Continuously tunable attenuation stage for weak-light radiance calibration using an integrating sphere and a dual-aperture tube.

Abstract

We present a continuously tunable weak-light attenuation stage combining an integrating sphere with a coaxial dual-aperture tube. An exact view-factor model provides the geometry-based reference, and a monitor-normalized calibration produced a 22×22 attenuation matrix spanning 0-40.36 dB. A separable correction reduced the in-grid residual RMS to 0.017 dB. Independent target-setting validation over 5.0-39.1 dB yielded an RMS residual of 0.091 dB. Measured spatial and angular departures of the input field were propagated into the uncertainty budget, giving an expanded uncertainty of 0.021-0.036 dB (k=2). Spectral-shape RMS deviations remained within 0.477% up to 15 dB.