Dual-photodiode radiometer design for simultaneous measurement of irradiance and centroid wavelength of light sources with finite spectral bandwidth.

Abstract

We present the design of a radiometer that can simultaneously measure both centroid wavelength and irradiance of a light source without recording its spectrum, when the light source has a finite spectral bandwidth. It consists of two photodiodes separated with a beam splitter in its basic construction, which can be referred to as a dual-photodiode radiometer. This radiometer is calibrated by measuring the spectral responsivities of two photodiodes against the spectral irradiance at the input aperture. The concept of the simultaneous measurement is valid under the condition that the spectral responsivities are linear against wavelengths within the spectral bandwidth of the source to be tested. The feasibility and expected accuracy are analyzed by numerical simulations and experimentally tested for the realization of a UVA irradiance meter, which shows an agreement within 0.2nm and 0.6% for centroid wavelength and irradiance, respectively, with other reference instruments.