Characterizing large-area electro-optic crystals toward two-dimensional real-time terahertz imaging.

We have characterized the homogeneity of large-area (>10 mm x 10 mm) CdTe(110) and ZnTe(110) crystals using a raster electro-optic scanning method to assess their usability in two-dimensional electro-optic terahertz (THz) imaging with parallel read out. The spatial variation in the detected THz signal (at 0.2 and 0.645 THz, respectively) is due to nonuniform residual birefringence and scattering. For CdTe, this depends critically on the growth method, and has an important contribution from slip planes in the crystals, as is evident in the scanned images. For the highest-quality CdTe(110) crystals investigated, the rms signal variations are less than 15%, comparable to those for ZnTe(110). For electro-optic scanning, we introduce a hybrid measurement system based on a fs Nd:glass laser and a continuous-wave electronic THz source.