Perfect blazing with echelle gratings in Littrow mount

Perfect blazing with echelle gratings in a high order Littrow mount exists simultaneously in TE and TM polarizations /1/. This finding contradicts with a heuristic explanation as why perfect blazing is not possible simultaneously in TE and TM polarizations given in (E. G. Loewen and E. Popov, Diffraction Gratings and Applications, New York: Marcel Dekker (1997)). As a matter of fact, in the ideal case of infinite conductivity, light is diffracted in the Littrow order with 100% efficiency for both polarization states. For metal gratings a small loss occurs. Three conditions are necessary for perfect blazing. The most intriguing property is the blaze angle being 4° to 6° larger than the Littrow angle. Typically the difference between the two angles is smaller than 1.0°. The ingredients for perfect blazing are shown and its behaviour and further conditions are discussed. /1/ Bernd H. Kleemann, "Perfect blazing with echelle gratings in TE and TM polarization", Opt. Lett., accepted for publication.