Presentations

    Applications of femtosecond lasers in materials processing, at Conference on Lasers and Electro-Optics Europe (Munich, Germany), Wednesday, June 17, 2009:
    Chemical bonding, phase transitions, and surface processes occur on timescales comparable to the natural oscillation periods of atoms and molecules, in the range of femtoseconds (1 fs =10�15 s) to picoseconds (1 ps = 10�12 s). Advances in the generation of ultrashort laser pulses in the past two decades have made it possible to directly observe these fundamental processes. These advances have taken us from the picosecond timescale a generation ago, to the femtosecond timescale in the past decade, and recently into the attosecond (1 as = 10�18 s) regime. Materials science,... Read more about Applications of femtosecond lasers in materials processing
    Nanosurgery with Femtosecond Lasers, at 2009 OSA Frontiers in Optics (San Jose, CA), Wednesday, October 14, 2009:
    We use femtosecond laser pulses to manipulate sub-cellular structures inside live and fixed cells. Using only a few nanojoules of laser pulse energy, we are able to selectively disrupt individual mitochondria in live bovine capillary epithelial cells, and cleave single actin fibers in the cell cytoskeleton network of fixed human fibro-blast cells. We have also used the technique to micromanipulate the neural network of C. Elegans, a small nematode. Our laser scalpel can snip individual axons without causing any damage to surrounding tissue, allowing us to study the function of individual... Read more about Nanosurgery with Femtosecond Lasers
    Gender, interactive teaching, and barriers to change, at Women in Science and Engineering Workshop, Thomas Jefferson National Accelerator Facility (Newport News, VA), Monday, November 16, 2009:
    Can pedagogy alleviate the well-known "gender gap" in performance and representation in the physical sciences? I will show that women can succeed on par with male students in introductory classes that are taught cooperatively, rather than competitively. At the same time we found that the level of perceived confusion increases in classes that challenge every student to think about and respond to questions asked during class. This increase is a potential barrier to reform even though we have shown it to anti-correlate with performance.
    Optical Hyperdoping; Using lasers to tailor the optoelectronic properties of semiconductors, at 2009 Fall MRS Meeting: Ultrafast Materials Science Symposium (Boston, MA), Wednesday, December 2, 2009:
    Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
    Black silicon, at SPIE Photonics West (San Francisco, CA), Monday, January 25, 2010:
    Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
    Optical Hyperdoping: Transforming Semiconductor Band Structure for Solar Energy Harvesting, at Third-Generation Solar Technologies Multidisciplinary Workshop: Synergistic Chemistry-Materials-Mathematical Sciences Approaches to Addressing Solar Energy Problems (San Francisco, CA), Monday, April 5, 2010:
    Harvesting solar energy at the terawatt scale requires technologies that can be produced inexpensively using Earth-abundant materials. Although technologies built from Earth-abundant materials exist for converting solar energy to electrical energy or chemical energy, none are yet cost-competitive with fossil fuels. Meeting the challenge of harvesting solar energy with Earth-abundant materials such as Si and TiO2 will require transformative approaches to increase efficiency, lower manufacturing cost, and reduce material requirements. While these materials have been widely studied, we bring a... Read more about Optical Hyperdoping: Transforming Semiconductor Band Structure for Solar Energy Harvesting
    Black silicon: Engineering an intermediate band in silicon for sensing and energy harvesting, at Nanophotonics and Plasmonic Technologies Workshop, Harvard University (Cambridge, MA), Friday, May 7, 2010:
    Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
    Direct writing of metallic structures for metamaterial applications, at Tri-Service Metamaterials Review (Virginia Beach, VA), Wednesday, May 26, 2010:
    Ultrafast-laser micromachining allows for 3D fabrication of structures much smaller than the diffraction limited laser spot size in transparent media such as glass. Under a linear regime, the media does not absorb light at the operating wavelength of the laser. However, using ultrafast pulses, we can obtain material modification through non-linear absorption. The technique can also be used to induce chemical reactions. High intensity femtosecond laser pulses can induce the photoreduction of metal ions through non-linear absorption. We use solutions containing metal salts to grow metal... Read more about Direct writing of metallic structures for metamaterial applications
    Femtosecond laser micromachining of transparent materials, at Topical Meeting on Bragg Gratings, Photosensitivity and Poling in Glass Waveguides (Karlsruhe, Germany), Monday, June 21, 2010:
    When femtosecond laser pulses are focused tightly into a transparent material, the intensity in the focal volume can become high enough to cause nonlinear absorption of laser energy. The absorption, in turn, can lead to permanent structural or chemical changes. Such changes can be used for micromachining bulk transparent materials. Applications include data storage and the writing of waveguides and waveguide splitters in bulk glass, fabrication of micromechanical devices in polymers, and subcellular photodisruption inside single cells.
    Impact of Peer Instruction on underrepresented groups, at American Association of Physics Teachers Summer Meeting 2010 (Portland, OR), Monday, July 19, 2010:
    This talk discusses the performance of traditionally underrepresented groups (women and underrepresented racial and ethnic minority groups) when taught introductory physics using Peer Instruction, either with traditional discussion sections or combined with other interactive engagement strategies. On average, students from these underrepresented groups enter with weaker preparation; for data obtained at Harvard University, we examine end-of-semester performance results, both end-of-semester conceptual inventory data and student grades, controlling for student background. We also summarize... Read more about Impact of Peer Instruction on underrepresented groups
    Black silicon: engineering an intermediate band in silicon for photovoltaic applications, at 240th National Meeting of the American Chemical Society (Boston, MA), Wednesday, August 25, 2010:
    Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye. The properties of this 'black silicon' make it useful for a wide range of commercial devices, from highly-sensitive PIN photodetectors to photovoltaics.
    Why teaching problem solving is a problem, at 2010 Science and Technology in Society Forum (Kyoto, Japan), Sunday, October 3, 2010:
    Of all the skills that are important in life in general and science, math and engineering education I n particular, the one that is most generally considered to be the most important one is problem solving. But what is problem solving? Problem solving is the process of moving toward a goal when the path to that goal is uncertain. The traditional approach to education largely fails to teach real problem solving. What can we do to address this problem?
    Nonlinear optics at the nanoscale, at OPTOEL 2011 (Santander, Spain), Thursday, June 30, 2011:
    We explore nonlinear optical phenomena at the nanoscale by launching femtosecond laser pulses into long silica nanowires. Using evanescent coupling between wires we demonstrate a number of nanophotonic devices. At high intensity the nanowires produce a strong supercontinuum over short interaction lengths (less than 20 mm) and at a very low energy threshold (about 1 nJ), making them ideal sources of coherent white-light for nanophotonic applications. The spectral broadening reveals an optimal fiber diameter to enhance nonlinear effects with minimal dispersion. We also present a device that... Read more about Nonlinear optics at the nanoscale
    Memorization or understanding: are we teaching the right thing?, at OCPA7, Sun Yat-sen University (Kaohsiung, Taiwan), Thursday, August 4, 2011:
    Education is more than just transfer of information, yet that is what is mostly done in large introductory courses -- instructors present material (even though this material might be readily available in printed form) and for students the main purpose of lectures is to take down as many notes as they can. Few students have the ability, motivation, and discipline to synthesize all the information delivered to them. Yet synthesis is perhaps the most important -- and most elusive -- aspect of education. I will show how shifting the focus in lectures from delivering information to synthesizing... Read more about Memorization or understanding: are we teaching the right thing?
    Science and Technology Diplomacy and International Collaboration, at 8th Science and Technology in Society Forum (Kyoto, Japan), Monday, October 3, 2011:
    Science has been used to defuse political tension long before the term “science diplomacy” was coined. During the cold war these was an active exchange of US and Soviet scientists. When Nixon visited China in 1972, the US and China identified science as an area of cooperation. It is important, however, that science diplomacy be more than governments involving scientists in international collaborations. Scientists themselves must take the lead in rethinking their approach to science education and help educate the future decision and policy makers about science. Only then will the world be... Read more about Science and Technology Diplomacy and International Collaboration
    Pushing a physics discovery towards commercial impact, at APS March meeting (Boston, MA), Thursday, March 1, 2012:
    In 1997 my research group discovered that shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The resulting textured surface is highly absorbing and looks black to the eye, making this 'black silicon' useful for a wide range of commercial devices, from highly-sensitive detectors to improved photovoltaics. Over the following ten years we investigated this material and developed a prototype detector. The prototype gave us the confidence to commercialize black silicon. Together... Read more about Pushing a physics discovery towards commercial impact

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