From studies of time-resolved reflectivity and microstructural changes, we
have obtained direct evidence of CO2 laser-induced melting above
a threshold energy density. Results of the optical measurements,
transmission electron microscopy, and secondary ion mass spectrometry are
reported. The measurements show that melt depths as deep as 1 μm can be
achieved with pulsed CO2 laser radiation. By using differential
absorption between layers with different free-carrier densities, we find
that a CO2 laser can be used to melt regions which are embedded
in the material. It is likely that this observed phenomenon is impossible to
obtain with a visible or ultraviolet laser.