Laura E. Davis

Elucidating secondary organic aerosol from diesel and gasoline vehicles through detailed characterization of organic carbon emissions

Emissions from gasoline and diesel vehicles are predominant anthropogenic sources of reactive gas-phase organic carbon and key precursors to secondary organic aerosol (SOA) in urban areas. Their relative importance for aerosol formation is a controversial issue with implications for air quality control policy and public health. We characterize the chemical composition, mass distribution, and organic aerosol formation potential of emissions from gasoline and diesel vehicles, and find diesel exhaust is seven times more efficient at forming aerosol than gasoline exhaust. However, both sources are important for air quality; depending on a region’s fuel use, diesel is responsible for 65% to 90% of vehicular-derived SOA, with substantial contributions from aromatic and aliphatic hydrocarbons. Including these insights on source characterization and SOA formation will improve regional pollution control policies, fuel regulations, and methodologies for future measurement, laboratory, and modeling studies.

Measurement of Thermal Lensing for the LiCaAlF6: Cr3+ Laser Material

It has been demonstrated in a series of recent articles that the new crystal, LiCaAlF6: Cr3+, (known as Cr:LiCAF), holds substantial promise as a practical laser material.1-3 The laser output is tunable from 720-840 nm, and the Cr3+ ion exhibits two broad absorption bands in the visible range, thereby permitting the efficient absorption of flashlamp light. In this paper we report measurements of the thermal and thermo-optical properties of Cr:LiCAF that are relevant to the laser performance. The thermal lensing of Cr:LiCAF has been directly measured and compared to that of alexandrite (BeAl2O4:Cr3+).4

Organic Nonlinear Crystals And High Power Frequency Conversion

We are searching for new second and third harmonic generators among the salts of organic acids and bases. We discuss the relevant properties of crystals from this group of compounds, including their nonlinear and phasematching characteristics, linear absorption, damage threshold and crystal growth. In addition, we summarize what is known concerning other nonlinear optical properties of these crystals, such as two-photon absorption, nonlinear refractive index, and stimulated Raman thresholds. A preliminary assessment is made of the potential of these materials for use in future high power, large aperture lasers such as those used for inertial confinement fusion experiments.

Dispersion Measurements Of Microcrystals In The Near Ultraviolet And Infrared

Procedures for measuring the linear optical properties of small, transparent crystals are described. Using a spindle stage refractometer, the refractive indices for light from 0.38 to 1.10 μm can be determined. The methods are employed to study new nonlinear crystals to evaluate their potential as second and third harmonic generators of light at 1.064 μm. The measurements can be made on single crystal fragments as small as 50 μm, thus permitting preliminary evaluations to be made prior to extensive crystal growth efforts.