Ultra-compact and portable fibre gas laser for bio-defense applications – UVfactor

During past few years, research on the development of compact, low-cost and high efficiency ultraviolet sources has been thriving. This is driven by both the military and the academic domains which are in a pressing need for compact UV laser sources. These fields relate to the atmospheric pollutant and bio-defense by LIDAR and Raman spectroscopy, the photobiology and the microelectronics industry. Hitherto, the most common UV sources widely used in industry are the excimers lasers based on the electrical discharge of a gas mixture. However, the latter are known for their intrinsic drawbacks making them unsuitable to the emerging industrial of miniaturization and ease of maintenance. As a result, it appears essential to seek alternative solutions to these existing gas laser systems capable of meeting future industrial and medical market demand. The aim of this ambitious and innovative proposal is thus to transpose for the first time the conventional UV gas sources to the world of optical fibres. The latter have shown during the past decade their awesome potential, one of the most remarkable results obtained being the development of Hollow-Core Photonic Crystal Fibre (HCPCF) guiding light in air which has opened up many opportunities as the insertion of gas mixture into the hollow-core. Such a gas-filled fibre have shown unprecedented results based on the strong interaction between gas and light in micro-confined core area along the fibre. For instance, Benabid and colleagues have recently demonstrated that a gas-filled fibre can be coiled on a typically 2 cm diameter mandrel to create the world’s first photonic micro gas-cell (gas volume being only a few µL per meter of fibre). In parallel, XLIM has recently proposed the first experimental demonstration of UV light guiding in specific HCPCF. Finally, very recently, preliminary experiments done jointly by LPGP and XLIM have demonstrated for the first time the creation of a very stable and robust plasma (running more than 1 day) in capillaries waveguide with core diameters less than 100 µm by using an original microwave discharge scheme. This proof of principle demonstrates the judiciousness of the proposed approach. Consequently, the combination of these three impressive scientific breakthroughs holds the prospect of the advent of a disruptive technology that could radically transform the field of UV lasers in particular and gas lasers in general. Here, we propose to fabricate what would be the first UV microplasma discharge based on gas-filled HCPCF that exhibits an unprecedented compactness, low-cost and high conversion efficiency. It is also important to highlight that the same principle could be extended to the mid-IR range by simply changing the nature of the gas. Two salient and original features of the proposed UV fibre gas source are noteworthy. Firstly, the microwave excitation we are exploring enables to achieve on one hand an ionisation fraction more important compared to conventional DC excitation (factor 10 given the fact that the microwave power is much better coupled into the plasma medium), and on the other hand it seems much less sensitive to charge accumulation as our preliminary results have demonstrated it. Moreover, this is accomplished while keeping the fibre-ends free for an easy optical access. Secondly, with a suitable design, the HCPCF can act both as a frequency filter through a tailorable transmission window (selection of narrow and stable emission lines from the excited gas mixture filling the hollow-core) and a spatial modal filter via a phase-matching of the guided microplasma and optical mode. This proposal gathers two partners namely XLIM which has a strong and recognized knowledge in the development of optical fibres and laser sources and LPGP which is one of the leader in the microwave plasma source devices. In a context of strong photonic international competitions, such advances could put the French defense in a strategic position.