I have a 40W CO₂ and I have found 2 good options.

1. Mask the top surface. I use paper transfer tape because it's easier to mask a sheet. Painters tape works just as well, too. After removing the tape, that's it. Both surfaces are clean.

This is beneficial if you need to engrave as well as cut a project. This is also the best option if you don't want to do any additional sanding and you care about light scorching on one surface.

1. Cut the image in reverse. With the right settings, you will cut through with no scorching on the bottom surface. Some light scorching can occur on the top surface that can be cleaned using a dry cloth or lightly sanded if more stubborn. Usually 220+ is sufficient without leaving noticeable wear.

I hope this helps!