Precise Evaluation of a Phase Locked THz Quantum Cascade Laser
We have demonstrated the phase locking of a THz quantum cascade laser (THz QCL) toward the realization of an accurate and stable local oscillator for a high resolution receiver. The beat note between the THz QCL and a THz reference was obtained by heterodyne mixing in a superconducting hot electron bolometer mixer (HEBM) and used for stabilizing the phase of 3.1 THz radiation from the THz QCL. The phase locked 3.1 THz radiation was fully evaluated with a superlattice harmonic mixer operating in the THz band, and this revealed that the THz QCL synchronized with the microwave reference with a fractional frequency instability of 3x10 15 at an averaging time of 100 s, corresponding to a center frequency deviation within 1 mHz, and the imposed phase noises during the heterodyne mixing were negligibly small.
IEEE Transactions on Terahertz Science and Technology