Transport par fibre optique de longueur métrique d'impulsions lumineuses de durée inférieure à 20 fs et d'énergie supérieure à 1 nJ

National audienc

Mesure d'impulsions femtosecondes ultra-courtes par interférométrie spectrale résolue temporellement : " Wideband-SPIRIT "

National audienc

Transport d'impulsions lumineuses ultra-brèves

Les impulsions femtosecondes ont trouvé un large panel d'applications dans des domaines variés comme la spectroscopie, le traitement des matériaux ou l'imagerie biomédicale [1]-[2]. Pour un bon nombre d'applications comme l'imagerie biomédicale in vivo in situ, il est nécessaire d'acheminer des impulsions ultra-courtes par fibres optique sur des distances de quelques mètres pour exciter de façon non linéaire certaines cellules fluorescentes que l'on souhaite imager. Le déport des impulsions par fibres optique est cependant problématique. En effet, lors de leur propagation dans des milieux matériels, elles subissent de fortes distorsions linéaires et non linéaires. Elles sont élargies temporellement et spectralement par les effets combinés de dispersion chromatique et d'automodulation de phase de type Kerr

Spectral interferometry for the characterization of ultra-short light pulses: Wideband Spirit

International audienceRecent developments in femtosecond Optics and applications have fostered deep interest on characterization of ultra-short pulses. Unlike iterative methods, spectral shearing interferometry provides complete real-time information of ultra-short optical signals. Spectral interferometry resolved in time (SPIRIT) is a passive and self-referenced characterization technique that has shown to be suitable for a variety of pulse conditions. SPIRIT Wideband represents a novel configuration aimed for the measurement of a few optical cycle pulses. We present the experimental scheme of SPIRIT Wideband and report preliminary experimental results dealing with the characterization of a few femtosecond pulses

Femtosecond pulse coherent shaping based on liquid crystal 2D spatial light modulator

International audienc

Pulse measurement by time to frequency conversion with a quadratic

International audienceWe demonstrate a new method of aberration-free time-to-frequency conversion through temporal lensing in a wave mixing process, for the spectrotemporal imaging and femtosecond pulse direct, real-time measurement. The nonlinear-spectronic reference pulse, self-shaped in a single-mode fiber, makes our technique a self-reference one

Fiber delivery of sub-30 fs pulses at 830 nm using a grism-based dispersive line

International audienceFemtosecond pulse delivery with fiber is desirable for many applications (e.g. non linear endomicroscopy). We present the direct delivery of compressed ultrashort (sub-30 fs) nanojoule (1.2 nJ) pulses at 830 nm through a standard single mode fiber (SMF) and also through a large mode area (LMA) fiber. For delivery with the SMF, the pulse coming from a standard femtosecond oscillator (10 nm bandwidth) is first spectrally and temporally broadened in a first SMF under the combined effects of self-phase modulation (SPM) and positive second order dispersion (SOD). Then it passes through an anomalous dispersive line in which it is largely negatively stretched. During its final propagation inside the delivery fiber the signal is temporally and spectrally compressed [1]. This is obtained when the anomalous dispersive line is adjusted to compensate for the positive SOD and for the positive third order dispersion (TOD) of the two fiber pieces (Fig. 1 up). For delivery with the LMA, the setup was composed of a large bandwidth oscillator (80 nm bandwidth), of the same grism-based stretcher and of the fiber delivery (the first fiber was removed) (Fig. 1 down). For simultaneous SOD and TOD compensation, conventional dispersive lines (e.g. prism line [3], grating line [4]) were previously combined with a multi-pass chirped mirror pair [2] resulting in a cumbersome setup involving expensive elements. We worked with a home-built dispersive line made of two grisms (association of a diffraction grating in contact with a prism) [5]. Playing with the distance d between the two grisms and with the incidence angle θ permitted simultaneous adjustments of SOD and TOD. It allows us to obtain what is to the best of our knowledge, the shortest pulses ever delivered directly by an optical fiber. We demonstrated the delivery of 55kW sub-30fs pulses directly at the output of LMA fiber. SMF setup gave rather close results. For the two setups, we used the same home-built grism-based stretcher which was made of usual components (40° BK7 prisms, 600 g/mm gratings). Our grism-based stretcher efficiency amounted to 34%

Déport par fibre optique d'impulsions femtosecondes de duree record egale a 17,8 femtosecondes a 820 nm

International audienceNous montrons qu'il est possible de délivrer à l'extrémité d'une fibre optique microstructurée air-silice à coeur solide et large aire modale (LMA) de 2,7 mètres de long des impulsions compressées de durée record égale à 17,8 femtosecondes et d'énergie égale à 1 nJ. Les impulsions provenant d'un oscillateur au saphir dopé titane (l=820 nm) à bande ultralarge (Dl=70 nm) sont préalablement étirées par une ligne à dispersion anormale constituée d'une paire de grisms. Cette solution rend possible la précompensation de la dispersion de la fibre jusqu'à l'ordre 3 inclus. Cet ensemble [étireur à grisms - compresseur à fibre] est dans un deuxième temps alimenté par un oscillateur femtoseconde standard, i.e. à bande plus étroite (Dl=10 nm), suivi d'une première fibre SMF conventionnelle siège d'effets non linéaires. Dans ce cas les impulsions compressées en sortie de fibre LMA ont une durée égale à 32 fs ce qui est plus de 3 fois inférieure à la durée disponible en sortie d'oscillateur (i.e. 100 fs). L'énergie par impulsion est alors égale à 1,6 nJ. Pour ces deux configurations le remplacement de la fibre LMA par une fibre SMF standard à maintien de polarisation est étudié. De façon inattendue, cette fibre standard procure des performances voisines voire même parfois supérieures à celles liées à l'emploi de la fibre LMA

Direct space-to-time femtosecond pulse shaping based on 2D phase-only spatial light modulator

International audienceWe present a very compact revisited DST-PS by using a phase-only 2D LC-SLM, without additional grating and mask. For conventional DST-PS, output pulse is directly repeating the form of a shaping mask which is imaged onto a passive diffraction grating. We introduce the following innovative feature: computer controlled reflective phase only LC-SLM with high spatial resolution (i.e. 8μm) can act as an inhomogeneous programmable blazed phase grating

Sub-30-fs pulse compression and pulse shaping at the output of a 2-m-long optical fiber in the near-infrared range

International audienceWe experimentally demonstrate fiber delivery of sub-30-fs pulses in the near-infrared range achieving 1.6 nJ at the output of a 2-m-long standard single-mode fiber, starting with 150 fs pulse duration at laser output and with a standard system. It results from the compensation of linear and nonlinear effects by a grism-based stretcher giving a pulse compression factor of 5, representing the best temporal, energetic, and tunable performance. We compare these results with the fiber delivery of nanojoule pulses changing the fiber for a 2-m-long large mode area one, giving similar results, but with a longer pulse duration. Then, we experimentally demonstrate the adaptation of the fibered setup to shape the spectrum in amplitude and phase at the fiber output with a shaping module placed before the fiber