Gain measurements in strain-compensated quantum cascade laser

Spectrally resolved gain measurements of a strain-compensated quantum cascade laser, emitting at 4.8 μm, are presented. Measurements have been acquired using a multisection cavity technique. The shape of the gain is compared with electroluminescence measurements whereas gain coefficients are compared to values obtained from laser data, studying the dependence of the laser threshold current with cavity length. Gain coefficients of 9.9 cm kA−1 at 80 K and 3.2 cm kA−1 at 322 K are found and we show that the temperature dependence of the gain coefficient is governed by optical phonon scattering.