I made these using pine to give a chunky rustic look but if you don't have this available you could cutout some squares from plywood or acrylic using your laser. 

If you are cutting out your own coasters I would recommend making them around 100mm square or round.  

Once you have chosen your material it is time to engrave. The settings needed will vary greatly depending on the material and laser being used.

The coaster pictured was engraved using a xTool D1 Pro with the settings listed above.

If you have used plywood or solid wood like me you might want to add some dye or varnish to give a glossy finish and make the design standout.

I used an oak coloured dye and clear varnish to protect and enhance natural beauty of the wood.