The present popularity of the type H-3 mercury lamp justifies a further consideration of mercury monochromats. he design of mercury monochromats represents a choice of glasses and thicknesses to achieve the highest purity (ratio of transmission at the designed wave-length to total transmission) permitted by the energy distribution of the source and the spectral response of the receiver. The filter glasses (usually two) in the monochromat are selected by considering the steepness of slope of their transmission curves near the designed wave-length and their degree of opacity in adjoining regions. The proportionate thick-nesses can then be varied for the most favorable values of transmission at the desired wave-length and of purity. The best thickness ratio between the components is found by computing the purities of several combinations whose total thicknesses are adjusted to give constant transmission at the designed wave-length. It is assumed that the best thickness ratio is practically independent of the thickness of the total filter over the range investigated. By varying the total thickness, keeping the ratio constant, a relation between the transmission at the designed wave-length and the purity will be shown. Monochromats have been de-signed for use with the type H-3 mercury lamp utilizing caesium and sodium surface photo-tubes, the selenium surface barrier-layer cell, the thermopile and the eye as detectors. Curves will be given showing the best values of urity and transmission at the desired wave-length for the various source-filter-receiver combinations.
ELIZABETH M. STAATS, "The Design of Monochromatic Filters for the Type H-3 Mercury Lamp," J. Opt. Soc. Am. 28, 112-119 (1938)