Wavenumber

In spectroscopy, the wavenumber indicates the number of EM waves that would fit in a unit of length. The normal units for wavenumbers are inverse centimeters cm^-1. A different name for this unit is kayser (after Heinrich Kayser). Light with a wavelength of 500 nm (green) has a wavenumber of 20,000 cm^-1 or 20 kK. Photon energy and frequency are proportional to wavenumber: 10 kK corresponds to 1.24 eV.

Historically, wavenumbers were introduced by Janne Rydberg in the 1880's in his analyses of atomic spectra.

Wavenumbers ($v'$), wavelength ($\lambda$), and frequency ($v$) are related:

$v'[cm^{-1}]={\frac {1}{\lambda [cm]}}={\frac {v[sec^{-1}]}{(c{\frac {m}{sec}})(100{\frac {cm}{m}})}}$