Abstract
Quantum-cascade lasers operating at lambda approximate to 3.9 mu m at room temperature with narrow w approximate to 5 mu m ridge widths are described. The lateral confinement due to the narrow ridge is similar to the vertical confinement and the resulting beam is circular in cross section with a single TM(00) spatial mode. The beam divergence is 46 degrees both parallel and perpendicular to the surface. The beam quality factor along the slow axis is about M(2)=1.6. The narrow ridges also increase the relative lateral heat dissipation from the active region, resulting in a thermal conductance per unit area of about G(th)=380 W K(-1) cm(-2) for a 3 mm long laser. Maximum average power is obtained with duty cycles between 10% and 30%; in spite of the very narrow ridge, the total average power with thermoelectric cooling exceeds 60 mW with a peak power of 460 mW. The circularly symmetric beam with very good beam quality suggests essentially zero astigmatism and indicates that these narrow-ridge quantum-cascade lasers are well suited for applications in midinfrared spectroscopy and imaging. (C) 2008 American Institute of Physics.