I spent countless hours of my PhD trying to get the White light continuum stable enough to do measurements with. Our laser wasn't powerful enough to use air as

I spent countless hours of my PhD trying to get the White light continuum stable enough to do measurements with. Our laser wasn't powerful enough to use air as medium, so we would use sapphire (very good, stable and predictable), Calcium Fluoride (absolutely bloody terrible, but it did give out a lot more UV light) and water (never got any measurements out of that, so unstable)