Publications

    T. Her, R. J. Finlay, C. Wu, and E. Mazur. 1998. “Surface femtochemistry of CO/O2/Pt(111): The importance of nonthermalized substrate electrons.” J. Chem. Phys., 108, Pp. 8595–8598.Abstract
    We studied the surface femtochemistry of CO/O2/Pt(111) induced with 0.3-ps laser pulses over a wide range of wavelength and fluence. Below 10 J/mm2, the yields depend linearly on fluence. Above 10 J/mm2, the yields scale nonlinearly in the fluence. From the dependence of the yields on wavelength, we determine that the nonlinear surface femtochemistry is influenced by nonthermal substrate electrons.
    E. Mazur. 1998. “Moving the Mountain: Impediments to Change.” In . Third Annual NISE Forum.Abstract
    There is no doubt that since the beginning of this century the United States ranks first in generating outstanding scientists. It is therefore ironic that, as a whole, the population of the United States scores low in Science and Mathematics. One only need turn to the media to see that our society does not value science and science education as it did just a few decades ago. In spite of all the advances in science and the many contributions of related technological developments to society, science illiteracy is rampant. The average person has little faith in scientists, and more pressing problems than science education are on the agenda of most people. These developments are worrisome because for everyone to understand at least what science is about is in the interest of society. No one can deny the formidable advances that have been achieved in science and their impact on the quality of life advances that would not have been made without the outstanding quality of American scientists. What happens now in the classrooms across the United States will directly affect the health and well-being of this country in the next century. We must act now to prevent losing our edge in science and technology.
    C. B. Schaffer, N. Nishimura, and E. Mazur. 1998. “Thresholds for femtosecond laser-induced breakdown in bulk transparent solids and water.” In . SPIE Annual Meeting. Publisher's VersionAbstract
    We present thresholds for optical breakdown in bulk transparent solids and water with 100-fs laser pulses. In solids, we used microscopy and scattering techniques to determine thresholds for plasma formation and permanent damage in a wide variety of materials. Transmission measurements show that damage occurs at energies where there is little absorption of the laser pulse. In water, we used scattering and acoustic techniques to measure the breakdown threshold for 100-fs pulses. In contrast to solids, transmission measurements in water indicate that there is no plasma or bubble formation unless there is significant absorption. For comparison, we also measured breakdown thresholds for 200- ps pulses.
    C. B. Schaffer, E. N. Glezer, N. Nishimura, and E. Mazur. 1998. “Ultrafast laser induced microexplosions: explosive dynamics and sub-micrometer structures.” In . Photonics West. Publisher's VersionAbstract
    Tightly focused femtosecond laser pulses can be nonlinearly absorbed inside transparent materials, creating a highly excited electron ion plasma. These conditions exist only in a small volume at the laser focus. This tight confinement and extreme conditions lead to an explosive expansion a microexplosion. In solid materials, a microexplosion can result in permanent structural changes. We find that the damage produced by femtosecond pulses in this way is surprisingly small, with only a 200-nm diameter. Material left at the center of the microexplosion is either amorphous and less dense or entirely absent. The threshold for breakdown and structural change is nearly independent of material. Time-resolved measurements of microexplosions in water allow us to observe the dynamics of the explosive expansion. The structural changes in solids resulting from microexplosions allow for three-dimensional data storage and internal microstructuring of transpa
    L. Huang, J. Paul Callan, E. N. Glezer, and E. Mazur. 1998. “GaAs under ultrafast excitation: response of the dielectric function.” Phys. Rev. Lett., 80, Pp. 185–188. Publisher's VersionAbstract
    {We used a new broadband spectroscopic technique to measure the dielectric function of GaAs over the spectral range of 1.5 - 3.5 eV following intense 70-fs laser excitation. The results provide the most detailed information thus far on the electron and lattice dynamics both above and below the fluence threshold for permanent damage
    T. Her, R. J. Finlay, C. Wu, S. Deliwala, and E. Mazur. 1998. “Microstructuring of silicon with femtosecond laser pulses.” Appl. Phys. Lett., 73, Pp. 1673–1675. Publisher's VersionAbstract
    We report that silicon surfaces develop an array of sharp conical spikes when irradiated with 500 laser pulses of 100-fs duration, 10-kJ/m2 fluence in 500-torr SF6 or Cl2. The spikes are up to 40-m tall, and taper to about 1-m diameter at the tip. Irradiation of silicon surfaces in N2, Ne, or vacuum creates structured surfaces, but does not create the sharp conical spikes.
    N. Nishimura, C. B. Schaffer, E. Herbert Li, and E. Mazur. 1998. “Tissue ablation with 100-fs and 200-ps laser pulses.” In . IEEE Engineering in Medicine and Biology. Publisher's VersionAbstract
    We used water and human skin tissue to compare the surgical potential of 100-fs and 200-ps laser pulses. For investigation of threshold behavior of 100-fs and 200-ps pulses, we use water as a model for tissue. In addition to having a lower threshold, we find that energy deposition is much more consistent with 100-fs pulses. We also compared 100-fs and 200-ps laser pulse effects on the surface and in the bulk of human skin tissue. On the surface, pulses with 100-fs and 200-ps duration leave similar size ablation regions. In the bulk both 100-fs and 200-ps pulses produce cavities, however, 100-fs pulses result in a smaller cavity size. On both the surface and in the bulk 100-fs pulses show less collateral tissue damage than 200-ps pulses.
    R. J. Finlay, T. Her, C. Wu, and E. Mazur. 1997. “Surface femtochemistry of oxygen and coadsorbates on Pt(111).” In Femtochemistry and Femtobiology: Ultrafast Reaction Dynamics at Atomic-Scale Resolution, edited by Villy Sundstrm, Pp. 629–659. Imperial College Press. Publisher's VersionAbstract
    We review the photoprocesses of oxygen on Pt(111), both with and without coadsorbates, and recent progress in describing these processes. We present new data that address the chemical pathway to formation of CO2 in CO/O2/Pt(111) induced by subpicosecond laser pulses. The data show conclusively that the O2 desorbs molecularly. We also find that if the CO reacts by an atomic pathway then the capture of oxygen atoms by the CO is highly efficient; if it reacts by a molecular pathway then the oxygen atoms in the transition state are inequivalent.
    A. Feder. 1997. “Optical studies of monolayers at the air/water interface”. Publisher's VersionAbstract
    Monolayers of amphiphilic molecules at the air/water interface, Langmuir monolayers, provide an experimentally accessible system for the study of physics in two dimensions. As a function of temperature and density, Langmuir monolayers display a series of phases and phase transitions; this thesis describes several optical experiments which clarify the macroscopic properties of some of these monolayer phases. In one experiment a combination of two techniques, laser light scattering and Brewster angle microscopy, is used to study the effect of inhomogeneous monolayers on the damping of capillary waves. It is shown that the monolayer contributes to the capillary wave damping when the size of a typical monolayer domain is equal to or larger than the capillary wavelength. Secondly, a new technique to measure the tilt angle of molecules from the surface normal is described. The validity of the technique is demonstrated by comparison to previously performed x-ray scattering experiments. The tilt angle of a monolayer of long-chain alcohol molecules is measured as a function of temperature and pressure near first- and second-order phase transitions from tilted to untilted monolayer phases. Finally, depolarized Brewster angle microscopy is used to study orientational fluctuations in a two-dimensional smectic-C liquid crystal. The results are in excellent agreement with theoretical predictions. In addition, the first measurements of orientational elasticity and viscosity in a liquid crystal system with variable density are presented.
    R. J. Finlay, T. Her, C. Wu, and E. Mazur. 1997. “Reaction Pathways in Surface Femtochemistry: Routes to Desorption and Reaction in CO/O2/Pt(111).” Chem. Phys. Lett., 274, Pp. 499–504. Publisher's VersionAbstract
    We present new data that address the chemical pathway to desorption of O2 and formation of CO2 in CO/O2/Pt(111) induced by subpicosecond laser pulses. The data show conclusively that the O2 desorbs molecularly. We also find that if the CO oxidizes by an atomic pathway then the capture of oxygen atoms by the CO is highly efficient; if the CO oxidizes by a molecular pathway then the oxygen atoms in the CO3* transition state are inequivalent.
    E. Mazur. 1997. “Peer Instruction: Getting Students to Think in Class.” In The Changing Role of Physics Departments in Modern Universities, Part Two: Sample Classes, edited by Edward F. Redish and John S. Rigden, Pp. 981–988. American Institute of Physics. Publisher's VersionAbstract
    No abstract available. This paper, part of the proceedings for the International Conference on Undergraduate Physics Education held in College Park, Maryland in August 1996, is a reprint of Chapter 2 of "Peer Instruction: A User's Manual" by Eric Mazur (Prentice Hall, 1997). The chapter is available separately for downloading.
    A. Feder, Y. Tabe, and E. Mazur. 1997. “Orientational Fluctuations in a Two-Dimensional Smectic-C Liquid Crystal with Variable Density.” Phys. Rev. Lett., 79, Pp. 1682–1685. Publisher's VersionAbstract
    We studied orientational fluctuations in a smectic-C Langmuir monolayer. Our measurements of orientational correlations are in excellent agreement with theoretical predictions. In addition, we present the first measurements of orientational elasticity and viscosity in a two-dimensional system whose density can be varied. The orientational viscosity strongly depends on temperature and density, changing by more than an order of magnitude with a 2.5% increase in temperature or a 20% change in density. The orientational elasticity is only weakly dependent on temperature and density.
    J. Paul Callan, A. M.-T. Kim, L. Huang, E. N. Glezer, and E. Mazur. 1997. “From semiconductor to metal in a flash: observing ultrafast laser-induced phase transformations.” In . Materials Research Society Fall Meeting. Publisher's VersionAbstract
    We use a new broadband spectroscopic technique to measure ultrafast changes in the dielectric function of a material over the spectral range 1.53.5 eV following intense 70-fs laser excitation. The results reveal the nature of the phase transformations which occur in the material following excitation. We studied the response of GaAs and Si. For GaAs, there are three distinct regimes of behavior as the pump fluence is increased lattice heating, lattice disordering, and a semiconductor-to-metal transition.
    E. N. Glezer and E. Mazur. 1997. “Ultrafast-laser driven micro-explosions in transparent materials.” Appl. Phys. Lett., 71, Pp. 882–884. Publisher's VersionAbstract
    We initiate micro-explosions inside fused silica, quartz, sapphire, and other transparent materials using tightly-focused 100-fs laser pulses. In the micro-explosions, material is ejected from the center, forming a cavity surrounded by a region of compacted material. We examine the resulting structures with optical microscopy, diffraction, and atomic force microscopy of internal cross-sections. We find the structures have a diameter of only 200250 nm, which we attribute to strong self-focusing of the laser pulse. These experiments probe a unique regime of light propagation inside materials at intensities approaching 1021 W/m2, the electron ionization that accompanies it, and the material response to extreme pressure and temperature conditions. The micro-explosions also provide a novel technique for internal microstructuring of transparent materials.
    L. Huang. 1997. “Semiconductor under Ultrafast Laser Excitation: Optical Studies of the Dynamics”. Publisher's VersionAbstract
    This thesis presents studies of semiconductors under intense femtosecond laser irradiation. In order to investigate the nature of the electronic and structural changes induced by laser pulses, a novel broadband technique is developed to measure the linear optical property of semiconductors dielectric function over the entire visible spectrum (1.53.5 eV) with femtosecond time resolution. By employing this broadband spectroscopic technique, the response of the dielectric function of GaAs following an intense 70-fs, 1.9 eV pump pulse is measured. The results provide the most detailed information thus far on the electron and lattice dynamics both above and below the fluence threshold for permanent damage. It is shown that electronic effects, manifested in changes in the band structure, dominate during the first few hundred fs following the excitation. After a few picoseconds, three distinct structural changes are observed depending upon the excitation strength: At low pump fluences, the dielectric function shows heating of the lattice caused by carrier relaxation. At intermediate fluences, the dielectric function reveals a temporary disordering of the lattice. At even higher fluences, a semiconductor-to-metal transition occurs even below the damage threshold. The latter two effects are attributed to the lattice instability caused by the destabilization of the covalent bonds. The time-integrated photoluminescence is also measured to investigate the dynamics of GaAs following fs laser excitation. The luminescence images reveal a reduction of emission due to the structural changes in GaAs. The spectral measurements provide new insight in the carrier dynamics. In addition, a series of II-VI semiconductors are also studied using similar techniques. The response of crystalline Si following fs laser excitation is also explored using the broadband spectroscopic technique. The dielectric function measurements show that lattice heating and semiconductor-to-metal transitions take place within a few picoseconds. The long time (up to 400 ps) behavior is investigated with both reflectivity and dielectric function measurements, providing detailed information on the relaxation of both electronic and structural changes following the excitation.
    E. Mazur. 1997. Peer Instruction: A User's Manual, Pp. 253. Prentice Hall. Publisher's VersionAbstract
    An instructor's resource book, developed with funds from the National Science Foundation and the Pew Charitable Trust, that presents an entirely new approach to teaching introductory physics, complete with a step-by-step guide for converting conventional lectures to a more interactive format and a ready-to-use set of classroom materials in print and on disk. FROM THE BACK COVER: Eric Mazur is Gordon McKay Professor of Applied Physics and Professor of Physics at Harvard University. He has taught introductory physics at Harvard since 1984. In addition to leading a research program in optical physics, Mazur maintains an active interest in educational innovation. In 1991, Eric Mazur developed Peer Instruction, a simple yet effective method for teaching science. His approach involves students in the teaching process, making physics significantly more accessible to them. His technique has been highly successful and numerous instructors are already using Mazur's approach in their classes. Many instructors have pointed out the benefits of teaching by questioning over the more traditional approach of teaching by telling. Here, at last, is a book that not only explains how to teach by questioning but also provides all the necessary tools to implement this new approach with a mimimum of effort.
    E. N. Glezer, C. B. Schaffer, N. Nishimura, and E. Mazur. 1997. “Minimally disruptive laser-induced breakdown in water.” Opt. Lett., 22, Pp. 1817–1820.Abstract
    We produce minimally disruptive breakdown in water using tightly focused 100-fs laser pulses, and demonstrate the potential of this technique for microsurgery of the eye. Using time-resolved imaging and piezoelectric pressure detection we measure the magnitude and speed of propagation of the pressure wave produced in the breakdown. Compared to breakdown with longer pulses, we find a much lower energy threshold for breakdown of 0.2 J, a smaller shock zone diameter (11-m for 1-J pulses), and consistent energy deposition.
    E. N. Glezer, C. B. Schaffer, N. Nishimura, and E. Mazur. 1997. “Minimally disruptive laser-induced breakdown in water.” In . Conference on Lasers and Electro-Optics. Publisher's VersionAbstract
    Using tightly focused 100-fs, 800-nm laser pulses we produce breakdown in water using less than 1 J of energy. By imaging the cavitation and pressure wave propagation we find that the supersonic expansion is limited to an 11-m diameter for 1-J pulses, increasing to a 20-m diameter for 30-J pulses.
    E. Mazur. 1997. “Understanding or memorization: Are we teaching the right thing.” In Conference on the Introductory Physics Course on the occasion of the retirement of Robert Resnick, edited by Jack Wilson, Pp. 113–124. Wiley. Publisher's VersionAbstract
    When people I meet ask me what I do for a living and I tell them I am a physicist, I frequently hear horror stories about high school or college level physics – almost to the point of making me feel embarrassed about being a physicist! This general sense of frustration with introductory physics (mechanics, electricity and magnetism) is widespread among non-physics majors who are required to take physics courses. Even physics majors are frequently dissatisfied with their introductory courses and a large fraction of students initially interested in physics end up majoring in a different field. Frustration with introductory physics courses has been commented on since the days of Maxwell and has recently been publicized by Sheila Tobias. Tobias asked a number of graduate students in the humanities and social sciences to audit physics courses and describe their complaints. One may be tempted to brush off complaints by non-physics majors as coming from students who are ipso facto not interested in physics. Most of these students, however, are not complaining about other required courses outside their major field

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