Microlens coupled interdigital photoconductive switch

A large-area terahertz emitter based on an interdigital finger electrode photoconductive switch on low-temperature grown GaAs attached to a hexagonal microlens array is demonstrated. The hexagonal arranged microlenses direct the incident IR excitation pulses into specified electrode gaps, resulting in constructive interference in the terahertz far field. Using a Ti:sapphire oscillator running at 80 MHz with 150 fs pulses, 6.5 mu m THz average power at 540 mW optical excitation is obtained. The maximum IR-to-terahertz conversion efficiency achieved is >= 1.35x10(-5).