Intracavity near-field optical imaging of a mid-infrared quantum cascade laser mode

We report the direct imaging of Fabry–Pérot standing waves inside the cavity of a mid-infrared quantum cascade laser via apertureless scanning near-field optical microscopy. The quantum cascade devices employed present an evanescent wave at the top surface, whose magnitude is directly proportional to the cavity mode intensity in the device core region. Apertureless scanning near-field optical microscopy measurements provide experimental results about the nature of this evanescent field in good agreement with calculations (effective index and electric field decay length).