Explain the process of space and time. The incident laser beam freely penetrates the first material layer, losing a small fraction (eg, 1%) of its total energy when interacting with the pristine white TiO2 particles, turning them black. The same thing happens in the second layer, and so on, until most of the laser pulse energy is absorbed in the top 50-100 layers. In practice, the process is very limited in time and space, as the total pulse duration is typically below 30ns and the marking depth does not exceed around 50um.
The short nanosecond laser pulses prevent periodic heat exchange between the additive and surrounding material, thereby limiting any structural and/or chemical modification of the pigment particles themselves. Obviously, this mark is not easy to remove because most of it is distributed on the top layer, not on the surface.