Scientists at the Washington University School of Medicine in St. Louis were testing their new infrared laser, when people around the lab started seeing green flashes:
The only photons with the right amount of energy to change a human chromophore are in the 390-720 nanometer wavelength range. Infrared, in the 1000 nanometer wavelength range, is too big and too low-energy to knock a chromophore into changing its shape.
But if huge amounts of infrared photons flooded the eye over a short period of time, two infrared photons could hit the chromophore at once. Their combined energy is enough to cause it to change its structure and allow people to see what they otherwise wouldn’t. Two 1000 nanometer photons add up, energetically speaking, to one photon of around 500 nanometers – which is in the green range of the visual spectrum. So infrared light, if concentrated enough, would leave us seeing green.
Photons are absorbed by atoms and molecules when they excite electrons from a lower-energy orbital to a higher-energy one. There has to be an exact match between the wavelength (energy) of the photon and the energy difference between the orbitals. If the molecule or atom lacks orbitals that match the wavelength energy, the photon cannot be absorbed. This results in the well know absorption spectra of atoms and molecules which always exhibit sharp absorption bands.
Two photons on a lower energy level might add up to one photo of a higher level, but they cannot raise an electron between orbits separated by the higher level. That is classical physics which does not apply (anywhere at any scale).
So the proposed explanation of the effect is suspect and needs some further elucidation.
MDs are generally bat-shit stupid about science, so their explanation need not be believed.
Two-Photon Absorption
“Considering the reason for these units, one can see that it results from the product of two areas (one for each photon, each in cm2) and a time (within which the two photons must arrive to be able to act together).”
Who says QM is counterintuitive?
There is a finite time where the photon might be absorbed, but hits quantum forbiddings. If a second photon considers, so to speak, the rhodopsin molecule during this interval, if their intervals overlap, then sometimes the rhodopsin will absorb both at once.