High-power operation of uncoated 22-μm-wide quantum cascade lasers(QCLs)emitting at λ≈4.8 μm is reported.The emitting region of the QCL structure consists of a 30-period strain-compensated In0.68 Ga0.32As/In0.37Al0.63As superlattice.For a 4-mm-long laser in puIsed mode,a peak output power is achieved in excess of 2240 m W per facet at 81 K with a threshold current density of 0.64 Ka/cm2.The effects of varying the cavity lengths from 1 to 4mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4cm-1 is extracted.