Volume 95, Issue 6, 15 March 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
95(2004); http://dx.doi.org/10.1063/1.1645676View Description Hide Description
We have fabricated three-dimensional metallodielectric photonic crystals that consist of bismuth and gallium metals infiltrated into porous synthetic opals that have 300 nm diam silica balls. The specular reflectivity was measured in a broad spectral range from 0.3 to 25 μm using a variety of light sources, detectors and spectrometers. In addition to broadening of the original Bragg stop bands in the visible spectral range that give rise to iridescence colors, we also found a dramatic decrease of reflectivity in the visible/near-infrared spectral range. For frequencies below a cut-off frequency in the mid-infrared range the reflectivity increases to its normal bulk value in the respective metal, as predicted by theory and fitted by a model calculation.
95(2004); http://dx.doi.org/10.1063/1.1650531View Description Hide Description
When a high-power laser beam is focused into liquid, it results in a shock wave emission and cavitationbubble generation. Upon inserting a rigid substrate into the liquid, the bubbles migrate towards the substrate due to the Bjerknes attractive force. Due to bubble–substrate and/or bubble–free-surfaceinteraction, a high-speed liquid jet is formed during bubble collapse, and a collapse shock wave is generated at the moment of bubble collapse near the substrate. These shock waves and liquid jet induce large forces acting on the substrate to remove particles from it. For a substrate several millimeters away from the laser focus point, the collapse shock wave and liquid jet play key roles in removal of particles. The cleaning efficiency increases with an increase of laser fluence and decreases with an increase of distance between substrate surface and laser beam focus point or depth below liquid surface. In a case of bubbles close to substrate and liquid-surface boundaries, implosion of the bubbles will give rise to shock waves and liquid jets oblique to the substrate surface with the parallel and perpendicular components of the forces onto the particles. These oblique liquid jets and shock waves result in high cleaning efficiency. A liquid, such as alcohol and commercial washing solution, as the surrounding medium, rather than air or vacuum, can reduce adhesion force and enhance cleaning efficiency.
95(2004); http://dx.doi.org/10.1063/1.1649809View Description Hide Description
An intense green upconversion emission due to a photonavalanche mechanism has been observed in codoped fluroindate glasses, measured at 200 K, under excitation at around 750 nm. The influence of the concentration on the photonavalanche process has been studied. The pump power threshold of the avalanche mechanism decreases as the concentration is increased. A reduction by about a factor of 3 is observed from the single dopedglass to the codoped glass. This effect has been related to an extra feeding of the intermediate level of ions via and energy transfer and back transfer processes, respectively.