> provided the scanning movement of the dot of light is 'a lot' faster than
> the movement of the detector then some form of integrator on the signal
> being detected would fix this for you...

The fly in the ointment here is time. At 10m from the source and 115 degree
sweep angle the dot has to cover 20m. Even at a slow 10 scans/sec this is
200,000 mm/s. The sweet spot of the detector is <5mm, and assuming it's
at the right place at the right time to be hit this gives a window of only
25us. And there's a good chance the detector will be in the wrong place
and be completely unhit in the 0.1s the dot isn't there. Upping the scan
rate to perhaps 100/sec makes things worse unfortunately. Parabolic
reflectors to catch the beam are an option, but I think the times are too
short for the carrier (probably 40kHz) to be picked up reliably. There's a
possibility that 2 or 3 of these plane beams may be present, which is
why they need to be identifiable

> As you pointed out, there are lenses that do what you want
> There aren't any high-volume mid-quality uses for these, and so no one
> is producing them.

I happened to see an optometrist's ad on TV last night. He grinds his own
customer's lenses, if I can get the specs for an LG that might be worth a
look, as would the photographic lenses. I did try a piece of perspex rod
and it does make a pretty good line but, like Ben says, quite faint at the
edges. Might be possible to use more than one rod and have some
overlap. I'll take a look at Power Technology. Not against buying off the
shelf, don't want to get robbed

> Why not use a regular LED?  You can get some very high power leds
> for little more than a very cheap laser.  You might even be able to find
> one with a lens that projects a 90 degree cone.  If so, just place some
> thing in front of it with a slit.  You may have to make your detectors a
> little more sensitive, but with a modulated light beam it should be easy
> to deal with.

Finding a LED with a 90d cone is easy enough. The thing is though, by
putting a slit in front of it you're losing a pretty big percentage of the
available light output and the edges of the slit would cause some
scattering. It  would be much more preferable to channel all the energy
forward through a lens

> Are there any specific reasons to use a laser?

Well, it's a very strong point source with a collimating lens, it's a done
deal for around NZ$20. As far as efficiency goes, do you get more
bang for your buck with LEDs or lasers ?

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