Benoît Beaudou

Millijoule laser pulse delivery for spark ignition through kagome hollow-core fiber

We report on power handling oriented design of kagome lattice hollow-core fiber and demonstrate through it for the first time nanosecond laser pulses induced spark ignition in a friendly manner. Two different core designs and transmission bands are investigated and evaluated. The energy threshold damage was measured to be in excess of the 10 mJ level and the output power density is approaching the TW/cm2 after focusing; demonstrating the outstanding ability of such fiber for high power delivery.

Optical Properties of Low Loss (70dB/km) Hypocycloid-Core Kagome Hollow Core Photonic Crystal Fiber for Rb and Cs Based Optical Applications

We report on hypocycloid core shaped hollow-core Kagome fiber with a record loss of 70 dB/km at a spectral range of around 750-850 nm, which is compatible with Cs and Rb based applications. The fiber exhibits a single mode operation in a core diameter as large as 40 μm, and very low sensitivity to bend. We show experimentally that the bending-loss is limited by coupling between the guiding core mode and the modes in the cladding holes.

Over-five octaves wide Raman combs in high-power picosecond-laser pumped H 2 -filled inhibited coupling Kagome fiber

We report on the generation of over 5 octaves wide Raman combs using inhibited coupling Kagome guiding hollow-core photonic crystal fiber filled with hydrogen and pumped with 22.7 W average power and 27 picosecond pulsed fiber laser. Combs spanning from ~321 nm in the UV to ~12.5 µm in the long-wavelength IR (i.e. from 24 THz to 933 THz) with different spectral content and with an output average power of up to ~10 W were generated. In addition to the clear potential of such a comb as a laser source emitting at spectral ranges, which existing technology poorly addresses like long-wavelength IR and UV, the combination of high Raman net gain and short pump-pulse duration makes these spectra an excellent candidate for intra-pulse waveform synthesis.

Matched cascade of bandgap-shift and frequency-conversion using stimulated Raman scattering in a tapered hollow-core photonic crystal fibre.

We report on a novel means which lifts the restriction of the limited optical bandwidth of photonic bandgap hollow-core photonic crystal fiber on generating high order stimulated Raman scattering in gaseous media. This is based on H(2)-filled tapered HC-PCF in which the taper slope is matched with the effective length of Raman process. Raman orders outside the input-bandwidth of the HC-PCF are observed with more than 80% quantum-conversion using a compact, low-power 1064 nm microchip laser. The technique opens prospects for efficient sources in spectral regions that are poorly covered by currently existing lasers such as mid-IR.

Macro Bending Losses in Single-Cell Kagome-Lattice Hollow-Core Photonic Crystal Fibers

We report on numerical and experimental results on macro bending losses in single-cell Kagome-lattice hollow-core photonic crystal fibers. Fibers with different cladding layer numbers have been investigated. Results show that a cladding with at least two rings produces a reduction in bend sensitivity by more than one order of magnitude relative to a single layer cladding. This result is an original way to confirm the main role played by the inhibiting coupling mechanism in such microstructured fibers.

Fusion splice between tapered inhibited coupling hypocycloid-core Kagome fiber and SMF

We report for the first time on tapering inhibited coupling (IC) hypocycloid-core shape Kagome hollow-core photonic crystal fibers whilst maintaining their delicate core-contour negative curvature with a down-ratio as large as 2.4. The transmission loss of down-tapered sections reaches a figure as low as 0.07 dB at 1550 nm. The tapered IC fibers are also spliced to standard SMF with a total insertion loss of 0.48 dB. These results show that all-fiber photonic microcells with the ultra-low loss hypocycloid core-contour Kagome fibers is now possible.

Hollow core fiber delivery of sub-ps pulses from a TruMicro 5000 Femto edition thin disk amplifier

We report on the fiber-based transmission of sub-ps single-mode pulses with an average power of 50 W at a wavelength of 1030 nm generated by a TruMicro Series 5000 Femto Edition thin disk amplifier. The air-filled hollow-core Kagométype delivery fiber exhibits a hypocycloid core wall and is tailored to offer very low dispersion and nonlinearity at 1030 nm. It minimizes the mode overlap with the glass components to obtain a sufficiently high damage threshold. With propagation losses of only 20 dB/km and an optimized mode matching and coupling by means of a telescope and a 5- axes table we achieve an overall transmission efficiency of more than 80% with a resulting M2 of 1.15. Our laser source offers the selection of repetition rates from 200 to 800 kHz which translates to pulse energies between 60 and 250 μJ. The pulse duration of 900 fs is maintained at the fiber exit, while the spectral width broadens to 20 nm due to self phase modulation in the air core, which could be used to further compress the pulses temporally. Using a fiber-based beam transport allows for mechanical decoupling of the processing head from the laser source, increasing flexibility for applications in the field of material processing with ultra-short pulsed lasers.

Inhibited-coupling HC-PCF based beam-delivery-system for high power green industrial lasers

We report on an ultra-low loss Hollow-Core Photonic Crystal Fiber (HC-PCF) beam delivery system (GLO-GreenBDS) for high power ultra-short pulse lasers operating in the green spectral range (including 515 nm and 532 nm). The GLOBDS- Green combines ease-of-use, high laser-coupling efficiency, robustness and industrial compatible cabling. It comprises a pre-aligned laser-injection head, a sheath-cable protected HC-PCF and a modular fiber-output head. It enables fiber-core gas loading and evacuation in a hermetic fashion. A 5 m long GLO-BDS were demonstrated for a green short pulse laser with a transmission coefficient larger than 80%, and a laser output profile close to single-mode (M2 <1.3).

Experimental optimization of curvature and silica thickness core contour of inhibited-coupling Kagome fibers

The dramatic progress in power-scaling of ultra-short pulse (USP) lasers and their continuous expansion use in industrial applications call for flexible and robust beam delivery systems (BDS) over several meters. Recently, a new branch of hollow-core photonic crystal fiber (HC-PCF) based on inhibited coupling (IC) mechanism has been proposed and successfully applied to demonstrate the delivery of milliJoule 600 femtosecond pulses in a several meter long piece and in robustly single-mode fashion [1]. Despite this breakthrough, it is desirable to reduce further the attenuation and enlarge the operating bandwidth of such fiber to increase the capability of the BDS whilst keeping the same delivery performances. In this context, a carefully optimization of the geometrical parameters of the core contour (i.e., the curvature b [2] and the silica thickness t) is studied resulting in the fabrication of new state-of-the-art IC Kagome HC-PCF combining losses less than 10 dB/km for the first time and associated to an enlarged transmission bandwidth able to cover all the entire industrial spectral range.

Parametric four-wave mixing sidebands in strongly driven Raman molecular D2-filled HC-PCF

The development of the Raman gas-filled hollow core photonic crystal fibers allow to exacerbate the light-matter interaction with extremely high efficiency. Among the nonlinear optical effect that were extensively explored we count stimulated Raman scattering, with demonstrations like over 5-octaves wide Raman comb using H2-filled inhibited coupling guiding HC-PCF pumped with a picosecond pulsed laser [1]. Furthermore, Raman-active gases are known to exhibit very weak susceptibility outside the Raman frequencies, and thus are considered to be poor media for the generation of new frequencies through parametric four-wave mixing (FWM).