Measurement Of Extinction Cross Section Research Articles

High spectral resolution lidar at the university of wisconsin-madison

This paper describes the modifications done on the University of Wisconsin-Madison High Spectral Resolution Lidar (HSRL) that improved the instrument’s performance. The University of Wisconsin HSRL lidars designed by our group at the Space Science and Engineering Center were deployed in numerous field campaigns in various locations around the world. Over the years the instruments have undergone multiple modifications that improved the performance and added new measurement capabilities such as atmospheric temperature profile and extinction cross-section measurements.

Direct measurements of the optical cross sections and refractive indices of individual volatile and hygroscopic aerosol particles.

We present measurements of the evolving extinction cross sections of individual aerosol particles (spanning 700-2500 nm in radius) during the evaporation of volatile components or hygroscopic growth using a combination of a single particle trap formed from a Bessel light beam and cavity ring-down spectroscopy. For single component organic aerosol droplets of 1,2,6-hexanetriol, polyethylene glycol 400, and glycerol, the slow evaporation of the organic component (over time scales of 1000 to 10,000 s) leads to a time-varying size and extinction cross section that can be used to estimate the refractive index of the droplet. Measurements on binary aqueous-inorganic aerosol droplets containing one of the inorganic solutes ammonium bisulfate, ammonium sulfate, sodium nitrate, or sodium chloride (over time scales of 1000 to 15,000 s) under conditions of changing relative humidity show that extinction cross-section measurements are consistent with expectations from accepted models for the variation in droplet refractive index with hygroscopic growth. In addition, we use these systems to establish an experimental protocol for future single particle extinction measurements. The advantages of mapping out the evolving light extinction cross-section of an individual particle over extended time frames accompanied by hygroscopic cycling or component evaporation are discussed.

On definition and measurement of extinction cross section

Following the recent analyses of extinction by Berg et al. [J Opt Soc Am A 2008;25:1504–1513; J Opt Soc. Am A 2008;25:1514–1520], we show that although it is possible to define and measure the extinction cross section for a single particle using a detector of light facing the incident beam, this requires certain theoretical assumptions and experimental precautions.

Assessment of moisture content of fibres and fabrics by measurement of extinction cross-section in an open resonator

A new application of a large, computer-controlled open resonator is described. Measurement of the extinction crosssections of samples of wet materials are recorded very quickly and continuously throughout the drying period. The measurements may be taken throughout the interval 8–12 GHz and provide a complete record of the drying process.

A technique for the measurement of extinction cross section

A method is described for the measurement of the acoustic extinction cross section of an object underwater. Use is made of the forward-scattering theorem which directly relates the extinction cross section of an object to the quadrature component of the scattered field in the forward direction. In the measurement technique the forward-scattered field is separated from the incident field by a simple cancellation process. The extinction cross section of a number of spheres and discs have been measured and the results are shown to be in good agreement with theoretical predictions. It is anticipated that this measurement technique could be extended to irregularly shaped bodies, such as fish.

Extinction cross-section measurements on single falling water drops at 100 GHz

An open resonator with 100 GHz source is used to determine the extinction cross-section of water drops falling freely through the atmosphere. Results show a very close agreement with the theoretical values computed using classical Mie scattering theory and values of complex refractive index from an empirical model.

Measurement of extinction cross-section of single particles at 100 GHz

The extinction cross-section of single particles of dimensions comparable with the wavelength has been measured using a double resonance technique at 100 GHz. Results agree well with Mie's theory. The technique is applicable to moving particles with velocities up to a few metres per second.