Showing papers by "Charles V. Shank published in 1985"
TL;DR: The thermal ionization time of excitons at room temperature for the first time is measured, and it is found that $\ensuremath{\tau}\ensure math{\sim}300$ fs.au$ produces more absorption bleaching than equal densities of free-carrier pairs.
Abstract: We investigate the effect of excess excitonic populations created by resonant ultrashort excitation on the optical-absorption properties of GaAs quantum wells. We find that under these conditions at room temperature excitons produce more absorption bleaching than equal densities of free-carrier pairs. This bleaching partly recovers as the excitons ionize to give free carriers. Hence, we directly measure the thermal ionization time of excitons at room temperature for the first time, and find that $\ensuremath{\tau}\ensuremath{\sim}300$ fs.
252 citations
TL;DR: In this article, a simple imaging technique that can be used to photograph ultrafast processes with time resolution determined by the duration of pump and probe laser pulses is described, showing that the melted material emerges as liquid droplets several hundred angstroms in diameter, which atomize in less than a nanosecond.
Abstract: We describe a simple imaging technique that can be used to photograph ultrafast processes with time resolution determined by the duration of pump and probe laser pulses. We demonstrate this technique by photographs having 100-fsec time resolution of a silicon surface undergoing melting and evaporation following intense excitation by an ultrashort laser pulse. These photographs resolve the increase in surface reflectivity caused by surface melting both temporally and spatially. Material evaporation from the melted surface further alters the image of the surface by absorbing and scattering the illuminating laser light. Our analysis of this selectively imaged light suggests that the evaporated material emerges as liquid droplets several hundred angstroms in diameter, which atomize in less than a nanosecond.
181 citations
TL;DR: In this article, the authors describe recent investigations of delayed Auger heating in Si and present a detailed analysis of the properties of the delay-delay-Auger process in Si semiconductors.
Abstract: The advent of femtosecond optical pulse techniques has provided new opportunities for the investigation of the dynamical properties of highly excited semiconductors. In this paper we describe recent investigations of delayed Auger heating in Si.
2 citations