Bradley Ferguson wrote:

> On 6/30/05, Robert Rolf <Robert.Rolf@ualberta.ca> wrote:
> 
>>PicDude wrote:
>>
>>
>>>Some time ago, I tried to get a couple clean thin lines with laser pointers to
>>>form a crosshair on my drill press for drilling PCB holes (and other things).
>>>Could not get the lines clean though.  Perhaps you might?
>>
>>To make this work you need to cast a shadow from a small aperature.
>>Laser pointers have lousy beam shape unless corrective lenses are used.
> 
> 
> Does this really work?

Yes, up to a point.

>  I would think the aperture would have to be a
> long ways away (relatively) from the laser source to actually cast a
> sharp shadow. 

There are diffractive effects that make it less than perfect,
but it does improve beam quality. Apertures get used quite a
bit in holography to clean up spurs in the beam profile.

> Even though the beam shape is lousy, it is still fairly
> collimated, so most of the divergent rays would pass through the
> aperature unless it was really tiny, in which case, you lose a lot of
> your energy. 

You use TWO apertures, of fairly large diameter to minimize
diffraction effects, and to get a clean beam edge.
Try it with a couple of pieces of aluminum foil with pin pricks
in them. Works rather well if the holes are large enough (0.5mm).

? It would work better to have a really bright (energy
> inefficient, but cheap) light source and use that to cast the shadow.

Nope. Multiwavelength sources produce wide diffraction fields.

  > Don't most of the shaped laser pointers use a lens (as you said) to
> provide the shape to the output, whether that's a smiley face or
> "happy birthday?"

No, they use a holographic diffraction pattern. If you through
the lens you see a flat CLEAR image. The embossed image diffracts
the beam to create the pattern.

Robert

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