SpectroscopicUnits.jl

This small package was created to convert easily between units commonly used to describe the energy, frequency or wavelength of the electromagnetic spectrum. It exports a single function convert_unit that wraps uconvert from Unitful.jl and uses the same calling convention. Since spectroscopic units such as Hz, eV, μm or nm have not necessarily the same dimensions, we could not just extend uconvert which requires the same dimensions.

Example

As an example, let's convert from a wavelength in nm to a frequency in Hz.

julia> convert_unit(u"Hz", 600.0u"nm")
4.996540966666666e14 Hz

Just as in Unitful.uconvert, the first argument is a unit and the second is a quantity of type Unitful.Quantity{T,D,U}.

Supported units

For now, the following units are supported: Hz, radHz, eV (and most energy units), and all length units. Everything can be converted into everything.

To make writing units slightly easier, we created aliases for the most common ones:

const Hz = u"s^-1"
const radHz = u"rad*s^-1"
const eV = u"eV"
const m = u"m"
const cm = u"cm"
const mm = u"mm"
const μm = u"μm"
const nm = u"nm"

which are all exported.

Interface

To extend the conversion for units of your own package, two methods should be defined which convert your unit to Unitful.LengthUnits and a length back to your unit. We show here the example for Hz:

function convert_unit(unit::Unitful.LengthUnits, quantity::Quantity{T,D,U}) where {T<:Real,D, U<:Unitful.FrequencyUnits}
    return uconvert(unit, c_0 / quantity)
end

convert_unit(unit::U, quantity::Unitful.Length) where {U <: Unitful.FrequencyUnits} = uconvert(unit, c_0 / (quantity |> m))

where c_0 is the speed of light in vacuum obtained from PhysicalConstants.jl. Converting everything between lenght units allows us to convert between all units. The choice of length units is quite arbitrary and we could have taken any other unit.

Important note

In this package, the unit radHz is understood as the unit of pulsation ω = 2πν where ν is the frequency in Hz. Hence, when we convert a frequency in Hz to radHz, the frequency is then multiplied by 2π. This is different from the convention used in Unitful.jl where 1 Hz = 1 radHz.