The physical parameters of the plasma-induced ablation mechanism were investigated using a picosecond Nd:YLF laser system. The laser consists of a diode-pumped oscillator and a lamp- pumped regenerative amplifier. It operates at a wavelength of 1.053 micrometers with pulse durations of 30 ps and pulse energies up to 1 mJ. The laser beam was expanded to a diameter of 4 mm and focussed to spot sizes of about 30 micrometers . At these high power densities a localized plasma was induced at the focal spot. Surfaces of extracted human teeth were used as target material. In order to study the effect of accompanying shock waves, dye penetration tests, hardness tests and polarized microscopy were performed. At moderate pulse energies no significant impact of shock waves was observed. Because of this result, the terms `plasma- induced ablation' or `plasma-mediated ablation' are more appropriate for ablations solely induced by plasma ionization, and should be distinguished from photodisruptive ablations. In another series of experiments the generated plasma sparks were spectroscopically analyzed. From the measured spectra, mean plasma temperatures of about 5 eV and mean electron densities of about 10¹⁸/cm³ were estimated.

Date Published: 18 January 1995
PDF: 9 pages
Proc. SPIE 2323, Laser Interaction with Hard and Soft Tissue II, (18 January 1995); doi: 10.1117/12.199193

Published in SPIE Proceedings Vol. 2323:
Laser Interaction with Hard and Soft Tissue II
Hans Joerg Albrecht; Guy P. Delacretaz; Thomas H. Meier; Rudolf W. Steiner; Lars Othar Svaasand; Martin J. C. van Gemert, Editor(s)