium and said metal film with a beam of light having divergent rays obliquely incident to said interface, said beam of light simultaneously irradiating said interface at a first region opposite said first area and a second region opposite said second area to provide a first partial beam defined by the refractive index of said first sample and a second partial beam defined by the refractive index of said second sample;
• D) arranging a first linear scanned array of photoelectric cells to receive said first partial beam and a second linear scanned array of photoelectric cells to receive said second partial beam;
• E) determining a location of a resonance induced flux minimum associated with said first sample on said first linear scanned array and a location of a resonance induced flux minimum associated with said second sample on said second linear scanned array;
• and
• F) calculating said difference in refractive index based on said locations of said flux minimums determined in said step (E).