Scientists have suspected that light can create its own conical wakes, like a sonic boom, but how do you capture something that happens so quickly? With a very fast camera, naturally. Washington University in St. Louis has recorded these photonic shockwaves using a “streak camera” that measures both the image and temporal data at 100 billion frames per second. To visualize the cones, the team shot very fast green laser pulses (just 7 picoseconds long) through a tunnel full of dry fog and placed between plates made from aluminum oxide and silicone rubber. Since the laser moved faster in the tunnel than in the plates, it produced a sonic boom-like effect as some of the light dragged behind.
The approach to the camera is particularly important. Other techniques for capturing very fast events usually require many, many exposures to see anything; the streak camera only needs one. On top of the simplicity, this lets you capture events that won’t repeat in the exact same way, such as the laser pulses.
This could provide new insights into light, of course, but the scientists are ultimately interested in biology. Their system is fast enough to track neurons as they fire, and map brain activity in real time. You could track even the smallest details, which could improve our understandings of both the mind and brain-related diseases.