Abstract

A computer controlled high-gain amplifier has been designed for sensitive detection of optical signals. Based on the use of digital-to-analog converters DACs, the gain and offset of a transimpedance amplifier are adjusted through a computer trying to match ideal amplifier parameters for optical detection with different experimental conditions. The amplifying modules have been developed for optical-rheometry techniques that provide information about the microstructural properties of fluids by measuring optical anisotropies induced by transient flows. Characterization of these programmable gain amplifiers shows that they provide gains and bandwidths more than adequate for experiments involving signals that evolve rapidly and with a large dynamic range. Hence, the use of DACs allows for the possibility of computer controlling both gain and offset in real time, with a significant reduction of the spurious contributions from the amplifying stages during data acquisition. In spite of being designed for optical rheometry, the amplifiers could be useful for any other laboratory arrangements requiring an amplifying stage with real-time gain and offset adjustment capabilities.