Sending femtosecond pulses in circles: highly non-paraxial accelerating beams

We use caustic beam shaping on 100 fs pulses to experimentally generate non-paraxial accelerating beams along a 60 degree circular arc, moving laterally by 14 \mum over a 28 \mum propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of non-paraxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic

The NA48 event-building PC farm

The NA48 experiment at the CERN SPS aims to measure the parameter $\Re(\epsilon'/ \epsilon)$ of direct CP violation in the neutral kaon system with an accuracy of $2 \times 10^{-4}$. Based on the requirements of: \\\\ * high event rates (up to 10 kHz) with negligible dead time;\\ * support for a variety of detectors with very wide variation in the number of readout channels;\\ * data rates of up to 150 MByte/s sustained over the beam burst;\\ * level-3 filtering and remote data logging in the CERN computer center; \\\\ the collaboration has designed and built a modular pipelined data flow system with 40 MHz sampling rate. The architecture combines custom-designed components with commercially available hardware for cost effectiveness and flexibility. To increase the available data bandwidth and to add filtering and monitoring capabilities, the original custom-built event builder hardware has been replaced by a farm of 24 Intel PentiumII based PCs running the Linux operating system during the shutdown between the 1997 and 1998 data taking periods. During the data taking period 1998 the system has been successfully operated taking ca. 70 Terabyte of data

A Statistical Analysis of STEVE

There has been an exciting recent development in auroral research associated with the discovery of a new subauroral phenomenon called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is as yet an unidentified upper atmosphere phenomenon. Observed first by amateur auroral photographers, STEVE appears as a narrow luminous structure across the night sky over thousands of kilometers in the east‐west direction. In this paper, we present the first statistical analysis of the properties of 28 STEVE events identified using Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imager and the Redline Emission Geospace Observatory (REGO) database. We find that STEVE occurs about 1 hr after substorm onset at the end of a prolonged expansion phase. On average, the AL index magnitude is larger and the expansion phase has a longer duration for STEVE events compared to subauroral ion drifts or substorms. The average duration for STEVE is about 1 hr, and its latitudinal width is ~20 km, which corresponds to ~¼ of the width of narrow auroral structures like streamers. STEVE typically has an equatorward displacement from its initial location of about 50 km and a longitudinal extent of 2,145 km

Real-time full bandwidth measurement of spectral noise in supercontinuum generation

The ability to measure real-time fluctuations of ultrashort pulses propagating in optical fiber has provided significant insights into fundamental dynamical effects such as modulation instability and the formation of frequency-shifting rogue wave solitons. We report here a detailed study of real-time fluctuations across the full bandwidth of a fiber supercontinuum which directly reveals the significant variation in measured noise statistics across the spectrum, and which allows us to study correlations between widely separated spectral components. For two different propagation distances corresponding to the onset phase of spectral broadening and the fully-developed supercontinuum, we measure real time noise across the supercontinuum bandwidth, and we quantify the supercontinuum noise using statistical higher-order moments and a frequency-dependent intensity correlation map. We identify correlated spectral regions within the supercontinuum associated with simultaneous sideband generation, as well as signatures of pump depletion and soliton-like pump dynamics. Experimental results are in excellent agreement with simulations

Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

Nightside auroral zone localized flow channels, typically associated with auroral poleward boundary intensifications and streamers, are an important component of high‐latitude ionospheric plasma dynamics. We investigate the structure of these flow channels using two‐dimensional line‐of‐sight flow observations from the Super Dual Auroral Radar Network (SuperDARN) radars and auroral images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground‐based all‐sky imager (ASI) array. Radar echoes captured <~500 km horizontal distance from the radars were mainly used to detect small‐scale flow structures that would otherwise be missed or poorly resolved in long‐range radar echoes. After identifying 135 auroral streamers in the ASI images at close‐radar capture locations, we examined the associated ionospheric flow data in the radar echoes. Flow bursts and streamers are invariably correlated in all events. The flow bursts are often directed equatorward and appear simultaneously with the streamers. Equatorward flows are located just to the east of the streamers. Less frequently (~10% of the time), a poleward flow enhancement was detected even when a streamer propagated equatorward, the poleward flow enhancement being located to the west of the auroral streamer, or to the east of the equatorward flow enhancement, consistently with the spatial relationship between flow shear and upward field‐aligned currents in plasma sheet flow bursts. The azimuthal width of the flow channel is, on average, ~75 km, and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is ~57 km eastward. This study demonstrates the capability of radar‐imager pairs for identifying the 2‐D structure of localized flows associated with plasma sheet flow bursts. Key Points Structure of flow channels using SuperDARN radars and THEMIS ASI is investigated Simultaneous flow bursts and streamers are invariably correlated in all events 3‐D structure of flows consistent with plasma flow shears around a BBF channelPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106072/1/jgra50744.pd

Filamentation of high-angle nondiffracting beams and applications to ultrafast laser processing

International audienceWe report on filamentation of nondiffracting beams and show that the intense light-matter interaction regime achieved on long distances allows for an enhanced control on ultrashort laser deep ablation

The NA48 LKr calorimeter digitizer electronics chain

The 13 500 channels of the NA48 liquid-krypton electromagnetic calorimeter readout electronics were put into operation in 1997. The digitizer electronics employs a new gain switching technique that expands the dynamic range of a standard 10-bit ADC to 14 bits at 40 MHz sampling rate employing a custom-developed integrated circuit (KRYPTON). The KRYPTON has been fabricated in 1.2 μm BiCMOS technology and was successfully developed together with industry on a short timescale. The performance and the experience from the first year of the operation of the liquid-krypton calorimeter electronics will also be briefly discussed

A semi-parametric approach to estimate risk functions associated with multi-dimensional exposure profiles: application to smoking and lung cancer

A common characteristic of environmental epidemiology is the multi-dimensional aspect of exposure patterns, frequently reduced to a cumulative exposure for simplicity of analysis. By adopting a flexible Bayesian clustering approach, we explore the risk function linking exposure history to disease. This approach is applied here to study the relationship between different smoking characteristics and lung cancer in the framework of a population based case control study