Thanks, no beam angle as I don't have a negative lens yet. I'm trying to determine the appropriate negative focal length lens I need to buy for use with a 10 inch diameter plano-convex objective lens with a 24 inch focal point for a uber beam expander. I suppose many negative focal length lenses will work, just that the amount of expansion will be affected, more expansion with a shorter negative focal point.
I've been thinking about this project for months now, from time to time, and it appears to me to be able to expand a laser beam to something approaching 10 inches diameter would require more than one stage, perhaps several inter-coupled beam expanders. Since a collimated laser beam has such a small diameter, the first lens you use with it must be small too, so that the beam falls across the majority of the diameter of the lens, otherwise if the first lens is too big, the beam will pass right through the center which is relatively flat and acts more like a window, than a lens. Because the first lens is so small I then have to deal with a power density issue when using a 50 watt output FAP 808nm laser. I am not convinced this will work using a FAP anyway, but it does have divergence too, as any collumated laser beam so maybe there is no issue.
I just want the beam to be expanded so much that it is easily detectable at a great distance as a spotlight, not as a high power tiny diameter beam which will burn through anything, this is to make a tight but wide low divergence spot beam.
