Invited

Applications of femtosecond lasers in materials processing, at Data Storage Institute, NUS (Singapore), Friday, March 30, 2012:
The intersection of materials research and ultrafast optical science is producing many valuable fundamental scientific results and applications, and the trend is expected to evolve as new and exciting discoveries are made. Femtosecond laser micromachining presents unique capabilities for three-dimensional, material-independent, sub-wavelength processing. At the same time the surface processing of materials permits the creation of novel materials that cannot (yet) be created under other conditions.

In this talk we will discuss how shining intense, ultrashort laser pulses on the surface of...

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Hyperdoped and microstructured silicon for solar energy harvesting, at PIERS 2012 (Kuala Lumpur, Malaysia), Wednesday, March 28, 2012:
We have developed a unique technique to significantly change the optoelectronic properties of silicon through hyperdoping and texturing. By irradiating silicon with a train of amplified femtosecond laser pulses in the presence of a wide variety of dopant precursors, we can hyperdope silicon to > 1 at.% in a 300-nm thin layer. In addition, laser-induced semi-periodic surface textures have excellent anti-reflection and light-trapping properties. The technique is robust: it is effective on both crystalline and amorphous silicon and for both thin films and thick substrates. When the dopant is... Read more about Hyperdoped and microstructured silicon for solar energy harvesting
Fabricating nanostructured TiO2 by femtosecond laser irradiating titanium, at PIERS 2012 (Kuala Lumpur, Malaysia), Wednesday, March 28, 2012:
many materials including titanium. Laser structuring of titanium surfaces has been investigated for a variety of applications, including biocompatibility and solar energy harvesting. We use femtosecond laser irradiation of titanium to create nanometer scale laser-induced periodic surface structures and study the influence of atmospheric composition on these surface structures. Altering the gas composition and pressure does not change the surface morphology, but it does impact the chemical composition of the surface. We demonstrate that irradiation of titanium in oxygen containing atmospheres... Read more about Fabricating nanostructured TiO<sub>2</sub> by femtosecond laser irradiating titanium
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
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
Femtosecond laser doped silicon for photovoltaic applications, at SPIE Optics & Photonics (San Diego), Friday, August 12, 2011:
Doping silicon to concentrations above the metal-insulator transition threshold yields a novel material that has potential for photovoltaic applications. By focusing femtosecond laser pulses on the surface of a silicon wafer in a sulfur hexafluoride (SF6) environment, silicon is doped with 1% atomic sulfur. This material exhibits near-unity, broadband absorption from the visible to the near infrared (< 0.5 eV, deep below the silicon bandgap), and metallic-like conduction. These unusual optical and electronic properties suggest the formation of an intermediate band. We report on the... Read more about Femtosecond laser doped silicon for photovoltaic applications
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?
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

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