Two color laser ablation: Enhanced yield, improved machining

Laser ablation of semiconductors with nano- and picosecond lasers can be significantly improved, both in terms of yield and surface quality, by simultaneous irradiation of the sample with the fundamental beam (λ = 1064 nm) and a small amount of its second harmonic (SH) produced in a thin nonlinear crystal. While the total energy fluence is conserved, the small fraction of the second harmonic serves to excite electrons into the conduction band to get the ablation process started. For femtosecond laser pulses, the effect becomes insignificant, since sufficient conduction band population is provided by multiphoton absorption.