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freesword writes:

We've all seen the colorful laser bolts of science-fiction movies, but what would a real world laser bolt look like (if we could actually make it out)? According to engineering.com, a group of researchers at the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences in cooperation with the Faculty of Physics at the University of Warsaw (IPC PAS and FUW) have managed to answer that question. Their tests of a new compact high-powered laser have given them the opportunity to film the passage of an ultrashort laser pulse through the air.

"If you wanted to film a single light impulse to move as slowly on film as in our recording, you would have to use a camera operating at a speed of a billion frames per second", says Dr. Yuriy Stepanenko, leading the team responsible for the construction of the laser.

Since cameras recording billions of frames per second do not exist, the researchers used an earlier known trick of synchronizing a camera with the laser generating the pulses at a rate of approx. 10 shots per second. The synchronization was such that with each shot the camera image was minimally delayed from the previous one.

"In fact, a different laser pulse can be seen in every frame of our film", explains Dr. Paweł Wnuk, (LC of IPC PAS and FUW) and adds: "Luckily, the physics always stays the same. So, on the film one can observe all the effects associated with the movement of the laser pulse in space, in particular, the changes in ambient light depending on the position of the pulse and the formation of flares on the walls when the light passes through the dispersing cloud of condensed water vapour".

The laser used in the test was powerful enough to immediately ionize the atoms around it resulting in a plasma fibre – filament – to be formed alongside the pulse. The laser was set up to balance the interactions between the pulse's electromagnetic field and the plasma filament so that the light beam did not disperse in air but instead underwent self-focusing, resulting in the pulse moving a much greater distance than low-power pulses while maintaining it's original parameters.

"It is worth noting that although the light we are shooting from the laser is in the near infrared range, a laser beam like this travelling through the air changes colour to white. This happens since the interaction of the pulse with the plasma generates light of many different wavelengths. Received simultaneously, these waves give the impression of white", adds Dr. Stepanenko.