GB765441A - Spectroscopic device - Google Patents

Abstract

765.441. Spectroscopic apparatus. FASTIE, W. G., and SINTON, W. M. Feb. 24, 1954 [March 24, 1953], No. 5461/54., Class 97(1) In spectroscopic apparatus including a dispersing element. and reflecting means associated therewith so that incident radiation is subjected to two or more separate dispersions by the dispersing element, optical deflecting means are interposed in the radiation following are dispersion for so directing the radiation that the final spectrum does not overlap any other spectrum. As shown, a light beam g from a slit 12 is dispersed by a concave reflecting grating 14 into a beam h focused as a spectrum on a circle 18 passing through the grating 14. The beam h falls on a right-angled reflecting prism 28 and is returned to the grating 14 as a beam i displaced from the beam h. The beam i is itself dispersed by the grating to form a beam j which is reflected by a second right-angled prism 26 and by a rhombic prism 30 to be returned to the grating 14 as a beam k incident on the grating from below the plane of the circle. The dispersed beam l from the beam k therefore forms a spectrum 42 located above the plane of the circle 18 in which the other spectra are located thereby avoiding overlap. By providing a second prism 28, diplaced from the first a further dispersed different portion of the 'spectrum may be produced on the circle 18 on the opposite side of the slit 12 to that produced by. the beam j by providing further prisms 36 and 30, the latter being oppositely arranged to the first-mentioned prism 30, another spectrum may be framed below the circle 18 and -the spectrum 42. The prisms may be replaced by plane reflectors, the reflectors 20, Fig. 8, being so mounted that their relative angular position can be adjusted by rotating one mirror by a screw 106 rotating both mirrors about a horizontal axis by a screw 106', while the reflectors 38, Fig. 9, are. similarly adjusted by screws 106<SP>11</SP> and 106<SP>111</SP>. The invention may be applied to the system described in Specification 731,943 and shown in Fig. 13. Light from a curved entrance slit 88 is collinated by a portion 77 of a concave mirror 78 and directed to a plane reflecting grating 14<SP>1</SP>. The dispersed beam is focused by a portion 79 of the mirror 78 to form a spectrum. adjacent a mirror 80 which reflects it thereon mirror 84 back to the mirror 78. After again being dispersed by the element 14<SP>1</SP> the beam is directed by the mirror 80 on to parallel mirrors 87, 89 by which it is displaced from the other beams and reflected back to the mirror 78 by a mirror 90 finally forming a spectrum on the curved exit slit 86 which is displaced from the plane of the other spectra. Alternatively the mirrors 87 and 89 may be omitted and the mirror 80 replaced by two relatively inclined mirrors which prevent superposition of the spectra.