Collimation method using a double grating system

Abstract

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.

Lissajous figure-based single-frame collimation technique

“…We can observe that the ellipticity reaches a minimum for z = 0, as it was expected. We can also see that this parameter is an excellent option for determining the collimation degree since it has a very sharp dependence, as was proposed in [10].…”

“…Most of them are based on interferometry [1][2][3][4][5] or on self-imaging techniques [6][7][8][9]. In addition, several techniques have been proposed in the last years [10][11][12][13][14][15]. In particular, several collimation methods based on self-imaging that do not need a lateral displacement of the grating have been proposed, being these devices simple an stable.…”

“…Another robust and accurate technique was proposed in [10]. In this technique the light beam passes through a diffraction grating of period p and a mask located at a Talbot plane of the grating, situated at z T = 2p 2 / , [3,8,16].…”

“…In this work we develop a new collimation technique based on that proposed in [10]. The beam collimation is achieved by using a diffraction grating and a mask formed by several amplitude Ronchi gratings with known lateral shift.…”

“…When the emitter is exactly placed at the focal point of the lens, z = |z 0 − f| = 0, the beam after the lens is properly collimated and the period of the self-images is equal to that of the grating. On the other hand, when the emitter is not exactly at the focal plane, z / = 0, the intensity distribution at a distance z 2 from the grating results in [10] I(x 3 , z 2 ) = I 0 n,n a n a n e i q 1+˛z 2 (n−n )…”