That's really slow motion...

A snapshot of a laser beam taken by researchers at the university of Edinburgh. You can see the "start" of the beam!

My digital camera can take some 6 frames per second and when in movie mode it can go up to 30 frames per second.  It is not one of the best in this respect. There are a few point and shoot that can go up to 1,000 frames per second!

With a 1,000 frames per second you can capture something that happens in one millisecond, that's quite a feat! And yet, a light ray would cover 300km in that time frame!  Impossible to catch it. 

Now researchers at the Edinburgh university have published a video on YouTube (see the clip below) where they show a laser beam as it moves from the laser to a sequence of mirrors. And to do that they have used a video camera that can capture 20 billions frames per second!

The feat is based on research carried out at MIT and several of the researchers that worked in that research were part of this experiment too. Actually the camera used at MIT in 2011 had a frame rate close to 650 Billion per second, but it was not able to capture a beam, just a snapshot, a photon.

At Edinburgh they have been able to develop a much smaller camera, not bigger than a point and shoot that can actually take sequences of frames that can be used to reconstruct the beam, as shown in the clip. For this particular clip the camera "looked" at about 2 million laser pulses over a period of 10 minutes.

This is the first time that we can look at a laser beam. Interesting to notice its shape, not a perfect rectangular form. more like a spear.

OK, this is great fun, but could it also have some interesting practical applications?

Indeed it can. This camera shows that we can record both the spacial and the temporal path of photons and this can be applied to create digital images of things that would normally be hidden to a camera. An example is to take a picture of objects behind a wall. As long as there is an opening in the wall, sooner or later a few photons will bounce on objects behind the wall and find the way to go through the opening (like a door in the room). This allows the rendering of the space behind the wall.  It provides a boost at LIDAR, actually an amazing step forward.

Author - Roberto Saracco

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