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Laser trimming of thin-film filters

The use of a photosensitive material for manufacturing the spacer of bandpass thin-film filters is a very attractive way for enabling the post-processing of such devices with the help of a light beam, either to correct with a high accuracy the consequences of some deposition errors on the filter properties (central wavelength out of specifications, inadequate spatial uniformity) or to create entirely new filtering devices with controlled spatial properties (for instance, variable filters with arbitrary profile). A theoretical presentation of the main problems arisen by such a laser trimming will be done, first for bandpass thin-film filters but also for multiple-cavity Solid Spaced Etalons (SSE). After a comprehensive analysis of the possible materials which can be selected for such an application, we will conclude our presentation by the description of the first experimental results obtained by our team in this new field, including a rapid presentation of the dedicated control means needed by this spatially localized approach of a filtering device.