Standardization of Acousto-optic Tunable Filter NIR spectrometric instrument

Abstract

By employing an Acousto-optic Tunable Filter (AOTF) as the spectroscopical device, a Near-infrared (NIR) spectrometer that is compact, rugged and having random wavelength access has been built. In this paper, the working principle of Acousto-optic Tunable Filter and the schematic design of the instrument are described in details. As a spectrometer for on-site use, the instrument adopts a double beam scheme for self-calibration, modulation of light intensity is employed to reduce interference of noise, and different configurations of the probe offer more versatility in measurement. Specifications for the instrument are quantified. After the instrument’s performance is qualified for wavelength accuracy and scale precision, glucose solution samples are prepared and transflectance spectra are sampled on the instruments. PLS model has been set up through the spectra of aqueous solution of glucose and cross-validation is used to test its predictability. Calibration transfer is attempted between instruments. Direct Standardization (DS) and Piecewise Direct Standardization (PDS) algorithms are briefly described here. It should be noted in this experiment that the proper determination of rank of transformation matrix plays an important role in estimating the quality of spectra transfer. Calibration transfer is performed between instruments and a satisfactory prediction error of 1.5~2 times larger is achieved by applying DS and PDS method.