Appl Phys A (2010) 98: 849–853 DOI 10.1007/s00339-010-5550-2 Cross-sectional study of femtosecond laser bulk modification of crystalline α -quartz M. Budiman · E.M. Hsu · H.K. Haugen · G.A. Botton Received: 7 October 2009 / Accepted: 6 January 2010 / Published online: 27 January 2010 © Springer-Verlag 2010 Abstract Bulk irradiation of crystalline α-quartz was per- formed with ∼170-fs laser pulses with a wavelength of 800 nm focused below the sample surface. Investigations were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques. We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded by a highly strained crystalline struc- ture. The alternating sub-surface structures are parallel to the laser’s electric field polarization and exhibit a spac- ing which is close to the laser wavelength in air. Crack- ing was also observed in the near proximity of these struc- tures. M. Budiman · G.A. Botton ( ) Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S 4M1, Canada e-mail: gbotton@mcmaster.ca Fax: +1-905-5212773 M. Budiman e-mail: budimam@mcmaster.ca Fax: +1-905-5289295 E.M. Hsu Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4M1, Canada e-mail: hsue2@mcmaster.ca Fax: +1-905-5278409 H.K. Haugen Department of Engineering Physics and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada e-mail: haugenh@mcmaster.ca 1 Introduction Ultra-short-pulse laser micromachining is a promising tech- nique that offers precise and reproducible means of surface patterning and structuring, processing, energy deposition in minimized volume and heat-affected zone (HAZ), as well as contamination-free modification that is required for medical and biological applications. The precise processing and the minimum HAZ are made possible by the pulse duration that is shorter than the typical electron–phonon coupling time [1–3]. Cleaner features with minimal collateral damage can, in principle, be obtained. Nevertheless, there have been a number of reports on observed modifications of materials re- sulting in the formation of nanocrystalline, resolidified lay- ers or even amorphous regions, suggesting melting of the material [4–9]. Certain applications such as waveguides [10, 11], mi- crofluidic channels [12], and three-dimensional optical stor- age [13] can require modified regions embedded inside transparent materials. There have been a number of works on bulk irradiation of several crystalline and amorphous ma- terials where localized refractive index, structural, as well as phase changes have been reported (see e.g. [10, 11, 13–24]). In some of these studies, chemical etching following laser ir- radiation revealed further structures in the irradiated volume [19–24]. Amongst transparent materials of potential tech- nological interest, amorphous and crystalline quartz have wide applications in the fields of optoelectronics and pho- tonics technologies because of its wide transparency rang- ing from the ultraviolet to the infrared region of the electro- magnetic radiation. Given the technological importance and limited studies of laser irradiation of the bulk, we therefore report a detailed structural investigation with scanning elec- tron microscopy (SEM) of quartz following laser irradiation, as well as cross-sectional transmission electron microscopy