Presentations

    Nanosurgery with Femtosecond Lasers, at 2009 OSA Frontiers in Optics (San Jose, CA), Wednesday, October 14, 2009:
    We use femtosecond laser pulses to manipulate sub-cellular structures inside live and fixed cells. Using only a few nanojoules of laser pulse energy, we are able to selectively disrupt individual mitochondria in live bovine capillary epithelial cells, and cleave single actin fibers in the cell cytoskeleton network of fixed human fibro-blast cells. We have also used the technique to micromanipulate the neural network of C. Elegans, a small nematode. Our laser scalpel can snip individual axons without causing any damage to surrounding tissue, allowing us to study the function of individual... Read more about Nanosurgery with Femtosecond Lasers
    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:
    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
    Black silicon: hot properties and many open questions, at Atomic and molecular physics at surfaces, ITAMP (Cambridge, MA), Thursday, June 14, 2001:
    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.
    Ultrafast laser microtexturing of silicon for optoelectronic devices, at Photonics West: Commercial and Biomedical Applications of Ultrafast Lasers (San Jose, CA), Thursday, January 24, 2002:
    Arrays of sharp, conical microstructures are obtained by texturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless texturing process drastically changes the optical and electronic properties of the original silicon wafer. These properties make the textured silicon viable for use in a wide range of commercial devices. Near-unity absorption of light, from visible to infrared wavelengths, offer opportunities for use in optically active devices such as solar cells and detectors. Significant enhancement of below-band-gap photocurrent... Read more about Ultrafast laser microtexturing of silicon for optoelectronic devices
    Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies, at Department of Physics Seminar, Fudan University (Shanghai, China), Wednesday, October 16, 2002:
    Arrays of sharp, conical microstructures are obtained by texturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless texturing process drastically changes the optical and electronic properties of the original silicon wafer. These properties make the textured silicon viable for use in a wide range of commercial devices. Near-unity absorption of light, from visible to infrared wavelengths, offer opportunities for use in optically active devices such as solar cells and detectors. Significant enhancement of below-band-gap photocurrent... Read more about Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies
    Femtosecond laser-assisted microstructuring of silicon for novel detector, sensing, and display technologies, at IEEE/LEOS 2002 Conference on Electro-Optic Sensors and Systems (Glasgow, Scotland), Monday, November 11, 2002:
    Arrays of sharp, conical microstructures are obtained by texturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless texturing process drastically changes the optical, material and electronic properties of the original silicon wafer. These properties make the textured silicon viable for use in a wide range of commercial devices. First, near-unity absorption of light, from visible to infrared wavelengths, offer opportunities for use in optically active devices such as solar cells and detectors. Significant enhancement of below-band-gap... Read more about Femtosecond laser-assisted microstructuring of silicon for novel detector, sensing, and display technologies
    Nano-textured Surfaces, at DEAS Industrial Outreach Workshop, Harvard University (Cambridge, MA), Friday, April 11, 2003:
    Arrays of sharp, conical microstructures are obtained by texturing the surface of a silicon wafer using femtosecond laser-assisted chemical etching. The one step, maskless texturing process drastically changes the optical, material and electronic properties of the original silicon wafer. These properties make the textured silicon viable for use in a wide range of commercial devices. First, near-unity absorption of light, from visible to infrared wavelengths, offer opportunities for use in optically active devices such as solar cells and detectors. Second, chemical functionalization of the... Read more about Nano-textured Surfaces
    Femtosecond laser-assisted microstructuring of silicon surfaces for novel detector, sensing, and display technologies, at 41st Annual Technical Meeting of the Society of Engineering Science, University of Nebraska, Lincoln (Lincoln, NE), Monday, October 11, 2004:
    Irridiating silicon surfaces with trains of ultrashort laser pulses in the presence of a sulfur containing gas drastically changes the structure and properties of silicon. The normally smooth and highly reflective surface develops a forest of sharp microscopic spikes. The microstructured surface is highly absorbing even at wavelengths beyond the bandgap of silicon and has many interesting novel applications.
    High photoconductive gain and broad spectral sensitivity enabled by femtosecond laser doping of silicon, at SPIE Photonics West 2008 (San Jose, CA), Wednesday, January 23, 2008:
    Femtosecond laser doping of silicon produces near-unity absorption from the ultraviolet to the short wave infrared. The resulting ‘black silicon’ has great potential for applications in photoactive devices. We have successfully incorporated black silicon into new silicon devices with unique characteristics including: high efficiency, room-temperature photoconductive gain, broad-spectral silicon photodetection, and enhanced near-infrared photovoltaic response. We present the current state of the research and discuss the potential for this processing technique to develop other new materials.
    Black silicon, at SPIE Photonics West (San Francisco, CA), Monday, January 25, 2010:
    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. The properties of this 'black silicon' make it useful for a wide range of commercial devices. In particular, we have been able to fabricate highly-sensitive PIN photodetectors using this material. The sensitivity extends to wavelengths of 1600 nm making them particularly useful for applications in communications and remote sensing.
    Black silicon: engineering an intermediate band in silicon for photovoltaic applications, at 240th National Meeting of the American Chemical Society (Boston, MA), Wednesday, August 25, 2010:
    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. The properties of this 'black silicon' make it useful for a wide range of commercial devices, from highly-sensitive PIN photodetectors to photovoltaics.
    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
    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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    Femtosecond Laser Nanostructuring of Semiconductors and Metals, at 13th International Symposium on Laser Precision Microfabrication (LPM), The Catholic University of America (Washington, DC), Thursday, June 14, 2012:
    We have developed a unique technique to change the optoelectronic properties of many materials through hyperdoping and texturing [1]. By irradiating materials, such as silicon and titanium dioxide, with a train of amplified femtosecond (fs) laser pulses in the presence of a wide variety of dopant precursors, we can introduce dopants above the solubility limit while producing surface structures that have excellent anti-reflection and light-trapping properties.

    Femtosecond-laser texturing originates from the formation of laser induced period surface structures (LIPSS) and consists of semi...

    Read more about Femtosecond Laser Nanostructuring of Semiconductors and Metals

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