Presentations

    Direct Laser Writing of 3-D Diffraction Gratings and Diffraction Optics, at MRS 2014 Fall Meeting and Exhibit, Symposium L: Optical Metamaterials and Novel Optical Phenomena Based on Nanofabricated Structures (Boston, MA), Thursday, December 4, 2014
    Integrated diffractive optics has many applications in beam shaping and control on the micro-scale. Fabrication using lithography is limited to planar or layered geometries. We demonstrate fabrication of diffractive elements via direct laser writing. We have tested 3D diffraction gratings and zone plates designed for operation at visible wavelengths. Direct laser writing is a promising technique to fabricate integrated 3D and multi-layer diffraction optics. We have previously developed a laser writing technique that enables fabrication of disconnected metal structures in a polymer matrix,... Read more about Direct Laser Writing of 3-D Diffraction Gratings and Diffraction Optics
    Microexplosions: Highly supersonic plasma expansion following femtosecond laser induced breakdown, at OSA Annual Meeting (Baltimore, MD), Thursday, October 1, 1998:
    Tightly focused ultrashort laser pulses are used to produce a hot, dense plasma in water. Using time-resolved imaging and scattering techniques we map the supersonic expansion of this plasma. The expansion reaches a speed of 90 km/s, the fastest expansion witnessed to date in laser induced breakdown. Extreme temperature and pressure drive this expansion.
    Molecular orientation in Langmuir monolayers studied by surface second harmonic generation, at APS Centennial Meeting 1999 (Atlanta, GA), Tuesday, March 23, 1999:
    We used surface second harmonic generation (SHG) to study molecular orientation in a smectic-C liquid-crystal Langmuir monolayer at an air/water interface. The molecules under investigation are 4-octyl-4'-(3-carboxytrimenthyleneoxy) azobenzene (8AZ3). Because water is inversion symmetric, the SHG signal comes only from the surface. Furthermore, the magnitude of the surface SHG signal depends on the orientation of molecules, which makes SHG a sensitive probe of the phase of the monolayer. We measured the response of the SHG signal as we compressed the monolayer from a smectic-C phase to a more... Read more about Molecular orientation in Langmuir monolayers studied by surface second harmonic generation
    Femtosecond laser micromachining of bulk glass at oscillator energies, at Gordon Conference on Nonlinear Optics, Colby Sawyer College (New London, NH), Tuesday, July 27, 1999:
    Using femtosecond laser pulses generated by a 25-MHz Ti:Sapphire laser oscillator, we micromachine bulk glass. The laser is focused by a 1.4 numerical aperture microscope objective, allowing the breakdown threshold to be reached with modest energies (4.5 nJ). Single-shot damage is sub-micron in size. Because the pulses arrive faster than energy can diffuse out of the focal volume, multiple shot damage with this laser is thermal in nature. Successive pulses add more and more heat to the sample, melting a micron-sized volume. Using this thermal machining, we have written single-mode waveguides... Read more about Femtosecond laser micromachining of bulk glass at oscillator energies
    Peer Instruction: Getting Students to Think in Class, at 1999 Sigma Xi Forum (Minneapolis, MN), Thursday, November 4, 1999:
    Most introductory undergraduate science courses are taught in large lectures. Although an efficient use of instructor time, passive lectures rarely challenge students to think critically in class, often reinforcing the common expectation that learning science amounts to acquiring information. Many students respond by memorizing facts or formulas without understanding the fundamental concepts. To actively engage students during class and focus their attention on underlying concepts, we have developed a student-centered approach to teaching large courses, Peer Instruction. Lectures are... Read more about Peer Instruction: Getting Students to Think in Class
    How To Get to Know 200 Students (Almost) Overnight, at American Association of Physics Teachers Winter 2000 Meeting (Kissimmee, FL), Monday, January 17, 2000:
    Direct interaction between students and teacher is essential to effective teaching. Unfortunately, it is often lacking in large classes. We have developed a system which facilitates efficient asynchronous communication between teacher and students. Students' questions are stored in a database, and the contents of the database are accessed via the Web in various forms. For example, the teacher can review all student questions on a particular topic, prepare a single answer to a common question, and store the answer in the database. Students' grades and pictures are stored with their questions (... Read more about How To Get to Know 200 Students (Almost) Overnight
    Assessing the initial state of knowledge of first-year genetics students, at ASM Eighth Undergraduate Microbiology Education Conference, American Society for Microbiology (Orlando, FL), Saturday, May 19, 2001:
    A survey was designed to assess students' understanding of concepts and familiarity with biology terminology at the beginning of a new introductory genetics course. The class, which serves as the first college biology course for all students majoring in Biological Sciences or fulfilling premedical requirements, assumes no prior knowledge and enrolls mainly first-year students. The survey asked students to rate their familiarity with over 80 words in genetics and to define a selection of these terms. Students were also asked to answer a few conceptual questions as well as provide background... Read more about Assessing the initial state of knowledge of first-year genetics students
    Femtosecond laser-structured silicon: properties and structure, at Gordon Conference on Laser Interactions With Materials (Andover, NH), Tuesday, July 23, 2002:
    Silicon surfaces that are microstructured with femtosecond laser pulses in a sulfur hexafluoride environment exhibit several remarkable properties, including near-unity below-band gap optical absorption (C. Wu et al., Appl. Phys. Lett. 78, 1850 (2001)). We report new structural and chemical characterization of this material, including cross-sectional TEM images of the microstructures. Our results indicate that the below-band gap absorption most likely comes from a surface layer of polycrystalline silicon roughly 1 micrometer thick, which includes nanopores, nanocrystals, and a high... Read more about Femtosecond laser-structured silicon: properties and structure
    Transition from repetitive to cumulative thermal processing in femtosecond laser induced machining of embedded waveguides, at Photonics West (San Jose, California), Saturday, January 25, 2003:
    In previous work, we have demonstrated laser writing of embedded waveguides in silicate glasses with only nanojoules of energy. The laser system is an unamplified 25 MHz laser oscillator generating 24-nJ, 55-fs pulses. Laser machining at this high repetition rate results in a cumulative thermal mechanism of material modification which leads to structural index of refraction changes beyond the focal volume. We present a parametric study of the role of the laser repetition rate in the size of the machined structures. The material used for the study is a chalcogenide glass, As_2S_3. We identify... Read more about Transition from repetitive to cumulative thermal processing in femtosecond laser induced machining of embedded waveguides
    Morphology and optical properties of femtosecond irradiated glass with variable pulse repetition rates, at Glass & Optical Materials Division Fall 2004 Meeting (Cocoa Beach, FL), Tuesday, November 9, 2004:
    We investigated the morphology of femtosecond irradiated borosilicate glass with respected to two variables: the number of shots and the laser repetition rate. For the laser repetition rate we have covered the range from 250 kHz to 25 MHz. We identify two distinct regimes of femtosecond processing in the kHz to MHz range. As the time interval between pulses is reduced, we observe a transition from a repetitive modification process (identical to what is frequently called multiple shot damage) to a cumulative thermal mechanism. In the repetitive regime, each pulse acts independently and the... Read more about Morphology and optical properties of femtosecond irradiated glass with variable pulse repetition rates
    Optical waveguide wiring using femtosecond laser pulses between multiple pieces of glass for optical sensor applications, at 2005 SPIE Photonics West Conference, Program on Laser Micro-/Nanoengineering and applications, Commercial and Biomedical Applications of Ultrafast Lasers VI (San Jose, CA), Tuesday, January 25, 2005:
    We demonstrate optical waveguide wiring between multiple pieces of glass using high-repetition rate femtosecond laser pulses focused with a 1.4 NA oil-immersion microscope objective. In conventional waveguide wiring techniques, connecting optical waveguides in different pieces of glass requires special attention because of the very small core size of the waveguides. Connecting waveguides therefore necessitates highly accurate positioning stages and is a time consuming process. We demonstrate that it is possible to write optical waveguides across the gap between two pieces of glass with a... Read more about Optical waveguide wiring using femtosecond laser pulses between multiple pieces of glass for optical sensor applications
    Femtosecond laser dissection of neurons in C. elegans, at Industrial Outreach Program, Harvard University (Cambridge, MA), Wednesday, April 27, 2005:
    Tightly-focused femtosecond laser pulses of a few nanojoules sever individual dendrites in the nematode worm C. elegans. Quantification of the resulting behavioral deficits identifies the contribution of the dissected structures. The dissection has submicrometer resolution with no collateral damage, permitting precise studies on live animals. Future work include an examination of the molecular basis of neurodegeneration that has application to diseases such as Parkinsons and Alzheimers.
    Optoelectronic devices using femtosecond laser microstructured silicon, at NATO ASI Course on New developments in optics and related fields: modern techniques, materials, and applications, Centro Ettore Majorana (Erice, Italy), Sunday, June 12, 2005:
    Arrays of sharp, conical microstructures are obtained by stucturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless structuring process drastically changes the optical, material and electronic properties of the original silicon wafer. These properties make microstructured silicon viable for use in a wide range of commercial devices including solar cells, infrared photodetectors, chemical and biological sensors, and field emission devices.

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