You’re looking at a photograph sealed inside a solid block of glass: no entry wound, no surface scratch, just an image suspended in the middle of a flawless cube. The method is subsurface laser engraving, and it works by breaking the usual rule about where a laser is allowed to deposit its energy. The medium, almost always optical-grade K9 crown glass, is transparent to the laser’s wavelength, so a beam aimed straight through it crosses the surface untouched. The trick is focus. A high numerical-aperture lens converges the beam to a point only microns wide deep inside the block. Along the entire path the irradiance stays harmless, but at that focal point it spikes into the gigawatt-per-square-centimetre range. At that intensity glass stops behaving linearly: • Multiphoton absorption lets several photons combine to bridge a bandgap no single photon could clear • The freed electrons seed an avalanche that ionizes a microscopic plasma • The plasma expands and cracks a void a few mic...