Microscope Spectrophotometry with a Continuous Interference Filter

Abstract

Operating principles are described for microscope spectrophotometry using a continuous interference filter (CIF) powered by a DC motor operated from programmable relays and a multimeter. Optical fibers illuminated from green and red helium-neon lasers were used for calibration. A relatively slow “step, stop and measure” method for scanning through the spectrum was compared with continuous scanning, making measurements as the CIF was moving. Two vectors for wavelength and light intensity were integrated in a stepwise manner (31 wavelengths from 395 nm to 705 nm with a band-pass of 10 nm). The methods were tested against the difficult operating conditions created by measuring reflectance spectra through optical fibers, where there was a crossover between illuminating and measuring pathways and a restricted dynamic range of the photomultiplier at the edges of the spectrum. Both methods gave equally acceptable results with good operating conditions, and equally unacceptable results with bad operating conditions.