obj = CSpectralFWHMListener(caColors)
  obj = CSpectralFWHMListener(caColors, vPlotForEnvelope)
  obj = CSpectralFWHMListener(caColors, sAxis)
  obj = CSpectralFWHMListener(caColors, sAxis, vPlotForEnvelope)
  sAxis = 'Angular Frequency' (default) 'Frequency' /
  'Wavelength' / 'Wavenumber'