Characterization of an Acousto-optic Tunable Filter and Use in Visible Spectrophotometry

The use of a paratellurite acousto-optic tunable ® lter (AOTF) is demonstrated as a monochromator for spectrophotometry. This device operates in the range of 400 to 700 nm with a resolution from 2.5 nm (at 633 nm) to 0.5 nm (at 400 nm). Results of the initial characterizations indicate that behavior follows the theoretical model in terms of frequency/wavelength relationships, dependence of the output wavelength upon the incident radiation angle, and bandpass as a function of wavelength. Initial results of spectroscopic characterizations of permanganate, cobalt(II), holmium(III), praseodymium( III), and neodymium(III) solutions are presented. Placing a polarizer in the light path reduced the amount of stray light reaching the detector. Two types of photomultiplier tubes were used as detectors. The sensitivity of the PMTs varied at different wavelengths, which affected spectral responses and the effects of scattered light.We gratefully thank the E. L. Ginzton Research Center, Varian Associates, Incorporated, for their financial support of this project