Interaction of vector electromagnetic beams with metasurfaces based on the geometrical phase control

One of the ideas of this project is to find vector solutions for electromagnetic wave equations in cylindrical coordinate systems and to use them in order to control the shape of an optical focus flexibly both on the axis of propagation (linear design) and in cross-section (beam shaping). Along with the emergence of vector components, such pulsed beams provide the ability to flexibly control the polarization state of the beam. Electromagnetic field polarization control enables to profile various parameters of laser radiation such as intensity, linear and angular momentum, electromagnetic stress tensors.
These parameters are important for both amorphous and crystalline transparent media undergoing laser microprocessing. In the first approximation they influence the thermal gradients when laser beams are interacting with certain glasses. The polarization of the electric field also becomes important in crystalline media. Since the interaction of transparent media occurs mainly via multiphoton ionization, and the optimal interacting temporal scale is femtosecond, the question arises whether it is possible to further optimize this interaction? This is what will be the answer to this project.
The work performed by a PhD student can be either solely theoretical (priority would be analytical methods and their numerical schemes) or mixed one – some numerical modelling performed along with the experiment (in this case the supervisor will be responsible for theoretical background and the student would perform modelling and experiments).
During the project the design of optical focal line will be performed using innovative elements of the geometric phase (GP) which will be produced by the laboratory. GP elements will be manufactured according to the innovative, original and patented technology of the Lithuanian laser company UAB "Altechna R&D". This company is a partner of the project's executor - FTI Laboratory.
During the production of GP elements, femtosecond laser beams generates nano gratings in the glass volume. The nanoscale grating behaves like wave plate element, whose fast and slow axes are controlled by controlling the polarization of the electric field of the recording pulse. In this way, the illumination of these nanoscale gratings with the main laser mode creates a controlled vector electric field structure with the desired amplitude and / or phase. Such a laser beam continues to diffract by creating the desired field distribution or is focussed with a large numerical aperture lens.
This microprocessing technique is much more flexible than competing technologies such as spatial light modulators and Q-plates. In addition the work done by Lithuanian specialists in this PhD project will contribute significantly to the development of this field of science.
For more information, please contact the theme supervisor S. Orlovas.