P.-A. Lacourt

University of Franche-Comté, Besançon, Franche-Comte, France

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Publications (35)32.53 Total impact

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    ABSTRACT: We numerically investigate the spatiotemporal structure of Bessel beams generated with spatial light modulators (SLMs). Grating-like phase masks enable the spatial filtering of undesired diffraction orders produced by SLMs. Pulse front tilt and temporal broadening effects are investigated. In addition, we explore the influence of phase wrapping and show that the spatiotemporal structure of SLM-generated femtosecond Bessel beams is similar to Bessel X-pulses at short propagation distance and to subluminal pulsed Bessel beams at long propagation distance.
    Journal of the Optical Society of America A 04/2014; 31(4):790-3. · 1.67 Impact Factor
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    ABSTRACT: Fiber supercontinuum (SC) generation is a well-known process widely studied over the last decade [1]. Recently, the particular case of noise-driven SC has received increasing attention because of novel instability properties and links with other systems in the formation of extreme events [2]. SC fluctuations have been investigated experimentally typically through RF measurements technique [3] or considering only a specific region of the SC spectrum with filtering [2]. Recently, the development of the dispersive time-stretch Fourier transform technique has been applied to map spectral fluctuations of modulation instability sidebands into temporal fluctuations that could be measured using a real time oscilloscope [4]. In this study, we apply the technique of dispersive time-stretching to implement the first complete study of real-time fluctuations across the full bandwidth of a supercontinuum generated around 1550 nm.Our experiments use 70 W peak power 3.5 ps pulses power to excite SC in 20 m of highly nonlinear fiber (HNLF) with anomalous dispersion. We characterize SC intensity noise over the full bandwidth using a dispersive time stretch system, with 1 nm equivalent spectral resolution using a 12 GHz real-time detection system [4]. The SC generation arises from noise-driven modulation instability (MI) associated with high shot to shot spectral fluctuations [1,2]. Fig. 1(i) is a false color plot of 500 spectral measurements showing the significant variation in spectral width and structure. Fig. 1(ii) plots the spectra on a logarithmic scale, and also plots the mean spectrum to highlight the significant noise at each wavelength in the SC. We can readily extract from this data intensity histograms at different wavelengths as shown, allowing us to identify regions of Gaussian fluctuations (around the pump) and long-tailed rogue-wave like fluctuations (in the wings). We can also readily calculate from the data higher-order statistical moments of coefficient of variatio- , skew and kurtosis, and these are shown in Fig. 1(iii). Summary statistics such as these are especially useful to quantify the wavelength variation of the SC statistics, and can be readily compared with the predictions from stochastic numerical simulations. Simulation results are also presented in Fig. 1(iii) showing very good agreement. These results confirm the power of dispersive time stretching as a technique for SC spectral noise characterization. The ability to determine SC statistics at arbitrary wavelengths and to calculate metrics of higher-order moments reveals effects that are not apparent in averaged measurements, and is highly complementary to other techniques such as RF spectral analysis.
    International Quantum Electronics Conference; 05/2013
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    ABSTRACT: form only given. Femtosecond laser micro and nano-processing is a versatile material processing tool which has opened up a broad range of technologies and applications. However, in the particular context of the fabrication of deep trenches and channels, precise control of profile of the ablated structure is extremely challenging. We have recently developed a novel approach to fabricate controlled high aspect structures using novel Bessel and Airy beams, and this contribution will review our recent work in this field.
    The European Conference on Lasers and Electro-Optics; 05/2013
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    ABSTRACT: We report femtosecond laser micromachining of micron-size curved structures using tailored accelerating beams. We report surface curvatures as small as 70 μm in both diamond and silicon, which demonstrates the wide applicability of the technique to materials that are optically transparent or opaque at the pump laser wavelength. We also report the machining of curved trenches in silicon. Our results are consistent with an ablation-threshold model based on calculated local beam intensity, and we also observe asymmetric debris deposition which is interpreted in terms of the optical properties of the incident accelerating beam.
    Applied Physics Letters 08/2012; 101(7). · 3.52 Impact Factor
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    ABSTRACT: We use caustic beam shaping on 100 fs pulses to experimentally generate nonparaxial accelerating beams along a 60° circular arc, moving laterally by 14 µm over a 28 µm propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of nonparaxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic.
    Optics Letters 05/2012; 37(10):1736-8. · 3.39 Impact Factor
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    ABSTRACT: The ability to measure real-time fluctuations of ultrashort pulses propagating in optical fiber has provided significant insights into fundamental dynamical effects such as modulation instability and the formation of frequency-shifting rogue wave solitons. We report here a detailed study of real-time fluctuations across the full bandwidth of a fiber supercontinuum which directly reveals the significant variation in measured noise statistics across the spectrum, and which allows us to study correlations between widely separated spectral components. For two different propagation distances corresponding to the onset phase of spectral broadening and the fully-developed supercontinuum, we measure real time noise across the supercontinuum bandwidth, and we quantify the supercontinuum noise using statistical higher-order moments and a frequency-dependent intensity correlation map. We identify correlated spectral regions within the supercontinuum associated with simultaneous sideband generation, as well as signatures of pump depletion and soliton-like pump dynamics. Experimental results are in excellent agreement with simulations.
    Scientific Reports 01/2012; 2:882. · 5.08 Impact Factor
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    ABSTRACT: We review our recent results applying the stable nonlinear propagation of nondiffracting Bessel beams to femtosecond laser ablation in dielectric materials. We describe our spatial light modulator setup that allows for flexible and reconfigurable beam profile synthesis, we interpret the physics in terms of the formation of a steady plasma channel, and we present results of both multishot and single shot machining.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
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    ABSTRACT: We generate arbitrary convex accelerating beams by direct application of an appropriate spatial phase profile on an incident Gaussian beam. The spatial phase calculation exploits the geometrical properties of optical caustics and the Legendre transform. Using this technique, accelerating sheet caustic beams with parabolic profiles (i.e. Airy beams), as well as quartic and logarithmic profiles are experimentally synthesized from an incident Gaussian beam, and we show compatibility with material processing applications using an imaging system to reduce the main intensity lobe at the caustic to sub-10 micron transverse dimension. By applying additional and rotational spatial phase, we generate caustic-bounded sheet and volume beams, which both show evidence of the recently predicted effect of abrupt autofocussing. In addition, an engineered accelerating profile with femtosecond pulses is applied to generate a curved zone of refractive index modification in glass. These latter results provide proof of principle demonstration of how this technique may yield new degrees of freedom in both nonlinear optics and femtosecond micromachining.
    Optics Express 08/2011; 19(17):16455-65. · 3.55 Impact Factor
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    ABSTRACT: Ultrafast laser pulses are a powerful tool to process dielectrics. Here, we review our recent work concerning high aspect ratio micro and nanochannel processing in glass. We show how femtosecond Bessel beams overcome many of the difficulties associated with Gaussian beams. We report on single shot processing of nanochannels with aspect ratio up to 100. Underlying physical phenomena are discussed.
    Proc SPIE 02/2011;
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    ABSTRACT: We report high aspect ratio nanochannel fabrication in glass using single-shot femtosecond Bessel beams of sub-3 μJ pulse energies at 800 nm. We obtain near-parallel nanochannels with diameters in the range 200–800 nm, and aspect ratios that can exceed 100. An array of 230 nm diameter channels with 1.6 μm pitch illustrates the reproducibility of this approach and the potential for writing periodic structures. We also report proof-of-principle machining of a through-channel of 400 nm diameter in a 43 μm thick membrane. These results represent a significant advance of femtosecond laser ablation technology into the nanometric regime.
    Applied Physics Letters 08/2010; 97(8):081102-081102-3. · 3.52 Impact Factor
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    ABSTRACT: The novel propagation characteristics of Bessel beams have been widely applied to optical manipulation and harmonic generation, and have provided new perspectives on fundamentals of ultrashort laser pulse propagation in nonlinear media. Fully exploiting their many unique properties, however, requires the development of techniques for the generation of high quality Bessel beams with flexible adjustment of the beam parameters. Moreover, long working distances are needed to produce Bessel beams inside bulk samples. In this paper, we report on the development of a novel spatial light modulator based setup that combines the properties of parameter flexibility, long working distance, high throughput and operation on micron-scale. We report both on the general characterization of the beam properties as well as a specific application in surface nanoprocessing.
    Proc SPIE 01/2010;
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    ABSTRACT: Although ultrafast lasers have demonstrated much success in structuring and ablating dielectrics on the micrometer scale and below, high aspect ratio structuring remains a challenge. Specifically, microfluidics or lab-on-chip DNA sequencing systems require high aspect ratio sub-10 mu m wide channels with no taper. Micro-dicing also requires machining with vertical walls. Backside water assisted ultrafast laser processing with Gaussian beams allows the production of high aspect ratio microchannels but requires sub-micron sample positioning and precise control of translation velocity. In this context, we propose a new approach based on Bessel beams that exhibit a focal range exceeding the Rayleigh range by over one order of magnitude. An SLM-based setup allows us to produce a Bessel beam with central core diameter of 1.5 mu m FWHM extending over a longitudinal range of 150 mu m. A working window in the parameter space has been identified that allows the reliable production of high aspect ratio taper-free microchannels without sample translation. We report a systematic investigation of the damage morphology dependence on focusing geometry and energy per pulse.
    Proc SPIE 01/2010;
  • 7th International Conference on Multi-Material Micro Manufacture; 01/2010
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    ABSTRACT: In this paper, we propose a new approach for the generation of ultralow jitter optical pulses using optoelectronic microwave oscillators. The short pulses are obtained through time-lens soliton-assisted compression of sinusoidally modulated prepulses, which are self-started from a conventional single-loop optoelectronic oscillator. The inherent ultralow phase noise of optoelectronic oscillators is converted into ultralow timing jitter for the generated pulses. We provide a time-domain model for the slowly varying amplitudes of the microwave and optical oscillations, and our analytical study is confirmed by numerical simulations and experimental measurements. We demonstrate the generation of 4.1 ps pulses along with a microwave whose phase noise is -140 dBc/Hz at 10 kHz from the 10 GHz carrier, with 2.7 fs jitter in the 1-10 kHz frequency band.
    Journal of Lightwave Technology 12/2009; · 2.56 Impact Factor
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    ABSTRACT: We propose a new optoelectronic oscillator (OEO) architecture, able to generate at the same time ultra-low jitter optical pulses and ultra-low phase noise microwaves. This new system relies on the single-loop OEO, with two modulation branches: an intensity modulation for the formation of sinusoidal pre-pulses, and a phase modulation to chirp them. The train of chirped pre-pulses is then strongly amplified by an erbium-doped fiber amplifier and subsequently launched into a single-mode optical fiber. Owing to the combined effects of dispersion and self-phase modulation, the pre-pulses are optimally compressed with a compression factor which may be as high as 20, following a scenario referred to as time-lens soliton-assisted compression.
    01/2009;
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    ABSTRACT: Femtosecond laser micromachining is a laser processing technology with proven potential for the fabrication of a wide range of photonic devices. In the context of developing integrated components for microfluidics, a key issue is the machining of high aspect ratio micro and nano-channels, and the use of diffraction-free Bessel beams for this purpose has attracted much attention. However, although Bessel beams possess several attractive characteristics for this purpose, we show here that their practical use for high aspect ratio micromachining requires a careful selection of focussing and pump laser parameters. We report results of a systematic study of Bessel beam micromachining of structures of diameter < 5 mum in fused silica, and we describe conditions under which high quality and high aspect ratio structures can be reproducibly obtained. Within the parameter regimes identified here, Bessel beams present quantitative advantages when compared to diffractive Gaussian beams, especially for the drilling of channels of sub-10 mum diameter. Outside this parameter regime, there is little benefit in the Bessel beam approach.
    01/2009;
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    ABSTRACT: A numerical study of soliton spectral tunnelling in an index-guiding photonic crystal fibre with a sub-wavelength central air core defect is presented. Specifically, for a fibre design where two regions of anomalous dispersion bracket a 90 nm wide region of normal dispersion, simulations show tunnelling from 1300 to 1475 nm across the forbidden normal dispersion regime, with near unity efficiency. In addition, this effect can be exploited to obtain over a factor of two nonlinear pulse compression by interrupting propagation at the distance at which soliton tunnelling occurs.
    Electronics Letters 02/2007; · 1.04 Impact Factor
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    ABSTRACT: Optimised compression of femtosecond fibre laser pulses in highly nonlinear fibre is demonstrated. Specifically reported are compressed pulse durations below 30 fs using a simple setup where a single sub-10 cm segment of highly nonlinear fibre is directly spliced to the output pigtail of a commercial femtosecond fibre laser. The compressed pulse quality is confirmed through frequency resolved optical gating measurements.
    Electronics Letters 02/2007; · 1.04 Impact Factor
  • CLEO/Europe - IQEC 2007. European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference. 01/2007;
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    ABSTRACT: Nonlinear pulse compression techniques are of course very well-known, exploiting the initial spectral broadening and temporal compression phase of higher-order soliton evolution in the anomalous dispersion regime of an optical fiber. However, the presence of effects such as Raman scattering, higher-order dispersion or input pulse noise can induce pulse break-up and instabilities through soliton-fission processes. Recent studies of soliton fission in the context of supercontinuum generation have provided improved insight into the way these processes can be avoided, allowing significant improvement in achievable compressed pulse quality and duration. In this paper we focus on providing an overview of a series of our own experiments around 1550 nm where we have used parabolic pulse similariton amplifiers to generate low noise pulses that have been linearly and nonlinearly compressed to the sub-30 fs regime using controlled compression in highly nonlinear fiber. In addition, we also describe recent results where comparable pulse durations have been obtained using sub-10 cm lengths of highly nonlinear fiber directly spliced to the output pigtail of a commercial femtosecond source.
    Proc SPIE 01/2007;