Wavenumber

In science, the wavenumber indicates the number of wavelengths that would fit in a unit of length, and is numerically equal to the reciprocal of the wavelength. 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.

The wavevector($k$), wavelength ($\lambda$), and frequency ($f$) are related:

$k={\frac {2\pi }{\lambda }},\qquad k={\frac {2\pi f}{v}},$

where $v$ is the speed of the wave.

Sometimes ($k$) is also referred to as wavenumber, but is greater by a factor of $2\pi$ than the wavenumber described earlier as the reciprocal ($1/\lambda$) of the wavelength.