Pardon me for posting, but I was wondering if anyone could help me with a somewhat technical question…I’m familiar with the “X-Ray lasers” proposed for the SDI program, which would fire a focused stream of Neutrons at a target in space. I’m wondering (As the thread title says) what would happen if an X-Ray laser was fired within Earth’s atmosphere, at a ground target. Assuming for the purposes of this question you had some Science-Fictiony way of powering the laser WITHOUT blowing it up with a nuclear weapon in the process. Would something hit by the beam be vaporized, or just “burned away”? Could the beam be visible, and would there be any residual radiation left in the area if the target after you’ve stopped firing?
Well, thanks for everyone’s time, and I hope my preconceptions about the science involved aren’t turning TOO many noted scientists over in their graves.
First off, the only misconception you have is that an X-ray laser wouldn’t fire neutrons - the beam would be made up of photons just like with a normal laser. Secondly, X-ray lasers do actually already exist. From an SDI point of view, these designs would have to be absurdly large pieces of kit to do anything against warheads, so that’s never been a serious possibility. All the fuss about X-ray lasers there was in the 80s was, as you recognise, in using nuclear bombs in orbit to power them. Famously, this turned out to be a technical and political quagmire, as chronicled in Broad’s Teller’s War (Simon & Schuster, 1992). Quite what the current techical consensus about such a scheme is (or even what the original data was showing), I don’t know, but the Federation of American Scientists list this as a “former project”.
None of this rules out your thought experiment. And the answer to that is it depends on things like how far away the target is, how powerful your laser is, how big the target is and how long could you fire it. For instance, the atmosphere is quite good at stopping X-rays. Good enough for this to have been a major constraint in arguments about the SDI X-ray laser. But, yes, I’d expect the beam (or rather it’s effect on the air) to be visible and given the right circumstances, yes, you probably could vaporise something … very small. There’s been at least one GQ thread recently about the effects of the airbourne laser being developed for BMDO and I’d guess that the basic effects are similar. It’s just a question of what you’d be prepared to accept as a plausible scaling up for your imaginary weapon. As for residual radiation, X-rays are sufficiently energetic compared to visible light that you can in theory get nuclear effects. But I’d be very surprised if those were observable in practice, even in a lab setting.