Tailorable Topological Multimode Nanolaser with Mutually Incoherent Modes

We demonstrate a tailorable topological multimode nanolaser that supports simultaneous lasing in modes belonging to different topological classes and exhibiting no mutual phase correlation. Arrays of gold nanoparticles (NPs) with varying diameters were fabricated and embedded in a fluorescent dye gain medium, enabling the systematic investigation of the emergence and interplay between topologically trivial dipolar and topologically nontrivial quasi-bound-state-in-the-continuum (qBIC) modes. Angle- and wavelength-resolved measurements reveal single- and dual-mode lasing behavior, with far-field emission patterns and threshold characteristics strongly dependent on nanoparticle size. Spatial and temporal coherence characterization using interferometry shows mode-dependent coherence distributions across both the source plane and the far-field. We show that the relative contributions of the lasing modes can be tuned by adjusting the nanoparticle geometry, providing insights into the interplay between topologically distinct photonic modes and coherent light emission. Cross-correlation frequency-resolved optical gating measurements further resolve the temporal dynamics of the topologically trivial and qBIC modes, showing that these modes, having orthogonal polarizations at the sample plane, are mutually incoherent. This is in stark contrast to our previous results on topologically trivial superlattice modes, where shared excited-state molecular populations led to mode locking. The absence of mutual phase correlations is advantageous for applications requiring minimal crosstalk between lasing channels, such as multiplexed communication and multichannel sensing.