Optics and Photonics Society of Iran

The interference pattern of Fresnel double mirror can be used to determine the wavelength of incident light knowing the apex angle of Fresnel double mirror. Here, we have used the diffraction pattern of Fresnel double mirror to determine the wavelength and the apex angle of Fresnel double mirror, simultaneously. Abrupt changes in the phase gradient of the wave at the apex of Fresnel double mirror causes Fresnel diffraction patterns. The diffracted intensity distribution is calculated using Fresnel-Kirchhoff integral. It is shown that intensity of the diffracted field varies with constant period along the average propagation direction. Measuring this value and the fringe spacing of the interference pattern on a plane normal to the average propagation direction, the apex angle of Fresnel double mirror and wavelength of the incident light is simultaneously derived. The experimental results analyzed and the wavelength of He-Ne laser is determined 633±1 nm.