Brewster's angle attenuator for terahertz pulses

A variable attenuator for terahertz (THz) pulses is developed on the basis of the change in reflectivity of lithium niobate wafers with incident angle in a Brewster configuration. We can vary the THz field transmission from 22% to 54%, a change of a factor of 2.5, while preserving the shape of the THz pulse spectrum. Changes in the THz spectrum are shown to be much smaller when the Brewster attenuator is used than when either the near-infrared pump power or the bias voltage on a THz photoconductive antenna is varied. The Brewster attenuator should prove especially useful for varying THz field strength in nonlinear optical studies that use broadband THz pulses.