Drilling in to concrete lintels?

lemontart

hammer drill, masonry bit and steady hand done it loads of time and as others have said put a wooden baton on to attach curtain rail too.
https://www.youtube.com/watch?v=NjE6nsfdjpo

DaftyDuck

If you were doing a curtain rail, I might suggest fixing a thin wooden baton to the lintel with multiple screws(so there would be no need for substantial impact or penetration on the lintel). However, if you are doing a curtain pole, this will not look as neat, and would more likely fail.

Me, I'd hang the rail from the ceiling, ensuring I screwed the rail supports directly into a joist. Unless I wanted the rail-visible look, and I probably wouldn't, given it's a modern window, I'd then box the rail in, so it would be immaterial/invisible as to whether it was wall or ceiling mounted.

System

SDS drill did the trick, no real trouble drilling it, just made a lot of noise!