Microwave Bragg diffraction in a model crystal lattice for the undergraduate laboratory

• Published in: American journal of physics Vol. 72; no. 2; pp. 154 - 158
• Main Authors: Cornick, M. T., Field, S. B.
• Format: Journal Article
• Language: English
• Published: Woodbury American Institute of Physics 01-02-2004
• Subjects: Crystallography; Microwaves; 60; 01.50.P
• ISSN: 0002-9505; 1943-2909
• DOI: 10.1119/1.1615527

We describe an undergraduate laboratory experiment in which Bragg diffraction is studied using microwave diffraction from a two-dimensional crystal consisting of a square lattice of metal rods. This apparatus demonstrates the fundamental ideas of the Bragg theory of crystal diffraction using a macroscopic model. Thus, the geometrical relations between the crystal planes and the incoming and scattered wave directions are clearly visible. A key element of the apparatus is a computer interface that allows diffracted intensity measurements at all orientations of crystal and detector. No a priori assumptions need be made concerning the relation between the incident and refracted angles. We also present results of computer simulations of the scattering from our crystal. These simulations have been useful in understanding the differences between the simple Bragg theory and the results from our experiment on a small crystal with finite source and detector distances.