Search results for "FEMTOSECOND"
showing 10 items of 238 documents
Absolute frequency and isotope shift measurements of mercury 1S0–3P1 transition
2019
We report the measurement of the absolute frequencies of the 6s2 1S0−6s6p 3P1 transition (253.7 nm) and the relevant isotope shifts in five mercury isotopes 198Hg, 199Hg, 200Hg, 202Hg, and 204Hg. The Doppler-free saturated absorption measurements were performed in an atomic vapour cell at room temperature with a four-harmonic generated (FHG) continuous-wave (cw) laser digitally locked to the atomic transition. It was referenced with a femtosecond optical frequency comb synchronized to the frequency of local representation of the International Atomic Time to provide traceability to the SI second by the 330 km-long stabilized fibre optical link. The transition frequencies and isotope shi…
Mid-infrared supercontinuum generation in suspended-core Chalcogenide and Tellurite optical fibers
2013
We report the experimental generation of mid-infrared supercontinuum in tellurite and chalcogenide suspended-core fibers pumped close to their zero-dispersion in femtosecond regime. The resulting supercontinua extend until 2.8µm in tellurite and 3.2µm in chalcogenide fibers.
Grating-assisted third-harmonic generation in photonic crystal fibers using a pulse pump
2011
We demonstrate that quasi-phase-matching of the third-harmonic generation process can be obtained for a pulse pump in the photonic crystal fiber with a refractive-index grating. Conversion efficiency is calculated numerically using a system of coupled generalized nonlinear Schrodinger equations. We propose a special design of the microstructured fiber for the third-harmonic generation and analyze different phenomena limiting the maximum efficiency for short (femtosecond) and long (picosecond) pump pulses. Moreover, we show that a certain level of a group-velocity mismatch between the pump and the third harmonic can increase the maximum efficiency in the long pulse regime.
Radiation Vulnerability of Fiber Bragg Gratings in Harsh Environments
2015
International audience; The difficulties encountered in the implementation of a temperature or strain sensor based on fiber Bragg grating (FBG) in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femtosecond laser. The radiation response of these gratings was also studied under radiation at dose up to 1 MGy. The comparison between Ge-free and Ge-doped fibers was highlighted.
Dual Luminescence, Interligand Decay, and Nonradiative Electronic Relaxation of Cyclometalated Iridium Complexes in Solution
2016
Femtosecond broadband photoluminescence studies are presented for Ir(ppy)3 (Ir1), Ir(ppy)2(pic) (Ir2), Ir(ppy)2(bpy)(PF6) (Ir3), Ir(ppz)3 (Ir4), and Ir(ppz)2dipy (Ir5) (where ppy = 2-phenylpyridine, pic = picolinate, bpy = 2,2′-bipyridine, ppz = 1-phenylpyrazole, and dipy = 5-phenyldipyrrinato) in solution. Upon 400-nm excitation of Ir1–Ir3, we observed a prompt population of the lowest MLCT states. The higher states decay on an ultrafast time scale (3MLCT state undergoes further vibrational relaxation on a 1-ps time scale. In Ir3, this relaxation is accompanied by an interligand decay from the ppy to the bpy ligand in ∼1.5 ps. For the ppy-containing complexes (Ir1 and Ir2), we found that, …
Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response
2018
Carbon dots (CDs) are an emerging family of nanosystems displaying a range of fascinating properties. Broadly speaking, they can be described as small, surface-functionalized carbonaceous nanoparticles characterized by an intense and tunable fluorescence, a marked sensitivity to the environment and a range of interesting photochemical properties. CDs are currently the subject of very intense research, motivated by their possible applications in many fields, including bioimaging, solar energy harvesting, nanosensing, light-emitting devices and photocatalyis. This review covers the latest advancements in the field of CDs, with a focus on the fundamental understanding of their key photophysica…
Laser wavelength effects on the refractive index change of waveguides written by femtosecond pulses in silica glasses
2018
We investigate the influence of two fs-laser wavelengths (343 and 800 nm) on the induced refractive index change (Δn) of waveguides written in silica materials. Results show that Δn is higher for waveguides photo-inscribed with UV photons.
Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds
2008
We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank-Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrat…
Polarization shaping for unidirectional rotational motion of molecules.
2015
Control of the orientation of the angular momentum of linear molecules is demonstrated by means of laser polarization shaping. For this purpose, we combine two orthogonally polarized and partially time-overlapped femtosecond laser pulses so as to produce a spinning linear polarization which in turn induces unidirectional rotation of N2 molecules. The evolution of the rotational response is probed by a third laser beam that can be either linearly or circularly polarized. The physical observable is the frequency shift imparted to the probe beam as a manifestation of the angular Doppler effect. Our experimental results are confirmed by theoretical computations, which allow one to gain a deep p…
Field-free molecular alignment for probing collisional relaxation dynamics
2013
International audience; We report the experimental study of field-free molecular alignment in CO2 gas mixtures induced by intense femtosecond laser pulses in the presence of collisional processes. We demonstrate that the alignment signals exhibit specific features due to nontrivial collisional propensity rules that tend to preserve the orientation of the rotational angular momentum of the molecules. The analysis is performed with a quantum approach based on the modeling of rotational J- and M-dependent state-to-state transfer rates. The present work paves the way for strong-field spectroscopy of collisional dynamics.