Blaze characteristics of echelle gratings

A new model for the blaze function of the two in-plane mountings of echelle gratings is described and extended to account for defects in the edges of the grooves. Expressions for the relative efficiency are given. The model shows that the wavelength for the maximum blaze intensity differs slightly from the wavelength lambda(0) satisfying mlambda(0) = d[sinalpha + sin(2theta - alpha)], the difference being a function of the spectral order. The off-blaze orders of the wavelengths diffracted at the central blaze for the mounting alpha < theta (alpha = angle of incidence, theta = blaze angle) lie at the minima of the blaze function for a perfect echelle. Results are given from measurements of the blaze angle and the groove edge defects of three echelles.