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When a low-intensity light beam passes through a transparent material, component, or system, little or no effect may be observed except for a slight transmission loss due to absorption or scatter, or some degree of beam distortion. Although these may seem slight to the nontechnical observer, they often pose nearly insurmountable problems to those working at the edge of detectability or to those who require high resolution.
When the intensity of the beam is increased, a whole range of extra,
reversible interactions starts to come into play. These include temperature rise, thermal expansion, strain, distortion, birefringence, nonlinear transmittance or absorption, electro-optic effects, second harmonic generation, optical parametric oscillation, and self-focusing.
When the intensity of the beam is increased further, these phenomena give way to nonreversible changes in the material or component, such as cracking, pitting, melting, vaporization and violent shattering.
These multifarious effects can sometimes be allowed for, sometimes
minimized, sometimes used to advantage, but they must always be taken into account or else the performance of the material, component, or system may be ruined. We will be looking at some of these problems in the following sections. I hope that this will help you to understand the objectives of this tutorial and even see some of your own problems in a fresh light. I need to emphasize that although my background and expertise is in the theory and measurement of laserinduced damage of optical materials, this tutorial is designed to try to help you - the user of laser systems - to understand the constraints that limit the power- and energy-handling capability of the materials, components, and/or the systems you are using or developing. In other words, I am trying to show you the maximum power and energy that you can put into or transmit through your optical system. In many cases this maximum is well below the LIDT.
One of the main reasons for providing this tutorial at the present time is that we are into a second generation of laser engineers. The first generation grew up alongside the development of the laser, experienced difficulties firsthand, and grew to understand the physical reasons behind the engineering development. The engineers leaving graduate school now do not have this same insight into the technology, because the lasers coming off the production lines are much more stable, efficient, and controlled. They can therefore get on with the job of using, rather than nursing, the laser. However, important insights into the use and performance of the laser and optical systems can be lost unless we remind ourselves at periodic intervals of the problems our predecessors had to face.
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