Machining
Inside Bulk Material
With
respect to machining inside bulk materials, if you have gotten
this far, then you have all the tools needed to understand
this process.
As we
all know, some materials are transparent at some wavelengths
of light. Glass, for example, is transparent for all wavelengths
of light in the visible. That is, it does not absorb visible
light - provided the intensity stays below the threshold for
multiphoton absorption. We can exceed that threshold by focusing
ultrafast laser pulses to a spot inside the materials.
When
the intensity exceeds the threshold for plasma formation,
very localized absorption does occur at the focal point spot.
Once again, this plasma expands. But this time it is confined
by the surrounding material. The effect of the expansion is
to create a void within a very dense shell of material - a
pit within the glass itself. This process is not limited to
glass. Pits can be created in any material by focusing an
ultrafast laser pulse inside the material, whether it is amorphous
or crystalline.
