My general experience is the opposite re: crossing fields - I run across many people doing software dev with a MS or PhD in something else. Just this past week

My general experience is the opposite re: crossing fields - I run across many people doing software dev with a MS or PhD in something else. Just this past week I interviewed at a research institute where one of the primary developers had a PhD in biology. He didn't give me the impression that doing only software dev was his first choice, but clearly he was working. I would guess from your experience "building scientific instruments and software to control them" you would be able to find a job doing dev. If you can swing it while you're still a student, I would highly, highly recommend you do some internships with companies writing software, even if it is doing the same type of code you currently do. If you can't do that, pick up a minor in CS while doing your physics grad work.