What we do...

 

The mainstream activity of the LIDAR group in Ag-Wöste has always been linked to atmospheric sounding using various types of LIDARs. However, a fascinating world of non-linear phenomena, which using today's femtosecond lasers are initiated directly in air, has broaden a spectrum of our interest far beyond this classical method of remote sensing.

The focus of our recent research is mainly related to applications of non-linear optical phenomena in many branches of applied optics. Starting from femtosecond- or SHG- LIDARs to remote laser induced breakdown spectroscopy or triggering of real atmospheric lightnings using filaments. These applications rely primarily on peculiar properties of white light filaments.

Working with filaments is always challenging. Their onset and position is to large extent indeterministic and result from random fluctuations of air density and/or beam profile impurities. In the lab we, therefore, try to influence filamentation in such a way that it can be controlled. How do we do it? For example, using different beam geometries. We have recently shown that a certain spatial phase pattern across a laser beam can effectively regularize filamentation on distances up to several meters. The other method is to use two phase locked crossed laser beams. In such a case filamentation takes place in the volume confined to the intersection region and the white light is propagating collinearly to symmetry axis between the two beams. This is of a great importance for many experiments and allows to avoid strong background of the fundamental laser wavelength.

Besides the questions like:

• what type of measurements can benefit from filamentation,
• how to enhance stability and robustness of filamentation,
• how to increase efficiency of filament white light generation,
• how to control their spatial pattern and onset,
• is it possible to increase a number of filaments inside a laser beam,
• what happens to filaments when they propagate through an optically thick medium like cloud,
• can they survive atmospheric turbulence,
• can the length of a filament be extended to single kilometers or more

are of a great interest for us. Answering them will help to design sending and receiving optics of future filament-based LIDARs, as well as construct new devices of extended capabilities and performance.