A light-sensitive crystal is opening the door to a new era of “light-written” technology. Arsenic trisulfide can be reshaped and permanently altered using simple light, creating ultra-fine optical patterns without expensive manufacturing tools. Scientists even etched a nanoscale portrait of Eins tein and high-density patterns that could act as secure optical signatures. This breakthrough could power everything from advanced sensors to next-generation AR devices. ...read more read less