Advances in Thin Films

Abstract

Physical processes giving rise to color have always been of scientific interest. In everyday life, color effects resulting from optical interference processes are found in examples as diverse as the oil film on water to the brilliancy of certain species of seashell (abalone) and butterfly (lepidoptera). At a technological level, optical thin films underpin a multitude of applications since they provide the means of processing light by the manipulation of amplitude, frequency, phase, and polarization, separately or in combination. Thin films are found in all optical systems ranging from the simplest lens to the most complex satellite imaging system. They are also appearing to an increasing extent in the consumer world, for example in novel decorative paints, artwork, and as components of technology used to combat fraud. Within the defense environment, thin-film optical devices also play an important role in determining the degree to which complex electro-optic systems survive in the battlefield. For example, transparent erosion-resistant coatings have been developed for the protection of external surfaces of airborne systems to meet critical demands in terms of retained performance over the operational lifetime of the system. Other thin-film devices are enablers for the advance of laser technology with requirements for all spectral bands. A major challenge here has been to provide mirror designs capable of surviving the intense fluences existing within the cavity. For pulsed lasers, various nonlinear processes determine the laser damage thresholds of the mirrors, and few materials are capable of surviving fluences of greater than 100 J/cm2. The control of emissivity in the infrared is also becoming a significant factor, not only for military applications, but also in the search for a means of reducing heat losses from buildings and the corresponding impact on the environment. This review addresses advances and trends in several areas, including • The design of thin-film interference structures, • Techniques for thin-film deposition, • Monitoring and process control during the manufacture of complex multilayer structures, • Characterization of optical coatings, • Tunable and active devices, • Application drivers.