Year 3 Project

I started the project work feeling the energy and motivation. The first surprise was for me to find out how differently I find work at the university office and in a large private company office. It started with the fact that most of the academic staff are often out of the department, therefore it was sometimes difficult to ask for a help. At the same time, the offices at our department are very modest, full of various laser components chaotically lying on the floor including many other but often interesting objects. First, I tried to stick to the scheduled tasks. But as I found, I will have to accept a little of the chaos and to be patient. The project was designed to run a computer simulation at first with predefined pulse parameters. Based on this simulation, a theoretical model should be established leading to the formulation of a null hypothesis. Last but not least, the project should focus on laboratory measurements and a test of the formulated null hypothesis. When I first saw the simulation code on my computer, I was lost, there was not a thorough documentation and a clear structure. I suggested as a possible solution to code the simulation again using all the conventions and writing a documentation. This inconvenience forced me to undergo an intensive research of the topic.

Laser filament propagation is observed when a pulse with a short duration experiences a self-focusing leading to a high concentration of energy. As a consequence, atoms of gas are ionized and plasma is produced. A pulse propagation is described by both the linear and nonlinear optics. To simulate the propagation, it is necessary to numerically solve the nonlinear Schrödinger equation which requires extensive computational resources with the aim to obtain a reasonable precision. The potential applications in industry are, for instance, an improvement of the quality of microwave transmission through a waveguide which is, in this case, a "tunnel" created by the plasma, or the possibility of efficient constituent determination of distant objects. When I entered the laboratory where the laser filament propagation experiments take place for the first time, I was surprised at how small room the whole apparatus was assembled. I did not understand how it is possible to observe the nonlinear pulse self-focusing on such short distances. I found that this apparent problem is simply solved by placing a lens that focuses the pulse. The last question was how to perform the measurements. The phenomenon of laser filament propagation changes the shape of the transmitted pulse and broadens its spectrum. Consequently, pulses contain a signature of the substances they were passed through. An intuitive way of performing the measurements is to place a spectrometer in the apparatus and measure the intensity of individual pulse wavelengths.

I was assured that in the conditions of our laboratory, the experiment is safe. Nevertheless, I was not quite sure about it when I saw all the warning signs. However, I was supervised permanently, and together with my supervisor we already made the first measurement. When comparing the reference and measured intensities of the individual beam wavelengths, I observed the broadening of the spectrum. Now I'm performing a data analysis. Hopefully, I will be able to compare the resulting laboratory spectrum with a computer-simulated spectrum.