Picosecond time-resolved imaging using SPAD cameras

Abstract

The recent development of 2D arrays of single-photon avalanche diodes (SPAD) has driven the development of applications based on the ability to capture light in motion. Such arrays are composed typically of 32x32 SPAD detectors, each having the ability to detect single photons and measure their time of arrival with a resolution of about 100 ps. Thanks to the single-photon sensitivity and the high temporal resolution of these detectors, it is now possible to image light as it is travelling on a centimetre scale. This opens the door for the direct observation and study of dynamics evolving over picoseconds and nanoseconds timescales such as laser propagation in air, laser-induced plasma and laser propagation in optical fibres. Another interesting application enabled by the ability to image light in motion is the detection of objects hidden from view, based on the recording of scattered waves originating from objects hidden by an obstacle. Similarly to LIDAR systems, the temporal information acquired at every pixel of a SPAD array, combined with the spatial information it provides, allows to pinpoint the position of an object located outside the line-of-sight of the detector. A non-line-of-sight tracking can be a valuable asset in many scenarios, including for search and rescue mission and safer autonomous driving.Keywords: temporal imaging, single photon detection Capturing light in motion presents an interesting challenge, as a resolution of the order of 100 picosecond is needed to freeze flight on a centimetre scale. The ability to do so opens the door to diverse applications, both for fundamental studies of optical phenomena and for sensing applications such as 3D imaging and non-line-ofsight object detection. Much effort has therefore been made in the last decades to develop methods that allow to visualise light in motion, or perform "light in flight" measurements. This term was coined in 1978 by Abramson, 1 who developed a technique based on holography to record the dynamics of light phenomena such as reflection, focusing and interference. To record the propagation of light, short pulses were sent onto a scattering surface at a grazing angle in such a way that the laser beam intercepted the surface at different times at different points and then scattered light towards a holographic plate. The holographic plate was simultaneously illuminated by a reference beam, also composed by short pulses of light incident at an angle. The hologram hence captured the spatial distribution of the scene at different times, and illuminating the recorded hologram plate at different positions allowed to play back a movie of light propagating across the scattering surface, with a resolution of about 10 ps. Since this seminal work, different techniques have been developed to push the limits of light-in-flight imaging. Velten et al. have shown that streak cameras can be used to perform measurements of laser pulses propagating in a scattering medium or across a scene with high temporal and spatial resolution, 2 and Gao et al...

Time-of-Flight Imaging at 10 ps Resolution with an ICCD Camera

“…Currently, ICCDs with their temporal resolution of 200 ps cannot separate the components of biexponential decays [24]. Therefore, there is a constant drive towards the improvement of the temporal capabilities of these cameras [25,26,27,28,29].…”