https://youtu.be/f-QxLAxwxkM?si=N9ltCiSSxgGkkdTR
Glad you asked.
One of these things, apparently.
https://hackaday.com/2022/09/07/improve-cd-sound-by-shaving/
This is so stupid, CDs have error correction codes. Special redundancy that fixes reading errors up to some level. If your reader is so junky that it gets uncorrectable errors, no amount of “trapping the light in the CD” is gonna change that. And even if you get some incorrect bit the player will probably try to guess it and unless your ear is some kind of specialty ultrafast tuning equipment you won’t hear the difference.