A system for determining the optical properties of a sample material, the system comprising: a light source (314, 320) for generating a first light beam having first and second lightwaves, the first lightwave having a first linear polarization and the second lightwave having a second linear polarization, the first and second linear polarizations being substantially orthogonal to each other, the first and second lightwaves being in phase relative to each other; an optical retarder for providing a total of a substantially 90 degree phase shift between the first and second lightwaves by imposing a relative delay between the first and the second lightwaves; a transducer (370, 390) having an optical interface for reflecting the first light beam from the sample material under total internal reflection conditions, wherein the first linear polarization is in a plane of incidence and the second linear polarization is normal to the plane of incidence, wherein the transducer comprises a sensing material immobilized on the optical interface, wherein the sensing material is capable of interacting with the sample material by complementary chemistries, and wherein the sample material comprises nucleic acid, proteins, polypeptides, viral particles, or bacteria; a polarizing beam splitter for splitting the first light beam into a second light beam and a third light beam after the first light beam is reflected from the optical interface, the second and third light beams consisting of combined projections of mutually orthogonal polarization components on the main axes of the beam splitter, wherein the substantially 90 degree phase shift is provided before the first light beam reaches the polarizing beam splitter; one or more optical components (311, 312, 316) located in the path of the first light beam wherein the one or more optical components convert the polarization of the first light beam from substantially elliptical polarization into substantially circular polarization before the first light beam is transmitted to the polarizing beam splitter; a first detector and a second detector for measuring the intensities of the second and third light beams, respectively; and a signal processor for measuring the intensity difference between the second and the third light beams and calculating therefrom the phase difference induced by the sample material, the signal processor receiving a first intensity measurement from the first detector and a second intensity measurement from the second detector. a light source (314, 320) for generating a first light beam having first and second lightwaves, the first lightwave having a first linear polarization and the second lightwave having a second linear polarization, the first and second linear polarizations being substantially orthogonal to each other, the first and second lightwaves being in phase relative to each other; an optical retarder for providing a total of a substantially 90 degree phase shift between the first and second lightwaves by imposing a relative delay between the first and the second lightwaves; a transducer (370, 390) having an optical interface for reflecting the first light beam from the sample material under total internal reflection conditions, wherein the first linear polarization is in a plane of incidence and the second linear polarization is normal to the plane of incidence, wherein the transducer comprises a sensing material immobilized on the optical interface, wherein the sensing material is capable of interacting with the sample material by complementary chemistries, and wherein the sample material comprises nucleic acid, proteins, polypeptides, viral particles, or bacteria; a polarizing beam splitter for splitting the first light beam into a second light beam and a third light beam after the first light beam is reflected from the optical interface, the second and third light beams consisting of combined projections of mutually orthogonal polarization components on the main axes of the beam splitter, wherein the substantially 90 degree phase shift is provided before the first light beam reaches the polarizing beam splitter; one or more optical components (311, 312, 316) located in the path of the first light beam wherein the one or more optical components convert the polarization of the first light beam from substantially elliptical polarization into substantially circular polarization before the first light beam is transmitted to the polarizing beam splitter; a first detector and a second detector for measuring the intensities of the second and third light beams, respectively; and a signal processor for measuring the intensity difference between the second and the third light beams and calculating therefrom the phase difference induced by the sample material, the signal processor receiving a first intensity measurement from the first detector and a second intensity measurement from the second detector.