Step 1: Supplies
Spoon - or something else to scoop out pumpkin insides
Laser Cutter - I used a 60 watt Epilog Helix machine
Step 2: Choose an Image
Step 3: Clean Out the Pumpkins
Use your spoon to scoop out the insides into a bowl.
In this step, it may also be helpful to scrape away some of the meat of the pumpkin to make the walls thinner. It will be faster and easier to cut through a thin pumpkin shell.
Step 4: Build a Jig
Step 5: Testing, Testing...
I recommend using long thin boxes to test various vector and raster settings. The length isn't too important, but you will probably want boxes that go from the edge of the pumpkin to the top of the pumpkin to see the effect of focal distance. The purpose of thin boxes is simply to fit as many setting samples as possible on the pumpkin.
The high water content of the pumpkin increases the energy required to burn through it. As a result, I found that high power and very low speed settings worked best. In the end I was able to cut through about 1" of pumpkin flesh.
Step 6: Focus
The second image above shows a vector cut where the laser was focused at the highest point of the pumpkin. This meant that the edges of the pumpkin were about 3" out of focus. You can see that the vector lines became huge at that point, about 1/8" wide.