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Presentations

    Laser melting of silicon: the first few picoseconds, at Annual Meeting of the Electrochemical Society (Chicago, IL), Saturday, October 1, 1988
    The use of a streak camera makes it possible to improve the study of the melting of silicon during picosecond laser annealing. Its time resolution of 1.8 ps enables us to confirm that the molten silicon is heated above the melting temperature. It also provides spatial information on the melting process.
    Femtosecond measurement of laser-induced phase transformation in GaAs:linear and nonlinear properties, at OSA Annual Meeting (Dallas, TX), Saturday, January 1, 1994
    We measured the dielectric constant and second-harmonic generation in GaAs following femtosecond laser-pulse excitation. From these measurements, we extract the behavior of the second-order optical susceptibility, which monitors crystal symmetry, during a laser-induced phase transformation. This is the first time, to our knowledge, that the effect of large changes in the dielectric constant has been taken into account explicitly in determining the second-order susceptibility.
    Femtosecond measurement of laser-induced phase transformation in GaAs:linear and nonlinear properties, at OSA Annual Meeting (Dallas, TX), Saturday, January 1, 1994
    We measured the dielectric constant and second-harmonic generation in GaAs following femtosecond laser-pulse excitation. From these measurements, we extract the behavior of the second-order optical susceptibility, which monitors crystal symmetry, during a laser-induced phase transformation. This is the first time, to our knowledge, that the effect of large changes in the dielectric constant has been taken into account explicitly in determining the second-order susceptibility.
    Ultrafast broadband spectroscopic studies of GaAs under intense laser excitation, at OSA Annual Meeting 1996 (Rochester, NY), Tuesday, October 1, 1996
    An ultrafast broadband spectroscopic technique (350 to 900 nm) is employed to measure the dielectric function of GaAs in response to a 70-fs laser pulse excitation. We observe drastic changes in the dielectric function within 1ps of the excitation, which we attribute to an ultrafast non-thermal structural transition. These broadband measurements provide extensive information on the initial electronic excitation and the dynamics of the subsequent phase transition.
    Physics in the (ultra)fast lane: femtosecond laser-induced dynamics in solids, at OSA Annual Meeting (Baltimore, MD), Thursday, October 1, 1998
    We developed a broadband ultrafast technique to measure a material's dielectric function (from near-UV to near-IR) with 100-fs time resolution. This technique enables identification of phase changes following intense laser excitation. We will present data for semiconductors and discuss future experiments to study plasma generation dynamics in transparent materials.
    Ultrafast Phase Transition Dynamics in GeSb Films, at Optical Society of America Annual Meeting, Optical Society of America (Providence, RI, USA), Thursday, October 26, 2000:
    talk_363.pdf
    We measure the dielectric function of thin a-GeSb films over a broad energy range (1.5 - 3.5 eV) with a time resolution of 70 fs after the excitation with an ultrashort laser pulse. The results reveal an ultrafast transition to a new non-thermodynamic phase which is not c-GeSb as previously believed.
    GeSb thin films: read-write optical data storage on the subnanosecond time scale., at Ultrafast Electronics and Optoelectronics 2001, Optical Society of America (Lake Tahoe, NV), Thursday, January 11, 2001:
    talk_364.pdf
    The transition from the low reflectivity amorphous to the highly reflective crystalline phase of a-GeSb films is studied with fs time resolution. The results reveal an ultrafast transition to a new non-thermodynamic phase which is not c-GeSb as previously believed.
    Two-Photon Absorption FROG: measuring white-light continuum pulses, at Conference on Lasers and Electro-Optics (Baltimore, MD), Monday, May 7, 2001
    We demonstrate a new type of frequency resolved optical gating using the two- photon-absorption nonlinearity. The resonant enhancement and lack of phasematching re- quirements enable the FROG measurement of ultrashort white-light continuum laser pulses.
    Ultrafast Lattice-Bonding Dynamics in Tellurium, at CLEO/QELS 2002 (Long Beach, CA), Tuesday, May 21, 2002:
    talk_429.pdf
    We measure the ordinary and extraordinary dielectric function of Te with femtosecond time resolution after coherent phonons are generated with an ultrashort laser pulse. The results reveal oscillatory behavior in the bonding-antibonding split at ~ 3 THz.
    Ultrafast Lattice-Bonding Dynamics of Tellurium, at Ultrafast Electronics and Optoelectronics 2003 Conference (Washington, DC), Wednesday, January 15, 2003:
    talk_453.pdf
    A pump-probe technique measuring the dielectric function is presented and applied to the ultrafast dynamics of coherent phonons in Te. Oscillations in the bonding-antibonding splitting are revealed, allowing for THz modulation of a semiconductor-semimetal transition.
    Ultrafast Phase Transitions in Solids, at International School of Atomic and Molecular Spectroscopy (Erice, Sicily, Italy), Saturday, May 24, 2003:
    talk_513.pdf
    In this talk we present the coherent excitation and coherent control of the A1 phonon mode in Te. First, the underlying theory about the excitation of the A1 phonon mode, and only this, in a certain class of materials is discussed. The theory, called Displacive Excitation of Coherent Phonons (DECP), predicts the excitation of the A1 phonon mode as a result of electronic excitation following absorption of an ultrashort laser pulse by the material. Since there is no symmetry breaking mechanism in the electronic excitation through absorption the effect can only take place in materials which... Read more about Ultrafast Phase Transitions in Solids
    Ultrafast reflectivity dynamics in highly excited bulk ZnO, at Photonics West 2008 (San Jose, CA), Sunday, January 20, 2008:
    talk_1371.pdf
    Large bandgap semiconductors like ZnO are currently of interest as detectors and lasing media. Advances in these device technologies rely on a fundamental understanding of carrier dynamics and excitonic effects at high excitation densities. High carrier densities in semiconductors can be induced by excitation with intense, ultrashort laser pulses, and the resulting dynamics can be determined through our broadband time-resolved pump-probe reflectivity technique. We use a Ti:Sapph fs-laser pulse to excite the c-plane of a crystalline ZnO sample just below its damage threshold of 3 kJ/m2, under... Read more about Ultrafast reflectivity dynamics in highly excited bulk ZnO

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