Refractive Index Finding using Multiple Light Reflections with Modified Sagnac Interferometer

Refractive index finding using multiple light reflections with modified Sagnac interferometer is proposed here. The thickness of the material and fringes pattern are fundamental parameters in such measurement. In this proposed technique, multiple light reflections, by the two parallel mirrors attached to a piezo-electric transducer (PZT) vibrating at a frequency of 420Hz, introduced the phase retardation. The phase retardation and reflected angles could be found and employed for refractive index determination. Four identical interferograms were obtained by a half-wave plate (HWP) oriented at 0, π/2, π and 3π/2 rad with respect to the incident plane. The intensities at their respective patterns were evaluated and the phase shift could be computed. Using numerous reflections with a Sagnac interferometer, this technique is presented to obtain multiple fringes with a sample fixed in position at certain carrier frequencies.