Study of bone ablation dynamics with sequenced pulses
The dynamics of the ablation process was investigated in bone using two pulses separated by a variable time delay. In one experiment two sub-threshold 7.5 nsec duration pulses at λ = 355 nm with pulse separations ranging between 1 ns and 100 msec were used to ablate bone. Crater depths remained approximately constant for pulse separations up to approximately 100 nsec, then decreased monotonically in time to zero at 10 msec pulse separation. In another experiment the second pulse was replaced by a 7.5 nsec duration pulse at λ = 532 nm. The combination of sub-threshold pulses at two different wavelengths also ablated bone with a cutting quality matching that of the more strongly absorbed λ = 355 nm wavelength. Crater depths from dual wavelength ablation increased with increasing fluence in either contributing pulse. Practical consequences of these experiments are discussed.