Abstract: A spectrograph for an extended spectral field having an inlet slot for defining a source of light to be analyzed and a dispersive system constituted by a concave holographic grating which has recording points with coordinates in relation with the coordinates of the light source to be analyzed to produce for each of respective bands of wavelengths, which in total cover the entire range of wavelengths of the spectral field to be analyzed, tangential focal lines for different wavelengths which are disposed in the same plane. The concave holographic grating is rotatable around an axis passing through the center of the grating and perpendicular to a plane passing through the center of the inlet slot so that the respective partial plane diffraction spectra are successively formed in the same plane when rotating the grating around its axis.

Abstract: A spectrograph for use in analyzing an extended spectral field comprising a dispersive system consisting solely of one or more concave holographic gratings, each grating being specified so that the diffraction spectrum is formed in a plane. Where a plurality of gratings are provided they are formed on a common concave support and are specified so that the planes of the diffraction spectra formed thereby are offset and in total cover the wavelengths of the total spectral field.

Abstract: Monochromator comprising a concave grating, the lines of which are situated at the intersection of the concave surface with a family of surfaces geometrically like the equiphasic surfaces obtained as loci of the luminous intensity maxima produced by the interference of two beams from two point sources C and D, an entry slit A and an exit slit B, wherein the polar coordinates of the points C and D and of the entry slit A and exit slit B in a system of polar coordinates having as its origin the apex of the grating and as reference axis the axis of the grating in a plane of reference passing through this axis are connected by the following relationships: ##EQU1## in which (.alpha., l.sub.A), (.beta., l .sub.B), (.beta., l.sub.C) and (.delta., l.sub.D) are the polar coordinates of A,B,C and D, respectively, R is the radius of curvature of the grating, .omega.=(.alpha.+.beta.) /2 and .phi.=(.alpha.-.beta.)/2.