Carl Liebig

Université Jean Monnet, Saint-Étienne, Rhône-Alpes, France

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Publications (6)18.89 Total impact

  • Carl M. Liebig, E. Audouard, J. Solis, Razvan Stoian
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    ABSTRACT: The use of ultrafast laser pulses to initiate solid-state phase-transitions in certain materials has shown promise in achieving sub-nanosecond phase changes with different optical properties. These phase changes have been well studied using pulse durations between femtoseconds and nanoseconds to determine the dynamics for the reversible phase changes on multiple time scales. In this study femtosecond pulse shaping techniques, driven by evolutionary algorithms, were used to obtain optimized temporally shaped ultrashort laser pulses to induce and control permanent phase changes in GeSb thin-films. Through monitoring the pulse effects it has been determined that the crystalline-to-amorphous phase transition is minimized using optical pulses with pulse widths less than the electron–phonon coupling time. It is maximized by using pulses longer than the time required for energy transfer from the excited carriers to the lattice.
    Optical Materials 06/2011; 33(8):1210–1214. · 1.92 Impact Factor
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    Carl M Liebig, Yaguo Wang, Xianfan Xu
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    ABSTRACT: For semimetals such as bismuth, ultrafast femtosecond laser-excited coherent phonons at laser fluences below the damage threshold have been studied extensively. In this work, we investigate whether or not coherent phonon oscillations contribute to material's permanent damage, or can enhance or suppress such damage. We employed temporally-shaped femtosecond pulses to either enhance or cancel coherent phonon oscillations. Our results showed a clear difference in material's damages caused by femtosecond pulses that enhance and cancel phonon oscillations, demonstrating the possibility of controlling phase changes by coherent control of phonon oscillations.
    Optics Express 09/2010; 18(19):20498-504. · 3.55 Impact Factor
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    ABSTRACT: Using automated laser pulse temporal shaping we report on enhancing spectral emission characteristics of ablation plasmas produced by laser irradiation of brass on ultrafast time scales. For different input irradiance levels, control of both atomic and ionic species becomes possible concerning the yield and the excitation state. The improved energy coupling determined by tailored pulses induces material ejection with lower mechanical load that translates into hot gas-phase regions with higher excitation degrees and reduced particulates.
    Optics Express 05/2010; 18(11):11159-72. · 3.55 Impact Factor
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    ABSTRACT: Ultrafast time-resolved measurements were conducted to investigate long-wavelength acoustic phonon scattering and velocity reduction in Bi2Te3/Sb2Te3 superlattices. We show that both these phenomena suppress heat transfer process, with the phonon scattering contributing more in differentiating the lattice thermal conductivities among films with different periods. Measurements of reduction in the acoustic phonon amplitudes support the decrease in the thermal conductivity for certain superlattice periods, which is not predicted by acoustic mismatch theory. This study is a direct measurement of coherent acoustic phonons in superlattices which is of significant interest to thermoelectrics.
    Applied Physics Letters 01/2010; · 3.79 Impact Factor
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    ABSTRACT: The influence of temporal pulse shaping on plasma plume generated by ultrafast laser irradiation of aluminum is investigated. Time resolved plasma emission spectroscopy is coupled with a temporal shaping procedure in a closed loop. The ionic emission is enhanced relative to the neutral one via an adaptive optimization strategy. The plasma emission efficiency in case of optimized and ultrashort temporal shapes of the laser pulses are compared, evidencing an enhancement of the ionization degree of the plasma plume. Simplified temporal shapes of the femtosecond laser pulses are extracted from the optimized shape and their corresponding effect on laser induced plasma emission is discussed.
    Applied Surface Science 01/2009; 255(255):5163–5166. · 2.54 Impact Factor
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    ABSTRACT: A resonant waveguide grating based on a high reflectivity mirror causes a 2pi phaseshift of adjustable slope in the spectrum of an ultrashort light pulse, giving rise to a controllable, lossless temporal pulse splitting. This monolithic phase shifter can simply be placed on the path of the beam as a mirror. A functional element was designed and fabricated. Temporal splitting of a femtosecond laser pulse is experimentally demonstrated. The possibility of obtaining variable delay between subpulses is theoretically discussed.
    Optics Express 11/2008; 16(21):17119-30. · 3.55 Impact Factor