A Modified Set-Up for Spectral Transmittance Measurement

摘要

An automated single beam grating based spectral transmittance measurement setup is used in UME. System has been modified to obtain better measurement accuracy values for optical densities of three and higher in the 200 to 2500 nm region. Improvements on both condenser and output optics, and the progress in the measurement results are discussed in detail. Basically the set-up consists of a double grating monochromator, condenser and output optics, detector and related electronics units. The original input optics was replaced by a condensing configuration employing flat, spherical and cylindrical mirrors. A 30W Deuterium and a 250 W Quartz Halogen lamps are used as light sources from UV to near infrared. The spherical mirror is used for collimating the light, and the cylindrical mirror for focusing the collimated light on the input slit of the monochromator. In the output optics, a spherical mirror was used for collimating the light that emerged from the exit slit of the monochromator. A collimated beam area of around 50×25 mm are obtained in this configuration. Another paraboloidal concave mirror is used for focusing the collimated beam onto the photodetector surface. High accuracy measurements are obtained with these modifications, typically a few parts in 10~(4). The most significant feature of this system is that it has a large uniform collimated beam so that measurements on large samples can be carried out.