Re: [CAD_CAM_EDM_DRO] Re: added laser cutter to my mill (pics)

> From: "skykotech" <rick@s...>
> Date: Tue Aug 3, 2004 6:26 am
> Subject: added laser cutter to my mill (pics)

> I just added an attachment to my cnc mill. It is a 10 watt Synrad
> CO2 laser (doing about 17 watts, go figure).

<snip>

> I read that the beam from a
> Synrad laser is square in profile at exit and becomes round and
> gaussian at about .6 meters from the laser output.

Some tests that you can perform to get beam profiles.

Mount the laser in a fixed position so that it is directed parallel to
the X axis. Mount a YZ plane target on the XY table.

Move the X axis to the next distance for taking data. and move the Y
axis a distance greater than beam width. Fire the laser for a fixed
period, say 10ms. Just long enough to leave a mark on the target that
represents the beam size at the target.

Do this for several distances from laser to target. One inch steps in
range will tell you something about the laser beam. This will leave a
series of burn marks on your target with each burn at a known distance
from the laser. This will give you some idea of the beam cross section
at various ranges.

To test the effect of your lens, install the lens a know fixed distance
from the laser. Start with the target close to the lens. Move the target
farther from the lens (X axis) and to a fresh area (Y axis) then fire
the laser for a fixed period. This will produce a series of spots that
indicate the spot size as a function of distance from the lens. You
should need a microscope to get a good look at, and to measure, the burn
spots.

Change the distance between the laser and the lens and repeat the test
for the new laser/lens seperation. I would leave the lens in place and
move the laser if that is practical. That way the lens to target
distance needs to be calibrated only once, and that can be a sensitive
distance.

The distance from laser to lens can be measured with a tape measure.
Seperation changes of 1 inch will be fine enough. You could mount the
laser on a plate with 1/4-20 tapped holes on 1 inch centers. Then moving
the laser 1 inch is done by moving the laser to the next set of holes.

A traditional term in optics is "depth of focus". A common way to
quantify this is to find the positions where the fluence or power
density is half that of the peak.

First find the waist. That is where the beam is smallest and the
concentration of energy the greatest. Then find the positions on either
side of the waist where the beam has half the power density. This is
tough to do without a photometer. A way to estimate the half power
positions is to find the place where the beam area is double that of the
waist area. This often corresponds to where the beam diameter is 1.4142
times the waist diameter.

This method does not work well if the laser waist is inside the laser.
In that case you cannot measure the waist by making a burn. You would
need to use some lenses to relay the waist to a place outside the laser
where you can make and measure a burn.

Tom Hubin
thubin@...