Showing papers by "Richard E. Russo published in 2001"

Room-temperature ultraviolet nanowire nanolasers

Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis

Room-Temperature Ultraviolet Nanowire Nanolasers.

Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.

Existence of phase explosion during laser ablation and its effects on inductively coupled plasma-mass spectroscopy.

Abstract: A sudden increase in crater depth was observed during high irradiance (>1010 W/cm2) laser ablation of silicon, and it is attributed to the phenomenon of phase explosion. The threshold irradiance for phase explosion showed a dependence on two laser parameters: laser beam spot size and wavelength. For a larger beam size and longer incident wavelength, a higher laser irradiance was required to generate phase explosion. The rapid increase of crater depth above the phase explosion threshold irradiance correlated with a significant increase in the ICPMS signal intensity. The ratio of crater volume to ICPMS intensity, which represents entrainment efficiency, remained the lowest at laser irradiances slightly above the phase explosion threshold. However, this ratio increased at irradiances well above the threshold (>1011 W/cm2). Chemical analysis using laser ablation at irradiance above 1011 W/cm2 provides increased sensitivity via improved entrainment and transport efficiency and increased ablation rate.

Energy deposition at front and rear surfaces during picosecond laser interaction with fused silica

Abstract: The difference between front-surface and rear-surface energy deposition of a 35 ps laser pulse (λ=1064 nm) in fused silica was investigated using shadowgraphic and laser-deflection techniques. Shock waves were observed in the glass and in air. Shock waves generated in air at the front surface are stronger than at the rear surface. Less than 35% of the energy incident on the surface drives the air shock waves at the rear surface. Up to 90% of the incident energy drives the air shock waves at the front surface. Laser-plasma interaction is responsible for this difference and for limiting the amount of energy deposited inside the sample during front-surface ablation. Energy deposition at the rear surface is mostly limited by self-focusing inside the material.

Influence of preformed shock wave on the development of picosecond laser ablation plasma

Abstract: Using picosecond time-resolved shadowgrams, we measured the development of an expanding air plasma during double picosecond pulse laser ablation of solids Prior to the formation of the air plasma, a shock wave was established by the first laser pulse interaction with the solid target The second picosecond laser pulse interacted with the shock wave and induced the air plasma at the interface between the shock wave front and the ambient air After the end of the second picosecond ablation laser pulse, the temporal expansion of the air plasma was found to follow the relation r∼t2/5 Results from this air plasma suggest that the shock wave induced by the first laser pulse only absorbs approximately 5% of the energy of the second picosecond laser pulse Nevertheless, the expansion of the air plasma towards the target results in an enlarged heat-affected zone at the target surface

Laser ablation inductively coupled plasma mass spectrometry of pressed pellet surrogates for Pu materials disposition

Abstract: Successful Pu disposition by immobilization in glass or ceramic form requires accurate and precise knowledge of impurity amounts. Analysis of Pu material by conventional liquid nebulization requires dissolution, which is difficult due to the refractory nature of the samples. Laser ablation is a suitable sampling technique for direct analysis of solids. This paper demonstrates the procedures that were established for PuO2 analysis using laser ablation inductively coupled plasma mass spectrometer (ICP-MS). Pressed pellets prepared from CeO2 were used to simulate PuO2. Effects of laser conditions, sample preparation, and matrix composition, specifically mass of a matrix element and color, on the analyses of CeO2, Bi2O3, and PtO2 based pressed pellets were examined. Influence of mixing/grinding time on particle sizes, sample homogeneity, and ablation efficiency were investigated. Laser conditions that produce stoichiometric sampling were examined.

Representative sampling using single-pulse laser ablation with inductively coupled plasma mass spectrometry

Abstract: Single pulse laser ablation sampling with inductively coupled plasma mass spectrometry (ICP-MS) was assessed for accurate chemical analysis. Elemental fractionation (e.g. Pb/U), the quantity of ablated mass (crater volume), ICP-MS intensity and the particle contribution (spike signal) during single pulse ablation of NIST 610 glass were investigated. Pb/U fractionation significantly changed between the first and second laser pulse and showed strong irradiance dependence. The Pb/U ratio obtained by the first pulse was usually higher than that of the second pulse, with the average value close to the representative level. Segregation during laser ablation is proposed to explain the composition change between the first and second pulse. Crater volume measurements showed that the second pulse produced significantly more ablated mass. A roll-off of the crater depth occurred at {approx}750 GW/cm{sup 2}. The absolute ICP-MS intensity from the second pulse showed no correlation with crater depth. Particle induced spikes on the transit signal showed irradiance and elemental species dependence.

Laser induced desorption and ablation: mechanism of metal removal from an Al-Cu-Fe alloy and a quasicrystal of the same composition

Abstract: Quasicrystals are a special class of metallic alloys that share some of the properties of crystals. Their structures reduce to a single repeating unit like that of the unit cell of a crystal. The quasi-unitcell is representative of a cluster like structure where electrons cannot move with freedom as in metals. Quasicrystals are formed of metallicelements but they do not have metallic properties.

Representative sampling using single-pulse laser ablation with inductively coupled plasma mass spectroscopy

Abstract: Representative sampling using single-pulse laser ablation with inductively coupled plasma mass spectrometry Haichen Liu 1 , Xianglei Mao, Richard E. Russo ∗ Lawrence Berkeley National Laboratory, Berkeley, California 94720 Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, P.R. China, 510640 Abstract Single pulse laser ablation sampling with inductively coupled plasma mass spectrometry (ICP-MS) was assessed for accurate chemical analysis. Elemental fractionation (e.g. Pb/U), the quantity of ablated mass (crater volume), ICP-MS intensity and the particle contribution (spike signal) during single pulse ablation of NIST 610 glass were investigated. Pb/U fractionation significantly changed between the first and second laser pulse and showed strong irradiance dependence. The Pb/U ratio obtained by the first pulse was usually higher than that of the second pulse, with the average value close to the representative level. Segregation during laser ablation is proposed to explain the composition change between the first and second pulse. Crater volume measurements showed that the second pulse produced significantly more ablated mass. A roll-off of the crater depth occured at ~750 GW/cm 2 . The absolute ICP-MS intensity from the second pulse showed no correlation with crater depth. Particle induced spikes on the transit signal showed irradiance and elemental species dependence. To whom correspondence should be addressed: (e-mail) rerusso@lbl.gov.