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 80MHz with 150fs pulses, 6.5μmTHz average power at 540mW optical excitation is obtained. The maximum IR-to-terahertz conversion efficiency achieved is ⩾1.35×10−5.