STARR II is a planned NIST facility for spectral measurements of specular reflectance and diffuse bidirectional reflectance distribution function (BRDF) that is the follow-on to the current NIST STARR (Spectral Tri-function Automated Reference Reflectometer) facility. STARR II will improve and expand on the measurement capabilities of STARR, increasing spectral coverage in the short-wave infrared spectral region and adding out-of-plane BRDF measurement capability. We present characteristics of a tunable light source constructed for STARR II, which is based upon a supercontinuum fiber laser and has a tuning range from 500 nm to 2450 nm, alongside those of the current lamp-based system in STARR. We then discuss considerations for measuring BRDF using this source. The STARR II goniometer will employ an articulated robotic arm to center and orient the sample, and we calculate the transformations from orientation of the sample and receiver to incident and scattering angles for measurements of in-plane and out-of-plane BRDF. We also present, for the first time, an analytic expression for the correction of measured BRDF to true BRDF due to the finite illumination area and collection aperture, and to the effects of uniformity of illumination. Finally, we present exploratory BRDF measurements on a diffuse sample made using the tunable supercontinuum source.
Proceedings Title: Optics and Photonics 2012: Advanced Metrology
Conference Dates: August 12-16, 2012
Conference Location: San Diego, CA
Conference Title: Reflection, Scattering, and Diffraction from Surfaces III (Conference 8495)
Pub Type: Conferences
bidirectional, diffuse, BRDF, laser, reflectance, STARR, STARR II, supercontinuum