Determining non-linear optical properties using the Z-scan technique
Date
2005-03
Authors
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Journal ISSN
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Publisher
Stellenbosch : University of Stellenbosch
Abstract
The extremely high light intensities produced by lasers and the increasing use of lasers highlights
the need for measures to prevent damage to materials due to exposure to high intensity
laser light. In particular it necessitates the development of systems to protect optical sensors,
including the human eye. In this work optical limiters were investigated as a system for protecting
sensors. An optical limiter transmits ambient light, but absorbs high intensity light. This
makes it ideal for protecting sensors from laser radiation, since it allows the sensor to operate
unhindered at design intensities while protecting it from harmful high intensity radiation.
There are various mechanisms used for optical limiting, and in this work the nonlinear
absorption and the nonlinear index of refraction changes of materials were investigated. A
facility was established to measure the nonlinear optical properties of a variety of materials,
in order to classify them as possible optical limiters. This entailed creating a so called Zscan
setup, which enabled us to measure the nonlinear absorption coefficient and the nonlinear
index of refraction of a material. The theory and the design of the setup are discussed and
experimental results obtained using this setup are presented.
A wide variety of material types were investigated to show the versatility of the experimental
setup. These included C60, which was analyzed in solution; ZnO which is a crystal; CdS quantum
dots in solution; and poly(dioctyl-fluorene), which is a large polymer molecule, in solution.
The materials investigated in this work were chosen based on their known strong nonlinear optical
properties. Emphasis was placed on measuring the nonlinear absorption coefficients since
it was the dominant optical limiting effect of the materials under investigation.
The results obtained displayed the same trends as published results and it shows that the
established facility was capable of measuring the nonlinear properties of these samples. The
experimental limitations of the setup were determined, and critical experimental parameters
were identified for measurements of this nature. Improvements to the experimental facility are
suggested to improve the accuracy of future measurements.
Description
Thesis (MSc (Physics))--University of Stellenbosch, 2005.
Keywords
Nonlinear optics, Optical scanners, Scanning systems, Dissertations -- Physics, Theses -- Physics