Fiber Lab.

In quantum optics and quantum electro dynamics one is interested in the study of strong interactions between light and matter. To do so one has to build an interface, between
the light field and the piece of matter, that enhances the interaction probability. This interface is provided by optical resonators where the light field is strongly confined
between two mirrors, i.e. photons bounce back an forth repeatedly. This can be quantified by the so called finesse of the resonator, that corresponds to the avarage number of
roundtrips of a photon. Therefore building high finesse resonators is a crucial building block for strong interaction experiments and can only be achived by using curved, ultra
smooth mirrors.

© Pia Fürtjes

To provide such high finesse resonators we have a CO2-laser based mirror shootingsetup in our group. Here the Gaussian intensity profile of the laserbeam is imprinted into the surface of fused-silica glass substrates and optical fibers forming Gaussian shaped depressions. These depressions have a spherical shape in the center that then can be coated and used as a cavity mirror. The imprintig process is based on the strong absorption of the laserlight by the glass, leading to localized evaporation of the surface. This evaporation is accompanied by melting of the uppermost layer providing ultra smooth surfaces due to surface tension. This smoothness allows extremly high finesses, much higher than one can reach with ordinary grinding techniques. Especially the usage of optical fibers as mirrors is of high interest for our experiments. They provide intrinsic fiber coupling and are small in size making them essential for miniturization applications. Apart from that, their geometric measures lead to small beam waists inside the cavity witch provide even stronger light-matter coupling. To aim the shots on the substrates and to recover the curvature of the mirrors we shoot, a phaseshifting
mirau-interferometer is used.

Several master students already worked successfully on this experiment. In the past we improved the pulse creation, the beam characteristics and the overall level of automatization. A lot of time was well spend to understand, characterise and improve the shooting process and to develop specialized shooting patterns for individualized structures. In the future machine learning shall be used to improve the shooting process further and the fabrication of different glasses than silica is to be investigated.

© Andreas von Haaren
© Moritz Scharfstädt


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Moritz Scharfstädt

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