Gain measurements on GaAs-based quantum cascade lasers using a two-sectioncavity technique

A two-section cavity device has been used to measure gain spectra and waveg uide losses of a GaAs-based quantum cascade laser. The device operates at 8 .9 mu m and optical confinement is obtained by means of Al-free cladding la yers. We investigated the gain characteristics in a spectral window of simi lar to 60 meV and up to 200 K, For current densities ranging from 1 to 8 kA /cm(2), we report a constant gain coefficient of 13 cm/kA at 4K and 6 cm/kA at 200 K, At low temperatures and for current densities above 8 kA/cm(2),w e observe gain saturation which we attribute to a reduced electron injectio n in the active region caused by space charge effects, We report a value of 22 cm(-1) for the waveguide tosses in good agreement with previous measure ments.