We have showed recently, that the well-known parametric down conversion process can actually be used to perform an absolute calibration of a spectrometer and as such could complement black body radiation as a measurement standard. Both regimes of the process, the spontaneous low gain regime as well as with a high gain pump power, one can perform a relative and an absolute calibration of spectrometer over a broad wavelength range. How? Just have a look at our work published in Nature Physics.
Congratulations to Sam and all co-authors for the great work.