New design to measure absolute spectral reflectivity

Abstract

A new type of normal incidence scanning reflectometer is designed and constructed. In the system design, instead of using a reference reflective sample or the optical path adjustment methods as in traditional design, we use a fused quartz M-type prism to split the beam of incidence light into two beams in a total internal reflection configuration. The spot sizes, intensities, and spectral responses of these two light beams, therefore, are identical. One reference beam goes directly to the detector. Another sampling beam goes to the sample and is measured by the same detector after beam reflection. A metal disk having three holes is driven precisely by a stepping motor and is used to control the reference and reflection beams as well as the background signals, which are measured in sequence. In terms of the three signals, the absolute reflectivity of the sample at a certain wavelength can be determined immediately using the computer. The system is controlled automatically by the computer with a working wavelength range from 400 to 800 nm. The incidence angle is fixed and equals about 5 deg. The details of the system design, optical configuration, and error reduction are given and discussed. The measured spectral results of the reflectivity for a few testing samples are also given, and are shown to be in good agreement with those measured by other optical methods. The designed system, however, is simpler and can be used in many optical studies.