Enhancing the spectral response of filled bolometer arrays for submillimeter astronomy

The future missions for astrophysical studies in the submillimeter region will need detectors with very high sensitivity and large field of view. Bolometer arrays can fulfill these requirements over a very broad band. We describe a technique that enables bolometer arrays that use quarter wave cavities to have a high spectral response over most of the submillimeter band. This technique is based on the addition on the front of the array of an anti-reflecting dielectric layer. The optimum parameters (layer thickness and distance to the array) are determined by a 2D analytic code. This general principle is applied to the case of the Herschel PACS bolometers (optimized for the 60 - 210 micron band). As an example, we demonstrate experimentally that a PACS array covered by a 138 micron thick silicon layer can improve the spectral response by a factor 1.7 in the 450 micron band.