Goniometric optical scatter instrument (GOSI)
The bidirectional reflectance distribution function (BRDF) quantifies the angular distribution of light scattered from a surface as a function of wavelength, polarization state, and angle of incidence. The bidirectional characterization of optical scatter from surfaces is a useful metrological tool in evaluating elements contained within optical systems that require the minimization of scattered light for high image contrast or radiant energy density control. It is also effective for the characterization of materials and surfaces in control and inspection processes in manufacturing settings. The Goniometric Optical Scatter Instrument (GOSI) at NIST employs ultraviolet and visible laser light sources and highly sensitive detection schemes. This instrument is well-suited for studying low-scatter surfaces such as silicon wafers and optically smooth mirrors. Other applications include assessment of the uniformity of periodic structures such as gratings, patterned photoresists, or built-up patterns on semiconductor surfaces.