Abstract
Currently, different competing waveguide and resonator concepts exist for terahertz quantum-cascade lasers (THz QCLs). We examine the continuous-wave (cw) performance of THz QCLs with single-plasmon (SP) and metal-metal (MM) waveguides fabricated from the same wafer. While SP QCLs are superior in terms of output power, the maximum operating temperature for MM QCLs is typically much higher. For SP QCLs, we observed cw operation up to 73 K as compared to 129 K for narrow (≤ 15 μm) MM QCLs. In the latter case, single-mode operation and a narrow beam profile were achieved by applying third-order distributed-feedback gratings and contact pads which are optically insulated from the intended resonators. We present a quantitative analytic model for the beam profile, which is based on experimentally accessible parameters.
Highlights
By today, terahertz quantum-cascade lasers (THz QCLs) are established sources for various applications in the field of spectroscopy and imaging
While SP waveguides are well suited for many applications and superior in terms of output power [3, 4], all records in terms of operating temperatures are held by THz QCLs based on metal-metal (MM) waveguides, for which the active region is sandwiched between two metal layers [5,6,7]
Based on the same wafer, we investigated the performance of THz QCLs with SP and MM waveguides, where in the latter case the focus has been on MM wire QCLs for which the ridge width is small compared to the emission wavelength
Summary
Terahertz quantum-cascade lasers (THz QCLs) are established sources for various applications in the field of spectroscopy and imaging (for reviews see [1, 2]). Due to the strong sub-wavelength confinement, edge emitting MM QCLs suffer from a poor beam profile. To overcome this limitation, many efforts have been put into the development of surface emitting MM QCLs [8]. In contrast to MM wire QCLs, typical SP QCLs are more or less classical edge emitters, which perform best if the ridge width is of the same dimension or even larger than the free space wavelength [3, 4, 12]. For studies on SP and MM waveguides in general, we refer the reader to the literature [12,13,14]
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