Micro lens coupled large area photoconductive switch for powerful THz emission

Powerful THz emission based on a finger electrode photoconductive switch attached to a micro lens array is presented. A hexagonal packed lens array directs the incident pump light into specified electrode gaps, yielding only constructive interference in the THz far-field. Using a Ti:Sapphire system operating at 80 MHz with 150 fs pulses and 3 W maximum optical excitation, 0.28 mW THz average power is obtained. The maximum IR-to-THz conversion efficiency is 1.3×10-4.