Search results for "FEMTOSECOND"
showing 10 items of 238 documents
Photoemission time-of-flight spectromicroscopy of Ag nanoparticle films on Si(111)
2004
Abstract Time-of-flight photoemission electron microscopy was used to measure spatially resolved energy distribution curves of electrons emitted from Ag nanoparticle films with different mass thicknesses. Two-photon photoemission (2PPE) was induced by femtosecond laser pulse excitation with 3.1 eV photon energy and 200 fs pulse width. Regions of Ag nanoparticles with different average sizes and one region with a continuous 100 nm thick Ag film were deposited as a stepped wedge on a Si(1 1 1) substrate. Upon laser excitation the nanoparticle films exhibit a very high electron emission yield in the images, whereas the uncovered Si surface and the continuous Ag film are dark. The time-of-fligh…
Multiphoton photoemission electron microscopy using femtosecond laser radiation
2002
Abstract The interaction of intense, pulsed laser radiation with surfaces results in non-linear optical effects that are responsible for emission of electrons even if the photon energies are below the work function. In the present study, photoelectrons have been excited by means of femtosecond laser pulses from a frequency doubled Ti:sapphire laser with a photon energy of 3.1 eV. The spatial distribution of the photo emitted electrons was imaged using a photoemission electron microscope. All samples exhibit centres of enhanced second or higher order photoemission yield, so called ‘hot spots’. These ‘hot spots’ were preferentially excited with s-polarised light. This behaviour may be explain…
Coherent master equation for laser modelocking
2020
Modelocked lasers constitute the fundamental source of optically-coherent ultrashort-pulsed radiation, with huge impact in science and technology. Their modeling largely rests on the master equation (ME) approach introduced in 1975 by Hermann A. Haus. However, that description fails when the medium dynamics is fast and, ultimately, when light-matter quantum coherence is relevant. Here we set a rigorous and general ME framework, the coherent ME (CME), that overcomes both limitations. The CME predicts strong deviations from Haus ME, which we substantiate through an amplitude-modulated semiconductor laser experiment. Accounting for coherent effects, like the Risken-Nummedal-Graham-Haken multim…
The spatial distribution of non-linear effects in multi-photon photoemission from metallic adsorbates on Si(1 1 1)
2001
Multi-photon excitations from thin metallic films on silicon substrates have been observed utilising photoemission electron microscopy. The photoelectrons have been excited by means of high power femtosecond laser pulses with a photon energy below the work function threshold. The strong spatial variations of the non-linear effects became directly visible in electron emission from the adsorbed thin films. Centres of enhanced photoelectron yield, so-called hot spots, were observed on the surfaces of various samples. The multi-photon electron yield of the metallic films (permalloy and lead) depends strongly on the sample topography and the photon polarisation.
Dynamical binary modulation of ultrabroadband light beams by using principal states of polarization of liquid crystal devices
2009
Dynamical modulation of ultrabroadband beams, such as those produced by femtosecond laser or incoherent sources, is not an easy task due to the dispersive nature of the devices commonly employed. Phase modulation has been performed by means of deformable micromirror arrays. These devices are expensive and do not permit amplitude modulation. For micro- and nano-structuring of materials with femtosecond lasers is common to pattern the surface with the light irradiance produced by a computer generated hologram implemented onto a liquid crystal (LC) type spatial light modulator. This enables dynamical patterning [1,2]. Reduced spectral bandwidths, of the order of tens of nanometers, have been u…
Cell and Tissue Response to Modified by Laser-induced Periodic Surface Structures Biocompatible Materials for Dental Implants
2016
The use of femtosecond laser-induced periodic surface structures (LIPSS) for dental implants surface modification for improving cell adhesion and proliferation is reported. Results demonstrated higher response of cells on modified surface compared to untreated ones.
Disclosing the emissive surface traps in green-emitting carbon nanodots
2021
Abstract The bright photoluminescence of surface-functionalized carbon nanoparticles, known as carbon nanodots (CDs), has been studied for more than a decade because of its fundamental photo-physical interest and strong technological potential. However, the essential nature of the electronic states involved in their typical light emission remains very elusive. Here, we provide conclusive evidence that surface carboxylic moieties are the key to CD fluorescence. The synergy of nanosecond and femtosecond optical studies, cryogenic fluorescence, computational investigations and chemical engineering of a strategically chosen model CD system, allows to demonstrate that their visible-light transit…
Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels
2014
International audience; We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230 degrees C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750 degrees C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower t…
A study of electron transfer in Ru(dcbpy)2(NCS)2 sensitized nanocrystalline TiO2 and SnO2 films induced by red-wing excitation.
2008
Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a…
UV photoexcitation of a dissolved metalloid Ge9 cluster compound and its extensive ultrafast response.
2015
Femtosecond pump-probe absorption spectroscopy in tetrahydrofuran solution has been used to investigate the dynamics of a metalloid cluster compound {Ge9[Si(SiMe3)3]3}(-). Upon UV photoexcitation, the transients in the near-infrared spectral region showed signatures reminiscent of excess electrons in THF (bound or quasi-free) whereas in the visible part excited state dynamics of the cluster complex dominates.