Plasma photonics in hollow-core photonic crystal fibers
Résumé
The confinement and interaction between light and a gas-phase medium in the Hollow-Core Photonic Crystal Fiber (HC-PCF) technology has recently demonstrated many coherent and non-linear optical phenomena as Raman comb or electromagnetic induced transparency. The idea to extend this concept to plasma-phase, i.e. of an ionized gas, becomes today a key challenge amplified by the large number of applications (photo-lithography, biomedical...). Also, afterward, this progress can be advantageously applied towards the development of a new expected compact UV fibered laser source, being now hampered by the restricted emission of rare earth ions beyond the UV domain and by the nature of the solid-core fiber. To date, experiments carried out on breakdown of a gas in capillary discharge-waveguides have been done by using the well-known DC excitation system with electrodes, showing difficulties to sustain stable plasmas in discharge-capillary exhibiting small core diameter. Also, this technique doesn't permit to reach high ionization rate. These limitations have motivated our group to recently propose a new route to achieve a plasma-phase generation in a real photonic structure by bringing together the HC-PCF technology and the microwave plasma field. In this communication, we will report on the ignition of a microwave microplasma in a Kagome-latticed HCPCF. We succeeded in sustaining a 6 cm long Ar-plasma column in a gas-filled 100 μm core diameter Kagome fiber (see below a picture of the generated plasma column), and in guiding in a quasi-single mode behaviour Ar II lines. This particular plasma is created by a coupler, corresponding to a microwave resonator with a leaky coupling area, developed and optimized here especially for the micrometric dimensions of Kagome-latticed HCPCFs. This system, allowing the creation and propagation of a Surface-Wave (electric field is maximum at the plasma/silica core surround interface) that transfers power to gas/plasma, has permi- ted to reach high ionization rate and power densities level without any damage on the microstructure of the fiber while having gas temperatures as high as 1300 K in the fiber core. Forces and plasmas dynamics involved in such a very small core dimension will be described, leading to an impressive confinement that explains coexistence of high gas power densities with low temperatures but close to the silica transformation. Finally, for compactness needs, another microwave-driven solution developed and based on Microstrip Split-Ring Resonators (MSRR) is currently explored. The first results obtained with this new design will be presented.