Optics and Lasers in Engineering 40 (2003) 5–11 Photoacoustic detection of microcracks induced in BK7 glass by focused laser pulses M. Navarrete a, *, M. Villagr ! an-Muniz b ,L.Ponce c , T. Flores d a Instituto de Ingenier ! ıa, Edificio 12, Secci ! on de Ing. Mec ! anica T ! ermica y Fluidos, Universidad Nacional Aut ! onoma de M! exico, Apartado Postal 70-472, Mexico, D. F. b Centro de Instrumentos, Unidad de Fotof ! ısica, Universidad Nacional Aut ! onoma de M! exico, Apartado Postal 70-186, Mexico, D.F. c CICATA-Instituto Polit ! ecnico Nacional, Altamira, km 14.5 Carretera a Tampico, Puerto Industrial, Altamira, C.P. 89600. Mexico, Tamaulipas d IMRE, Universidad de la Habana, San L ! azaro y L. Vedado, Habana 4, CP-10400, Cuba Abstract Anexperimentalinvestigationontheinduceddamagebyaccumulativepulsesgeneratedby a Nd:YAG laser beam focused into the bulk of the BK7 glass is reported in this work. The laser was operated at the single-pulse damage energy threshold of the sample. The optical detonation generates a shock wave emission and microcrack formation. The induced photoacoustic wave emerging from the sample was monitored by piezoelectric detection. These signals provide a simple, reliable and highly sensitive indication of damage, processes involved, and the most appropriate laser parameters for two- and three-dimensional engraving. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Laser photodisruption; Laser-induced damage (LID); Photoacoustic technique 1. Introduction With the increasing use of powerful lasers in research and industry, failure of materialsusedtotransmitintenselaserradiationisacommonevent.Estimatingthe pulsed laser damage in bulk transparent materials is particularly unreliable in practice because it depends on such variables as: the laser wavelength, pulse duration,pulserepetitionfrequency,focalspotdiameterandsampletemperature[1]. There is also a cumulative statistical aspect to laser damage: the probability of *Corresponding author. +52-56-22-80-91; fax: +52-56-22-80-90. E-mail address: mnm@pumas.iingen.unam.mx (M. Navarrete). 0143-8166/03/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0143-8166(02)00066-0