Tests of a new compact high-power laser have given researchers at the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Physics, University of Warsaw (IPC PAS and FUW) the opportunity to film the passage of an ultrashort laser pulse through the air. The film shows the journey of a light projectile at an extremely slow rate, similar to that watched on cinema screens by science-fiction aficionados.
"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.
Cameras recording billions of frames per second in one sequence do not exist. In order to film the travelling laser pulse, researchers from the Laser Centre of IPC PAS and FUW used an earlier known trick. A suitably adapted camera was synchronised with a laser generating laser pulses at a rate of approx. 10 shots per second. It was done in such a way that with every subsequent pulse the camera recorded an image minimally delayed than 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".
"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.
The ability of the light pulses from the new laser to penetrate the atmosphere over long distances is a feature that the Warsaw researchers made use of when demonstrating LIDAR, a device that can be used for the remote testing of atmospheric pollution. The fact that the pulses generate white light during passage is an important advantage in this context. Light at different wavelengths interacting with the atoms and molecules in the air is able to provide a far greater wealth of information. This means that LIDAR constructed using the new laser will be able to detect a larger number of elements and compounds polluting the atmosphere.