Evaluation of Transmission Near the Christiansen Wavelength for Dynamic Sand Samples.

Many optical applications, including free-space optical communications, lidar, and astronomical measurements, are impacted by the presence of light-scattering particles also known as obscurants. Scattering from particles consisting of sand, dust, dirt, and other substances can significantly degrade optical signals. For many obscurants, the index of refraction is dependent on the wavelength of light, and there exists a Christiansen wavelength (λ) at which scattering is at a minimum.

Measurement of the Optical Constants of Sand Samples Using Ellipsometry on Sand-Adhesive Composites.

In order to model the propagation of light through a sand cloud, it is critical to have accurate data for the optical constants of the sand particles that comprise it. The same holds true for modeling propagation through particles of any type suspended in a medium. Few methods exist, however, to measure these quantities with high accuracy.

Surface-Enhanced Raman Spectroscopy for Environmental Monitoring of Aerosols.

Surface-enhanced Raman spectroscopy (SERS) is conducted from single aerosol particles held in a linear electrodynamic quadrupole trap. SERS measurements from two representative types of ambient aerosol particles, semi-liquid and solid aerosols, are demonstrated; aerosol composed of adenine where the metallic nanoparticles (MNPs) are volume distributed throughout the particle and aerosol composed of polystyrene latex (PSL) beads where the MNPs are surface coated. An enhancement factor > 10 is demonstrated from 5 μm aerosols containing trace amounts of adenine (0.

Optical measurements from single levitated particles using a linear electrodynamic quadrupole trap.

We have recently made advancements in a linear electrodynamic quadrupole (LEQ) device for capturing and levitating either single or multiple micro-particles that provides significant improvements in capture efficiency, reliability, and optical measurement access. We have used our LEQ to trap particles ranging from 30 to less than 0.5 μm in size and provide a controlled environment to study particle physical/chemical dependencies on temperature, relative humidity, and gas constituents.

Metallic-nanoparticles-enhanced fluorescence from individual micron-sized aerosol particles on-the-fly.

Fluorescence spectra from individual aerosol particles that were either coated or embedded with metallic nanoparticles (MNPs) was acquired on-the-fly using 266 nm and 355 nm excitation. Using aqueous suspensions of MNPs with either polystyrene latex (PSL) spheres or dissolved proteins (tryptophan or ovalbumin), we generated PSL spheres coated with MNPs, or protein clusters embedded with MNPs as aerosols. Both enhanced and quenched fluorescence intensities were observed as a function of MNP concentration.