With this mounting a single ruled echelette grating may be used “in the blaze” over a very wide range of wave-lengths. This is accomplished by tilting the grating with respect to the incident light as in a Littrow mounting, and then rotating the grating about an axis perpendicular both to the grating elements and the incident beam. By this rotation the path difference between beams of light reflected from successive elements of the grating may be varied from a maximum value, the ordinary blaze wave-length, to zero. The spectrum reflected from the grating may then be reflected from a plane mirror, rotating with the grating, to produce a constant deviation mounting. The image of the slit is found to be tilted as the grating rotates. This can be compensated by a rotation of the slit. In a trial, using an echelette designed for the near infra-red, all orders of the sodium D-lines from the fifth to the first were caused to pass an observing telescope, successively in the blaze, by a 55-degree rotation of the grating mounting.
© 1950 Optical Society of AmericaFull Article | PDF Article
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