A modified streak camera is fast enough to capture the movement of a single laser pulse in real time. Streak cameras measure the intensity variation in a pulse of light with time, but in only one dimension. Researchers at Washington University gave their camera 2-D capabilities using a wider aperture and a technique they call compressed ultrafast photography (CUP). The imaging speed of CCD and CMOS sensors is limited to about 10 million fps by their on-chip storage and electronic readout speed. In contrast, CUP captures events at up to 100 billion fps, enabling temporal resolution of tens of picoseconds. The CUP system configuration. Courtesy of Washington University in St. Louis. “For the first time, humans can see light pulses on the fly,” said lead researcher professor Dr. Lihong Wang. “Because this technique advances the imaging frame rate by orders of magnitude, we now enter a new regime to open up new visions. Each new technique, especially one of a quantum leap forward, is always followed by a number of new discoveries. It’s our hope that CUP will enable new discoveries in science — ones that we can’t even anticipate yet.” Light interacts with several components in the CUP system before reaching the streak camera. After passing through three lenses it arrives at an encoding system with 1 million 7-µm2 mirrors, which reflect it back through a beamsplitter and into the streak camera’s widened slit. At the camera, the photons are converted to electrons, which are then sheared with the use of two electrodes. The electrodes apply a voltage that ramps from high to low, so the electrons will arrive at different times and land at different vertical positions. A CCD stores all the raw data, which are assembled by a computer. The setup is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. Other recent experiments have visualized laser pulses in slow motion, but those involved making composite videos of several pulses. The CUP technique is able to visualize the propagation of a single pulse. Wang and his colleagues used the technique to create movies showing a laser pulse reflecting off a mirror; a pulse refracting at the interface of two media; two pulses racing in different media; and faster-than-light propagation of noninformation. The technique can be used to study the lifetimes of fluorophores in bioimaging; it may also find applications in forensics and astronomy. “These ultrafast cameras have the potential to greatly enhance our understanding of very fast biological interactions and chemical processes and allow us to build better models of complex, dynamical systems,” said Dr. Richard Conroy, program director of optical imaging at the National Institute of Biomedical Imaging and Bioengineering, part of the NIH, which funded the CUP research. The research was published in Nature (doi: 10.1038/nature14005). For more information, visit www.wustl.edu.