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International audience; We report on the use and qualification of the recently developed single-mode hybrid hollow-core photonic crystal fiber for a robust and long-life acetylene photonic micro-cell based optical frequency reference.

We report on a 100-fs GHz burst laser with up to 100-W average output power. This laser is based on a Tangor femtosecond laser with GHz burst option followed by nonlinear pulse compression in a gas-filled hollow core Kagome fiber. Combining pulse compression with hollow core fiber transport is an attractive extension for industrial femtosecond lasers. Laser ablation of metals, silicon, and sapphire have been performed with this new laser source in order to study the impact of the ultrashort pulse duration on the laser matter interaction with GHz bursts.

International audience; In this talk, we report on recent developments on inhibited-coupling guiding hollow-core optical fibers ranging from the understanding of the guidance mechanism to application fields. We show that a deep understanding of the cladding properties of those fibers allow to obtain fibers with optimized properties. In particular, we demonstrate that, by adequately designing and controlling the fiber physical parameters, one can obtain ultralow loss fibers for the ultraviolet, visible and infrared ranges. Additionally, we show that convenient alterations in the fiber cladding can modify the fiber mode loss hierarchy allowing it to act as a mode shaper, and polarization discriminator.

Gas-filled Hollow Core Photonic Cristal Fibres (HCPCF) or Photonic MicroCell (PMC) [1] has proven to offer an outstanding gas-cell for laser metrology and spectroscopy applications. Sub-Doppler spectral features, generated via electromagnetically induced transparency (EIT) or saturated absorption (SA), have been generated in molecular gases despite the weak strength of their optical transitions [1–4], and an optical frequency reference with excellent accuracy has been demonstrated [1]. So far, the reported stand-alone PMCs are either made by hermetically splicing the HCPCF tips to an all-solid optical fibre [1,2] or by encapsulating them to a glass cell [3]. All these techniques show limitations. For example, the splicing based all-fibre PMC technique is not adapted to all fibres as it requires matching the outer-diameter and/or mode-field-diameters of the two fibres. Also the use of fibre tapering to reduce this mismatch [2] remains too cumbersome for the obtained splice-loss figures, which are >2 dB and exhibit asymmetric loss. Furthermore, the use of Helium (He) gas during the "air-ambient" splicing process to avoid air pollution in the fibre core renders this technique too sensitive to residual gas contamination. Conversely, the technique of encapsulating the fibre tip in an enlarged borosilicate capillary [3] presents potential contamination during and after fabrication because of the use of Epoxy glue, and the ensued outgassing, which is detrimental for optimized observation of sub-Doppler features and for the life time of the PMC.

International audience; We report on several ultra-short pulse compression schemes based on hollow-core photonic crystal fiber filled with a chosen gas-phase medium and undertaken in a versatile module coined "FastLas". The scheme relies on dispersion management by both fiber design and gas pressure management to offer a highly versatile pulse compressor. Furthermore, the gas is also used to set the required optical nonlinearity. This type of hollow fiber based compressor is scalable with the laser wavelength, pulse energy and initial pulse-width. Among the achieved pulse compression, we list a self-compression of 500-600 fs ultra-short pulse Yb-laser and with energy range of 10-500 µJ. By simply scaling the fiber length we demonstrated pulses as short as ~20 fs for the whole energy range. Here, the self-compression is achieved through solitonic dynamic. Conversely, we demonstrated pulse compression based on self-phase modulation by adjusting the fiber and gas dispersion. Among the pulse compressors we have developed, based on self-phase modulation, we cite the compression of a frequency-tripled micro-Joule pulse-energy Yb-laser with a pulse width of 250 fs. The results show compressed UVpulses with temporal width in the range of 50-60 fs.

Understanding cladding properties is crucial for designing microstructured optical fibers. This is particularly acute for Inhibited-Coupling guiding fibers because of the reliance of their core guidance on the core and cladding mode-field overlap integral. Consequently, careful planning of the fiber cladding parameters allows obtaining fibers with optimized characteristics such as low loss and broad transmission bandwidth. In this manuscript, we report on how one can tailor the modal properties of hollow-core photonic crystal fibers by adequately modifying the fiber cladding. We show that the alteration of the position of the tubular fibers cladding tubes can alter the loss hierarchy of the modes in these fibers, and exhibit salient polarization propriety. In this context, we present two fibers with different cladding structures which favor propagation of higher order core modes – namely LP11 and LP21 modes. Additionally, we provide discussions on mode transformations in these fibers and show that one can obtain uncommon intensity and polarization profiles at the fiber output. This allows the fiber to act as a mode intensity and polarization shaper. We envisage this novel concept can be useful for a variety of applications such as hollow core fiber based atom optics, atom-surface physics, sensing and nonlinear optics.

International audience; In this letter, we report on the fabrication of an inhibited-coupling guiding fiber with a cladding amorphous lattice of nine tubes exhibiting a record loss of 13.8 dB/km at 539 nm. The fiber has been drawn over a length of 1 km with high stability during the drawing process (outer diameter variation of ±0.2%). To our knowledge, this is the first time that loss figures and the fundamental Rayleigh scattering limit of silica are reported for a hollow-core optical fiber in the green spectral range. Also, this is the first report on a tubular fiber draw over such a long length. Additionally, this record loss figure is the lowest ever demonstrated with any kind of optical fibers in the green spectral range.

Hollow-core photonic crystal fibre (HCPCF) proved to be a powerful platform for optical pulse compression. Several results, reported in the last few years, show both exceptional compression performances over a large energy dynamic range and varied experimental conditions [1][2][3], and new physical dynamics [4]. Among the reported performances, we list those achieved with Inhibited-Coupling guiding HCPCF (IC-HCPCF), and where soliton self-compression down to the single or a few cycle regime were achieved with a ∼1.8 μm wavelength and 80 fs duration input-pulse [1], and with a 790 nm wavelength and 24 fs duration input-pulse [2]. Conversely, the low values and spectral profile of the IC-HCPCF dispersion, combined with its fine control through a judicious choice of a filling gas, enabled the observation of several nonlinear optical regimes as varied as modulation instability, self-phase modulation, supercontinuum generation, or plasma-induced soliton blue-shift and fission. Remarkably, in the latter regime, experimental and theoretical results show that soliton-plasma interaction and its high sensitivity to the input laser and IC-HCPCF parameters are overarching several novel solitonic phenomena[4]-[6] such as strong soliton self-compression, blue and red frequency-shift and fission.

International audience; We report on a user-friendly sub-100 fs nonlinear pulse compression platform named FastLas. The compressor is based on gas fillable inhibited-coupling fibers and can be scaled over a large parameter-space of the input pulse. OCIS codes: 320.5520, 320.7140, 060.5295 1. Introduction Over the last two decades, ultra-short pulse (USP) lasers have witnessed a dramatic progress in their design, performance and in their applications. Nowadays, commercially available table-top lasers emitting pulses with duration of hundreds of femtosecond and milli-Joule energy have become a common place. Among the most representative of these USP lasers, we count Ti:Sapph laser emitting at around 800 nm for, Yb-based laser emitting around 1 µm, and Er-based laser emitting around 1.5 µm, and their frequency-doubled and tripled versions. Within this landscape, the laser pulse-duration is often larger than 100 fs, and achieving sub-100 fs pulse duration still remains a challenge. Among the limiting factors in pulse compression is the narrow gain-bandwidth of some lasers (e.g. Yb-based and Er-based lasers), which requires further spectral-broadening followed with a post-compression, and/or nonlinear compression. Furthermore, even with larger gain bandwidth lasers such as Ti:Sapph, complex setup are required for efficient dispersion compensation. Finally, the high sensitivity of current pulse-compression schemes to well defined parameter set of the input laser such as pulse energy, pulse duration, and wavelength, makes it extremely challenging to have efficient and scalable USP compressors. This situation is illustrated by state-of-the-art of Yb-based lasers. The latter offers a superior power-scaling, it can be operated in different operational modes, such as emitting from CW regime to 100 fs pulses with repetition rate from kHz to GHz repetition rate. Achieving sub-100 fs remains a challenging task despite the implementation of ingenious schemes to overpass this limitation [1]. In turn, this limits their impact in some of the emerging industrial applications where processing of some materials such as dielectric or semiconductor require 10-100 µJ level pulses with pulse-width below 300 fs. Here, we exploit the engineerable dispersion, the broadband transmission and high energy handling of Inhibted-Coupling guiding hollow-core photonic crystal fiber (IC-HCPCF) to propose a USP compression platform coined FastLas, which operates on energy range between few microjoules to hundred microjoules and efficient for a wide variety of wavelengths.

We report on the development of an acetylene-filled photonic microcell based on an assembly process that is contaminant free and requires no helium buffer gas nor gluing procedure. The microcell consists of a 7-m-long and 30 µm core-diameter inhibited-coupling guiding hollow-core photonic crystal fiber filled with acetylene gas at a pressure in the range of 80 µbar, sealed by capping its ends with fusion-collapsing a glass-tube sleeve, and mounted on FC connectors for integration. The microcell shows a robust single-mode behavior and a total insertion loss of ∼ 1.5 d B . The spectroscopic merit of the formed microcell is tested by generating electromagnetic induced transparency and saturated absorption on R13 and P9 absorption lines, respectively. The sub-Doppler transparencies show a close to transit time limited linewidth of 17 ± 3 M H z . The latter was monitored for over 3 months. As a demonstration, the microcell was used to frequency stabilize a laser with fractional frequency instability improvement by a factor 50 at 100 s integration time compared to free running laser operation.

We report on the development of hypocycloid core-contour inhibited-coupling (IC) Kagome hollow-core photonic crystal fibers (HC-PCFs) with record transmission loss and spectral coverage that include the common industrial laser wavelengths. Using the scaling of the confinement loss with the core-contour negative curvature and the silica strut thickness, we fabricated an IC Kagome HC-PCF for Yb and Nd:Yag laser guidance with record loss level of 8.5 dB/km associated with a 225-nm-wide 3-dB bandwidth. A second HC-PCF is fabricated with reduced silica strut thickness while keeping the hypocycloid core contour. It exhibits a fundamental transmission window spanning down to the Ti:Sa spectral range and a loss figure of 30 dB/km at 750 nm. The fibers’ modal properties and bending sensitivity show these HC-PCFs to be ideal for ultralow-loss, flexible, and robust laser beam delivery.

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

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.

Recent results in laser beam delivery and ultra-short pulse (USP) compression using hypocycloid-core Kagome hollow-core photonic crystal fibers (HC-PCFs) [1] proved that this type of optical fiber is an excellent candidate as a photonic component for these applications. For example, it has been demonstrated that the fiber guides up to 1 mJ of600 fs long pulses with no damage, and by a simple choice of gas and fiber dispersion, the authors achieved both USP guidance with no pulse broadening nor narrowing, guidance with self-phase modulation (SPM) spectral broadening, and finally guidance with over 10-fold self-compression using solitonic dynamics. However, these compression results necessitated both fiber gas-loading-system and tailored fiber-fabrication, which are not necessarily accessible to the broader research community. Here, we report on a set of results of self-compression of a USP laser based on a commercially available Kagome fiber (PMC-C-YB-7C from GLOphotonics [2]) and with no need of gas loading management. The compression relies on pulse dynamics near the photoionization threshold, which shows a strong and abrupt self-compression via the formation of a soliton at a well-defined pulse energy value and then its breakup at higher energy values [3]. By simply adjusting the fiber length from 10 cm to 4 m, we achieved compression of an initial 600 fs from Yb-doped USP-laser down to ∼20 fs (a compression ratio ∼30) over an energy span of 10–500 μJ. Figure 1(a) shows a summary of calculated (dotted curves) and measured (solid curves) pulse duration evolution with input energy for different fiber lengths. All curves show a “step shape” corresponding to this sudden compression, and the input energy value at which the self-compression occurs increases with shortening fiber length. A typical experimental FROG [4] evolution of such dynamic is shown in Figure 1 (c) for the case of 2 m fiber length resulting in a spectral broadening, a soliton red-shift and a strong pulse compression as the energy is increased. For this conditions, the maximum compression occurs at an energy around 60 μΐ. For higher energy, the pulse breaks up via soliton fission.

The dramatic progress in power-scaling of ultra-short pulse (USP) lasers and their growing use in industrial applications call for flexible and robust beam delivery systems (BDS) over several meters with no temporal or modal distortions. Inhibited coupling (IC) hypocycloid Kagome hollow-core photonic crystal fiber (HC-PCF) has recently proved to be an excellent solution for guiding these USP. In order to reduce further the attenuation of such fiber and then to increase the BDS capabilities, we report on an optimized IC Kagome HC-PCF exhibiting record loss level (8.5dB/km at 1030nm) associated with a 225nm wide 3-dB bandwidth and low bend sensitivity.

International audience; Historically, nonlinear optical phenomena such as spectral broadening by harmonic generation have been associated with crystals owing to their strong nonlinear refractive indices, which are in the range of ∼10 −14 cm 2 ∕W. This association was also the result of the limited optical power available from early lasers and the limited interaction length that the laser-crystal interaction architecture could offer. Consequently, these limitations disqualified a large number of materials whose nonlinear coefficient is lower than n 2 ∼10 −16 cm 2 ∕W as suitable materials for nonlinear optics applications. For example, it is a common practice in most of optical laboratories to consider ambient or atmospheric air as a "nonlinear optically" inert medium due to its very low nonlinear coefficient (∼10.10 −19 cm 2 ∕W) and low density. Today, the wide spread of high-power ultra-short pulse lasers on one hand, and low transmission loss and high-power handling of Kagome hollow-core photonic crystal fiber on the other hand, provide the necessary ingredients to excite strong nonlinear optical effects in practically any gas media, regardless of how low its optical nonlinear response is. By using a single table-top 1 mJ ultra-short pulse laser and an air exposed inhibited-coupling guiding hollow-core photonic crystal fiber, we observed generation of supercontinuum and third harmonic generation when the laser pulse duration was set at 600 fs and Raman comb generation when the duration was 300 ps. The supercontinuum spectrum spans over ∼1000 THz and exhibits a typical spectral-density energy of 150 nJ/nm. The dispersion profile of inhibited-coupling hollow-core fiber imprints a distinctive sequence in the supercontinuum generation, which is triggered by the generation of a cascade of four-wave mixing lines and concluded by solitonic dynamics. The Raman comb spans over 300 THz and exhibits multiple sidebands originating from N 2 vibrational and ro-vibrational Raman transitions. With the growing use of hollow-core photonic crystal fiber in different fields, the results can be applied to mitigate air nonlinear response when it is not desired or to use ambient air as a convenient nonlinear medium.