I use a laser diode(Sculpfun S9) to engrave mirrors from the back side to great effect. The results are stellar. Then I saw a suggestion that engraving a mirror from the front, reflecting side, gives even better results. I tried this, and the results were better, giving a finer, more uniform engraving.
But, it then occurred to me that the reflecting surface of the mirror was reflecting the laser beam back, through the optical system, into the laser diode and this could potentially injure the laser diode.
Hence my question - Can engraving a mirror, from the front reflecting surface, with a laser diode, damage the laser module?
I have not experienced any adverse effects but that might be because I have only done it once.
I’m curious what’s going on physically to account for the difference. Are you focusing on the top of the glass when lasering the front of the mirror or are you accounting for the thickness of the glass and refraction to still aiming to focus at the reflective layer?
I’m wondering if it’s just a difference in focus or possibly a difference in how the material is being vaporized. I could see this being similar to how the backside of a sawcut is more likely to get tearout than the supported front side but not sure if that’s the right way to think about this.