They simply don't. Or not such a nice sharp beam as a laser beam. It's simply relatively coarse and divergent. Don't believe the nice pictures.

The beam from a fibre is divergent, too, but the angle is limited by the numerical aperture of the fibre; moreover, the fibre end can be usually positioned significantly closer to the object than a complete optical head plus electronics (this of course depends on the particular application). Of course, in both cases you have vast losses in the intensity until it returns to the receiver; but, as I mentioned several times, usually it is not the absolute intensity what is needed, rather, contrast and background suppression.


You certainly meant collimating lense...

JW