Search results for "EMT"
showing 10 items of 413 documents
Parallel laser micromachining based on diffractive optical elements with dispersion compensated femtosecond pulses
2013
We experimentally demonstrate multi-beam high spatial resolution laser micromachining with femtosecond pulses. The effects of chromatic aberrations as well as pulse stretching on the material processed due to diffraction were significantly mitigated by using a suited dispersion compensated module (DCM). This permits to increase the area of processing in a factor 3 in comparison with a conventional setup. Specifically, 52 blind holes have been drilled simultaneously onto a stainless steel sample with a 30 fs laser pulse in a parallel processing configuration.
New photonic devices for ultrafast pulse processing operating on the basis of the diffraction-dispersion analogy
2008
The space-time analogy is a well-known topic within wave optics that brings together some results from beam diffraction and pulse dispersion. On the above basis, and taking as starting point some classical concepts in Optics, several photonic devices have been proposed during the last few years with application in rapidly evolving fields such as ultrafast (femtosecond) optics or RF and microwave signal processing. In this contribution, we briefly review the above ideas with particular emphasis in the generation of trains of ultrafast pulses from periodic modulation of the phase of a CW laser source. This is the temporal analogue of Fresnel diffraction by a pure phase grating. Finally, we ex…
Cooperative atomic motion probed by ultrafast transmission electron diffraction
2015
In numerous solids exhibiting broken symmetry ground states, changes in electronic (spin) structure are accompanied by structural changes. Femtosecond time-resolved techniques recently contributed many important insights into the origin of their ground states by tracking dynamics of the electronic subsystem with femtosecond light pulses. Moreover, several studies of structural dynamics in systems with periodic lattice modulation (PLD) were performed. Since intensities of the super-lattice diffraction peaks are in the first approximation proportional to the square of the PLD amplitude, their temporal dynamics provides access to cooperative atomic motion. This process takes place on a fractio…
Optical control of vibrational coherence triggered by an ultrafast phase transition
2019
Femtosecond time-resolved x-ray diffraction is employed to study the dynamics of the periodic lattice distortion (PLD) associated with the charge-density-wave (CDW) in K0.3MoO3. Using a multi-pulse scheme we show the ability to extend the lifetime of coherent oscillations of the PLD about the undistorted structure through re-excitation of the electronic states. This suggests that it is possible to enter a regime where the symmetry of the potential energy landscape corresponds to the high symmetry phase but the scattering pathways that lead to the damping of coherent dynamics are still controllable by altering the electronic state population. The demonstrated control over the coherence time …
Dispersion Compensation in Holograms Reconstructed by Femtosecond Light Pulses
2014
This chapter describes how the spatiotemporal dispersion associated with the diffraction of broadband femtosecond light pulses through computer generated holograms (CGHs) can be compensated to a first order with a properly designed dispersion compensation module (DCM). The angular dispersion of the beam associated to CGHs leads to both spatial and temporal distortion of the pulse. Some experiments in one-shot second harmonic generation, wide-field two-photon microscopy, and parallel micromachining are shown to study the quality of the compensation performed with the DCM.
Assessing the risk to health care staff from long-term exposure to anticancer drugs--the case of monoclonal antibodies.
2010
Today the occupational health and safety risk involved when handling most anticancer drugs is well recognized and, as a result of regulatory requirements, safety measures have been established. There is little knowledge about the occupational hazard posed by handling monoclonal antibodies assigned to ATC Class L01XC. The aim of our study was to evaluate the occupational risk of monoclonal antibodies. Using the information obtained in a systematic review of the literature, the potentially dangerous properties of the active drug substances were assessed using a specially devised algorithm. As a result, all monoclonal antibodies in question were categorized as substances with developmental to…
Lesion load may predict long-term cognitive dysfunction in multiple sclerosis patients
2015
Background: Magnetic Resonance Imaging (MRI) techniques provided evidences into the understanding of cognitive impairment (CIm) in Multiple Sclerosis (MS). Objectives: To investigate the role of white matter (WM) and gray matter (GM) in predicting long-term CIm in a cohort of MS patients. Methods: 303 out of 597 patients participating in a previous multicenter clinical-MRI study were enrolled (49.4% were lost at follow-up). The following MRI parameters, expressed as fraction (f) of intracranial volume, were evaluated: cerebrospinal fluid (CSF-f), WM-f, GM-f and abnormal WM (AWM-f), a measure of lesion load. Nine years later, cognitive status was assessed in 241 patients using the Symbol Dig…
Dynamique induite par champ laser femtoseconde intense : alignement moléculaire en milieu gazeux dense et effet Kerr
2011
This thesis is devoted to the study of dynamics induced by intense femtoseconds lasers pulses. The first studied dynamics deals with molecular alignment of CO2-X mixtures (X=CO2, Ar, N2), in dense gases (up to 20 bar). Up to now, this regime has never been studied experimentally. In the field-free regime (after laser/matter interaction), molecular alignment exhibits two components : a permanent alignment and a transient one. The influence of collisions appears through population transfers between rotational states, which leads to a decrease of these two contributions. Permanent alignment relaxation time is only tied to inelastics collisions whereas transient alignment relaxation time is tie…
Ultrabroadband single-cycle terahertz pulses with peak fields of 300 kV cm-1 from a metallic spintronic emitter
2017
To explore the capabilities of metallic spintronic thin-film stacks as a source of intense and broadband terahertz electromagnetic fields, we excite a W/CoFeB/Pt trilayer on a large-area glass substrate (diameter of 7.5 cm) by a femtosecond laser pulse (energy 5.5 mJ, duration 40 fs, wavelength 800 nm). After focusing, the emitted terahertz pulse is measured to have a duration of 230 fs, a peak field of 300 kV cm$^{-1}$ and an energy of 5 nJ. In particular, the waveform exhibits a gapless spectrum extending from 1 to 10 THz at 10% of amplitude maximum, thereby facilitating nonlinear control over matter in this difficult-to-reach frequency range and on the sub-picosecond time scale.
Photoinduced interfacial electron injection in RuN3–TiO2 thin films: Resolving picosecond timescale injection from the triplet state of the protonate…
2008
Using femtosecond transient absorption spectroscopy we have studied light-induced electron injection from the sensitizer RuN3 and its partly deprotonated tetrabutylamonium salt to nano-structured TiO2 film. Previous studies have suggested significant differences in electron injection dynamics for these dyes and some results have indicated that aggregation of the sensitizer may lead to slow injection. By measuring transient absorption spectra and kinetics of RuN3 and RuN3-TBA in solution and attached to TiO2 film we show that the electron injection dynamics are very similar for the two forms of the dye and that aggregation has only moderate effects on the electron transfer dynamics. (c) 2008…