High-precision THz spectrum analyzer based on an unstabilized frequency comb

We perform high-precision frequency measurements in the THz spectral region using an unstabilized frequency comb, which acts as a transfer oscillator. To correct the beating signal resulting from the THz source and one comb line of the rectified optical comb for fluctuations of the laser repetition rate, a simple and flexible algorithm is used. By this, we achieve an accuracy of the measurement setup as high as 9·10^-14 for a 100 GHz test source. This is an improvement of two orders of magnitude compared to previously reported precision measurements in this frequency range employing femtosecond lasers.