Knowledge Bank

It has been known for some $time1$ that the intensity distribution observed in a continuous spectrum formed by a blazed diffraction grating may show marked deviation from that predicted by the classical equations. These deviation appear as sharp changes in the energy with the maximum change occurring at a wavelength predicted by $Rayleigh.2$ These sharp changes ran be undesirable in some applications e.g., wavelength scanning, constant energy-out devices. The sharp peaks are also extremely polarized. The objective of this paper is to present experimental data which indicate a possible method of effectively reducing some anomalies. The method requires a modification of conventional techniques in coating a reflection diffraction grating. Energy curves of gratings, coated in the conventional manner and of gratings coated by a method designed to reduce the anomalous effects, show a considerable change m the appearance of the anomalous structure formed by the gratings. In some cases the modified coating method can almost completely eliminate the more pronounced anomaly structure. Data will also be shown for a transmission grating of coarse grooves-which illustrates the difference in the appearance of the anomalies depending on whether they are observed in a spectrum formed by transmission through the grating, or by reflection from the grating.