Research on focal length determination technique of laser test system based on Talbot effect

Abstract

A method for measuring focal length based on Talbot effect is put forward, which suits determining focal length of long-focus lens. The variation of Moiré fringes occurs after typical phase object of measuring lens is laid between two gratings. The images of fringes taken by CCD camera are processed with MATLAB. The focal length of measuring lens is figured out accurately after calculating the slope of fringes, the separation angle between two grating lines and measuring the distance between lens and the second grating. Experimental data indicate that, for a system with laser wavelength of 0.65μm, measuring lens wth focal length of 420mm, the measurement accuracy is 0.10%.So this method has advantages of simple device, fast processing speed and high precision. It satisfies focal length determination of long focal-length lens used in SG-III Facility.