ConstReadonlyCROWN_GLASS: CauchyCoefficientsBK7-like crown glass: noticeably lower dispersion than flint, ~1.51-1.53 across the visible range.
ReadonlyFLINT_GLASS: CauchyCoefficientsDense flint glass: high dispersion, ~1.63 (red) to ~1.69 (violet) across the visible range.
ReadonlyFLUORITE: CauchyCoefficientsFluorite (CaF2): very low dispersion, ~1.43-1.45 across the visible range -- used in real apochromatic camera lenses specifically to minimize chromatic aberration.
Approximate Cauchy coefficients for common optical materials -- good enough for real-looking visual dispersion (correct color ordering, plausible spread), not spectroscopy-grade precision.
bis in micrometres^2, matchingOptics.cauchyIndex()'s convention.