Sökresultat

PURPOSE:To develop a phantom for validating MRI pulse sequences and data processing methods to quantify microscopic diffusion anisotropy in the human brain.METHODS:Using a liquid crystal consisting of water, detergent, and hydrocarbon, we designed a 0.5-L spherical phantom showing the theoretically highest possible degree of microscopic anisotropy. Data were acquired on the Connectome scanner usin

CONTEXT: Viral/bacterial infection is proposed as a trigger for the autoimmune thyroid diseases (AITD): Graves' disease (GD) and Hashimoto's thyroiditis (HT). Previous studies in European Caucasian AITD subjects found higher birth rates in the autumn/winter, suggesting those born in the autumn/winter experience increased viral/bacterial exposure after birth, impacting upon immune system developmen

We demonstrate theoretically and experimentally a robust method based on sequential filamentation to optimize compression of high-energy pulses in gases. We gain insight into this process by comparing compression dynamics for linear- and circularly-polarized pulses.

Attosecond extreme ultraviolet light pulses have the potential to resolve the ultrafast electron dynamics that govern basic properties of atoms, molecules, and solids. Here we present three different interferometric pump-probe methods aiming to access not only the temporal dynamics, but also state specific phase information after excitation/ionization using attosecond pulses.

2.5 TW laser pulses at 1053 nm are obtained in a compact set-up, from chirped pulses, successively stretched, amplified up to 1.6 J and compressed to 0.6 ps, at a repetition rate of one shot per minute.

We will present the new Lund HHG beamline designed for high photon flux, delivering pulse energies of more than 4 μJ per pulse in the spectral range from 20 eV to 45 eV. Focused XUV intensities above 1014 W/cm2 should become possible.

We investigate the performance of the recently introduced 'd-scan' technique for the characterization of ultrashort laser pulses by comparing it with a well-established technique (SPIDER). Good agreement is obtained from the two different measurements.

We present different approaches for high repetition rate, few-cycle pulse generation with μJ-level energy from compact OPCPA systems. The sources are based on octave spanning Ti:Sa oscillators with all-optical synchronization to state-of-the-art Ytterbium based amplifiers.

The confinement of high-harmonic-generation pulse train by modulation of the fundamental beam polarization is studied temporaly and spectrally. We observe a clear effect, beeing the maximal confinement compatible with 1-or-2 subfemtosecond pulse emission.

A compact, high-repetition rate OPCPA system with CEP-stable 6.3 fs pulses duration and 10 μJ of pulse energy is presented together with results from numerical simulations. First results of high harmonic generation will be shown.

We demonstrate a dispersion-free split mirror interferometric autocorrelator suitable for measuring pulses with durations from hundreds of attoseconds to tens of femtoseconds and spectral content from the near-UV to near-IR.

We present experimental measurements and theoretical calculations of single and double ionization time delays in various noble gases using an interferometric method. The measured delays allow us to extract information on the electron correlation.

We study the temporal and spectral behaviour of high order harmonics generated by pulses with temporally modulated polarization. We observe a harmonic temporal confinement and a harmonic spectral broadening, compatible with 1 -or-2 attosecond pulse emission.

We employ a pump-probe approach to molecular photoionization to study fast dissociation of Rydberg states in acetylene. By using time-resolved photoelectron spectroscopy to study the electronic state of the resulting ions we are able to monitor the system continuously during dissociation or rearrangement. We find that the predissociative lifetime for the 3R‴ (v′2 = 1) Rydberg state is about 150 fs

We present a 200 kHz XUV source driven by an optical parametric chirped pulse amplification system. The advantage for photoemission electron microscopy of this high-repetition rate will be discussed.

We perform interferometric attosecond timing measurements to study XUV photoionization in noble gases, to diagnose macroscopic phase-matching conditions in high-order harmonic generation, and to investigate single-photon double-ionization by detecting electron pairs in coincidence.

We present two interferometry schemes in the extreme ultraviolet, based on either the wave-front division of a unique harmonic beam (1st scheme) or two spatially separated, phase-locked harmonic sources (2nd scheme). In the first scheme using a Fresnel bimirror interferometer, we measure the degree of spatial coherence of the 13 th harmonic generated in xenon, as a function of different parameters