Continuously Tunable Coherent THz Synthesizer, Referenced to Primary Frequency Standards

Abstract

We present a highly coherent tunable THz source based on an optical frequency comb generator with frequencies referenced to primary frequency standards. The THz synthesizer is continuously tunable from 122.5 GHz to greater than 2.7 THz, with a spectral resolution of 10’s of Hz and a frequency accuracy of 1 part in 1012. The composite noise has been measured up to a record frequency of 300 GHz, and is -75 dBc/Hz at an offset frequency of 10 kHz, limited by the scaled phase noise of the reference synthesizer. A 2 THz quantum cascade laser with an output power of $\sim 2$ mW has been injection locked to the absolute frequency referenced, high spectral purity THz synthesizer to realize a high power, narrow linewidth source suitable for high-resolution spectroscopy.