GB861639A - Improvements in and relating to grating spectrometers - Google Patents

Abstract

861,639. Infra-red monochromators. GRUBB PARSONS & CO. Ltd., Sir H. March 7, 1958 [March 19, 1957], No. 8986/57. Class 97(1) In order to avoid superposition of spectra of different orders, the radiation in an infra-red monochromator is dispersed by one or more echelette gratings, at least one of which is such that the diffracted radiation therefrom lies on the same side of a normal to the surface of an individual groove as the incident radiation, and the smaller of the two angles made by the incident and diffracted radiation with said normal has a value in degrees greater than #N/5000 where # is the first order wavelength to which the grating is set and N is the number of lines per inch on the grating. In one form, Fig. 4, radiation from entrance slit S 1 is collimated at C and diffracted by echelette grating G, so that the diffracted radiation returns to mirror C and is focused thereby on exit slit S 2 , whence it is directed by mirrors M 2 , M 3 on to detector D. Before passing to the exit slit S 2 , the diffracted radiation from mirror C may in another embodiment be doubly reflected back on to the mirror C, and diffracted again at G. In a further form, Fig. 6, radiation from entrance slit S 1 after collimation at mirror C 1 is successively diffracted by echelette gratings G 1 and G 5 before being focused on exit slit S 2 . In order to vary the first order wavelength, the five gratings are linked together for simultaneous rotation. Two or more grating spectrometers of the above kind may be combined in series, a single slit acting as exit slit for the first monochromator and as entrance slit for the next monochromator. The arrangement may be employed in an infra-red spectrometer or gas analyser.