Publications

    R. J. Finlay. 1998. “Femtosecond-laser-induced reactions at surfaces”. Publisher's VersionAbstract
    We have experimentally studied chemical reactions at the surfaces of platinum and silicon using subpicosecond laser pulses to induce the reactions. The laser pulses stimulate electrons, which in turn stimulate molecules absorbed on the surface. Irradiation of CO/O2/Pt(111) with 300-fs laser pulses yields O2 and CO2. We measured the yields of O2 and CO2 induced by laser pulses of various wavelengths to determine that nonthermalized electrons stimulate the adsorbates. When the fluence in the laser pulses is high, the effective cross section for desorption is high compared to the cross section measured using an arc lamp source. We demonstrated that by controlling the fluence in the subpicosecond laser pulses we can access either the low or the high cross section regimes. We used isotopic labeling to show that the O2 desorption is molecular, and to discover some properties of the pathway to CO2. In many simulations of molecular dynamics following subpicosecond-pulsed laser excitation, the substrate is assumed to be static. We discovered, however, that subpicosecond laser pulses with fluences above 50 J/mm 2 induce reaction between O2 adsorbed on Pt(111) and atoms from beneath the surface – atoms near the surface move. Laser pulses of even higher fluence ablate the substrate. We irradiated silicon surfaces with 10 000-J/mm 2, 100- fs pulses in a chamber filled with halogen gases. We discovered that sharp spikes develop on the surface, and deduced some of the elements of a model for the spike formation. We also report discovery of an electron-beam induced reaction in C6H6/O2/ Pt(111) that yields phenol.
    E. Mazur. 1996. “The Problem with Problems.” In Optics and Photonics News, 6: Pp. 59–60. Publisher's VersionAbstract
    Standard, end-of-chapter textbook problems can generally be solved by rote memorization of sets of formulas and so-called 'problem-solving techniques.' Often, students solve problems by identifying quivalent problems that they have solved before. Don't we want our students to be able to tackle more challenging problems?Enrico Fermi was well known for his legendary ability to solve seemingly intractable problems in subjects entirely unfamiliar to him (e.g., How many piano tuners in Chicago?). Such 'Fermi problems' cannot be solved by deduction alone and require assumptions, models, order-of-magnitude estimates, and a great deal of self-confidence. We often use back-of-the-envelope estimates to familiarize ourselves with new problems. So why do we keep testing our students with conventional problems? Problems that contain the same number of unknowns and givens and frequently require nothing but mathematical skills. What distinguishes the successful scientist is not the ability to solve an integral, a differential equation, or a set of coupled equations but rather the ability to develop models, to make assumptions, to estimate magnitudes, the very skills developed in Fermi problems.
    E. N. Glezer, Y. Siegal, L. Huang, and E. Mazur. 1995. “The behavior of chi(2) during laser-induced phase transtions in GaAs.” Phys. Rev. B, 51, Pp. 9589–9596. Publisher's VersionAbstract
    We explicitly determine the second-order optical susceptibility of GaAs following intense femtosecond laser-pulse excitation from second-harmonic generation measurements. To separate the dependence of the 4.4-eV second-harmonic signal on the second-order susceptibility from its dependence on the linear dielectric constant, we use experimentally determined values for the dielectric constant of GaAs at 2.2 and 4.4 eV. The results show that the excitation of electrons and the resulting changes in the lattice affect the behavior of the second-order susceptibility. At pump fluences of 0.6 kJ/m2 and higher, the material loses long-range order on a time scale ranging from 100 femtoseconds to tens of picoseconds, depending on the pump fluence. A recovery of the second-order susceptibility to its initial value at pump fluences between 0.6 and 1.0 kJ/m2 shows that the loss of long-range order is reversible in this fluence regime.
    J. Wang and E. Mazur. 1993. “Rejection of Stochastic background noise in low-level light pulsed light scattering experiments.” Rev. Sci. Instrum., 64, Pp. 2550–2551. Publisher's VersionAbstract
    We present an electronic scheme for reducing stochastic noise in the detection of low-level light signals in experiments where the signal coincides in time with a probe laser pulse. This scheme has been applied successfully in Raman experiments to reject the noise generated by afterpulsing in photomultiplier tubes as well as by unwanted laser-induced-fluorescence.
    E. Mazur. 1986. “Computer-controlled Raman spectrometer for time-resolved measurements in low pressure gaseous sample.” Rev. Sci. Instrum., 57, Pp. 2507–2511. Publisher's VersionAbstract
    A spectrometer for measuring spontaneous Raman scattering in gaseous samples at pressures below 100 Pa (0.75 torr) with nanosecond time resolution is presented. The apparatus was developed for studying intramolecular vibrational energy distributions in infrared multiphoton excited molecules, and makes it possible to study the anti-Stokes Raman scattering from isolated molecules at pressures down to 14 Pa (110 mtorr). Because of the low level of the signals the measurements are completely computer-controlled. A detailed description of the apparatus, including the multichannel data-acquisition hardware and computer interface, is
    E. Mazur, E. Viswat, L. J. F. Hermans, and J. J. M. Beenakker. 1983. “Experiments on the viscosity of some symmetric top molecules in the presence of magnetic and electric fields.” Physica, 121A, Pp. 457–478. Publisher's VersionAbstract
    In order to obtain information on the scalar structure of non-equilibrium polarizations a comparison between the magnetic and the electric field effect on the viscosity of some symmetric top molecules has been carried out. It is shown that the polarization produced in viscous flow is more complicated than assumed so far.
    E. Mazur, G. W. t Hooft, L. J. F. Hermans, and H. F. P. Knaap. 1979. “The transverse Dufour effect.” Physica, 98A, Pp. 87–96. Publisher's VersionAbstract
    Experiments have been performed to study the influence of a magnetic field on the Dufour effect (or diffusion-thermo effect) in an equimolar N2-Ar mixture at room temperature. By comparing these experimental results with those obtained previously for the field effect on the thermal diffusion, an Onsager relation between these field effects is confirmed.