Measurement of the diameter of a gaussian beam

We describe an experimental setup to measure the diameter of gaussian beam with a bandwidth L, centered onto slit of width l. The method proposed by Mata-Mendez demands the measurement of two experimental values: the transmission coefficient tau and the diffracted intensity I(theta) from which we may able to determine the diameter of the incoming gaussian beam. In the case of a He-Ne laser, the numerical conditions are 0.001 less than or equal to lambda/l less than or equal to 0.1 and L/l greater than or equal to 1.5.