Electro-Optical Instrumentation Systems with Their Data Acquisition and Treatment

Abstract

The general principles of optical and photoelectronic detection schemes (Fig. 1) are common to all electro-optical instrumentation and have been described in a number of reviews on this subject (1–12). An electric field is applied to the sample, usually in the form of a short duration signal, for example, a single rectangular or bipolar pulse, a sinusoidal pulse train, or a condenser discharge. This results in a transitory perturbation of the sample. The signal, due to the reorientation of the particles, deformation or conformational changes caused by the electric field, is monitored through changes in one or more of several optical properties: absorbance (electric dichroism effect), refractive index (electric birefringence, double refraction, or Kerr effect), fluorescence (fluorescence polarization or intensity), light-scattering, Raman scattering, optical rotation, circular dichroism. Usually, the transient optical signal is detected by a photomultiplier which converts it into an electric signal which is analyzed after suitable amplification through an appropriate detection circuit. The time scales readily covered by these techniques extend, with conventional instruments, down to the microsecond range, and, with fast systems, down to the nanosecond range.