tailieunhanh - Nonlinear Optics - Chapter 12

Optically Induced Damage and Multiphoton Absorption Một chủ đề có tầm quan trọng thực tế lớn quang học gây ra thiệt hại của các thành phần quang học. Thiệt hại quang học là quan trọng vì nó cuối cùng giới hạn số tiền tối đa điện năng có thể được truyền thông qua một vật liệu quang học cụ thể. Quang thiệt hại do đó áp đặt một hạn chế về hiệu quả của nhiều quá trình quang học phi tuyến bằng cách giới hạn E lĩnh vực sức mạnh tối đa có thể được sử dụng để kích thích. | Chapter 12 Optically Induced Damage and Multiphoton Absorption . Introduction to Optical Damage A topic of great practical importance is optically induced damage of optical components. Optical damage is important because 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. There are several different physical mechanisms that can lead to optically induced damage. These mechanisms and an approximate statement of the conditions under which each might be observed are as follows Linear absorption leading to localized heating and cracking of the optical material. This is the dominant damage mechanism for continuous-wave and long-pulse 1 sec laser beams. Avalanche breakdown which is the dominant mechanism for pulsed lasers shorter than 1 sec for intensities in the range of 109 W cm2 to 1012 W cm2. Multiphoton ionization or multiphoton dissociation of the optical material which is the dominant mechanism for intensities in the range 1012 to 1016 W cm2. Direct single cycle field ionization which is the dominant mechanism for intensities 1020 W cm2. 543 544 12 Optically Induced Damage and Multiphoton Absorption Figure For a collimated laser beam optical damage tends to occur at the exiting surface of an optical material because the boundary conditions on the electric field vector lead to an enhancement at the exiting surface and a deenhancement at the entering surface. We next present a more detailed description of several of these mechanisms. We begin by briefly summarizing some of the basic empirical .