The "Star Wars" laser is pretty great: instead of bullets, it fires laser bolts -- short bursts of laser that can be used as a weapon. Unfortunately, the fictional device would not work that way in the real world. For starters, laser pulses, made of light, move at the speed of light -- too fast for the eye to see.
If it could exist in the real world, though, we can now see what it would look like, thanks to a team of researchers from the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Physics, University of Warsaw.
They used a new, compact, high-power laser to send an ultrashort laser pulse through the air, filming it using an old camera trick, since most cameras cannot shoot at a speed of billions of frames per second. A modified camera was synchronised with the laser, which shot pulses at a rate of 10 per second. The laser pulses and the camera were ever-so-slightly out of synch, so that the camera recorded each image at a minimal delay from the previous one. A cloud of water vapour was used to make the laser more visible.
In this way, the camera was able to film the passage of a laser pulse -- with each frame of the film a separate pulse.
"In fact, a different laser pulse can be seen in every frame of our film," said study co-author Paweł Wnuk. "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."
Each pulse lasted around a dozen femtoseconds (millionths of a billionth of a second), and was so powerful that it ionised the atoms around it, which in turn created a fibre of plasma. The team was able to prevent this from dispersing immediately by carefully calibrating the laser machine to balance the interactions between the pulse's electromagnetic field and the plasma. This meant the pulse held its shape, travelling a greater distance than low-power pulses.
"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," said study lead Yuriy Stepanenko. "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."
The use for these long-travelling pulses is not weaponisation: instead, because they can penetrate the atmosphere over long distances, the team believes that it can be adapted for remote testing of atmospheric pollution. The white light interacting with atoms in the air will provide valuable information about elements and compounds polluting the atmosphere.