Inclined plane diffraction grating monochromator - has concave mirror and paraxial entry and wavelength-selective exit optical fibres

摘要

The entry and exit fibres (5,6) are located in a conical aperture (4) formed in the grating (1) on the axis (3) normal to the centre of the concave mirror (2). The tip of the entry fibre (5) is at the focus of the mirror, which reflects a parallel beam on to the grating and focuses the diffracted beams on to one or more exit fibres (6). The pitch and inclination of the grating are chosen so that the desired wavelength is focused in the immediate vicinity of the axis. Pref. a mask (8) at the centre of the mirror arrests direct rays from the source (5) which would have been reflected into the exit fibres without diffraction. The same result can be achieved by a hole in place of the mask. Astigmatic aberration is reduced. For more wavelength selection a double or multiple monochromator can be realised with only one plane grating.