Strained layer InGaAs/GaAs SCH SQW (Separate Confinement Heterostructure Single Quantum Well) lasers were

grown by Molecular Beam Epitaxy (MBE). Highly reliable CW (continuous wave) 980-nm, broad contact, pump lasers were

fabricated in stripe geometry using Schottky isolation and ridge waveguide construction. Threshold current densities of the

order of Jth ≈ 280 A/cm2 (for the resonator length L = 700 um) and differential efficiency η= 0.40 W/A (41%) from one

mirror were obtained. The record wall-plug efficiency for AR/HR coated devices was equal to 54%. Theoretical estimations

of above parameters, obtained by numerical modelling of devices were Jth ≈ 210 A/cm and η = 0.47 W/A from one mirror,

respectively. Degradation studies revealed that uncoated and AR/HR coated devices did not show any appreciable degradation

after 1500 hrs of CW operation at 35oC heat sink temperature at the constant optical power (50 mW) conditions.

Lasers emitting mid-infrared (MIR) beams have become indispensable for spectroscopy, free space communication or remote security measures. To the one of the most promising families of the lasers suitable for these applications certainly belongs a group of the Quantum Cascade Lasers (QCL). However, among the conditions they must satisfy there is a high enough radiance of the beam they emit. Radiance depends in a complicated way on the laser output power and optical quality of the laser beam. This paper has been devoted to a description and a short analysis of the factors that decide about radiance of so far developed QCLs. Literature concerning both single devices and QCL arrays operating in beam combining systems have been examined and results described. The survey may be useful for estimation of how far the QCLs have come of age.