1. A rather complete list of references about this topic can be found in the report by U. TIMM: Coherent Bremsstrahlung of Electrons in Crystals, DESY, 69/14 (March 1969).
2. Interference Effects in High-Energy Bremsstrahlung from Crystals
3. Sulla “Bremsstrahlung” nei cristalli
4. See, for instance, the notes of the lectures given in 1969 at CERN, about The Bremsstrahlung in Crystals.