Active Stabilization of Terahertz Semiconductor Dual?Comb Laser Sources Employing a Phase Locking Technique

Dual-comb sources with equally spaced and low phase noise frequency lines are of great importance for high resolution spectroscopy metrology. In the terahertz range, electrically pumped semiconductor quantum cascade lasers (QCLs) suitable candidates comb dual-comb operation. For a single laser comb, repetition rate can be locked using microwave injection locking carrier to highly stable source. However, two combs, four frequencies (two rates offset frequencies) should simultaneously locked; If one only refers signal, relative frequencies, i.e., against those other laser, locked. Although techniques that have been successfully used be, in principle, applied source, complete considerably complicates implementation such system. Here, we propose method stabilize QCL source by radio (RF) synthesizer. This technique forces follow tone (keeping sum difference between combs as constant) exploiting self-detection avoids use an external detector. Through demonstration this technique, demonstrate generate periodic pulses over 2 us time scale, showing without control produce pulsed-type waveforms.