We report on increasing the sensitivity of electro-optic sampling detection of terahertz pulses by using the effect of terahertz field enhancement in a tapered metallic waveguide. A thin Si prism, placed in the narrower section of the waveguide, is used to synchronize the enhanced terahertz field with the probe laser pulse propagating in a LiNbO3 crystal attached to the obliquely cut end of the waveguide. A 40-µm-thick MgO-doped layer on the surface of LiNbO3 is used for guiding the probe pulse. The developed structure demonstrates a 20-fold higher detection sensitivity than a no-waveguide, Si-prism-coupled LiNbO3 crystal.

We have observed a significant enhancement in the electro-optic sampling efficiency for THz radiation by using focusing effect in a metallic tapered parallel plate waveguide and also an optical waveguide in LiNbO3 employed as an EO crystal. The total enhancement factor exceeds an order of magnitude as compared to the case with a bulk LiNbO3 crystal coupled with a Si prism.I.

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