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1998

Laser-induced microexplosions: ultrafast physics with clinical applications, at 20th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Hong Kong), Thursday, October 29, 1998:
talk_1114.pdf
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-... Read more about Laser-induced microexplosions: ultrafast physics with clinical applications
Understanding or Memorization: Are we Teaching the Right Thing?, at Fall workshop on educational outreach at Materials Research Science and Engineering Centers, University of California at Santa Barbara (Santa Barbara, CA), Thursday, October 22, 1998:
talk_250.pdf
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. Students get frustrated because they are unable to grasp simple concepts. Instructors get... Read more about Understanding or Memorization: Are we Teaching the Right Thing?
Peer Instruction: Turning a Lecture Into a Seminar, at Forum on Education, Optical Society of America Annual Meeting (Baltimore, MD), Thursday, October 8, 1998
With Peer Instruction, the instructor of a large lecture class periodically poses conceptual questions to the students. Students answer these questions individually and then discuss them in small groups. A student described this method as ""turning a lecture into a seminar."" This approach enhances student learning by confronting and correcting student misconceptions and generates student enthusiasm in the process.
Microexplosions: Highly supersonic plasma expansion following femtosecond laser induced breakdown, at OSA Annual Meeting (Baltimore, MD), Thursday, October 1, 1998:
talk_247.pdf
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.
Black silicon: A new light absorber for solar cells and photodetectors, at OSA Annual Meeting (Baltimore, MD), Thursday, October 1, 1998
We demonstrate a new light absorber for solar cells and optical detection devices. Micron-sized spikes generated by irradiating a silicon surface with femtosecond laser pulses in SF6 enhance light absorption in silicon to near 100%. We observe an increase of more than 60% in photocurrent compared to a flat silicon surface.
Physics in the (ultra)fast lane: femtosecond laser-induced dynamics in solids, at OSA Annual Meeting (Baltimore, MD), Thursday, October 1, 1998
We developed a broadband ultrafast technique to measure a material's dielectric function (from near-UV to near-IR) with 100-fs time resolution. This technique enables identification of phase changes following intense laser excitation. We will present data for semiconductors and discuss future experiments to study plasma generation dynamics in transparent materials.
Thresholds for femtosecond laser-induced breakdown in bulk transparent solids and water, at SPIE Annual Meeting, 1998 (San Diego, CA), Wednesday, July 15, 1998
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... Read more about Thresholds for femtosecond laser-induced breakdown in bulk transparent solids and water

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