This is sub surface laser engraving !
To do this we focus a pulsing laser at high energy through a “camera like lens” at a specific wavelength into a tiny dot in the middle of a block of optically pure glass. The laser light then passes through the glass without disturbing it “until” the exact focal point is reached, whereupon the energy level will cause the glass to vaporise and form a tiny oval shaped crack.
The laser will also be pulsing and moving to and fro, forming layers of millions of these tiny oval cracks, building up a 3D image in the glass, much like forming a picture with pencil dots.
These tiny cracks “refract light” and so create a beautiful lifelike replica of a person or shape.
the image created looks like a perfect sculpture within the glass block