Studies on far-field divergence of Tapered THz-QCLs

Summary form only given. The far-field divergence of Tapered THz quantum cascade lasers is studied experimentally and theoretically. A abnormal increase of the divergence has been found with either increasing the tapered angle or the device´s length. Then we want to answer either the thermal accumulation or the nonlinearity of the material account for it. Theoretical analysis suggests that the field-induced change of the refractive index of the active region may be the key reason for this phenomenon.