One thing you didn't touch on is what makes a laser a laser: all photons traveling in parallel paths (in nerd speak: 'collumnated'). If you're wondering why a laser beam doesn't have a point of focus, as would, say a giant mirror focusing light from the sun it's because the photons are all on parallel paths.
Pretty elementary; I'd guess you omitted it because we all probably knew this.
That mentioned, where are the power losses coming from? Conversion of electrical energy into photons? Collimation? Something else?
Thanks!