Passive Beam Shaping for Terahertz Quantum Cascade Lasers

We report the design and experimental demonstration of a passive beam-shaping module integrated into a terahertz (THz) imaging system. THz QCLs inherently produce highly divergent beams, posing challenges for beam shaping and system integration. The proposed module, comprising a feedhorn, a standard waveguide, and a transmitting horn antenna, was optimized using electromagnetic simulations to minimize coupling loss while achieving favorable far-field beam characteristics. Sensitivity analyses quantified the impact of fabrication and alignment tolerances. Far-field measurements confirm the generation of a low-divergence, single-lobe Gaussian beam, supporting high-resolution THz imaging and extending the utility of QCL-based systems to applications including biomedical diagnostics, security screening, and non-destructive testing.