Geometrical beam splitter and a sensor for multi-element detectors

The invention relates to a geometrical beam splitter, e.g. in a sensor, for transversally dividing a radiation beam (4) into at least one reflected beam portion (5R) and at least one passing beam portion (5T). The beam splitter (1) is composed of a piece (11) of rigid material having a non-transparent reflective surface (3) at an angle (alpha) deviating from the right angle in respect to the incident direction (RI) of said radiation beam. The beam splitter has a width (W) and a height (H) extending over a total effective cross-sectional area (A*) of the radiation beam (4) and e.g. two holes (2a, 2b) extending through said piece of rigid material. The holes allow passing of at least two beam portions (5T), and simultaneously the non-transparent reflective surface divert at least one reflected beam portion (5R) so that said beam portions have substantially similar wavelength distributions.