Optics / 01 / Units

One photon,
four descriptions.

Enter a vacuum wavelength, frequency, wavenumber or photon energy. The other quantities follow from exact SI constants.

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Result

Results to 4 significant figures. Displayed digits are not a measurement uncertainty.

ν = \frac{c}{λ_{0}}

frequency from the vacuum wavelength

σ = \frac{1}{λ_{0}} = \frac{ν}{c}

spectroscopic wavenumber

E = h ν, E_{eV} = \frac{E_{J}}{e}

photon energy, in joules and electronvolts

λ_{medium} = \frac{λ_{0}}{n}

wavelength in a medium of phase index n

c = 299 792 458 m/s, h = 6.626 070 15 × 10⁻³⁴ J s and e = 1.602 176 634 × 10⁻¹⁹ C are exact in the SI (NIST CODATA 2018).
λ₀ is the vacuum wavelength. Frequency and photon energy do not change in a medium; the wavelength becomes λ₀/n.
n is the phase index you enter for this frequency. Dispersion and air-wavelength tables are not modelled; standard air at 1064 nm has n ≈ 1.000 27, which shifts λ by about 0.29 nm.
Inputs are accepted for vacuum wavelengths from 1 pm to 1 m (gamma rays to microwaves); outside that range the page says so instead of showing a value.
σ is the spectroscopic wavenumber 1/λ₀ (cm⁻¹), not the angular wavenumber k = 2π/λ.