Characterization of an optically generated 3THz continuous wave using a phase-locked QCL and a HEB mixer

We characterized a 3THz continuous wave generated by photomixing two optical modes of a broadband optical frequency comb. This optically generated THz wave and the output beam of a 3THz quantum cascade laser phase-locked to a THz reference were coupled onto a hot electron bolometer mixer operated at 4K and the beat signal was precisely evaluated. This direct comparison at 3THz reveals that the optically generated 3THz wave has fractional frequency instability of 4×10⁻¹⁵ at 100sec averaging time and the power spectral density of −10 dBc/Hz at 1Hz Fourier frequency.