I've known about this effect for quite some time but since I had the lid off my laser cutter and I could video easily I thought now was a good time to share. When you're testing the alignment of the laser you cover the mirror with some masking tape and shoot the beam at it. The first shot burns a dot on the tape but subsequent shots increase the dot size, in essence burning a ring around the centre. This ring of burning turns into a ring of smoke which gently rolls upwards from the masking tape. Repeatedly shooting the tape eventually burns through it which may cause damage to your mirror but I did at least manage to capture a few on video.