Dual axis

This demo shows how to use dependent axes to create a secondary axis showing the same data in a different unit. In this case, the spectrum is drawn over the wavelength on the bottom $x$-axis and over the corresponding photon energy (related through $E=hc/λ$) on the top $x$-axis.

The data is a spectrogram of molecular oxygen, once measured by the author and a colleague with cavity-enhanced absorption spectroscopy.

#let (λ, intensity) = lq.load-txt(read("spectrum_o2.txt"), skip-rows: 2, delimiter: " ")

#let h = 6.62607015e-34
#let c = 299792458
#let e = 1.60217733e-19
#let k = 1e9 * h * c / e

#lq.diagram(
  width: 10cm,
  margin: 3%,

  xaxis: (offset: 0, mirror: false),
  xlabel: [Wavelength (nm)],
  ylabel: [Relative intensity],

  lq.plot(λ, intensity, mark: none),

  lq.xaxis(
    position: top,
    label: [Energie (eV)],
    offset: 0, 
    exponent: 0,
    tick-distance: 5e-5,
    functions: (λ => k / λ, E => k / E)
  )
)