Search results for "Femtosecond Laser"
showing 10 items of 14 documents
Shaping of a ground state rotational wavepacket by frequency-chirped pulses
2001
0953-4075; A coherent rotational superposition state is produced in the ground vibronic level of N2 through the interaction of the molecule with the electric field vector of a nonresonant laser pulse. This rotational wavepacket is shaped with a linear frequency chirp of the laser field. The structural shape of the rotational coherences shows a strong dependence with the frequency-chirp amplitude. A comparison with a theoretical model allows the interpretation of the observed effects in terms of dephasing of the wavepacket induced by the laser phase distortion. Application of the presented results to the phase characterization of short XUV pulses is suggested.
Application of time-resolved spectroscopy to concentration measurements in gas mixtures
2001
1296-2147; Concentration measurements using femtosecond Raman Induced Polarization Spectroscopy (RIPS) are performed in binary gas mixtures CO2-N2 and CO2-N2O at room temperature. The principle of these measurements is based on the nonlinear rotational time response of each molecular component of the mixture, The general form of this molecular response is a series of periodic transients with a period related to the rotational constant Be The relative strength of the individual responses allows an accurate determination of the concentration. Two techniques are presented using either two pulses (one pump and one probe) or three pulses (two pumps and one probe). (C) 2001 Academie des sciences/…
Multiphoton process investigation in silica by UV femtosecond laser
2022
We investigated the interaction processes between high intensity femtosecond ultraviolet laser pulses and amorphous silica, leading to permanent refractive-index changes that are at the basis of advanced manufacturing for photonics devices. The experiment, carried out as a function of the laser power, improves our understanding on the strong-field ionization process by the monitoring of the 1.9 eV and 2.65 eV emissions, related to nonbridging oxygen hole centers and self-trapped exciton, respectively, induced in the exposed glass region. Our results clearly proved that the UV laser light band-to-band absorption is allowed in the multiphoton ionization limit, whose consecutive relaxation lea…
Ultrafast ionization and rotational dynamics of molecules in strong laser fields
2021
The investigation of ultrafast molecular dynamics is of great importance towards the understanding of a variety of natural phenomena in physical and chemical sciences. With the rapid development of femtosecond laser systems and precision detection technologies, it is possible now to visualize and steer the motion of molecules in matter as well as the ultrafast dynamics of electrons and nuclei in molecules on a microscopic timescale. When a molecule is exposed to a strong laser field, its electrons can be freed or excited, which often triggers a rapid dissociation of the system, in which the released electrons and nuclei exhibit a strong correlation, while the electronic motion on attosecond…
High rate concentration measurement of molecular gas mixtures using a spatial detection technique
2010
International audience; Concentration measurement in molecular gas mixtures using a snapshot spatial imaging technique is reported. The approach consists of measuring the birefringence of the molecular sample when field-free alignment takes place, each molecular component producing a signal with an amplitude depending on the molecular density. The concentration measurement is obtained on a single-shot basis by probing the time-varying birefringence through femtosecond time-resolved optical polarigraphy (FTOP). The relevance of the method is assessed in air.
Cell and tissue response to nanotextured Ti6Al4V and Zr implants using high-speed femtosecond laser-induced periodic surface structures
2019
In this paper, the effect of femtosecond laser nanotexturing of surfaces of Ti6Al4V and Zr implants on their biological compatibility is presented and discussed. Highly regular and homogeneous nanostructures with sub-micrometer period were imprinted on implant surfaces. Surfaces were morphologically and chemically investigated by SEM and XPS. HDFa cell lines were used for toxicity and cell viability tests, and subcutaneous implantation was applied to characterize tissue response. HDFa proliferation and in vivo experiments evidenced the strong influence of the surface topography compared to the effect of the surface elemental composition (metal or alloy). The effect of protein adsorption fro…
Photoluminescence of Point Defects in Silicon Dioxide by Femtosecond Laser Exposure
2021
The nature of the radiation-induced point defects in amorphous silica is investigated through online photoluminescence (PL) under high intensity ultrashort laser pulses. Using 1030 nm femtosecond laser pulses with a repetition rate of 1 kHz, it is possible to study the induced color centers through their PL signatures monitored during the laser exposure. Their generation is driven by the nonlinear absorption of the light related to the high pulse peak powers provided by femtosecond laser, allowing to probe the optical properties of the laser exposed region. The experiment is conducted as a function of the laser pulse power in samples with different OH contents. The results highlight the dif…
Wavelength tuning of femtosecond pulses generated in nonlinear crystals by using diffractive lenses
2010
We demonstrate that diffractive lenses (DLs) can be used as a simple method to tune the central wavelength of femtosecond pulses generated from second-order nonlinear optical processes in birefringent crystals. The wavelength tunability is achieved by changing the relative distance between the nonlinear crystal and the DL, which acts in a focusing configuration. Besides the many practical applications of the so-generated pulses, the proposed method might be extended to other wavelength ranges by demonstrated similar effects on other nonlinear processes, such as high-order harmonic generation.
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.
Femtosecond Raman time-resolved molecular spectroscopy
2004
International audience; The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In additi…