Filming light at light speed

The human visual system can perceive only about 10 distinct images per second. So to record everyday life as we experience it, a standard video capture rate of 24 frames per second more than suffices. But many physical phenomena unfold faster than the eye can see. To record them, researchers seek ever-faster cameras. Now Lihong Wang and coworkers at Washington University in St. Louis have developed a camera that can capture 10¹¹ frames per second, good enough to record the movement of light at millimeter length scales. The camera exploits a technology called streak photography : Instead of opening and closing a shutter to capture a sequence of discrete images, a streak camera deflects incoming light in a way that maps a scene’s temporal component to a spatial dimension on the camera’s two-dimensional pixel array. Because one of the array’s dimensions is reserved for mapping time, conventional streak cameras can film in only one spatial dimension. Wang and company, however, found that they could record a 2D scene if they used a programmable mask to encode incoming light with a known pixel pattern. That allows them to detect information about all three dimensions—two spatial dimensions and time—on a single pixel array and then mathematically parse that information to recover a frame sequence that closely approximates the original scene. To demonstrate the technique, the group filmed light pulses reflecting off a mirror , illuminating striped walls , and exciting fluorescence in rhodamine dye . In the frame sequence pictured here, a light pulse nearly perfectly reproduces the path (dashed line) predicted by ray optics as it refracts at an air–resin interface. (L. Gao et al., Nature 516, 74, 2014 .)