Program stops responding

Hello

I am working on a DIY CO2 laser cutter/engraving project, but I experience some problems, and I would really appreciate if anyone could help me solving this issue.
The PSU and 40W CO2 laser tube are from ColeTech and the connector labeled with TL, WP and G are all connected to ground. As safety I cut the power to the PSU with a solid-state relay if any condition is wrong. The label IN are connected to an Arduino that runs on GRBL to control the laser. Because of some other issues I am experiences with the program during a raster operation, I have ordered a Smoothieboard to control the laser with GRBL-LPC, but this has not arrived yet.

The laser works perfectly when I disconnect the connectors (not the one that power the PSU) and uses the test button. I believe that I measured 3V on the “IN” connector during the test, which I interprets that the laser runs at 60% of max power. Also, when I run a program without the laser connected all the axes works like they are supposed to. But when I connect the laser and run a program, the program stops, and an error message says that the Arduino stopped responding. At this point the laser are still on, but no axes are moving. When I only disconnect the connector labeled IN, and run a program, the program works perfectly but the laser is on constantly, and I measure approximately 2V at the IN connector to the PSU.

So my question is: is it supposed to work like this, or is it something wrong with my setup?
Also, I would appreciate any tips for how to get the best out of my laser cutter, specially raster operations. Thanks.

Best regards