[Piskvorrr]

It would work better - but I'm pretty sure that the decisive factor was cost: back when this was conceived, getting a useful laser would have driven the cost 10x higher. Plus, I think there's some pesky law on coherent light output power and whatnot (and another which bans lasers outright if you're close enough to an airport).

[taesis]

Aah, makes sense that they wouldn't want to foul up any instruments that rely on RF/microwave. Thanks for the answer :D