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Titanium-doped sapphire (Ti:Al 2 O 3 ) is a gain medium with a very broad emission bandwidth allowing the generation and amplification of very short pulses (<

Photonic time-stretch enables to record electric field pulse shapes with picosecond resolution, at megahertz acquisition rates. Using this strategy, we could record the complex spatiotemporal evolution of relativistic electron bunches circulating in storage ring accelerators. We tested two complementary approaches. At SOLEIL, we monitored the THz pulses of coherent synchrotron that are emitted by the electrons. At ANKA, we monitored directly the electron bunch near-field.

In this paper, we present a diode-pumped multipass amplifier based on Yb:CaF2 using passive coherent combining in order to access the 100 mJ range without optical damage.

Summary form only given. A crucial issue in the field of high power lasers is the management of thermal effects, leading to mechanical distortions, thermal lenses and optical losses of the laser crystal. A suitable candidate for such application should combine a weak quantum defect and good thermo-mechanical properties in order to limit the heat production in the laser material. In this context, Yb3+:CaGdAlO4 is a promising new laser material with a very high thermal conductivity for 2% doped Yb (> 6.5 W K-1m-1) allowing high-power diode pumping. Decreasing the thermal load in high power laser materials could also be achieved by developing new laser architectures such as thin disk, slabs or fibers. Those devices were recently tested with some promising results.

Summary form only given. Thin-disk laser (TDL) technology has a crucial interest for high-power ultrafast laser oscillators. The thermal control of the gain medium allows the generation of high average power and high energy fs pulses directly out of an oscillator. From the past few years, some research efforts have focused on reducing the pulse duration using this technology [1]. In this point of view, we are presenting here the first femtosecond thin-disk oscillator using a very promising crystal, Yb:CALGO. This material combines atypical advantageous spectroscopic and thermal properties for an Yb-doped one. Moreover it has already demonstrated interesting results in bulk configuration with sub-50-fs pulses at low power and sub-100 fs with 12 W. These results motivated its use in the TDL configuration and the demonstration of high-power fs TDL using Yb:CALGO is shown with the production 28 W, 1.3 μJ, 300 fs pulses and 20 W, 0.9 μJ, 197 fs pulses.The femtosecond experiment was performed with a 2%-doped, 350-μm-thick, Yb:CALGO crystal. The setup is presented in fig. 1. The crystal diameter is 6 mm, and it is cut for the laser beam to propagate along the σ-axis, with access to both σ- and π-polarization. The pump diode delivers up to 230 W. The pump spot diameter on the disk is 2.9 mm and the laser beam waist diameter is 2.1mm. When the crystal is glued on a copper heat sink, one can observe a deleterious thermal astigmatism occurring for pump power around 130 W. In order to overcome this problem the crystal was glued on a diamond mount (fig. 1). In this case, in a multimode configuration we obtained up to 86 W in cw regime, corresponding to an optical-to-optical efficiency of 37.5 %. The cavity is optimized to operate in spatially single mode operation (fig. 1), with M2

Transport in low dimensional Hamiltonian chaos can be anomalous due to stickiness and rise of Levy flights. We suggest a signal processing method to detect these flights in signals, in order to characterize the nature of transport (diffusive or anomalous). We use time-frequency techniques such as Fractional Fourier transform and matching pursuit in order to be robust to noise. The method is tested on data obtained from chaotic advection.

Industrial applications of ultrafast lasers, notably in the field of precision micro-machining, are rapidly increasing. The quality and flexibility of the interaction process are well established. However, in order to fulfil the productivity requirement of industrial processes, it is necessary to continuously increase the average power of ultrafast lasers.

The thin-disk laser design [1] allows the generation and the amplification of ultrashort pulses with very high efficiency, high output power and good beam quality [2]. Many interesting results were published using Yb:YAG crystal, leading to the generation of high power pulses up to 80 W [3] with a pulse duration around 1ps. Nevertheless, the emission cross section of Yb:YAG limits the generation of very short pulses, which explains the need of other materials. This is why investigating new thin-disk materials is an interesting point of view in order to generate shorter pulses with high average power.

Since its first laser operation in 2004 [1], Yb:CaF 2 has been one of the most studied and promising crystals in the realm of Yb-doped materials for DPSSL applications [2,3]. In fact, this crystal gathers several interesting advantages for the development of high-power diode-pumped lasers, among which an excellent thermal conductivity of 9.3 W/m/K[4], comparable to YAG, a broad emission band, extending from about 1010 and 1070 nm and a long emission lifetime of 2.3 ms. And, the last but not the least advantage over its competitors concerns the fact that the crystal growth of pure CaF 2 is already well mastered and that ultra-high-quality and very large crystals of Yb:CaF 2 could be produced in the near future.

We present a new compact ground-based microwave radiometer dedicated to the study of middle atmospheric water vapor. The instrument detects the 616- 523 H2O transition line at 22.235 GHz. This radiometer has been designed to be easily transported and operated during measurement campaigns in remote places. The first retrievals, performed with the MOLIERE inversion and radiative transfer software, show good agreement with MIAWARA, the 22 GHz Radiometer developed at the University of Bern, Switzerland, and the Microwave Limb Sounder instrument onboard the Aura satellite.

The engagement of a methodology that makes an experimental link between the deliberative mechanism itself and a heuristic initiative which examines the contexts of the production of the discourse allows us to deepen our understanding of the logic used by citizens in constructing their opinions. The study of different tools both on and offline can help us to produce operational models that permit both the free expression of citizens' views and the analysis of the contexts of the production of the discourse. It is important to note that these models are not in their finished state. Their innovative use as experiments in a heuristic systematic and constructivist dynamic will lead to the establishment offully effective deliberative electronic tools.

In order to overcome the shortage of silicon feedstock that is currently affecting the photovoltaic industry, many efforts are being dedicated to the search of alternative substrates for solar cells. One of the possible solutions is to use low-cost substrates of upgraded metallurgical silicon, for which there are no supply issues. The solar cell is built on a thin layer of high quality silicon which is epitaxially grown over this substrate, with the use of a high throughput epitaxial reactor of novel design. This reactor can be fed with electronic grade source gases or with gases obtained in situ from metallurgical silicon. A reactor prototype has been constructed with a capacity of 50 wafers per run and a deposition velocity of approximately 2 microns per minute. The production of chlorosilanes by Si etching and the recirculation of gases for maximum efficiency are being studied. A solar cell process specific for these substrates has been developed, achieving an efficiency of 12,8%. Further improvements on the solar cell process are under investigation, with special emphasis on light trapping by plasma texturing and the application of a porous Si layer as internal reflector. A preliminary market study has been performed to understand the role of silicon feedstock in the current photovoltaic market and its projection in the next decades, looking at the expected role of epitaxial solar cells.

The SPIRaL project makes use of the very high intensity ion beams soon available at GANIL (over 10/sup 13/ pps at 95 MeV/u from He to Ar) to produce radioactive nuclei by the ISOL method. The facility will consist of a production target situated close to an ECRIS specially designed for this purpose, a very low energy beam line, a k=265 compact cyclotron as postaccelerator (2 to 20 MeV/u according to the Q/A factor), a medium energy beam line transferring the radioactive beams into the existing experimental looms through the /spl alpha/ spectrometer. The whole facility will be installed at the end of the existing machine. >

This study relates to the performance tests of a 66% efficient hybrid solar module "Capthel", and to the economic study of the combined generation of solar electricity and hot air ("Ecothel" solar cogeneration). The authors demonstrate that a-Si:H PV modules are best suited for cogeneration because they behave as if they had a positive temperature coefficient. They report experimental results on the first prototype and describe further improvements in the design of the thermal collector. They then study the potential savings and return on investment of an "Ecothel" installation connected to the grid of a private home using electric space heating like most of the modern houses in France and a commercial building with air conditioning.

Measurements of stratospheric ozone are made with a microwave radiometer tuned to the 110.836 GHz ozone line using the beam-switching observing technique proposed by Parrish et al. (1988). The line-of-sight of the instrument is alternately directed towards a low elevation direction and towards the zenith used as reference. The balance between signals obtained in both directions is realized by putting an absorber in the reference direction. The forward model taking into account the observing method produces modelled spectra that agree within 5% with measured ones. The analysis uses the Backus-Gilbert method to retrieve vertical ozone profiles within the altitude range 25 to 75 km with a vertical resolution of 6 km and the sequential optimal estimation proposed by Rodgers is then used to quantify various errors. Retrieved amounts are analyzed in order to estimate the diurnal and seasonal variations of ozone at different altitudes. >

A ground-based microwave receiver tuned to the 278 GHz hyperfine lines of chlorine monoxide has been operating at the Plateau de Bure in the French Alps (44.6/spl deg/N, 5.6/spl deg/E, 2550 metres high) since October 1992. This radiometer is part of the international Network for the Detection of Stratospheric Change and its aim is to monitor mid-latitude ClO on a regular temporal basis. The device is similar to the one operational in Mauna Kea, Hawai. Theoretical contributions of O/sub 3/, ClO and NO/sub 2/ and their associated diurnal variabilities are included in the radiative transfer calculation around 278.6 GHz. Sensitivity tests related to ClO activation in the lower stratosphere are also performed. Evidence suggests that spectra recorded from December 1993 do not show ClO activated by more than 0.5 ppbv in the lower stratosphere over Bure. >

The prevalence of signals on weighted graphs is increasing; however, because of the irregular structure of weighted graphs, classical signal processing techniques cannot be directly applied to signals on graphs. In this paper, we define generalized translation and modulation operators for signals on graphs, and use these operators to adapt the classical windowed Fourier transform to the graph setting, enabling vertex-frequency analysis. When we apply this transform to a signal with frequency components that vary along a path graph, the resulting spectrogram matches our intuition from classical discrete-time signal processing. Yet, our construction is fully generalized and can be applied to analyze signals on any undirected, connected, weighted graph.

International audience; This article deals with the use of optimal lattice and optimal window in Discrete Gabor Transform computation. In the case of a generalized Gaussian window, extending earlier contributions, we introduce an additional local window adaptation technique for non-stationary signals. We illustrate our approach and the earlier one by addressing three time-frequency analysis problems to show the improvements achieved by the use of optimal lattice and window: close frequencies distinction, frequency estimation and SNR estimation. The results are presented, when possible, with real world audio signals.

Mining useful clusters from high dimensional data has received sig- nificant attention of the signal processing and machine learning com- munity in the recent years. Linear and non-linear dimensionality reduction has played an important role to overcome the curse of di- mensionality. However, often such methods are accompanied with problems such as high computational complexity (usually associated with the nuclear norm minimization), non-convexity (for matrix fac- torization methods) or susceptibility to gross corruptions in the data. In this paper we propose a convex, robust, scalable and efficient Prin- cipal Component Analysis (PCA) based method to approximate the low-rank representation of high dimensional datasets via a two-way graph regularization scheme. Compared to the exact recovery meth- ods, our method is approximate, in that it enforces a piecewise con- stant assumption on the samples using a graph total variation and a piecewise smoothness assumption on the features using a graph Tikhonov regularization. Futhermore, it retrieves the low-rank rep- resentation in a time that is linear in the number of data samples. Clustering experiments on 3 benchmark datasets with different types of corruptions show that our proposed model outperforms 7 state-of- the-art dimensionality reduction models.