Ultrafast THz intersubband polariton saturable absorber integrated with a quantum cascade frequency comb

We devise a THz polaritonic saturable absorber exploiting ultra-strong coupled intersubband cavity polaritons generated in a multi quantum well (MQW) heterostructure. By coupling the polaritonic saturable absorber reflector with a high bandwidth heterogeneous THz QCL frequency comb (2.3-3.8 THz) we demonstrate spectral reshaping of the QCL emission and a major increase of the comb operational dynamic range up to 38% characterized by a stable single and narrow intermode beatnote.