Ultrathin Deployable Femtosecond Vortex Laser.

Ultrafast vortex lasers, capable of emitting structured femtosecond pulses with orbital angular momentum, hold great potential for high-speed optical communications, super-resolution imaging, and advanced laser processing. However, the direct generation of femtosecond vortex pulses in micro/nanoscale lasers remains a major challenge. Here, an ultrathin deployable femtosecond vortex laser based on a ≈200 nm-thick conjugated polymer gain membrane integrated with a square-lattice photonic crystal supporting symmetry-protected bound states in the continuum mode is demonstrated. The high-Q vortex modes driven by Purcell enhancement enable low-threshold (1.5 µJ cm), femtosecond (≈600 fs) vortex pulse emission with peak power reaching several MW/cm. The freestanding membrane can be modularly deployed onto arbitrary substrates, where direct laser fabrication is challenging. When deployed onto an optical mirror, the membrane laser achieved unidirectional emission, nearly doubling its output efficiency. Furthermore, a confocal optical path aligned the vortex laser coaxially with the pump light, highlighting its potential as an integrated module for simplifying super-resolution imaging and lithography techniques.