Re: Laser specs ? optics ?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<dave_mucha@...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@> wrote:
> >
> >
> > This is laser "speckle". It is a characteristic of ALL lasers,
> unless you
> > run the beam through a device called a spatial filter.

Laser beams don't contain speckle as such it is just an interference
phenomenon (for the discussion's benefit not your's Jon). In the same
way as you get fringes when two angled plane waves interfere at a
plane you get sets of fringes in all different directions combining to
produce speckle when the light interfering is not at all in phase.
Spatial filtering will make the collimated beam flatter and this can
be focused more tightly however you should be able to get a fair focus
from an un-unfiltered beam.

> I tried looking at a laser pointer dot and it appears that the
>speckle I am looking at has more to do with the surface, than the >beam.

The roughness of the surface will produce many different angles in the
reflected light. When your eye images this to the retina where the
image is built from many superimposed plane waves, because of all the
different angles comming off the rough surface they interfere
constructively and destructively in a random fashion, that is the
speckle that you see. If you were to shine the beam onto the array of
a camera (no lens), assuming it was not saturated you should however
just see a smallish dot on the screen.

Now to get back to the topic in hand.

I bought a 1W pig-tailed IR laser diode on ebay, I had reasonable
results focussing the beam using the lenses from CD-Roms it was able
to melt black plastics but could not mark wood as the vendor suggested
however the reasons for this are unclear, perhaps the lenses, perhaps
I damaged it perhaps...

Graham

p.s. Its true about 10.6um radiation, it is one of the more "eye safe"
laser types, well as safe as a blowtorch in the eye anyway, that's the
best way to think about it. Your eyes absorb the energy heat up and burn.