Improvement of terahertz imaging with a dynamic subtraction technique

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(-4). we also introduce a modified detection geometry that realizes near-field imaging capability with greatly improved spatial resolution. (C) 2000 Optical Society of America. OCIS codes: 320.7100, 110.2970, 320.7120, 250.5530.