Frederic Delahaye

Generation of surface-wave microwave microplasmas in hollow-core photonic crystal fiber based on a split-ring resonator.

We report on a new and highly compact scheme for the generation and sustainment of microwave-driven plasmas inside the core of an inhibited coupling Kagome hollow-core photonic crystal fiber. The microwave plasma generator consists of a split-ring resonator that efficiently couples the microwave field into the gas-filled fiber. This coupling induces the concomitant generation of a microwave surface wave at the fiber core surround and a stable plasma column confined in the fiber core. The scheme allowed the generation of several centimeters long argon microplasma columns with a very low excitation power threshold. This result represents an important step toward highly compact plasma lasers or plasma-based photonic components.

2-µm wavelength-range low-loss inhibited-coupling hollow core-PCF

We report on the design and fabrication of inhibited-coupling guiding hollow-core photonic crystal fiber with a transmission band optimized for low loss guidance around 2 μm. Two fibers design based on a Kagome-lattice cladding have been studied to demonstrate a minimum loss figure of 25 dB/km at 2 μm associated to an ultra-broad transmission band spanning from the visible to our detection limit of 3.4 μm. Such fibers could be an excellent tool to deliver and compress ultra-short pulse laser systems, especially for the emerging 2-3 μm spectral region.

Deep-UV plasma emission in hollow-core photonic crystal fiber

In this paper, after reviewing results in the emerging plasma photonics field, we report on a strong plasma emission in the Deep-UV (DUV) range using gas mixture for development of a tunable and miniaturized UV radiation source using microwave-driven plasma-core photonic crystal fiber. Several spectral lines in DUV were produced by Ar-N2-O2 plasmas and tailored by simply varying the gas ratio of this gas mixture. In addition, a planar technology was used to develop a special ring excitator for compact solution to sustain efficiently such plasmas with microwave power as low as the Watt-level.

Deep-UV plasma emission in hollow-core photonic crystal fiber using gas mixture

Atomic or molecular plasmas are an excellent media to produce a fluorescence light source emitting in the UV spectral range, which is of interest for many applications in biological, physical, chemical and other fields such as water decontamination, spectrophotometry, and photolithography. In parallel, the emergent hollow-core photonic crystal fiber (HC-PCF) technology has demonstrated its ability in micro-confining light and gases together [1]. Recently, this confinement has been extended to ionized gas with an Argon plasma that has been successfully generated inside the core of an inhibited-coupling (IC) HC-PCF with no damage to the fiber structural integrity [2]. This result opened an original platform ideal to realize very compact photonic components for DUV/UV laser systems. In this context, we report here on a broad DUV/UV emission using microwave-driven plasma-core PCF for development of such a tunable and miniaturized UV radiation source. By using a ternary gas mixture of argon, oxygen and nitrogen (Ar/O2/N2) with an adjustable gas ratio, we generated a stable micro-plasma column in IC Kagome HC-PCF over few cm length and demonstrated the emission of several fluorescence and guided lines in the 200–450 nm wavelength range. The optimum ratio of ternary gas mixture components for strongest emission in the DUV domain has been identified through systematic spectroscopic measurement campaign in HC-PCF. Figure 1 shows the transmitted spectra obtained at the output of a 19-cell core defect Kagomé HC-PCF (corresponding to 117 μm-core diameter) for various gas mixture ratios at a fixed microwave power of 35 W and a gas pressure of few mbar. Gradually, as we introduce the N2 and the O2 components (Fig. 1 (b) to (e)) to the Ar, several new lines appear due to the interaction of each molecule in the plasma ignition gas medium. From 275 nm up to 400 nm, one can observe the classical band emission of Nitrogen molecule from the Second Positive System. Then, the emission from 200 to 275 nm is assigned to the band emission of the ΝΟγ system. From these results, the ternary gas mixture ratio of 90%–5%–5% is found the optimum to demonstrate the broadest emission in the DUV/UV. A simulation study was also performed in such a gas mixture, using a 0D-global model, to determine the influence of the electron density on the radiation emission [3]. In Fig. 2 the theoretical evolution of the different spectral lines intensity of the Ar-O2-N2 plasma for both gas mixtures are plotted. The result shows a good agreement with experimental ones.