Method for focusing spherical holographic diffraction gratings working by reflection, and dispersive lenses and spectrometers applying this method

摘要

The disclosure relates to dispersive lenses and spectrometers for performing a method of focusing holograms in which the hologram that is placed on a spherical surface plays an active part in the focusing. Contrary to focusing methods of the prior art wherein the focusing locus is determined as a function of the tangential object and image focal lines, the described invention determines the focusing locus as a function of the sagittal object and image focal lines. A stigmatic mounting (i.e. a perfect mounting to eliminate odd order abberations) results in the tangential and sagittal focal lines being identical. The description sets forth equations to cover all points in the focusing plane by suitable action of the phase variations generated by the hologram. The diffraction grating used is reflective and includes a fixed entrance slit and at least one fixed exit slit.