Continuing with the same battered sunglass lens:
It’s now oriented with the back side of the lens toward the unfocused beam going into the laser head.
The front surface remains undamaged after two pulses at 500 ms 50% power:
The red disk in the middle of both wounds is new this time.
As seen from the rear, the first pulse shattered the rear glass layer:
The image is about 7 mm from side to side.
A chip of glass popped out of the upper part of the fracture, but the other pieces remained in place.
The distinct blue ring is 3 mm OD and marks the inner boundary of a purple disk surrounding the central burn. The disk appears only in reflected light (which is impossible to photograph with any setup I can manage), suggesting it comes from diffraction in a surprisingly uniform air layer blown between the glass and the plastic polarizing sheet.
Also seen from the rear, the second pulse produced a neater wound:
The blue ring is again 3 mm OD and the image is 7 mm across.
The central red spot probably comes from damage to the polarizing sheet.
The most surprising things, at least to me, didn’t happen:
- the glass lens didn’t disintegrate
- the laser beam didn’t punch completely through
Protip: Don’t depend on ordinary glasses, even fancy sunglasses, to protect your eyes from CO₂ laser beams.