Laser set-up

I am trying to cut shims. Thickness is from 0.1 - 1mm. On some thicknesses it cuts on others it doesn’t even leave a mark. I feel like the laser isn’t focused. Also how to reduce a poor quality cut. I have tried lesser power and more passes but nothing seems to change.

Which laser do you use?

The lasers normally reduce the power when enclosure is not closed. Do you have one?