A general description of electro-optic detection including non-collinear phase matching and finite transverse beam profiles is presented. It is shown theoretically and experimentally that non-collinear phase matching in ZnTe (and similar materials) produces an angular chirp in the ?- generated optical signal. Due to this, in non-collinear THz and probe arrangements such as single-shot THz measurements or through accidental misalignment, measurement of an undistorted THz signal is critically dependent on having sufficient angular acceptance in the optical probe path. The associated spatial walk-off can also preclude the phase retardation approximation used in THz-TDS. The rate of misalignment-induced chirping in commonly used ZnTe and GaP schemes is tabulated, allowing ready analysis of a detection system.
Walsh, D. A., Cliffe, M. J., Pan, R., Snedden, E. W., Graham, D. M., Gillespie, W. A., & Jamison, S. P. (2014). Role of misalignment-induced angular chirp in the electro-optic detection of THz waves. Optics Express, 22(10), 12028-12037. https://doi.org/10.1364/OE.22.012028