Biochar as a low-cost, eco-friendly, and electrically conductive material for terahertz applications

Monochromatic light measurement via geometric phase and Fourier-transform spectroscopy method

The paper introduces a method for the measurement of monochromatic light using the geometric phase shift in a polarizing interferometer and applying the Fourier transform spectroscopy method. This is achieved with no mirror displacement or change in the actual optical path difference. Our method uses the rotation of a half-wave plate with increments on the order of degrees of arc, which is easier to control and reliable to reproduce. This approach provides flexibility in choosing the spectral range and a novel way of performing such measurements. It is demonstrated how the achromatic nature of the geometric phase allows only for monochromatic measurements to be acquired. The method is described theoretically and its performance is validated via measurements of several low-coherence light sources. Three possible applications of the method are also described, two of which are advantaged by using a detector array and, surprisingly, the achromaticity of the geometric phase.