ABSTRACT
Blazed transmission gratings can be used as beam dividers and trapezoidal gratings as beam splitters. TE and TM curves present one crossover only, and follow similar shapes. The TE blaze peak is always slightly higher than the TM peak. One may wonder about the origin of the blaze effect of transmission gratings. Following the reasoning of scalar optics, generally pointed out by grating users and manufacturers, the blaze effects occurs "when the microprisms that are formed by each groove refract light at the same angle as the angle of diffraction of the ruling." Grism design is useful to have a dispersive system that provides in-line viewing at one central wavelength. This is realized in direct vision spectroscopes and is particularly useful in astronomical spectrographs. Modern’s observatories work at the top of high mountains where due to the elevation, any change in the observing apparatus is difficult and time consuming.
