Butler Timothy J A, Miller Johanna L, Orr-Ewing Andrew J
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom.
J Chem Phys. 2007 May 7;126(17):174302. doi: 10.1063/1.2723735.
A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650 nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25 kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient epsilonmin was determined to be 3x10(-6). Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4 microm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper.
一台工作在近红外波段、波长接近1650 nm的连续波分布反馈二极管激光器被用于测量单个气溶胶颗粒对光的消光。光反馈腔衰荡光谱技术(CRDS)被用于以1.25 kHz的重复频率测量CRDS事件。这种非常高的重复频率首次实现了对单个气溶胶颗粒对光的消光的多次测量,并证明了光散射对激光束内颗粒位置的依赖性。提出了一个模型来定量解释这一现象。确定最小可检测无量纲消光系数εmin为3×10^(-6)。从直径为4微米的单分散颗粒样品中获得的单个球形聚合物珠的消光值与米氏散射理论计算的值几乎定量一致。在配套论文中讨论了使用连续波激光通过CRDS测量消光时与米氏理论预期的偏差。