Near-infrared angular scattering, transmission, and Lambertian performance of transmissive optical diffusers

Optical diffusers are widely used in radiometry, remote sensing, and nephelometry, yet their angular scattering behavior in the near infrared (NIR) remains largely uncharacterized. Here, we present a systematic experimental study of the angular transmission distribution of common transmissive diffusers at 1064 nm using high-resolution goniometric measurements. Surface, bulk, and hybrid diffusers were evaluated under both collimated and diffuse illumination. Significant departures from visible-wavelength behavior were observed, including residual forward scattering, reduced angular redistribution, and strong dependence on source illumination geometry. Bulk opal diffusers provided the closest approximation to Lambertian behavior, while diffuser combinations improved angular uniformity at the expense of transmission. The results establish a quantitative framework for diffuser selection and reveal that both diffuser structure and source characteristics govern NIR angular performance. These findings provide guidance for the design and calibration of NIR optical measurement systems.