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Classroom Demonstrations: More Than Just Entertainment?, at Physics colloquium, Calvin College (Grand Rapids, MI), Thursday, September 27, 2001:
talk_414.pdf
Classroom demonstrations in science courses are intended to serve two important purposes: to increase students’ interest in the material being covered and to improve students’ understanding of the underlying scientific concepts. Student end-of-semester evaluations typically praise demonstrations as one of the most interesting parts of a course, suggesting that demonstrations accomplish the first objective. What about the second? Do demonstrations effectively help students learn the underlying concepts? We examined whether the manner of presentation of demonstrations affects their... Read more about Classroom Demonstrations: More Than Just Entertainment?
Laser induced microexplosions and applications in laser micromachining, at Annual Meeting of the Stanford Photonics Research Center, Standord University (Palo Alto, CA), Saturday, September 15, 2001:
talk_400.pdf
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. In this talk we will review recent results obtained in... Read more about Laser induced microexplosions and applications in laser micromachining
Black silicon: hot properties and many open questions, at Atomic and molecular physics at surfaces, ITAMP (Cambridge, MA), Thursday, June 14, 2001:
talk_388.pdf
A serendipitous discovery in our lab produced a novel form of microstructured silicon ("black silicon") that has many surprising properties: near unity absorption, even below the bandgap; production of photoelectrons in the visible and infrared; visible luminescence; and a strong field emission current. We are beginning to shed light on what might cause some of the material's remarkable properties. Much additional experimental and theoretical work is required to understand the surface physics and chemistry that leads to the formation of black silicon.
Micromachining and laser processing with ultrashort laser pulses, at Second International Symposium on Laser Precision Microfabrication (LPM2001) (Singapore), Wednesday, May 16, 2001:
talk_359.pdf
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. In this talk we will review recent results obtained in... Read more about Micromachining and laser processing with ultrashort laser pulses
Fabrication of Micrometer-Sized Conical Field Emitters Using Femtosecond Laser-Assisted Etching of Silicon, at MRS Spring Meeting (San Francisco, CA), Friday, April 20, 2001:
talk_378.pdf
We produce quasi-ordered arrays of sharp, conical microstructures by structuring the surface of a silicon wafer using femtosecond laser-assisted etching. Analysis of the arrays shows high, stable field emission without any further processing. The sharp, micrometer-sized conical structures result from irradiation of a silicon surface with hundreds of femtosecond-laser pulses in an atmosphere of SF6. These conical microstructures have sharp tips with a radius of curvature of about 250 nm and a subtended angle of less than 20°. They are 10–14 µm tall, have tip-to-tip separations of 6–10 µm, and... Read more about Fabrication of Micrometer-Sized Conical Field Emitters Using Femtosecond Laser-Assisted Etching of Silicon
Direct writing of optical waveguides in bulk glass using a femtosecond laser oscillator, at MRS Spring Meeting (San Francisco, CA), Tuesday, April 17, 2001:
talk_366.pdf
In recent years, femtosecond lasers have proven to be extremely useful for micromachining the surface and bulk of transparent materials. When a femtosecond laser pulse is focused into a transparent material, the intensity in the focal volume can become high enough to cause absorption through nonlinear processes, leading to optical breakdown and permanent structural change to the material. Because the absorption is nonlinear, this structural change can be localized in the bulk of the sample, allowing a three-dimensional structure to be micromachined. In this paper, we show that by focusing a... Read more about Direct writing of optical waveguides in bulk glass using a femtosecond laser oscillator
Ultrafast Phase Transitions in Semiconductors, at 2000 MRS Fall Meeting (Boston, MA), Tuesday, November 28, 2000:
talk_365.pdf
We present measurements of the dielectric function of various semiconducting materials (c-GaAs, a-GaAs and GeSb thin-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 time evolution of the dielectric function provides a wealth of information that allows identification and tracking of the electronic and structural dynamics triggered by the pump pulse. At elevated fluence levels all materials undergo a semiconductor to metal transitions.

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