At high power, laser light inside a multimode optical fiber is supposed to misbehave. The beam usually breaks into a noisy, scattered pattern as the light ricochets through many paths at once. But MIT researchers found a case where that expectation fails. Push the system close to its limit, line the beam up just right, and the optical mess can collapse into a tightly focused, self-organized “pencil beam.” That beam, the team reports, can do more than tidy up a physics problem. In experiments on a human model of the blood-brain barrier, it produced 3D images about 25 times faster than a standard approach. This was achieved while keeping similar cellular-level detail. The work appears in Nature Methods. “The common belief in the field is that if you crank up the power in this type of laser, the light will inevitably become chaotic. But we proved that this is not the case. We followed the evidence, embraced the uncertainty, and found a way to let the light organize itself into a novel solution for bioimaging,” …