Chapter 12 - Optically Induced Damage and Multiphoton Absorption

Abstract

Optical damage plays a critical role as it ultimately limits the maximum amount of power that can be transmitted through a particular optical material. Optical damage thus imposes a constraint on the efficiency of many nonlinear optical processes, by limiting the maximum field strength E that can be used to excite the nonlinear response without the occurrence of optical damage. In this context, it is worth pointing out that present laser technology can produce laser beams of sufficient intensity to exceed the damage thresholds of all known materials. Several different physical mechanisms can lead to optically induced damage, including linear absorption, avalanche breakdown, multiphoton ionization or multiphoton dissociation, and direct (single cycle) field ionization. The avalanche-breakdown mechanism is believed to be the dominant damage mechanism for most pulsed lasers. The nature of this mechanism is that a small number N0 of free electrons initially present within the optical material are accelerated to high energies through their interaction with the laser field. Multiphoton absorption and multiphoton ionization can lead to laser damage of optical materials and be used to write permanent refractive index structures into the interior of optical materials.