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Seminar n°9: Towards attosecond measurement in molecules and at surfaces
23/09/2014
by Jon Marangos,
Blackett Laboratory, Imperial College London
Salle XLIM 1
The seminar will cover the following topics based around our research programme at Imperial College. 
• Ultrafast electron and hole dynamics in molecules and solids 
• HHG spectroscopy of molecules including substituted benzenes 
• Attosecond pump-probe measurements of molecular hole dynamics 
• Surface streaking of disordered materials 
 
Jon Marangos is Professor of Laser Physics and holder of Lockyer Chair in Physics. He is also the Director of the Blackett Laboratory Laser Consortium. He is the Principal Investigator of the EPSRC Programme Grant "Attosecond Electron Dynamics in Molecular and Condensed Phase Matter" (starting 2011) and has been awarded an ERC Advanced Grant on "Attosecond Science by Transmission and Emission of X-rays (ASTEX)" (starting 2012). His major areas of research activity are in: (1) development of experimental methods for the measurement of processes on the attosecond time-scales; (2) non-linear optical processess for generation of coherent soft X-ray and VUV radiation and applications of these sources in atomic, molecular and muon physics; (3) High intensity laser- matter interactions especially looking at interactions with molecules and clusters; (4) investigation of atomic and molecular coherence effects (e.g. EIT) and enhanced non-linear frequency mixing. Recently he has been looking at the problems of controlling the electron dynamics driven in complex systems by strong laser fields and in developing high power sub-femtosecond light sources. He is involved in free electron laser science having led the UK New Light Source Project from 2008-2010 and is an active participant in experiments at LCLS, SLAC, USA and FLASH, DESY, Hamburg. He is a Fellow of the Optical Society of America and the Institute of Physics. 

Seminar n°8: TWENTY YEARS OF PHOTONIC CRYSTAL FIBERS
08/09/2014
by Philip Russell,
Max Planck Institute for the Science of Light, Erlengen, Germany.
Salle de Conférence XLIM
Conceived in 1991 and first demonstrated in 1995, photonic crystal fibres (PCFs) permit remarkable control of the propagation of light, including introducing a new theme – low-loss single mode guidance in a microscopic hollow channel. This last represents one of the most exciting opportunities in recent years, for it allows one for the first time effectively to eliminate beam diffraction in empty space or in materials with low refractive indices such as gases, vapours and liquids. As a result a new generation of versatile and efficient gas-based systems, such as pulse compression devices, light sources tunable from the vacuum UV to the near IR and nonlinear devices based on alkali metal vapours, is emerging. PCFs with solid glass cores continue to inspire applications beyond the well-established fields of soliton dynamics and supercontinuum generation. For example, when the fibre is twisted continuously (by thermal post- processing) along its axis, orbital angular momentum states are created in the cladding that couple to the core light at certain resonant wavelengths, creating deep dips in the transmitted spectrum. Another new field is that of opto-acoustic devices, where the light itself drives mechanical resonances in the core structure. These resonances act back on the light, leading to the generation of frequency combs and Raman-like self-pulsations. In the lecture I will briefly review the history of PCF and report on selected recent results from the work of my group.

Seminar n°7: Optical lattices shaken, not stirred: Simulating magnetism in triangular geometries 
16/05/2014
by Patrick Windpassinger,
Experimental Quantum Optics and Quantum Information de la Johannes Gutenberg University Mainz (Allemagne)
Salle de Conférence XLIM
The creation of artificial gauge fields is a key ingredient to the emulation of strong field physics with ultracold atoms in optical lattices. The talk focusses on techniques to experimentally realize tunable gauge fields by periodically diving an optical lattice [Phys. Rev. Lett. 108, 225304 (2012)]. After introducing the general idea, the talk discusses the study of frustrated classical magnetism in a triangular geometry and the observation of all possible magnetic spin states. In addition, symmetry breaking for strong spin frustration is shown [Science 333, 996-999 (2011)]. In the case of maximal frustration, the doubly degenerate superfluid ground state breaks both a discrete Z2 (Ising) symmetry and a continuous U(1) symmetry. By measuring an Ising order parameter, we observe a thermally driven phase transition from an ordered antiferromagnetic to an unordered paramagnetic state and textbook-like magnetization curves [Nature Physics 9, 738–743 (2013)].

Seminar n°6: Ultra-stable frequency/time transfer with optical fiber for metrology 
28/04/2014
by Giorgio Santarelli,
LP2N-Laboratoire Photonique, Numérique et Nanosciences de l’Université de Bordeaux 1
Salle de Conférence XLIM
The distribution and the comparison of ultra-stable frequency references using optical fibers have been greatly improved in the last ten years. I will present a review of the methods and the results obtained. The frequency/time stability and accuracy of optical links surpass the well-established methods using GNSS and geostationary satellites. It will be shown that it is possible to use public telecommunication network carrying Internet data to compare and distribute ultra-stable metrological signals of both frequency and time over long distances. In addition both frequency stability and accuracy are equivalent to those obtained with optical links developed using dedicated fiber networks. These technologies are implemented in REFIMEVE+, a project aiming at building a national-scale metrological network in France.

Author Biography:  Giorgio Santarelli received the degree "Laura in Ingegneria Elettronica" in 1990 from the University of Ancona, Italy, and the Ph.D. degree from the Université Pierre et Marie Curie (Paris VI, France) in 1996. From 1991 to 2012 he has been research staff at LNE-SYRTE, Observatoire de Paris. In 2013 he join ta new laboratory (the LP2N) hosted the brand new facilities of the Institut d’Optique d’Aquitaine, nearby Bordeaux. His research interests spans from very low phase noise frequency synthesis, cold atoms frequency standards, long distance fiber optical frequency dissemination to ultra-stable lasers and femtosecond laser combs. He is author and co-author of more than 90 peer review technical articles. Giorgio Santarelli is also Associate Editor of the IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

Seminar n°5: Novel lasers and optical frequency references
based on gas-filled kagomé fibers
11/04/2013
by Kristan L. Corwin 
Kansas State University, Dept. of Physics
Salle de Conférence XLIM
The advent of photonic bandgap and kagomé -structured optical fiber allows light and gas to interact over long lengths at relatively high intensity. This offers the opportunity for low-power nonlinear interactions in the gas, with important applications in spectroscopy and laser development. We have demonstrated 10 kHz accuracy in the measurement of absorption features in gas-filled hollow fibers, and 100 kHz in sealed fibers. The stability of these references when locked to both cw and modelocked lasers will be explored, toward the creation of an all-fiber referenced optical frequency comb, free of GPS. Further improvements in the sealed photonic microcells (PMC’s) should improve the accuracy and stability of the portable references. Recent demonstration of direct comb spectroscopy on these references further advances the goal of an all-fiber comb and reference system. 
Furthermore, optical pumping of a gas-filled fiber in the near IR has resulted in lasing in the mid- IR in HCN, C2H2 and other gases (in collaboration with the groups of Wolfgang Rudolph’s (UNM) and Fetah Benabid (CNRS)). These Hollow Core Optical Fiber Gas Lasers (HOFGLAS) based on population inversion promise a compact, low threshold laser, and should allow extension of laser emissions to new wavelength regions and higher output powers. Dramatic improvements in fiber performance at long wavelengths have driven much of this progress. 
This work is done in collaboration with Fetah Benabid’s group and Wolfgang Rudolph’s group at the Univ. of New Mexico, and the K-State group is funded by AFOSR.

Seminar n°4: Novel lasers and optical frequency references
based on gas-filled kagomé fibers
28/11/2012
by Franz X. Kärtner
Desy, Hambourg
MIT
Salle Vision XLIM 1
Over the last few years, advances in femtosecond lasers have opened up the possibility to construct fully coherent soft and hard x‐ray sources that range from table‐top size to kilometer long seeded FELs. The later facilities will be combined with laser and accelerator laboratories. 
Here, we discuss some of the key laser technologies and physics central to the development of such sources. The first part of the tutorial covers the use of femtosecond lasers in next generation large scale x‐ray FELs, that generate ultra‐short pulses with exceptionally high brightness well into the hard x‐ray range below 1 Angstrom, enabling atomic resolution, and, if necessary can generate many Watts of output power. Laser based seeding of these FELs may lead to a fully coherent output. Exciting new scientific frontiers are opened up with these machines ranging from nonlinear X‐ray physics in atoms, molecules, clusters and plasmas to ultrafast structural dynamics in condensed matter physics, chemistry and biology[1]. Most notably chemical reactions and its intermediate states can be mapped in time with short pulses of high brightness x‐rays, and, the structure and dynamics of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources can be determined on a femtosecond and potentially attosecond timescale [2]. The science cases, as well as the continued development of accelerator technology in general, demand that these light source facilities are equipped with a timing distribution system enabling synchronization of all laser and rf‐sources to sub‐10‐fs precision today and scalability to potentially 100 attosecond precision in the future. A set of ultrafast optical techniques for long‐term stable femtosecond synchronization of these large‐scale X‐ray FELs has been developed [3,4]. 
The second part of the talk will cover high energy and high power femtosecond laser technology necessary for the construction of coherent, compact EUV and soft‐x‐ray sources as well as optical pump‐probe techniques. These sources may be used as stand‐alone sources, or can be used to seed X‐ray FELs, such that their high energy output becomes temporally coherent, in contrast to the unseeded case producing self‐amplified spontaneous emission (SASE). Today, the only technique providing the necessary widely tunable, coherent EUV radiation is high order harmonic generation (HHG) [5,6]. Future light source facilities operating at 100 kHz or eventually even 1 MHz repetition rate add unique challenges to the large average power capabilities of femtosecond laser technology underlying the HHG process. Various possible technology choices addressing these needs will be highlighted. One approach to address this challenge is based on optical parametric chirped pulse amplification (OPCPA) pumped with cryogenically cooled Yb‐doped lasers, which enable both high pulse energies as well as large average power from compact systems. We discuss progress in the development of a widely tunable high energy femtosecond laser technology based on this technology. We discuss broadband seed generation from an octave spanning Ti:sapphire laser covering multiple octaves of bandwidth by using efficient adiabatic frequency conversion. Carrier‐envelope phase controlled few‐ to sub‐cycle high energy pulses can then be generated by OPCPA and coherent synthesis of multiple OPCPA outputs covering different wavelength ranges [7]. 

References: 
[1] National Science Foundation Light Source Panel Report: http://www.nsf.gov/attachments/109807/public/ LightSourcePanelFinalReport9-15-08.pdf 
[2] H. N. Chapman, et al., “Femtosecond X-ray protein nanocrystallography,” Nature 470, 73–77, doi:10.1038/nature09750 
[3] J. Kim, J. A. Cox, J. J. Chen, and F. X. Kärtner, “Drift-free femtosecond timing synchronization of remote optical and microwave sources,” Nature 
Photonics 2, 733-736 doi:10.1038/nphoton.2008.225 
[4] A. J. Benedick, J. G. Fujimoto and F. X. Kärtner, “Optical flywheels with attosecond jitter,” Nature Photonics 6, 97-100 doi:10.1038/nphoton.2011.326. 
[5] T. Togashi, et al., “Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphire laser,” Opt. Express 19, 317-324 (2011) and 
references therein. 
[6] L.-H. Yu, et al., “High-gain harmonic-generation free-electron laser,” Science 289, 932-934 (2000). 
[7] S-W. Huang, G. Cirmi, J. Moses, K-H. Hong, S. Bhardwaj, J. R. Birge, L-J. Chen, E. Li, B. J. Eggleton, G. Cerullo, and F. X. Kärtner, “ High-energy 
pulse synthesis with sub-cycle waveform control for strong-field physics,” Nature Photonics 5, 477 (2011).

Author Biography: Franz X. Kärtner received his Diploma and Ph.D. degree in Electrical Engineering from Technische Universität München. He heads the Ultrafast Optics and X-rays Division at the Center for Free-Electron Laser Science (CFEL) at DESY, Hamburg, and is Professor of Physics at University of Hamburg, and Adjunct Professor of Electrical Engineering at Massachusetts Institute of Technology (MIT). His research interests include few-cycle and ultralow jitter femtosecond lasers and its use in attosecond photonics and sience such as precision timing distribution in advanced accelerators and light sources and high order harmonic generation. He is a fellow of the OSA and IEEE.

Seminar n°3: Optical atomic clocks with emphasis on a mercury based optical lattice clock
16/05/2012
by John McFerran
School of Physics, University of Western Australia,
GPPMM

Salle Vision XLIM 1
Atomic clock research has now entered an era in which the frequency of specific optical transitions is measured with uncertainties lower than that of the best microwave standards (e.g. the primary frequency standard of Cs). Single‐ion clocks and neutral atom lattice clocks have become the avant‐garde of precision spectroscopy. The exquisite accuracy that is now achieved for certain specific atomic lines lies below the 10‐16 level. These accuracies permit tests searching for variations in fundamental constants such as the fine structure constant by comparing the frequency ratio between different transitions over yearly timescales (and eventually over decades). At the Paris Observatory two optical optical lattice clocks are now in operation, one based on Sr and the other Hg. The Sr experiment is more mature with 10 years of development, while the Hg project commenced in 2006. The Hg experiment is particularly demanding because all the required wavelengths lie in the ultraviolet (laser cooling, clock transition probing and lattice trapping). The frequency of the 199Hg clock transition has recently been measured to be 1 128 575 290 808 162.0 ±6.4 (systematic) ±0.3 (statistical) Hz (i.e., with fractional uncertainty = 5.7x10‐15). 
This talk will give an overview of today's most accurate atomic clocks as well as aspects of the Hg clock experiment at SYRTE, Paris. 

 Reference: McFerran et al., Phys. Rev. Lett, 108, 183004, 2012

Seminar n°2: Jeux démasqués entre diffraction et résonance: Résonateurs Littrow en guide large sur silicium
11/04/2012
by Henri Benisty
Laboratoire Charles Fabry, Institut d'Optique (Palaiseau), groupe NAPHEL
Salle de Conférence XLIM
Dans l'optique d'aujourd'hui où traitements temporels et fréquentiels sont sans cesse mobilisés, les propriétés de résonateurs particuliers sont d'une grande importance pour les fonctions linéaires et encore plus les fonctions nonlinéaires. Dans ce cadre, nous avons mis au jour des modes "Littrow" à l'aide de guide très larges (~5 μm) en SoI dont seul un bord est périodique, modes qui exploitent de façon combinée diffraction sur la période et résonance comme un Fabry‐Pérot. Cela conduit à un système original [1] qu'on peut caser aussi bien dans le monde des guides que dans celui des cavités, d'une façon complémentaire du "Coupled Resonator Optical Waveguide" (CROW) popularisé par A. Yariv. 
Nous relierons le fonctionnement de ces résonateurs à l'existence de bandes plates dans un modèle très général de croisement de multiplets connu en physique atomique. Enfin, nous présenterons les possibilités d'exploitation en optique nonlinéaire, notamment en lien avec une dispersion originale de ces modes propice aux applications de type génération de peigne. 
Je parlerai aussi des guides couplés avec "symétrie PT" (Une opération de parité échange gains et pertes), lorsqu'un des guides est plasmonique à perte fixe [2], en montrant que l'on peut faire persister un "point exceptionnel", dans la suite d'un travail récemment mené avec l'IEF à Orsay. 

[1]. H. Benisty, N. Piskunov, P. N. Kashkarov, and O. Khayam, "Crossing of manifolds leads to flat dispersion: Blazed Littrow waveguides," Phys. Rev. A 84, 063825 (2011). 
[2]. H. Benisty, A. Degiron, A. Lupu, A. De Lustrac, S. Chénais, S. Forget, M. Besbes, G. Barbillon, A. Bruyant, S. Blaize, and G. Lérondel, "Implementation of PT symmetric devices using plasmonics: principle and applications," Optics Express 19, 18004‐18019 (2011).

Seminar n°1: Novel laser sources for flow cytometry: Excitation across the entire visible spectrum
13/12/2011
by William G. Telford
National Cancer Institute National Institutes of Health Bethesda campus, USA
Salle de Conférence XLIM
In the last ten years we have seen dramatic improvements in the data collection and analysis capabilities of flow cytometry, a critical technique in the life sciences. Multilaser instruments are now the norm, with at least three lasers often being the minimum for comprehensive analysis. Simultaneous analysis of eight or more fluorescent parameters is now routine. The variety of fluorescent probes available for multicolor labeling has greatly expanded, and the software allowing analysis of high‐dimensional cytometry data is increasing in capability and complexity. Imaging has become a component of our cytometric analysis, opening up whole new avenues for individual cell analysis. 
So where do we go from here? Laser technology is now available that makes our excitation capabilities essentially limitless. We will discuss developments in both laser and detector technology that should continue to increase both the number of parameters we can analyze, and expand the flexibility of our instruments to excite and detect the ever‐expanding palette of fluorescent probes available to life scientists. We will also look at potential cytometry technologies that go beyond the visible spectrum, and take advantage of molecular technologies move beyond optical techniques completely.