Optical Behavior of Domains in KH2PO4

Below the Curie temperature, K${\mathrm{H}}_2$P${\mathrm{O}}_4$ is found to act as a layered dielectric waveguide for light propagating along the polar axis. Each thin (3×${10}^{-4\mathrm{}}$-10×${10}^{-4\mathrm{}}$ cm) domain is a waveguide for light polarized along its "slow" direction. The domain walls are parallel to one tetragonal axis and the polar axis and are continuous through the whole crystal. A collimated beam is diffracted at the exit face of the K${\mathrm{H}}_2$P${\mathrm{O}}_4$ crystal. Both regular (ordered) and irregular diffraction patterns were observed. When the incident light was plane polarized, the regular diffraction pattern consisted of even and odd orders (spots) which were in general plane polarized in different directions. These propagation effects are explained in terms of the domain structure.