Third-order susceptibility measurement in silica-based thin film by Zernicke imaging technique

Microscopic examination of silica-based thin film indicated that an ablation hole is produced when the film is near the laser focus. The Zernicke imaging technique (ZIT) used is based on a single laser shot reducing the risk of damages caused by cumulating laser shots at the same point. Using ZIT, the linear dependance between the variation of the refractive index and laser intensity with a linear regression line intersecting the origin is checked. This avoids any attribution of different optical effects to third-order nonlinearity.