Parity-Dependent THz Harmonic Generation in Electrically Pumped Micro-Lasers Exploiting Topological...

The intersection of topological photonics and nonlinear optics provides new opportunities for compact, tunable light sources. Here, we demonstrate even and odd harmonic generation, in the 6-10 THz range, in electrically driven micro-lasers by integrating a set of different topological insulator (TI)-metamaterials. The unique surface states of TI, characterized by robust symmetry properties, enable enhanced nonlinear interactions when coupled with the tailored dispersion and field confinement of metamaterials. By leveraging the nonlinear susceptibilities of the composite structure by electrical gating, we demonstrate controlled generation of second- or third-harmonic signals of up to 33 µW or 6.4 µW power, respectively, dominated either by the topological surface states or by the bulk. Moreover, by selectively pumping resonant infrared (IR) phonons with the intracavity-generated THz pulses, we induce dynamic lattice distortions that modulate the electronic band structure and further enhance the nonlinear optical susceptibilities. The interplay between phonon-driven lattice anharmonicities and the topologically protected surface states, leads to a pronounced enhancement in nonlinear THz response, offering new mechanisms for nonperturbative light-matter interactions in quantum materials. Our findings establish a novel versatile framework for compact, tunable sources of coherent radiation across multiple frequency bands, so far inaccessible in a solid-state laser, and pave the way for applications in integrated photonics, on-chip frequency conversion, and quantum information processing.