ABSTRACT
Photorefractive Glasses and the effect was termed fiber Bragg grating as a consequence. The general compositional approach was to use a glass with good intrinsic ultraviolet transmission, in particular in the vicinity of the intended exposure wavelength of 248 nm. The high-order multiphoton aspect combined with the high intensity produced by the focusing objective allows the focus spot to be positioned anywhere inside the glass without producing any effect except at the focal plane. The ability to write index changes in such a variety of glasses with widely different thermal and physical properties speaks to a mechanism independent of the specific glass composition. The model would be that during the fs pulse the glass would undergo an electric field breakdown where ionized bonds and ions would be created and be cooled after the pulse is removed.
