Phase signal definition for electromagnetic waves in X-ray crystallography

S´ergio L. Morelh˜ao

Instituto de F´ısica, Universidade de S˜ao Paulo, CP 66318, 05315-970 S˜aoPaulo, SP, Brazil

Diffracted X-ray waves in crystals have relative phases regarding the mathematical format used to describe them. A forward propagating wave can be defined with either negative or positive time evolution, i.e. k ・ r − !t or !t − k ・ r. Physically measurable quantities are invariant with respect to the choice of definition. This fact has not been clearly emphasized neither extensively explored when deriving well-established equations currently being used in many X-ray diffraction related techniques. Here, the most important equations are generalized and consequences of conflicting undertaken definitions discussed.