Wide spectral imaging of the rainbow from ultraviolet to infrared and 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. We show that 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 spectral imaging measurements of an artificial rainbow (a "spraybow") from 354 to 1650 nm and explain the challenges of capturing this data over such a wide spectral range. These include, to our knowledge, the first reported images of the rainbow in the SWIR 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 also provide quantitative measurements of the rainbow's spectral reflectance and compare the results to the theoretically calculated reflectance spectrum.