High brightness terahertz quantum cascade laser with near-diffraction-limited Gaussian beam

Abstract High-power and high-beam-quality terahertz (THz) quantum cascade laser as an emerging THz radiation solid-state source are attracting attentions for numerous applications including medicine, sensing, and communication. However, due to the sub-wavelength confinement of the waveguide structure, direct beam brightness upscaling with device area remains elusive due to several mode competition and external optical lens is normally used to enhance the THz beam brightness. Here, we propose a metallic THz double-lattice photonic crystal resonator with engineered phase design for single mode surface emission over a broad area. The quantum cascade surface-emitting laser is capable of delivering an output peak power over 185 mW with a narrow beam divergence of 4.4°×4.4° at 3.88 THz. A near-diffraction-limited beam with M² factor of 1.4 in both directions and a high beam brightness of 1.6×10⁷ W sr⁻¹m⁻² is achieved from a large device area of 1.6×1.6 mm² without using any optical lenses. The adjustable phase shift between the lattices enables stable and high-intensity surface emission over a broad device area, which makes it an ideal light extractor for broad-area THz emitters. Our research paves the way to high brightness THz laser sources and facilitates new applications in standoff THz imaging, detection, and diagnosis.