Abstract: The invention relates to a monochromator including a telecentric dispersive lens (TD0) in which the collimated diffracted beam (2) at an angle .beta. with respect to the normal to the telecentric dispersive lens (TD0) is focused at the focus of a telescope (T.sub.2) fitted with a straight slit (S') the optical axis of the telescope (T.sub.2) being merged with the direction of the diffracted beam (2) and the slit (S') being parallel to the direction of the lines of the telecentric dispersive lens (TD0), the collimated incident beam (1), at an angle .alpha. giving the collimated diffracted beam (22) at an angle .beta. after diffraction by the telecentric dispersive lens (TD0).

Abstract: 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.

Abstract: Various vacuum ultraviolet monochromators embodying a rotatable diffraction grating and fixed entrance and exit slits, and working at a predetermined magnification are disclosed which provide improved optical performances by a correction of the odd terms of the wavefront aberration. In one group of instruments the fixed angle 2.theta. between the entrance and the exit beams is 90.degree. and the magnification 1. In another group, grazing incidence instruments are considered, 2.theta. being equal to 166.degree..

Abstract: The invention provides a focalization process of spherical concave diffraction gratings, working by reflection for the dispersion of various radiations constituting a polychromatic light, in which fixed entrance and exit slits are used and in which only a certain rotation is imparted to the grating, the rotation is imparted to the grating in such a way as to make the radiations move in the exit slit. For a certain ruled width of a given grating and a given resolution, the sum of the object and image tangential focal length equations has a value .epsilon. different from zero and determined in function of the aberrations furnished by a concave grating corresponding to the retangular port.

Abstract: Spectrometric gratings formed by holographic techniques are disclosed. The gratings are employed in monochromator mounts of the type in which fixed entrance and exit slits are combined with simple rotation of the grating to scan the spectral range of interest, the angles of incidence and diffraction and the positions of the slits being so related that the mounts are characterized by improved optical performance due to phase balancing and improved focussing properties according both to geometrical and diffraction theories. The parameters involved in the holographic formation of the gratings, specifically the angularities and positions of the point sources forming the holographic image of the grating lines, are specifically related to the characteristics of the mount as to improve further their optical characteristics, particularly with respect to mounts either employing "normal" (i.e., relatively small) angles of incidence with large grating apertures or employing grazing incidence (i.e.