Publications

2011

• Picosecond time scale modification of forward scattered light induced by absorption inside particles
  
  • Kervella Myriam
  • d'Abzac François-Xavier
  • Hache François
  • Hespel Laurent
  • Dartigalongue Thibault
  Optics Letters, Optical Society of America - OSA Publishing, 2011, 20 (1), pp.32-41. The aim of this work is to evaluate the influence of absorption processes on the Time Of Flight (TOF) of the light scattered out of a thick medium in the forward direction. We use a Monte-Carlo simulation with temporal phase function and Debye modes. The main result of our study is that absorption inside the particle induces a decrease of the TOF on a picosecond time scale, measurable with a femtosecond laser apparatus. This decrease, which exhibits a neat sensitivity to the absorption coefficient of particles, could provide an efficient way to measure this absorption. © 2011 OSA (10.1364/OE.20.000032)
  DOI : 10.1364/OE.20.000032
• Microscopie optique non-linéaire quantitative utilisant un faisceau mis en forme
  
  • Schanne-Klein Marie-Claire
  • Beaurepaire Emmanuel
  • Strupler Mathias
  • Débarre Delphine
  • Olivier Nicolas
  • Mahou Pierre
  , 2011. L'invention concerne un microscope optique non-linéaire utilisant un faisceau laser de Bessel de façon à imager un échantillon avec une bonne résolution latérale et une profondeur de champ étendue. Ce microscope intègre un scanner de lames. L'échantillon est disposé sur une lame, qui est chargée automatiquement sur une platine motorisée, de sorte que le faisceau laser peut balayer la totalité de la lame. Les signaux utiles provenant de l'échantillon sont combinés avec l'image conventionnelle du scanner de lames de façon à obtenir une image globale mettant clairement en évidence avec une bonne résolution des éléments d'intérêts.
• Imagerie tridimensionnelle multiphotonique des tissus biologiques à l'aide d'impulsions façonnées
  
  • Labroille Guillaume
  , 2011. Cette thèse présente l'utilisation d'impulsions ultracourtes pour des expériences de microscopie non-linéaire et d'optique quantique. Dans un premier temps, nous exposerons plusieurs techniques de façonnage d'impulsions et nous détaillerons en particulier le fonctionnement et la caractérisation de notre dispositif de façonnage. Nous étudierons l'utilisation d'un masque de phase 2D diffractif adressé optiquement qui permet un façonnage à la fois en phase et en amplitude spectrale. Par la suite, nous verrons comment le façonnage d'impulsions ultra-courtes peut être un outil efficace pour sélectionner les fluorophores excités en microscopie à deux photons. Pour cela, nous présenterons une expérience de contrôle cohérent de l'absorption à deux photons dans un embryon de drosophile vivant avec notre système de façonnage programmable. Ensuite nous décrirons un schéma de façonnage simplifié à base de prismes, qui, conjointement avec une approche de multiplexage temporel des impulsions, permet d'imager simultanément plusieurs fluorophores. Enfin, nous discuterons l'utilisation d'impulsions ultracourtes pour des expériences de mesures de temps et de dispersion à la limite quantique. Nous détaillerons en particulier une étude théorique et expérimentale d'un système de façonnage original à base de matériaux biréfringents pour produire la dérivée temporelle d'un champ électrique ou bien la dérivée temporelle de son enveloppe.
• Measurement of cicular dichroism dynamics in a temperature jump experiment for the study of protein folding
  
  • Khuc Mai-Thu
  , 2011. The question how proteins fold into their specific three-dimentional structures provides an exciting challenge for biophysicists nowadays. The use of a fast temperature-jump is a very powerful technique for the study of the denaturation process of proteins. However, probing the secondary structure is a difficult challenge and rarely yields quantitative values. The main purpose of this PhD project is to develop a technical implementation of far-UV circular dichroism in a nanosecond T-jump experiment. Our CD/T-jump experiment allows us to follow quantitatively the change in the helical fraction of a poly(glutamic acid) peptide during its thermal denaturation with 12 ns time resolution.
• Polarisation des impulsions térahertz et développement de l'imagerie par réflexion interne totale pour l'étude d'objets d'intérêt biologique
  
  • Wojdyla Antoine
  , 2011. Le domaine des ondes térahertz est un zone encore peu explorée du spectre électromagnétique, en dépit des qualités que lui confère sa position intermédiaire entre les ondes radars et l'infrarouge. Les progrès technologiques récents permettent désormais de générer des impulsions térahertz très courtes et offrent la possibilité d'effectuer des mesures résolues en temps des champs électriques associés. La détermination conjointe de l'amplitude et la phase des impulsions laisse libre cours au développement de nouveaux procédés de mesures et ouvre un grand champ de possibilités dans le traitement des données recueillies. La notion de phase est importante dans l'étude des phénomènes mettant en jeu la polarisation des ondes, et revêt un aspect singulier lorsque l'on s'intéresse à des impulsions ultra-brèves. L'étude de ces particularités a motivé le développement de dispositifs achromatiques adaptés au domaine térahertz tirant parti de certaines conditions de réflexion aux interfaces diélectriques. Ces dispositifs permettent de modifier les amplitudes et les phases différentielles des deux composantes du champ électrique des impulsions THz, afin de générer tous types d'états de polarisation cohérents. Aux impulsions térahertz sont associées des longueurs d'onde submillimétriques, ce qui assure une résolution spatiale convenable lorsque l'on cherche à former des images d'objets, tout en permettant d'exploiter les informations sur la structure temporelle de l'onde. Nous avons mis en œuvre quelques procédés d'imagerie afin de déterminer lesquels sont les mieux adaptés à l'étude d'objets biologiques, majoritairement constitués d'eau. Afin d'en tirer parti de la sensibilité des ondes aux ions en solution et de limiter l'importance des effets d'absorption dus à l'eau, nous avons mis au point une technique d'imagerie fondée sur le phénomène de réflexion interne totale. Cette technique tire son avantage de la mesure de la phase tout en présentant une excellente résolution transverse, particulièrement adaptée lorsqu'il s'agit d'étudier des objets biologiques fins tels que des neurones ou des monocouches cellulaires.
• Simple characterisation of a deformable mirror inside a high numerical aperture microscope using phase diversity.
  
  • Débarre D.
  • Vieille T.
  • Beaurepaire Emmanuel
  Journal of Microscopy, Wiley, 2011, 244 (2), pp.136-43. We present a simple and versatile scheme for characterising amplitude and phase modulation by an active element, such as a deformable mirror, in the pupil plane of a high NA microscope. By placing a mirror in the vicinity of the focal plane of the objective and recording images of the reflected focal spot on a camera, we show that reliable measurements of the influence function of the mirror actuators in the pupil plane of the objective can be obtained using an iterative electric field retrieval algorithm. Compared to direct wavefront sensors, the proposed method allows characterisation for a variety of objectives with different NA and pupil sizes without modification of the setup, requires minimal space inside the microscope, and can be used with pulsed sources such as used for multiphoton microscopy. In order to validate our method, we compare our data to the results obtained with a Shack-Hartmann wavefront sensor, and show that comparable precision is achieved. (10.1111/j.1365-2818.2011.03518.x)
  DOI : 10.1111/j.1365-2818.2011.03518.x
• Saccharomyces cerevisiae chitin biosynthesis activation by N-acetylchitooses depends on size and structure of chito-oligosaccharides.
  
  • Becker Hubert F.
  • Piffeteau Annie
  • Thellend Annie
  BMC Research Notes, BioMed Central, 2011, 4 (1), pp.454. ABSTRACT: BACKGROUND: To explore chitin synthesis initiation, the effect of addition of exogenous oligosaccharides on in vitro chitin synthesis was studied. Oligosaccharides of various natures and lengths were added to a chitin synthase assay performed on a Saccharomyces cerevisiae membrane fraction. FINDINGS: N-acetylchito-tetra, -penta and -octaoses resulted in 11 to 25 % [14C]-GlcNAc incorporation into [14C]-chitin, corresponding to an increase in the initial velocity. The activation appeared specific to N-acetylchitooses as it was not observed with oligosaccharides in other series, such as beta-(1,4), beta-(1,3) or alpha-(1,6) glucooligosaccharides. CONCLUSIONS: The effect induced by the N-acetylchitooses was a saturable phenomenon and did not interfere with free GlcNAc and trypsin which are two known activators of yeast chitin synthase activity in vitro. The magnitude of the activation was dependent on both oligosaccharide concentration and oligosaccharide size. (10.1186/1756-0500-4-454)
  DOI : 10.1186/1756-0500-4-454
• Insights into folate/FAD-dependent tRNA methyltransferase mechanism: role of two highly conserved cysteines in catalysis
  
  • Hamdane Djemel
  • Argentini Manuela
  • Cornu David
  • Myllykallio Hannu
  • Skouloubris Stéphane
  • Hui-Bon-Hoa Gaston
  • Golinelli-Pimpaneau Béatrice
  Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2011, 286 (42), pp.36268-36280. The flavoprotein TrmFO methylates specifically the C5 carbon of the highly conserved uridine 54 in tRNAs. Contrary to most methyltransferases, the 1- carbon unit transferred by TrmFO derives from 5,10-methylenetetrahydrofolate and not from S-adenosyl-l-methionine. The enzyme also employs the FAD hydroquinone as a reducing agent of the C5 methylene U54-tRNA intermediate in vitro. By analogy with the catalytic mechanism of thymidylate synthase ThyA, a conserved cysteine located near the FAD isoalloxazine ring was proposed to act as a nucleophile during catalysis. Here, we mutated this residue (Cys-53 in Bacillus subtilis TrmFO) to alanine and investigated its functional role. Biophysical characterization of this variant demonstrated the major structural role of Cys-53 in maintaining both the integrity and plasticity of the flavin binding site. Unexpectedly, gel mobility shift assays showed that, like the wild-type enzyme, the inactive C53A variant was capable of forming a covalent complex with a 5-fluorouridine-containing mini-RNA. This result confirms the existence of a covalent intermediate during catalysis but rules out a nucleophilic role for Cys-53. To identify the actual nucleophile, two other strictly conserved cysteines (Cys-192 and Cys-226) that are relatively far from the active site were replaced with alanine, and a double mutant C53A/C226A was generated. Interestingly, only mutations that target Cys-226 impeded TrmFO from forming a covalent complex and methylating tRNA. Altogether, we propose a revised mechanism for the m5U54 modification catalyzed by TrmFO, where Cys-226 attacks the C6 atom of the uridine, and Cys-53 plays the role of the general base abstracting the C5 proton. (10.1074/jbc.M111.256966)
  DOI : 10.1074/jbc.M111.256966
• Achromatic polarizing elements for pulsed THz waves
  
  • Wojdyla Antoine
  • Gallot Guilhem
  , 2011, pp.1. We present two polarizing elements designed to produce linear and circular polarization for broadband, pulsed THz waves. The linear polarizer is made out silicon wafers arranged at Brewster's angle and the circular polarizer is made out of a silicon prism using total internal reflection differential phase-shift effect. (10.1109/irmmw-THz.2011.6105244)
  DOI : 10.1109/irmmw-THz.2011.6105244
• Total internal reflection Terahertz imaging
  
  • Wojdyla Antoine
  • Gallot Guilhem
  , 2011, pp.1-2. We present a new Terahertz imaging scheme based on total internal reflection that allows the study of aqueous samples while improving the longitudinal resolution. We were able to image a frog neuron using the spectral phase of the THz pulses using this technique. © 2011 IEEE. (10.1109/irmmw-THz.2011.6104845)
  DOI : 10.1109/irmmw-THz.2011.6104845
• Combined third-harmonic generation and four-wave mixing microscopy of tissues and embryos.
  
  • Mahou Pierre
  • Olivier Nicolas
  • Labroille Guillaume
  • Duloquin Louise
  • Sintes Jean-Marc
  • Peyriéras Nadine
  • Legouis Renaud
  • Débarre Delphine
  • Beaurepaire Emmanuel
  Biomedical optics express, Optical Society of America - OSA Publishing, 2011, 2 (10), pp.2837-49. Nonlinear microscopy can be used to probe the intrinsic optical properties of biological tissues. Using femtosecond pulses, third-harmonic generation (THG) and four-wave mixing (FWM) signals can be efficiently produced and detected simultaneously. Both signals probe a similar parameter, i.e. the real part of the third-order nonlinear susceptibility χ((3)). However THG and FWM images result from different phase matching conditions and provide complementary information. We analyze this complementarity using calculations, z-scan measurements on water and oils, and THG-FWM imaging of cell divisions in live zebrafish embryos. The two signals exhibit different sensitivity to sample size and clustering in the half-wavelength regime. Far from resonance, THG images reveal spatial variations |Δχ((3))(-3ω;ω,ω,ω)| with remarkable sensitivity while FWM directly reflects the distribution of χ((3))(-2ω(1) + ω(2);ω(1), -ω(2), ω(1)). We show that FWM images provide χ((3)) maps useful for proper interpretation of cellular THG signals, and that combined imaging carries additional structural information. Finally we present simultaneous imaging of intrinsic THG, FWM, second-harmonic (SHG) and two-photon-excited fluorescence (2PEF) signals in live Caenorhabditis elegans worms illustrating the information provided by multimodal nonlinear imaging of unstained tissue. (10.1364/BOE.2.002837)
  DOI : 10.1364/BOE.2.002837
• Monitoring micrometer-scale collagen organization in rat-tail tendon upon mechanical strain using second harmonic microscopy.
  
  • Goulam Houssen Yannick
  • Gusachenko Ivan
  • Schanne-Klein Marie-Claire
  • Allain Jean-Marc
  Journal of Biomechanics, Elsevier, 2011, 44 (11), pp.2047-52. We continuously monitored the microstructure of a rat-tail tendon during stretch/relaxation cycles. To that purpose, we implemented a new biomechanical device that combined SHG imaging and mechanical testing modalities. This multi-scale experimental device enabled simultaneous visualization of the collagen crimp morphology at the micrometer scale and measurement of macroscopic strain-stress response. We gradually increased the ultimate strain of the cycles and showed that preconditioning mostly occurs in the first stretching. This is accompanied by an increase of the crimp period in the SHG image. Our results indicate that preconditioning is due to a sliding of microstructures at the scale of a few fibrils and smaller, that changes the resting length of the fascicle. This sliding can reverse on long time scales. These results provide a proof of concept that continuous SHG imaging performed simultaneously with mechanical assay allows analysis of the relationship between macroscopic response and microscopic structure of tissues. (10.1016/j.jbiomech.2011.05.009)
  DOI : 10.1016/j.jbiomech.2011.05.009
• Polarization-resolved second harmonic generation microscopy in biological tissues
  
  • Latour Gaël
  • Gusachenko Ivan
  • Schanne-Klein Marie-Claire
  , 2011. In this study, we implemented a polarimetric SHG microscope and analyzed the linear propagation effects that affect polarization-resolved SHG imaging of thick anisotropic collagenous tissues. We developed a theoretical model to account for birefringence and diattenuation along the excitation propagation, and polarization scrambling upon scattering of the harmonic signal. We obtained an excellent agreement with polarization-resolved SHG images at increasing depth within a rat-tail tendon for both polarizations of the forward SHG signal (see Figure 1). Most notably, we observed interference fringes due to birefringence in the SHG depth profile when excited at π/4 angle from the tendon axis. (10.1109/CLEOE.2011.5942909)
  DOI : 10.1109/CLEOE.2011.5942909
• Quantitative assessment of collagen i liquid crystal organizations: Role of ionic force and acidic solvent, and evidence of new phases
  
  • de Sa Peixoto Paulo
  • Deniset-Besseau Ariane
  • Schanne-Klein Marie-Claire
  • Mosser Gervaise
  Soft Matter, Royal Society of Chemistry, 2011, 7 (23), pp.11203. Collagen I is the major structural protein in mammals where it exhibits highly organized fibrillar distributions in connective tissues. In vitro, acidic solutions of collagen I display lyotropic liquid crystal organization. These concentrated organized liquid phases can be stabilized by a pH increase to generate in vitro fibrillar matrices with specific organization. The aim of this work is to understand the mechanisms responsible for liquid crystal chirality at acidic pH in order to guide the synthesis of collagen matrices reproducing the great diversity of organizations found in biological tissues. For this purpose, we quantitatively analyze collagen liquid crystal organization by use of multiphoton microscopy, combining fluorescence and second harmonic generation contrasts. The concentration of the isotropic to liquid crystal phase transition and the evolution of the half pitch of the helical phase with collagen concentration are reported in five physico-chemical conditions using hydrochloric and acetic acids at different pHs and ionic strengths. A new phase transition is observed in highly concentrated solutions ranging from 90 mg ml-1 to 300 mg ml-1 depending on the solvent. Our results bring new quantitative information on collagen chemical physics and further substantiate the on-going analysis of the driving parameters generating twists in liquid crystals. These findings could be advantageously exploited to develop new strategies and protocols for tissue engineering. This is crucial for fundamental studies of cell behavior in biomimetic three-dimensional environments and for medical and pharmaceutical applications. Cop. The Royal Society of Chemistry 2011. (10.1039/c1sm06076g)
  DOI : 10.1039/c1sm06076g
• Toward high-content/high-throughput imaging and analysis of embryonic morphogenesis
  
  • Truong Thai V.
  • Supatto Willy
  Genesis - The Journal of Genetics and Development, Wiley-Blackwell, 2011, 49 (7), pp.555. In vivo study of embryonic morphogenesis tremendously benefits from recent advances in live microscopy and computational analyses. Quantitative and automated investigation of morphogenetic processes opens the field to high-content and high-throughput strategies. Following experimental workflow currently developed in cell biology, we identify the key challenges for applying such strategies in developmental biology. We review the recent progress in embryo preparation and manipulation, live imaging, data registration, image segmentation, feature computation, and data mining dedicated to the study of embryonic morphogenesis. We discuss a selection of pioneering studies that tackled the current methodological bottlenecks and illustrated the investigation of morphogenetic processes in vivo using quantitative and automated imaging and analysis of hundreds or thousands of cells simultaneously, paving the way for high-content/high-throughput strategies and systems analysis of embryonic morphogenesis. Cop. 2011 Wiley-Liss, Inc. (10.1002/dvg.20760)
  DOI : 10.1002/dvg.20760
• Impact of pulse polarization on coherent vibrational ladder climbing signals
  
  • Nuernberger Patrick
  • Vieille Thibault
  • Ventalon Cathie
  • Joffre Manuel
  Journal of Physical Chemistry B, American Chemical Society, 2011, 115 (18), pp.5554. We report a theoretical study that elaborates the influence of the polarization state of both the pump and the probe pulse in ultrafast coherent vibrational ladder climbing experiments in the mid-infrared. Whereas a subensemble in a randomly oriented sample of molecules is excited by the pump pulse in this multiphoton process, further inhomogeneities such as the spatial profile of the laser beams, the longitudinal attenuation in the sample, and the probe beam polarization have to be taken into account. Analytical expressions for a density function describing the number of molecules that are exposed to an effective pump intensity are introduced, and the variation of the population distribution and the actual transient absorption signal in dependence on the polarization-state combinations for pump and probe pulse are discussed in detail. In simulations on the model system carboxy-hemoglobin, it is demonstrated that the polarization states play important roles both for exciting a certain population distribution and for actually observing it. In particular, it will be discussed under which conditions experimental data indicates a population inversion. Cop. 2011 American Chemical Society. (10.1021/jp1113762)
  DOI : 10.1021/jp1113762
• Processing pipeline for digitalizing the lineage tree of early zebrafish embryogenesis from multiharmonic imaging
  
  • Luengo-Oroz Miguel Angel
  • Savy Thierry
  • Rubio-Guivernau José L.
  • Duloquin Louise
  • Faure Emmanuel
  • Olivier Nicolas
  • Ledesma-Carbayo María Jesús
  • Debarre Delphine
  • Bourgine Paul
  • Beaurepaire Emmanuel
  • Peyriéras Nadine
  , 2011, pp.1561-1564. The reconstruction of the cell lineage tree of early zebrafish embryogenesis requires the use of in-vivo microscopy imaging and image processing strategies. Second (SHG) and third harmonic generation (THG) microscopy observations in unstained zebrafish embryos allows to detect cell divisions and cell membranes from 1-cell to 1K-cell stage. In this article, we present an ad-hoc image processing pipeline for cell tracking and cell membranes segmentation enabling the reconstruction of the early zebrafish cell lineage tree until the 1K-cell stage. This methodology has been used to obtain digital zebrafish embryos allowing to generate a quantitative description of early zebrafish embryogenesis with minute temporal accuracy and μm spatial resolution. (10.1109/ISBI.2011.5872699)
  DOI : 10.1109/ISBI.2011.5872699
• Biological applications of rare-earth based nanoparticles
  
  • Bouzigues Cédric
  • Gacoin T.
  • Alexandrou Antigoni
  ACS Nano, American Chemical Society, 2011, 5 (11), pp.8488. Biomedicine and cell and molecular biology require powerful imaging techniques of the single molecule scale to the whole organism, either for fundamental science or diagnosis. These applications are however often limited by the optical properties of the available probes. Moreover, in cell biology, the measurement of the cell response with spatial and temporal resolution is a central instrumental problem. This has been one of the main motivations for the development of new probes and imaging techniques either for biomolecule labeling or detection of an intracellular signaling species. The weak photostability of genetically encoded probes or organic dyes has motivated the interest for different types of nanoparticles for imaging such as quantum dots, nanodiamonds, dye-doped silica particles, or metallic nanoparticles. One of the most active fields of research in the past decade has thus been the development of rare-earth based nanoparticles, whose optical properties and low cytotoxicity are promising for biological applications. Attractive properties of rare-earth based nanoparticles include high photostability, absence of blinking, extremely narrow emission lines, large Stokes shifts, long lifetimes that can be exploited for retarded detection schemes, and facile functionalization strategies. The use of specific ions in their compositions can be moreover exploited for oxidant detection or for implementing potent contrast agents for magnetic resonance imaging. In this review, we present these different applications of rare-earth nanoparticles for biomolecule detection and imaging in vitro, in living cells or in small animals. We highlight how chemical composition tuning and surface functionalization lead to specific properties, which can be used for different imaging modalities. We discuss their performances for imaging in comparison with other probes and to what extent they could constitute a central tool in the future of molecular and cell biology. Cop. 2011 American Chemical Society. (10.1021/nn202378b)
  DOI : 10.1021/nn202378b
• Structure and function of a novel endonuclease acting on branched DNA substrates
  
  • Creze C.
  • Lestini Roxane
  • Kühn Joëlle
  • Ligabue Alessio
  • Becker Hubert F.
  • Czjzek M.
  • Flament D.
  • Myllykallio Hannu
  Biochemical Society Transactions, Portland Press, 2011, 39 (1), pp.145-149. Branched DNA structures that occur during DNA repair and recombination must be efficiently processed by structure-specific endonucleases in order to avoid cell death. In the present paper, we summarize our screen for new interaction partners for the archaeal replication clamp that led to the functional characterization of a novel endonuclease family, dubbed NucS. Structural analyses of Pyrococcus abyssi NucS revealed an unexpected binding site for ssDNA (single-stranded DNA) that directs, together with the replication clamp, the nuclease activity of this protein towards ssDNA-dsDNA (double-stranded DNA) junctions. Our studies suggest that understanding the detailed architecture and dynamic behaviour of the NucS (nuclease specific for ssDNA)-PCNA (proliferating-cell nuclear antigen) complex with DNA will be crucial for identification of its physiologically relevant activities. ©The Authors Journal compilation ©2011 Biochemical Society. (10.1042/BST0390145)
  DOI : 10.1042/BST0390145
• Aberration-free three-dimensional multiphoton imaging of neuronal activity at kHz rates
  
  • Botcherby Edward J.
  • Smith Christopher W.
  • Kohl Michael
  • Débarre Delphine
  • Booth Martin J.
  • Juskaitis Rimas
  • Paulsen Ole
  • Wilson Tony
  Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences, 2011, 109 (8), pp.2919-2924. Multiphoton microscopy is a powerful tool in neuroscience, promising to deliver important data on the spatiotemporal activity within individual neurons as well as in networks of neurons. A major limitation of current technologies is the relatively slow scan rates along the z direction compared to the kHz rates obtainable in the x and y directions. Here,we describe a custom-built microscope system based on an architecture that allows kHz scan rates over hundreds of microns in all three dimensions without introducing aberration. We further demonstrate how this high-speed 3D multiphoton imaging system can be used to study neuronal activity at millisecond resolution at the subcellular as well as the population level. (10.1073/pnas.1111662109)
  DOI : 10.1073/pnas.1111662109
• Advances in multiphoton microscopy for imaging embryos
  
  • Supatto Willy
  • Truong T.V.
  • Débarre Delphine
  • Beaurepaire Emmanuel
  Current Opinion in Genetics and Development, Elsevier, 2011, 21 (5), pp.538. Multiphoton imaging is a promising approach for addressing current issues in systems biology and high-content investigation of embryonic development. Recent advances in multiphoton microscopy, including light-sheet illumination, optimized laser scanning, adaptive and label-free strategies, open new opportunities for embryo imaging. However, the literature is often unclear about which microscopy technique is most adapted for achieving specific experimental goals. In this review, we describe and discuss the key concepts of imaging speed, imaging depth, photodamage, and nonlinear contrast mechanisms in the context of recent advances in live embryo imaging. We illustrate the potentials of these new imaging approaches with a selection of recent applications in developmental biology. Cop. 2011 Elsevier Ltd. (10.1016/j.gde.2011.08.003)
  DOI : 10.1016/j.gde.2011.08.003
• Few femtosecond, few kiloampere electron bunch produced by a laser-plasma accelerator
  
  • Lundh Olle
  • Lim J.
  • Rechatin Clément
  • Ammoura L.
  • Ben-Ismaïl Ahmed
  • Davoine X.
  • Gallot Guilhem
  • Goddet Jean-Philippe
  • Lefebvre E.
  • Malka Victor
  • Faure Jérôme
  Nature Physics, Nature Publishing Group [2005-....], 2011, 7 (3), pp.219. Particle accelerators driven by the interaction of ultraintense and ultrashort laser pulses with a plasma(1) can generate accelerating electric fields of several hundred gigavolts per metre and deliver high-quality electron beams with low energy spread(2-5), low emittance(6) and up to 1 GeV peak energy(7,8). Moreover, it is expected they may soon be able to produce bursts of electrons shorter than those produced by conventional particle accelerators, down to femtosecond durations and less. Here we present wide-band spectral measurements of coherent transition radiation which we use for temporal characterization. Our analysis shows that the electron beam, produced using controlled optical injection(9), contains a temporal feature that can be identified as a 15 pC, 1.4-1.8 fs electron bunch (root mean square) leading to a peak current of 3-4 kA depending on the bunch shape. We anticipate that these results will have a strong impact on emerging applications such as short-pulse and short-wavelength radiation sources(10,11), and will benefit the realization of laboratory-scale free-electron lasers(12-14). (10.1038/NPHYS1872)
  DOI : 10.1038/NPHYS1872
• Sub-picosecond Raman spectrometer for time-resolved studies of structural dynamics in heme proteins
  
  • Kruglik Sergei G.
  • Lambry Jean-Christophe
  • Martin Jean-Louis
  • Vos Marten H.
  • Négrerie Michel
  Journal of Raman Spectroscopy, Wiley, 2011, 42 (3), pp.265. We describe a pump-probe Raman spectrometer based on a femtosecond Ti:sapphire laser, an optical parametric generator and two optical parametric amplifiers for time-resolved studies, with emphasis on the structural dynamics in heme proteins. The system provides a 100-fs pump pulse tunable in the range 500-600 nm and a transform-limited sub-picosecond probe pulse tunable in the range 390-450 nm. The spectrometer has spectral (25 cm(-1)) and temporal (similar to 0.7 ps) resolutions which constitute an effective compromise for identifying transient heme protein species and for following their structural evolution by spontaneous Raman scattering in the time range 0.5 ps to 2 ns. This apparatus was applied to time-resolved studies of a broad range of heme proteins, monitoring the primary dynamics of photoinduced heme coordination state and structural changes, its interaction with protein side-chains and diatomic gaseous ligands, as well as heme vibrational cooling. The treatment of transient Raman spectra is described in detail, and the advantages and shortcomings of spontaneous resonance Raman spectroscopy for ultrafast heme proteins studies are discussed. We demonstrate the efficiency of the constructed spectrometer by measuring Raman spectra in the sub-picosecond and picosecond time ranges for the oxygen-storage heme protein myoglobin and for the oxygen-sensor heme protein FixLH in interaction with the diatomic gaseous ligands CO, NO, and O-2. Copyright (C) 2010 John Wiley and Sons, Ltd. (10.1002/jrs.2685)
  DOI : 10.1002/jrs.2685
• Deep and fast live imaging with two-photon scanned light-sheet microscopy
  
  • Truong T.V.
  • Supatto Willy
  • Koos D.S.
  • Choi J.M.
  • Fraser S.E.
  Nature Methods, Nature Publishing Group, 2011, 8 (9), pp.757. We implemented two-photon scanned light-sheet microscopy, combining nonlinear excitation with orthogonal illumination of light-sheet microscopy, and showed its excellent performance for in vivo, cellular-resolution, three-dimensional imaging of large biological samples. Live imaging of fruit fly and zebrafish embryos confirmed that the technique can be used to image up to twice deeper than with one-photon light-sheet microscopy and more than ten times faster than with point-scanning two-photon microscopy without compromising normal biology. Cop. 2011 Nature America, Inc. All rights reserved. (10.1038/nmeth.1652)
  DOI : 10.1038/nmeth.1652
• Brewster's angle silicon wafer terahertz linear polarizer
  
  • Wojdyla Antoine
  • Gallot Guilhem
  Optics Express, Optical Society of America - OSA Publishing, 2011, 19 (15), pp.14099. We present a new cost-effective terahertz linear polarizer made from a stack of silicon wafers at Brewster's angle, andevaluate its performances. We show that this polarizer is wide-band, has a high extinction ratio (> 6 × 103) and very small insertion losses (inf 1%). We provide measurements of the temporal waveforms after linearly polarizing the THz beam and show that there is no distortion of the pulse. We compare its performances with a commercial wire-grid polarizer, and show that the Brewster's angle polarizer can conveniently be used to control the power of a terahertz beam. Cop. 2011 Optical Society of America. (10.1364/OE.19.014099)
  DOI : 10.1364/OE.19.014099