Frequency Characterization of a Terahertz Quantum-Cascade Laser

In this paper, the frequency characteristics of a terahertz quantum-cascade laser (QCL) operating around 2.5-THz in the pulsed regime have been studied by means of a heterodyne detection by using an optically pumped molecular laser as the local oscillator. The absolute frequency of the QCL can be determined with an accuracy of 1 MHz due to the pulse-to-pulse jitter of the QCL. The frequency tunability as a function of the injection current of the QCL is estimated to be around $+$2 GHz/A.