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

Area of Science:

• Photonics and Terahertz Science

Background:

• High-power terahertz (THz) quantum cascade lasers are crucial for medicine, sensing, and communication.
• Scaling THz beam brightness with device area is challenging due to mode competition and sub-wavelength confinement.
• External optical lenses are typically required to enhance THz beam brightness.

Purpose of the Study:

• To propose a metallic THz photonic crystal resonator with a phase-engineered design.
• To achieve single-mode surface emission over a broad area without external optics.
• To enable high-brightness, large-area THz sources for advanced applications.

Main Methods:

• Design and fabrication of a metallic THz photonic crystal resonator.
• Phase-engineered lattice structure for controlled surface emission.
• Characterization of output power, beam divergence, and brightness.

Main Results:

• Achieved peak output power over 185 mW at 3.88 THz.
• Demonstrated narrow beam divergence (4.4° × 4.4°).
• Obtained high beam brightness (1.6 × 10^7 W sr^-1 m^-2) from a large 1.6 × 1.6 mm^2 device area.
• Near-diffraction-limited M^2 factors (1.4) achieved without external lenses.

Conclusions:

• The phase-engineered resonator enables stable, high-intensity surface emission over a broad area.
• This technology is an ideal light extractor for large-scale THz emitters.
• Paves the way for high-brightness solid-state THz lasers and new applications in standoff imaging and detection.