Physics & Astronomy ETDs

Publication Date

8-1-1967

Abstract

The backscattered light from a single water drop is studied theoretically and experimentally for drop diameters of about one millimeter. G. Mie gave the exact mathematical solution to the problem of an infinite, plane, monochromatic, electromagnetic wave scattered from a perfect sphere of any radius and index of refraction in 1908. The results of this theory are applied to drops of size parameter (defined as the ratio of the drop circumference to the wavelength of the incident light) near 3000; this corresponds to a drop diameter of about one millimeter. Theoretically, it is shown that the backscattered light originates from the center of the drop and from the circumference of the drop. The backscattered intensity oscillates in magnitude as the size parameter of the drop changes monotonically. The change in size parameter necessary for one cycle of the sine wave oscillation of the intensity at the center of the drop is 1.18; the change in size parameter necessary for one cycle of the very complicated oscillation of the light from the circumference is .81. The origin of the light from the center of the drop is easily understood from quasi-geometrical optics, while that from the circumference of the drop is more difficult to explain. Several simple theories involving internal geometrical reflections as well as surface wave phenomena are discussed in an attempt to explain the origin and periodicity of the circumferentially backscattered light predicted by the Mie theory. It is shown that geometrical optics alone can not explain the backscatter phenomenon. The simple theory yielding results comparable with the complicated Mie theory is that involving surface waves traveling on the surface of the drop plus geometrical rays taking "jumps" through the interior of the drop. The experiment was performed in order to confirm the results of the theoretical work. A He-Ne laser beam was scattered from a single water drop, and the backscattered light was observed both photographically and photoelectrically. Experimentally, the backscattered light is found to originate from the center and from the circumference of the drop as predicted. Although there is not an exact correspondence between the experimental results and the theory, the circumferential light does show a very complicated oscillation composed of several different types of resonances as the drop evaporates. The experimental results also seem to confirm the Mie theory with respect to the periodicity of the back­scattered light with size parameter and to the structure of its sharp intensity resonances.

Degree Name

Physics

Level of Degree

Doctoral

Department Name

Physics & Astronomy

First Committee Member (Chair)

Howard Carnes Bryant

Second Committee Member

Colston Chandler

Third Committee Member

Victor H. Regener

Fourth Committee Member

Christopher Dean

Language

English

Document Type

Dissertation

Download

Share

COinS