  In the terahertz frequency range, the quantum cascade laser (QCL) is a
suitable platform for the frequency comb and dual-comb operation. Improved comb
performances have been always much in demand. In this work, by employing a
symmetric thermal dissipation scheme, we report an improved frequency comb and
dual-comb operation of terahertz QCLs. Two configurations of cold fingers,
i.e., type A and B with asymmetric and symmetric thermal dissipation schemes,
respectively, are investigated here. A finite-element thermal analysis is
carried out to study the parametric effects on the thermal management of the
terahertz QCL. The modeling reveals that the symmetric thermal dissipation
(type B) results in a more uniform thermal conduction and lower maximum
temperature in the active region of the laser, compared to the traditional
asymmetric thermal dissipation scheme (type A). To verify the simulation,
experiments are further performed by measuring laser performance and comb
characteristics of terahertz QCLs emitting around 4.2 THz mounted on type A and
type B cold fingers. The experimental results show that the symmetric thermal
dissipation approach (type B) is effective for improving the comb and dual-comb
operation of terahertz QCLs, which can be further widely adopted for
spectroscopy, imaging, and near-field applications.
