For the first time ever scientists have captured a video of a laser’s flight path as it moves through the air. The clip above was created using a new ultra high-speed camera capable of detecting single photons at a time — the smallest amount of light possible. To create the video, researchers from the Heriot-Watt University in Edinburgh in the UK recorded 2 million laser pulses over a 10 minute period, aggregating individual collisions of photons with air particles to map the laser’s entire flight path.
The new camera is so accurate that it shows the shape of the laser pulse
"This is the first time we’ve looked at light just passing by," lead researcher Genevieve Gariepy tells The Verge. "Usually you have to see light reflecting off things." In the case of lasers, observing the light is even more difficult as the photons are all moving in the same direction in a tightly focused beam. You only see the light from a laser when it bounces off an object or when something like smoke or gas is blown over it, giving the photons more particles to collide with. Gariepy explains that slightly smeared look of the laser in the video — a little like watching the aurora borealis in slow motion — shows just how precise the camera is. "The pulse has a shape: it’s not just a rectangle moving through the air."
The experiment is a step forward from research published in 2011 in which MIT physicists successfully recorded light pulses passing through a Coke bottle. The same scientists worked on this new experiment, and Gariepy explains that this process is quicker than the older work (taking 10 minutes to record instead of one hour) and uses a camera no bigger than a digital compact, while the MIT apparatus was projector-sized. "They also had to fill the bottle with water and milk [to record the laser], meaning that some of the light bounced off those particles," says Gariepy, who adds that the new camera may not capture as many frames per second, but it is "a lot more sensitive, allowing us to see the light bouncing off air molecules."
Technology like this could help us create cameras that can see around corners
The camera itself only records 1024 pixels in a 32 by 32 grid, but Gariepy says it paves the way for practical applications in the future. Being able to record photons this accurately offers two new channels of data, she says, spatial and temporal. The temporal information can be used to study dynamic processes that happen very fast while the spatial data could be used to see around corners by recording photons bouncing off hidden objects and returning to the camera. "It’s the same principle as LIDAR but more sensitive," says Gariepy. She explains that while work has already been done in this area (see the video below from 2012), the new camera is a step forward in terms of portability. "Right now it’s just plugged into my computer, but it could be used by just taking it outside and recording movies for yourself."