function for_freq_to_dens, freq, harmonic=harmonic ; written by Patrick McCauley Dec 2018 ; ;input = frequency in Hz ;output = density in cm^-3 const = ( 4.*(!const.pi^2)*!const.me*!const.eps0 ) / ( !const.e^2 ) if keyword_set(harmonic) then dens = const*((freq/2.)^2) $ else dens = const*(freq^2) density = dens / (100.^3.) return, density end