Intense Laser Illumination Research Articles

Optical properties of porous silicon layers processed with a HF:HCI:C2H5OH electrolyte

The properties of porous silicon samples prepared by adding hydrochloric acid to the usual hydrofluoric-acid electrolyte have been studied. These samples exhibit an intense photoluminescence that does not degrade over time and is unaffected by exposure to intense laser illumination. The peak photoluminescence from these layers of porous silicon occurs at photon energies of 1.85–1.9 eV. The photoluminescence signal from samples prepared in the standard way under the same initial conditions but without HCl in the composition of the electrolyte is two orders of magnitude less intense. Studies of the degradation of these porous silicon samples with time and exposure to various power levels of laser illumination revealed that the samples with the maximum content of HCl in the electrolyte composition emitted photoluminescence that was unaffected by laser illumination. In this work, the infrared spectra of the samples was measured in order to monitor the chemical state of their surfaces. It was found that the abrupt 100-fold increase in the intensity of the photoluminescence signal from samples made according to the method proposed here is associated both with distinctive features of the structure of porous silicon layers and with the presence of a thin crystalline layer of SiO2 on the surface of nanocrystallites.

Monte Carlo Simulation of Discrete Space Charge Effects in Photoelectron Emission Microscopy

Abstract: Interactions among discrete charges in the emission current of a photoelectron imaging system can limit its spatial resolution, significantly affecting the performance and design of emission microscopes employing high current densities. Under intense laser illumination a sample can emit photocurrent densities exceeding tens of amperes/cm2. This study describes Monte Carlo estimations of electron trajectory aberrations produced by discrete electron space charge interactions in a photoelectron emission microscope. The results also apply to photoelectron sources that might be used in other kinds of devices. A model of the emission process was used to assemble bunches of about 500 randomly positioned electrons whose individual trajectories were computed. Trajectory distortions of one member in each bunch that were due to the coulomb forces exerted by its neighbors were used to evaluate aberrations for a variety of voltages, current densities, and instrument configurations. Aberrations estimated in this way are smaller than those predicted by earlier theory or obtained in pulsed imaging experiments. Here we discuss the reasons for these differences, offer suggestions for improved instruments, and present experimental images.

Stable hydrogenated amorphous silicon films deposited from silane and dichlorosilane by radio frequency plasma chemical vapor deposition

Hydrogenated amorphous silicon films have been grown by radio frequency (rf) plasma chemical vapor deposition with the addition of small amounts (up to 20%) of dichlorosilane to the silane. Results show that as the amount of dichlorosilane is increased, the films are more resilient to the creation of light induced defects. Under intense pulsed laser illumination (5 mJ/pulse, 10 ns, 10 Hz) the steady state defect density measured by the constant photocurrent method (CPM) is reduced by over one order of magnitude to 4×1016 cm−3 as compared to ∼5×1017 cm−3 for films grown under identical conditions with pure silane. Furthermore, there is a threefold increase in the deposition rate over the range of mixture ratios studied here.

The optical properties of graphite under intense picosecond laser illumination

Picosecond laser ellipsometry has been used in the visible to estimate for the first time the index of refraction of highly oriented pyrolitic graphite samples at high temperatures. While recent experiments seem to indicate that molten graphite behaves in many respects as a metal, investigation of optical properties with picosecond laser pulses consistently shows a reduced reflectivity value as soon as the threshold value of laser fluence for surface melting is exceeded. This occurrence may be interpreted as a reduced conductivity of the liquid phase. The experimental conditions are discussed, and in particular, the possible occurrence of optically thick layers of matter in front of the hot surface during the measurements is evaluated.

Titanium Corrosion by a Hot Perfluoropolyether

Abstract The kinetics and mechanism of titanium corrosion by Krytox MLO-71-6 are reported. The rate of corrosion is found to be dependent on the presence of molecular oxygen in the environment. For titanium corrosion to occur, the lubricant chains must first break down into smaller reactive molecules. This degradation process is accelerated by TiF3 corrosion products on the metal surface, thus giving rise to a chain mechanism. The corrosion is not promoted by intense CW laser illumination at λ = 514nm.