We present a collimation technique based on a double grating system to locate with high accuracy an emitter in the focal plane of a lens. Talbot self-images are projected onto the second grating producing moiré interferences. By means of two photodetectors positioned just behind the second grating, it is possible to determine the optimal position of the light source for collimation by measuring the phase shift between the signals over the two photodetectors. We obtain mathematical expressions of the signal in terms of defocus. This allows us to perform an automated technique for collimation. In addition, a simple and accurate visual criterion for collimating a light source using a lens is proposed. Experimental results that corroborate the proposed technique are also presented.

ABSTRACT:We present a system for diffraction gratings engraving over cylindrical substrates. The manufacturing of the gratings is performed using a Q-switched nanosecond pulsed laser. We have used a mechanical system with six motorized stages. Five of them are linear stages, and the other one is a high precision rotator. The assembly also comprises various devices that monitorize in real time the manufacturing process. A home-made software synchronizes and controls the entire system.