HIGH-ACCURACY SPECTROMETER FOR MEASUREMENT OF REGULAR SPECTRAL TRANSMITTANCE

A high-accuracy spectrometer has been developed for measuring regular spectral transmittance. The spectrometer is an automated, single-beam instrument that is based on a grating monochromator, reflecting optics , and an averaging sphere detector unit with a silicon photodiode. The uncertainties related to wavelength calibration, detector nonlinearit y, system instability, beam displacement, polarization, stray light, i nterreflections, and beam uniformity are determined for the visible sp ectral range from 380 to 780 nm. A total uncertainty of 3 x 10(-4) (1 sigma) is estimated for transmittance measurements of homogeneous neut ral-density filters. The uncertainty of the wavelength scale is 0.06 n m. As a specific application, calibration of V(lambda)-correction filt ers is studied. To verify the accuracy of the transmittance measuremen ts, a comparison of the measured and predicted transmittances of a sam ple of high-purity fused silica is made, revealing agreement at the 5 x 10(-4) level.