Prof. Czyszanowski from the Faculty of Technical Physics, Information Technology and Applied Mathematics of Lodz University of Technology is trying to explain the novelty of the research:
The discovered phenomenon is a result of the abolition of degeneration of optical states in asymmetrical systems, which enables more effective forced emission. It can be imagined by a distant and inaccurate, but illustrative comparison to a sieve, through which sand passes. The sand in the sieve is the electrons collected near the laser area. The sand flying through the holes of the sieve are electrons entering the laser area, which convert their energy into photons, which join other photons to form a laser beam. If there is a higher density of holes in the sieve, then the sand will fly through the sieve faster.
Disrupting the cylindrical symmetry of the laser has an analogous effect to increasing the density of holes in the sieve. Electrons accumulated near the laser region become more likely to hit the laser region and convert their energy into a photon through a forced emission process, resulting in an increased number of photons in the laser beam.
Interest in semiconductor VCSELs (Vertical-Cavity Surface-Emitting Lasers) has exploded in recent years, with their use for 3D space imaging in devices and vehicles that move autonomously or monitor the surrounding space. The range of devices currently using VCSEL lasers is very wide, from mobile phones to robots, self-driving hoovers, cars and drones.
The attractiveness of VCSEL lasers stems from their cylindrical geometry, which distinguishes them from the more commonly known semiconductor laser diodes, also known as edge emission lasers. The use of cylindrical symmetry in VCSEL lasers allows to obtain a laser beam with circular cross-section and small divergence, impossible to obtain by laser diodes. Cylindrical symmetry also results from the specific technological processes used in the production of VCSEL lasers, as well as from the human desire to create ordered and therefore symmetric structures. In our research, we focused on the disruption of cylindrical geometry, which led us to the conclusion that, at least in the case of lasers, not everything that is ordered and symmetrical has to be the most efficient at the same time
- says Prof. Czyszanowski, who specialises in the design of semiconductor lasers and photonic structures.