From what I'm finding, most IR laser diodes have a fairly wide aperture and terrible divergence, because of that I'm not really worried about harm being done to any pilots eye sight with them if they are a thousand feet away, but some of the low powered single mode diodes you won't find in a commercially marketed laser pointer, can have small diode apertures below 5um (micro, and not meaning beam width, the emitting side of the chip itself). If you let the beam expand and then collimate it at a much wider beam, the divergence can be incredibly small, much smaller than most of our laser pointers, far less than even the good ones. In that case, you might have an IR laser pointer with a divergence of .01 mRad or better with just a 100mm diameter lens. However, these single mode diodes have low output power, about 300mw at most. So, they can be very good pointers with an incredibly long "throw" without dissipating very much for a distance of a hundred or more miles. From that, I'd expect, if you targeted the ISS and they had a camera capable of detecting it, and you were skilled enough to get and keep the beam centered on them, I suspect it would be one of the brightest man made point sources of IR at specific wavelength from the earth, from their view. This is only if you expand the beam enough, I believe a six inch expansion from 5um ought to do it at 300mw. Of course, expanding 300mw of IR out to six inches would dilute it quite a bit, so much I doubt it would be very dangerous close in but don't hold me to that, I haven't done the calculations to see.
According to some graphs I've found, 1um is a good wavelength to use from the standpoint of atmospheric absorption. There are better wavelength windows than 1000nm, but for what I could find available in single mode laser diodes of that kind, that's the least expensive part of the IR band to build something which can do that at a few hundred mW of power output.
I've made some WAG assumptions here, one of them being how much IR at what bands are emitted from the earth, manmade or not. Also, I don't know how sensitive our solid state cameras are to 1um, maybe not enough to be making such statements. If anyone with some expertise in this area can comment, I'm interested in knowing. Hope I'm not full of bull with these ideas, this is something I'm trying to nail down but can't find all the info I need to do so. Maybe I will make another thread in order this one isn't taken off topic. I don't want that to happen to this laser safety thread, the info is too important.
