Recently a remarkable phenomenon in ultrafast laser processing of transparent materials has been reported manifesting itself as a change in material modification by reversing the writing direction. It has been experimentally demonstrated that the pulse front tilt is responsible for the occurrence of directional dependence. Additionally, an anisotropic cavitation was observed in the vicinity of the focus at high fluences. The bubbles, formed in the bulk of the glass, can be trapped and manipulated in the plane perpendicular to the light propagation direction by controlling the laser writing direction relative to the tilt of the pulse front. Another intriguing effect recently discovered occurs when the direction of the femtosecond laser beam is reversed from +Z to - Z directions, the structures written in a lithium niobate crystal are mirror images when translating the beam along the +Y and -Y directions. In contrast to glass, the directional dependence of writing in lithium niobate depends on the orientation of the crystal with respect to the direction of the beam movement and the light propagation direction. A theoretical model was created to demonstrate how in the lithium niobate, the nonreciprocal photosensitivity manifests itself as a changing the sign of the light-induced current when the light propagation direction is reversed. Therefore, in a non-centrosymmetric medium, modification of the material can be different when light propagates in opposite directions.

Date Published: 1 March 2010
PDF: 15 pages
Proc. SPIE 7600, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIV, 760017 (1 March 2010); doi: 10.1117/12.845780

Published in SPIE Proceedings Vol. 7600:
Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIV
Jin-Joo Song; Kong-Thon Tsen; Markus Betz; Abdulhakem Y. Elezzabi, Editor(s)