A team of researchers at Washington University in St. Louis has taken images of a laser pulse generating an optical Mach cone: the equivalent of a sonic boom, but for light. To make an optical Mach cone, a pulse of light would need to be traveling faster than the waves it’s emitting can propagate forward. But the researchers were able to peel apart the properties of a laser beam, interacting separately with velocity, wavelength, and frequency. They directed the beam through a layered confection of silicone panels, aluminum oxide powder, and dry ice. The source of the light waves was moving faster than the waves themselves as they passed through the layers, leaving behind the optical Mach cone. Ultrafast cameras have been photographing sweet speed-based optical phenomena like Mach cones for a while, but this is the first time they’ve been able to catch an optical Mach cone in real time. To capture the cone itself, the researchers set up CCD cameras next to the cone-generating apparatus. One of the cameras was a streak camera, which exploits the motion of charged particles to create a spatial “pulse profile” that characterizes the light waveform in 3-space over time. Using the streak camera and the CCDs, the researchers captured a 2D sequence of images from three perspectives in a single take. They then spliced the images back together like a CAT scan to make a 3D model of the cone. Lead author Jinyang Liang hopes that these developments can be pressed into use not just in physics, but in neuroscience. Their imaging setup can capture 100 billion frames a second. With that kind of temporal resolution, researchers could capture neurons firing in real time.
Read More: ExtremeTech