There is a maximum power and energy that you can put into or transmit through your optical system; in many cases, this maximum is well below the laser-induced damage threshold. This tutorial explains the factors and constraints that limit the power- and energy-handling capability of optical materials, components, and/or systems. Because the lasers coming off the production lines are much more stable, efficient, and controlled than in the past, today's engineers often do not have the insight into the technology as was required of first-generation laser engineers. 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.
This tutorial text is an extension of the SPIE short course “Power and Energy Handling Capability of Materials, Components, and Systems,” which has been presented at meetings in San Diego and San Jose in recent years.
It is necessary to emphasize that although the laser-induced damage threshold of a material or component is, out of necessity, the maximum irradiance that that material or component can withstand, it is not necessarily the only mechanism that can limit the use of the system in which it resides. This course was therefore designed to cover slightly different ground than my earlier texts on laser-induced damage in optical materials. It must also be understood from the outset that the energy- or power-handling capability of any material, component, or system is a complex function of the material properties, dimensions and specifications, the wavelength of the electromagnetic radiation involved, the pulse width and shape, the spatial dimensions of the beam spot relative to the mount, the mounting environment, and the system specification and use.
Chapter 1 presents practical examples where optical performance is dominated by the interaction between the physical and chemical characteristics of the optical materials and the power/energy in the optical/laser beam. The treatment looks at the material characteristics and shows how these affect the performance of the optical components especially in practical systems.
Chapter 2 covers the physics of reflectance, transmittance, absorption, scatter, and finally the laser-induced damage threshold (LIDT). LIDT is split into thermal failure and dielectric breakdown, and the text shows the factors affecting the relationships between power, pulse length, spot size, and wavelength. The treatment emphasizes the necessity of using the correct units of measurement for the pulse-length regime in which the material or component is to be used.
Chapter 3 addresses the reasons why surface damage is nearly always lower than the bulk. This includes a discussion of the surface finish, the subsurface quality, coatings, and the ambient atmosphere. Finally, some comments are made on the relationship of coating design to the other physically measurable parameters.
Chapter 4 covers the current status of the ISO standards for classification, specification, and measurement techniques for a range of parameters relevant to lasers and laser-based systems. The section includes comments as to the reasons for the stringent control necessary to achieve repeatable measurements in different laboratories using the same samples.
Chapter 5 summarizes the course. The glossary of terms and the index are designed to make it easier to use as a book of reference. The chapters include references from which the text matter has been taken; and the references listed below can be used as a starting point for those who wish to delve deeper into the subject.
Roger M. Wood