To ensure Class 4 and Class 3B laser beams do not escape from laser laboratory or medical facilities, including hospital theatres, certified laser blocking material should be installed. Ordinary curtains are rarely capable of stopping a laser beam and specially designed certified laser blocking material must be used (certified to IEC/EN 60825-4).
Also, production facilities using Class 1 lasers, which are Class 4 under service conditions, may require ceiling-mounted curtains to allow other work to continue safely in the same room during service…
Poll: Should the UK’s railways be renationalised?
I'd hate to be disingenuous so I've replotted the data with the first trendline from 1946 to 1977 and the second using your chosen dates 1983 to 2018....