A spectrally tunable monochromatic integrating sphere photon source for spectral photon radiance responsivity calibration

Abstract

A spectrally tunable monochromatic integrating sphere photon source (ISPS) was built based on a laser driven plasma light source, a monochromator, an optical attenuator, and an integrating sphere. The wavelength of ISPS output photons can be tuned from 300 nm to 800 nm with a spectral bandwidth of 1 nm ~ 5 nm; the spectral optical radiant power into the integrating sphere can be adjusted over three decades through the optical attenuator; the diameters of the inner wall and the exit port of the integrating sphere are 100 mm and 50 mm, respectively. The spectral photon radiance of the ISPS can be measured by a photomultiplier-tube (PMT) based photon counter and two precision apertures. An integrating sphere was utilized in front of the PMT-based photon counter and the non-uniformity of the spectral optical radiant power responsivity was reduced to be ~0.5% over a 5-mm-diameter effective detection area. Two precision apertures were adopted to define the effective detection area and the solid angle extended for the field-of-view. The ISPS can be directly applied to calibrate the spectral photon radiance responsivity of a few-photon imaging system, which was demonstrated on a digital color camera and a focusing lens. The spectral photon radiance responsivity of a given imaging system can be effectively validated based on this ISPS apparatus.