Spartan negative divergence normal?

[Crichton]

I just realized this morning after about 3 days of owning this thing that I have negative divergence. Beam comes out about 2mm X 4mm, and comes to a pinpoint about 4-5 feet out. Burning at that spot is apocalyptic (output is a little over 1W to begin with). My initial divergence test the day I got it at 20 meters gave me around 2.3mRad, which I was perfectly happy with assuming DL eventually releases a new beam expander down the road, but I always thought beams with negative divergence had mRad ratings far worse than the 2 range. But I figure I'm measuring wrong giving the negative initial value.

And furthermore, what does this mean for compatibility with the beam expander? Will it simply not work, or do something crazy like cut the negative divergence by 10 so my pinpoint is that much further out.

That's a scary thought.

 

[Deleted member 10578]

I just realized this morning after about 3 days of owning this thing that I have negative divergence. Beams comes out about 1mm X 3mm, and comes to a pinpoint about 4 feet out. Burning at that spot is apocalyptic (output is a little over 1W to begin with). My initial divergence test the day I got it gave me around 2.3mRad, which I was perfectly happy with assuming DL eventually releases a new beam expander down the road, but I always thought beams with negative divergence had mRad ratings far worse than the 2 range.

And furthermore, what does this mean for compatibility with the beam expander? Will it simply not work, or do something crazy like cut the negative divergence by 10 so my pinpoint is that much further out.

That's a scary thought.

Hi Crichton,
Negative divergence is not possible.
What you see is that the laser is not collimated correctly for focus at infinity.
To measure divergence, you need to pick two points some distance beyond the focus point you mentioned at around 4 feet.
Measure the beam diameter at 10 feet and again at 40 feet then use those two diameters to calculate divergence based on the 30 feet distance between the points.

 

[DrSid]

Or use much larger distance, like 100 yards .. and ignore the first size (enter distance zero, size zero into calculators), it has little effect in this setup. With this you can also easily compute divergence as size/distance (units must be same of course).