Interferometry-aided delay lines for high-precision terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy relies on the knowledge of the time delay between two ultrashort laser pulses. This time delay is most commonly introduced by mechanically driven delay lines, where often a linear movement or in the case of oscillation based devices a sinusoidal movement is assumed or measured only imprecisely. We present a highly accurate method to measure the real time delay by overlapping the ultrashort pulse with one optical branch of a Mach-Zehnder interferometer. The interferogram provides an exact time base for the terahertz signal and enables high-precision time-domain spectroscopy even with inherently highly inaccurate delay lines.