Angular dependence of infrared emission spectra of thin organic and inorganic films on metal surface was investigated at 150 or 160°C in employing a conventional grating spectrophotometer. The sensitivity of spectrum increase markedly by the use of the beam polarized parallel to the plane of incidence at high angles of observation. The obtained results are in perfect agreement with the theoretical prediction by Greenler. Spectra of moderate contrast could be obtained with films as thin as 10 nm in thickness of polyvinyl acetate on gold substrate. So far as very thin films are concerned, emission intensity increases proportionally to the film thickness.
A method has been developed for computing the line profile of spectral images formed by a concave grating. The method takes into account the local groove efficiency of the grating in estimating line intensities from a spot diagram incorporating a scalar diffraction theory of the plane grating. Comparisons showing close agreement between the calculated and measured profiles are presented for Hg lines. This calculation method can also be used to determine the optimum width of a concave grating to provide spectral images with both high intensity and good resolution. An example is given for a Seya-Namioka monochromator.