LASER PROCESSING OF SAPPHIRE WITH PICOSECOND AND SUBPICOSECOND PULSES

Laser processing of sapphire using a Ti:sapphire laser at 790 and 395 nm and pulse widths varying between 0.2 and 5 ps is reported. A clear improvement in quality is demonstrated for multi-shot processing with sub-ps laser pulses. For fluences between 3 and 12 J/cm(2) two ablatio n phases were observed, in agreement with previous work from Tam et al . using 30 ps, 266 nm laser pulses [A.C. Tam, J.L. Brand, D.C. Cheng, W. Zapka, Appl. Phys. Lett. 55 (20) (1994) 2045]. During the 'gentle a blation' phase periodic wavelike structures, i.e. ripples, were observ ed on the Al2O3, surface, perpendicular to the laser polarisation and with a spacing almost equalling the laser wavelength, indicating metal lic-like behaviour.:The ripple modulation depth was in the order of a few tens of nm. For fluences between 1 and 2.5 J/cm(2), below the sing le-shot surface damage threshold and at a pulse width above 200 fs, mi crostructures could be produced at the rear side of a 1 mm thick sapph ire substrate without affecting the front surface. (C) 1997 Elsevier S cience B.V. PACS: 79.20.Ds.