In this work, the researchers focused on the saturable absorption properties of gold nanoparticles and their application to generate ultra-short laser pulses in a stabilized manner. For this, researchers have developed an experiment to study and control this phenomenon by mobilizing the laboratory’s know-how in laser design, nanotechnologies and near field optics.
Based on numerical predictions, plasmonic meta-surfaces – ie a two-dimensional tiling of arbitrarily shaped gold nanoparticles placed on a microscope slide – were fabricated using nanofabrication tools from the laboratory’s ARCEN CARNOT platform . The devices were then tested using equipment from the PICASSO platform in the Photonics department.
The desired effect was good for the first experiences, but its intensity was particularly surprising. In fact, where the usual materials used as saturable absorbents have absorption modulations of a few percent, certain meta-surfaces produced had modulation amplitudes greater than 50%. To explain this phenomenon, the researchers renewed their experiments by varying the shape and dimensions of the nanoparticles. Analysis of the results obtained in the different configurations finally made it possible to establish without ambiguity the link between the plasmon resonances of the gold nanoparticles and the unexpected intensity of the effect observed. The laboratory researchers finally integrated the best saturable meta-surfaces into a specially-doped fiber optic laser cavity. In this way, they were able to test their dynamic behavior by studying the duration and stability of the pulses generated by the laser cavity. In particular, for certain meta-surfaces, the pulse trains obtained have proved remarkably stable and this for pulse durations of a few hundred femtoseconds.
Schematic view of the laser architecture produced. Plasmonic metasurfaces (viewed with an insert scanning electron microscope) act as a saturable absorbent in an erbium-doped fiber (EDF) laser cavity to produce femtosecond pulses with high stability.
These results demonstrate the effectiveness of plasmonic meta-surfaces as a saturable absorbent whose non-linear transfer function can be adjusted by design. This work opens up a new field of application for metallic nanoparticles. This could find applications not only in the field of lasers but also in future neuromorphic calculators whose hearts are built around components with non-linear transfer functions.
- For more information : Jiyong Wang, Aurelien Coillet, Olivier Demichel, Zhiqiang Wang, Davi Rego, Alexandre Bouhelier, Philippe Grelu et Benoit Cluzel, Saturable plasmonic metasurfaces for laser mode locking, Light Sci Appl 9, 50 (2020)
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