Good luck shooting down something in space that casts a ray capable of incinerating anything it's looking at. You'd have to go into orbit and come at it that way, in all likelihood, especially if they had additional ones. Why nobody has done this yet is beyond me. It's basically a free "rule the planet" card. There's no way to actually prevent getting roasted by it. Something I saw pointed out that if fired at NYC, it would've instantly liquefied all the metal. Anything less durable, obviously, would just turn to ash and blow away.
Constructing and maintaining such a thing would be a near insurmountable nightmare. Youd have to assemble it in space because theres no way you could get something that big into orbit without destroying it. So first youd need space stations in place around it.
Then youd have to figure out how to actually move the thing not only to keep it in place but to appropriately aim the thing, and more importantly keeping it from reflecting energy to places on earth accidentally.
Not to mention that focusing concentrated sunlight onto the earth would likely damage the ozone layer and contribute to global warming along with possibly weakening the magnetic field and leaving us more vulnerable to solar radiation.
Based on the information we have available, during the late '50s / early '60s, Germany could've had it. I watched a documentary about it.
By that point hadnt many of the notable German scientists migrated to the US?
Even the article you posted clarified that there are no schematics available that show this was anything more than a concept ---