Wide spectral imaging of the rainbow from ultraviolet to infrared: locating the spectral limits of the rainbow

Measurements of the rainbow outside the visible spectral range are surprisingly rare, but excite our curiosity to explore the spectral limits over which the rainbow exists, from deep ultraviolet to the water absorption bands in the short-wave infrared. If our eyes were able to see over this entire range, with sufficiently bright UV and IR light we would see a rainbow almost 14° in width --- seven times wider than the ~1.9° width that we see in the visible spectrum. We also provide example spectral imaging measurements of an artificial rainbow (a "spraybow") from 354nm to 1002nm, and explain the challenges of capturing this data over such a wide spectral range. By taking advantage of the spectrally-resolved data, we show the individual Airy peaks at each wavelength, allowing us to compare the measured rainbow angular dispersion with scattering theory. Finally, we provide quantitative measurements of the rainbow's spectral reflectance, showing a reasonable correspondence with the theoretically calculated reflectance spectrum.