A few years ago (OK, about a decade - I'm old) we got the usual zero notice that some outpatient services were being moved to a local, new build GP surgery/residential flats building, close to the hospital.
No time to order and run in fibre so the only game in town was a laser link from the roof of the hospital wing opposite the GP building. The wing that houses our ED/Trauma/Resus services.
All worked well for a time and then the connection would intermittently drop and come back up. We began physically resetting the laser at the hospital end each time it happened and we'd see the connection come back.
Over time this got worse and worse and we just could not work out why. We did suspect that the trees between the hospital and the GP building were blocking the laser as they came back into leaf, maybe the blossom was having an effect.
We called in the company that originally fitted the kit to have a look and they ran some alignment checks at both ends. They discovered the root cause and implemented a fix.
On top of the roof of the ED/Trauma/Resus wing is the helipad for the Air Ambulance. Repeated heli-action vibrations had caused the laser head to slowly, slightly, lose alignment. The fix was a bigger mounting.
We ran in fibre soon after.