Аннотация:We conduct research of quantum cascade lasers (QCLs) emitting at 2.25, 2.27, 3.2 and 4.1 THz. Measuring the output power, we consider the potential mechanisms of QCL temperature degradation. Moreover, we present the spectra of the lasers measured in a wide temperature range 5 – 120 K, as well as the analysis of inter-mode distance and lasing frequency temperature drift.