Process and device for optimizing the position and the width of the cut-off band of an optical filtering device

摘要

In an optical fittering device comprising at least two fitters, the first filter (EF1) is tilted by an angle of incidence whose value is adjusted to bring the cut-off limit of the first filter (EF1) closer to one of the sides of the line of the illumination beam (FLA), which reduces the optical density of the first filter, while the association in series of the first (EF1) and second (EF2) filters enables to obtain a high-pass filtering whose global density corresponds to the sum of the densities of the first and second filters and whose cut-off limit is lower than that obtained by a single filter tilted to its optimum angle. A third filter (EF3) mounted in parallel with respect to the first and second filters (EF1 and EF2) enables to obtain, at the level of the common collection path (TCC), a band eliminating filtering whose cut-off limits are positioned on either side of the illumination line with a view to an optimum analysis of the low frequency lines.