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2000

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.
Ultrafast Phase Transition Dynamics in GeSb Films, at Optical Society of America Annual Meeting, Optical Society of America (Providence, RI, USA), Thursday, October 26, 2000:
talk_363.pdf
We measure the dielectric function of thin a-GeSb 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 results reveal an ultrafast transition to a new non-thermodynamic phase which is not c-GeSb as previously believed.
Micromachining optical waveguides using a femtosecond laser oscillator, at Optical Society of America Annual Meeting (Providence, RI), Wednesday, October 25, 2000:
talk_358.pdf
By tightly focusing femtosecond laser pulses, we achieve optical breakdown in a transparent material using only nanojoules of laser energy. Localized structural changes are produced in the focal volume and used for bulk micromachining. Using this technique, we fabricate single-mode optical waveguides and other photonics devices inside bulk glass.
Femtosecond micromachining of transparent materials, at OSA 2000 Annual Meeting (Providence, RI), Tuesday, October 24, 2000:
talk_313.pdf
By tightly-focusing femtosecond laser pulses, we achieve the intensity required for permanent structural change in transparent materials with only nanojoules of energy. We discuss the mechanisms and morphology of bulk structural changes produced by femtosecond laser pulses, and describe recent work on the direct writing of photonics devices using only a laser oscillator.
Below-band gap absorption in microstructured silicon, at Optical Society of America Annual Meeting (Providence, RI), Tuesday, October 24, 2000:
talk_360.pdf
We report two remarkable properties of silicon surfaces that are microstructured with laser-assisted etching: the absorptance for wavelengths between 0.25 and 2.5 micrometers is 97% or more, and photoelectrons are produced at 1.3 micrometers. We also report chemical and structural analysis of the microstructured material.
Microexplosions: controlling matter with light, at Frontiers in Chemistry and Materials Science Symposium, Lawrence Livermore National Laboratory (Livermore, CA), Thursday, October 19, 2000:
talk_357.pdf
Light travels undisturbed through a window pane because glass is transparent -- light and glass don't interact. With a powerful femtosecond laser pulse, however, nonlinear processes give rise to light-matter interactions that open the door to new studies in materials science, chemistry, condensed matter physics, and life sciences. Even at very modest energies, the intensity of a tightly-focused, femtosecond laser pulse can be high enough to cause nonlinear absorption of laser energy by a transparent material. The absorption is confined at the focus producing extreme conditions in the... Read more about Microexplosions: controlling matter with light
Stopping Time, at 2000-2001 Lowell First Friday Lectures, Museum of Science (Boston, MA), Friday, October 6, 2000:
talk_355.pdf
Time is of philosophical interest as well as the subject of mathematical and scientific research. Even though it is a concept familiar to most, the passage of time remains one of the greatest enigmas of the universe. The philosopher Augustine once said: "What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know." The concept time indeed cannot be explained in simple terms. Emotions, life, and death - all are related to our interpretation of the irreversible flow of time. After a short introduction to the concept of time, Dr. Mazur... Read more about Stopping Time
Memorization or Understanding: Are we teaching the right thing?, at Physics Colloquium, MIT (Cambridge, MA), Thursday, September 21, 2000:
talk_353.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 Memorization or Understanding: Are we teaching the right thing?
Understanding or Memorization: Are we Teaching the Right Thing?, at Physics Colloquium, Massachusetts Institute of Technology (Cambridge, MA), Thursday, September 21, 2000:
talk_356.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?

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