By use of dynamic subtraction it is feasible to adopt phase-sensitive detection with a CCD camera to reduce long-term optical background drift. We report on a two-order improvement of the signal-to-noise ratio. The improved system is used to image terahertz field distribution generated by an optically rectified electro-optic crystal with a modulation depth as small as 10<sup>−4</sup>. We also introduce a modified detection geometry that realizes near-field imaging capability with greatly improved spatial resolution.
© 2000 Optical Society of America
(110.2970) Imaging systems : Image detection systems
(250.5530) Optoelectronics : Pulse propagation and temporal solitons
(320.7100) Ultrafast optics : Ultrafast measurements
(320.7120) Ultrafast optics : Ultrafast phenomena
Zhiping Jiang, X. G. Xu, and X.-C. Zhang, "Improvement of terahertz imaging with a dynamic subtraction technique," Appl. Opt. 39, 2982-2987 (2000)