Spectral Unit Converter

Photon energy, wavelength, frequency, and wavenumber are four equivalent descriptions of the same electromagnetic radiation, interrelated by E = hν = hc/λ and ν̃ = 1/λ. Different disciplines favor different representations: laser engineers work in nanometers and terahertz, spectroscopists in wavenumbers (cm⁻¹), solid-state physicists in electron volts. This converter accepts any one representation — wavelength in nm, µm, Å, or m; optical frequency in THz, GHz, or Hz; wavenumber in cm⁻¹ or m⁻¹; or photon energy in eV, J, or keV — and outputs all equivalent values simultaneously. The spectral region (gamma ray through radio) is identified automatically. Constants are taken from the 2019 SI redefinition, in which c, h, and e are exact. A 532 nm photon, for example, corresponds to 563.5 THz, 18797 cm⁻¹, and 2.33 eV.