Spectral function basic principles

In order to understand the basis of test design and the limitations of particular tests, it is important to understand the basic principles of photochemistry. Concepts such as the relationship between the photon flux of a source and its irradiance quantum yield and only absorbed photons causing photochemical reactions (Moore, 1987, 1996a) are fundamental. The spectral power distribution (SPD) of a source (i.e., the energy emitted as a function of wavelength and the absorption spectrum of the exposed product) is important in determining the nature and extent of the photochemical reaction. 

A chemical sensor is a device that transforms chemical information into an analytically useful signal. Chemical sensors contain two basic functional units a receptor part and a transducer part. The receptor part is usually a sensitive layer, therefore a well founded knowledge about the mechanism of interaction of the analytes of interest and the selected sensitive layer has to be achieved. Various optical methods have been exploited in chemical sensors to transform the spectral information into useful signals which can be interpreted as chemical information about the analytes [1]. These are either reflectometric or refractometric methods. Optical sensors based on reflectometry are reflectometric interference spectroscopy (RIfS) [2] and ellipsometry [3,4], Evanescent field techniques, which are sensitive to changes in the refractive index, open a wide variety of optical detection principles [5] such as surface plasmon resonance spectroscopy (SPR) [6—8], Mach-Zehnder interferometer [9], Young interferometer [10], grating coupler [11] or resonant mirror [12] devices. All these optical... 

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