Ultrafast and versatile spectroscopy by temporal Fourier transform

published_or_final_versio

Ultra-flat wideband single-pump Raman-enhanced parametric amplification

We experimentally optimize a single pump fiber optical parametric amplifier in terms of gain spectral bandwidth and gain variation (GV). We find that optimal performance is achieved with the pump tuned to the zero-dispersion wavelength of dispersion stable highly nonlinear fiber (HNLF). We demonstrate further improvement of parametric gain bandwidth and GV by decreasing the HNLF length. We discover that Raman and parametric gain spectra produced by the same pump may be merged together to enhance overall gain bandwidth, while keeping GV low. Consequently, we report an ultra-flat gain of 9.6±0.5 dB over a range of 111 nm (12.8 THz) on one side of the pump. Additionally, we demonstrate amplification of a 60 Gbit/s QPSK signal tuned over a portion of the available bandwidth with OSNR penalty less than 1 dB for Q2 below 14 dB

Modifications of single-wall carbon nanotubes upon oxidative purification treatments

A systematic characterization of single-wall carbon nanotube (SWCNT) material after successive purification steps, including reflux treatment with nitric acid, air oxidation, and annealing, has been performed. Inductively coupled plasma–optical emission spectroscopy shows that a considerable reduction of the metal impurities by up to 95% can be obtained by the nitric acid reflux treatment. During this process, Raman spectroscopy clearly proves that HNO3 molecules are intercalated into the bundles of SWCNTs. At the same time, SWCNTs have suffered a high degree of degradation and defects are being introduced. The subsequent thermal processes lead to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO3 molecules. Transmission electron microscopy reveals that the remaining SWCNT bundles tend to form thick bundles. Thus the applied purification process results in a high-purity SWCNT material with a drastically reduced content of metal nanoparticles and composed of large bundles of SWCNTs.This work was supported by the European Commission under the Research Training Network contract NANOCOMP (HPRN-CT-2000-00037).Peer reviewe

Sensitivity of single wall carbon nanotubes to oxidative processing: structural modification, intercalation and functionalisation

The effect of oxidation on modification of single wall carbon nanotubes (SWCNTs) through successive purification steps has been studied. The efficient elimination of metal impurities has been followed by induced coupled plasma spectroscopy. Upon acid treatment, Raman spectroscopy clearly proofed that HNO3 molecules were intercalated into the bundles of SWCNTs. At the same time, SWCNTs also have suffered a high degree of degradation and defects were introduced. The subsequent thermal processes led to the removal of further defect carbon materials and to the almost complete de-intercalation of the HNO3 molecules. Changes in the structure of the SWCNT bundles have been observed by transmission electron microscopy. While bundles tend to separate upon acid treatment, after the complete purification process, the remaining SWCNTs tend to form thick bundles again. The existence of functional groups in the raw single wall carbon nanotubes material and their modification and almost complete removal after the final annealing step has been studied by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and temperature programmed desorption. Nitrogen adsorption isotherms analysed according to Brunauer–Emmet–Teller showed important changes in the pore volume and surface area through the purification steps.This work was supported by the European Commission under the Research Training Network contract NANOCOMP (HPRN-CT-2000-00037).Peer reviewe

Gain through losses in nonlinear optics

Instabilities of uniform states are ubiquitous processes occurring in a variety of spatially extended nonlinear systems. These instabilities are at the heart of symmetry breaking, condensate dynamics, self-organization, pattern formation and noise amplification across diverse disciplines, including physics, chemistry, engineering and biology. In nonlinear optics, modulation instabilities are generally linked to the so-called parametric amplification process, which occurs when certain phase-matching or quasi-phase-matching conditions are satisfied. In the present review article, we summarize the principle results on modulation instabilities and parametric amplification in nonlinear optics, with special emphasis on optical fibres. We then review state-of-the-art research about a peculiar class of modulation instabilities and signal amplification processes induced by dissipation in nonlinear optical systems. Losses applied to certain parts of the spectrum counterintuitively lead to the exponential growth of the damped mode themselves, causing gain through losses. We discuss the concept of imaging of losses into gain, showing how to map a given spectral loss profile into a gain spectrum. We demonstrate with concrete examples that dissipation-induced modulation instability, apart from being of fundamental theoretical interest, may pave the way towards the design of a new class of tuneable fibre-based optical amplifiers, optical parametric oscillators, frequency comb sources and pulsed lasers

Oxydation comparée du niobium et d'un alliage (P 353 M) à base de niobium

Etude par diffraction de rayons X de l'oxydation comparée du Niobium pur et d'un alliage à base de Niobium de composition suivante : W V Ti Zr C 10 % 1,5 % 0,5 % 3 % 0,25 % Nb élément de base à à à à à 12 % 2 % 0,7 % 4 % 0,40 % L'oxydation a été effectuée à l'air pour des températures variant de 800 °C à 950 °C et des temps s'échelonnant entre 1/2 h et 100 h. Dans les deux cas (niobium et alliage) on a mis en évidence la présence de trois formes de l'oxyde Nb 2O5 : — une forme de basse température B. T. ; — une forme de moyenne température M. T. ; — une forme de haute température H. T. Le Niobium et l'alliage P 353 M ont un comportement globalement identique quant à la nature des phases et à leur température d'apparition. L'oxydation de l'alliage est cependant retardée par rapport à celle du Niobium pur. On observe aussi dans le cas de l'alliage : — une stabilisation de la forme B. T. ; — une apparition plus tardive des formes M. T. et H. T. et une croissance plus lente de ces phases M. T. et H. T

Oxydation comparée du niobium et d'un alliage (P 353 M) à base de niobium

X ray diffraction study of the oxidation of pure Niobium compared whit an alloy of the following composition : W V Ti Zr C 10 % 1.5 % 0.5 % 3 % 0.25 % Nb main component to to to to to 12 % 2 % 0.7 % 4 % 0.40 % Oxidation has been achieved in atmospheric conditions at temperatures ranging from 800 °C to 950 °C and for periods of time ranging from 1/2 h to 100 h. In both cases (Niobium and alloy) 3 forms of the Niobium oxide Nb2O5 have appeared : — a low temperature form B. T. ; — a medium temperature form M. T. — and a high temperature form H. T. The Niobium and the P 353 M alloy behave most identically as to the different phases and their temperatures of appearance. Oxidation of the alloy is however delayed if compared with pure Niobium. With the alloy we can observed : — a stabilization of the B. T. form ; — a delayed appearance of the M. T. and H. T. forms and a slower growth of these M. T. and H. T. forms.Etude par diffraction de rayons X de l'oxydation comparée du Niobium pur et d'un alliage à base de Niobium de composition suivante : W V Ti Zr C 10 % 1,5 % 0,5 % 3 % 0,25 % Nb élément de base à à à à à 12 % 2 % 0,7 % 4 % 0,40 % L'oxydation a été effectuée à l'air pour des températures variant de 800 °C à 950 °C et des temps s'échelonnant entre 1/2 h et 100 h. Dans les deux cas (niobium et alliage) on a mis en évidence la présence de trois formes de l'oxyde Nb 2O5 : — une forme de basse température B. T. ; — une forme de moyenne température M. T. ; — une forme de haute température H. T. Le Niobium et l'alliage P 353 M ont un comportement globalement identique quant à la nature des phases et à leur température d'apparition. L'oxydation de l'alliage est cependant retardée par rapport à celle du Niobium pur. On observe aussi dans le cas de l'alliage : — une stabilisation de la forme B. T. ; — une apparition plus tardive des formes M. T. et H. T. et une croissance plus lente de ces phases M. T. et H. T