[waiquoo]

'All light causes evaporation' is not really true. IR heating works because the wavelength resonates with the vibration modes of the intramolecular bonds. Water has low absorption of visible wavelengths, so you would not expect light absorption in the visible spectrum to provide enough energy to knock individual water molecules free. Water is an interesting substance and a lot of the properties of water come from intermolecular hydrogen bonding and polarity. Even though it's a liquid, there are transient molecular structures that spontaneously occur in bulk due to hydrogen bonding between water molecules. The polarity of water causes interesting effect at interfaces (surface tension, electrical double layer, etc). It's possible that the water in the hydrogel is forming some hydrogen bonded structure that interacts with green light. Where the individual water molecules won't strongly interact, the larger structure does. That could lead to the ejection of 'packets' of water molecules as discussed in the paper. Why and what these multi-molecular structures are? No idea. But this is a very interesting effect.