High-speed optical scanning system for terahertz radiation with 10x10mm² scan field, 23mm working distance and 10kHz repetition rate

In this paper we present a confocal optical THz-scanner with real-time data acquisition at a measuring rate of 10kHz and scanning speed of 250mm/s. It comprises two THz modules with OAP collimation, a tip-tilt mirror and a refractive focusing lens made of silicon (diffraction limited, f = 30mm). The scanning field dimensions are about 10 x 10 mm². Reflectivity is simultaneously evaluated at four freely selectable frequencies between 0.1 and 0.8THz. To reduce Fresnel losses at the lens’s plano Si-air interface we design and evaluate a moth-eye structure acting as anti-reflection coating that was manufactured in-house by an ultrafast laser ablation process.