Silk Nanocrack Origami for Controllable Random Lasers.

The ancient art of Origami started to evolve as a contemporary technological method for the realization of morphologically induced and unconventional advanced functional structures. Here, directional random lasers (RLs) that are formed by folding (i.e., ori) dye‐doped natural protein silk fibroin (SF) film as paper (i.e., kami) are demonstrated. The folding stress induces parallel nanocracks that simultaneously function as diffuse reflectors and laser light outcouplers at the boundaries of the optical gain medium. Random lasing is observed after a threshold energy level of 0.8 nJ µm−2 with an in‐plane divergence‐angle of 13°. Moreover, the central laser emission wavelength is tuned from 588.7 to 602.1 nm by controlling the adjacent nanocracks distance and additional laser emission directions are introduced by further folding SF at different in‐plane angles that induce rectangular and triangular geometries. More significantly, RL is fabricated via a quick, scalable, and environmentally friendly stress‐induced nanocracking process maintaining its mechanical and optical properties even after 10,000 times of bending test. Hence, this study introduces a novel form of biocompatible, biodegradable, and large‐area protein microlasers by using an unconventional laser fabrication approach. [ABSTRACT FROM AUTHOR]