Optical spectra analysis of turbid liquids

• Main Author: Peiponen, K.-E. (Kai-Erik)
• Format: Doctoral Thesis
• Language: English
• Published: University of Oulu 2009
• Subjects: complex refractive index; data inversion; nanoparticles; phase retrieval; turbid liquid
• Online Access: http://urn.fi/urn:isbn:9789514291685; http://nbn-resolving.de/urn:isbn:9789514291685

Abstract This thesis is devoted to methods of analyzing optical spectra obtained from turbid liquids, i.e., liquids that are optically very thick and/or scatter light. Data for spectral analysis were obtained with a new, multifunction spectrophotometer developed for industrial liquid samples. One characteristic of the spectrophotometer is that spectral analysis methods can be implemented into the software. Here, the emphasis was on data inversion methods, particularly the Kramers-Kronig analysis and the maximum entropy method, which can be used to gain information on the wavelength-dependent complex refractive index of liquid samples. Relating to such characteristics as density and colour, the complex refractive index also helps to identify the species that form a liquid. The methods were applied to study the internal reflection of light from the prism-liquid interface of the probe and to analyze surface plasmon resonance spectra. This study provided new methods of investigating the optical properties of relatively difficult objects, like offset inks, and of assessing adhesion forces between ink and the substrate system. Another important part of the thesis was the exploration of spectral analysis methods to obtain optical properties of nanoparticles in a liquid matrix. Bounds for the optical properties of multi-component structures in a liquid were considered with the aid of Wiener bounds.