To help answer the perennial question ‘What does a laser path look like in slow motion?’ a team of researchers (published Open Access in Nature in August 2014) undertook an experiment at Heriot-Watt University that used a 2D silicon CMOS array of single-photon avalanche diodes (‘SPAD’) to essentially construct a 0.1 megapixel resolution camera capable of recording the path of laser pulses through a given area. While the article acknowledges that light has been captured in flight as early as 1978, the challenge addressed by the team is one of simplifying data acquisition and reducing acquisition times “by achieving full imaging capability and low-light sensitivity while maintaining temporal resolution in the picosecond regime” (Gariepy et al, 2014: 2). To produce an image (or rather a video) from the experiment, the raw sensor data was put through a sequence of processing steps categorised into 3 stages: noise removal, temporal deconvolution and re-interpolation – which is illustrated in the graphic below:
The video produced by the team (GIF excerpt below) is an overlay of the 500 picosecond pulse of laser light on top of a DSLR photograph of the experimental setup. The scattering of light that makes the beam visible is remarkably only through interaction with ambient gas molecules (Gariepy et al, 2014: 4), versus a more ‘dense’ medium that is traditionally required to highlight laser light (e.g. fog, participating media such as airborne dust, etc).
This laser path in flight is the missing step from the following video produced as part of the Scottish Ten project: we see the Leica C10 scanner laser spot reflecting from the surface of a bridge at the Eastern Qing Tomb, China. If we applied the same methodology as the research team in the article to the scanner, we might see the same phenomenon repeated at incremental spatial locations to record the environment around the scanner – perhaps the ultimate LiDAR demo?