How does laser cooling work?

Cool video (bad pun intended) :) But you omitted the crucial point to laser cooling actually working. After the photon is absorbed, it's not the end of the story yet! An electron will move in said atom to a higher energy state, and will eventually go back to original (as in, lowest) energy state, and emit a photon (with equal wavelength and hence energy and momentum). But it will do so in random direction. Hence, over many absorptions-emissions, overall momentum gain from emitting photons will cancel out - so in the end we successfully slowed the particle down in one direction :)