Ultra-low threshold lasing through phase front engineering via a metallic circular aperture

Semiconductor lasers with extremely low threshold power require a combination of small volume active region with high-quality-factor cavities. For ridge lasers with highly reflective coatings, an ultra-low threshold demands significantly suppressing the diffraction loss at the facets of the laser. Here, we demonstrate that introducing a subwavelength aperture in the metallic highly reflective coating of a laser can correct the phase front, thereby counter-intuitively enhancing both its modal reflectivity and transmissivity at the same time. Theoretical and experimental results manifest a decreasing in the mirror loss by over 40% and an increasing in the transmissivity by 104. Implementing this method on a small-cavity quantum cascade laser, room-temperature continuous-wave lasing operation at 4.5 μm wavelength with an electrical consumption power of only 143 mW is achieved. Our work suggests possibilities for future portable applications and can be implemented in a broad range of optoelectronic systems.

Лазерная генерация многопериодных квантово-каскадных лазеров на длине волны излучения 8 мкм при комнатной температуре

Room-temperature lasing at a wavelength of 8 μm in multistage quantum-cascade lasers pumped by current pulses is demonstrated. A quantum-cascade laser heterostructure based on the In_0.53Ga_0.47As/A_l0.48In_0.52As alloy heteropair, matched to an InP substrate, is grown by molecular-beam epitaxy and consists of 50 identical cascades placed in a waveguide with air as the top cladding. A threshold current density of ~5.1 kA/cm^2 at a temperature of 300 K is obtained in ridge lasers with a cavity length of 1.4 mm and a ridge width of 24 μm.