Invited

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.

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

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

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.