Under the condition of first-order blooming, a parallel dielectric slab, which is inserted in the path of an obliquely incident p- or s-polarized light beam, introduces multiple discrete attenuation levels given by 1/3, 4/27, 4/243,...... in reflection and 4/9, 4/81, 4/729,...... in transmission. These attenuation levels are independent of the slab refractive index, incident p or s linear polarization, or the presence of identical transparent surface coatings at the front and back sides of the slab. Therefore, the tilted slab provides multidecade reflectance and attenuation reference values that can be used in calibrating spectrophotometers and filters, and also for testing the linearity of photodetectors. For an uncoated dielectric slab, incidence angles that cause first-order blooming are determined as functions of the slab refractive index for incident p- or s-polarized light.
R. M. A. Azzam, "Tilted parallel dielectric slab as a multilevel attenuator for incident p- or s-polarized light," Appl. Opt. 48, 425-428 (2009).