SYNTHESIS & STUDY OF METAL DIELECTRIC THIN FILMS FOR OPTICAL COMPONENTS AND DEVICES

Abstract

Thin film technology is an extensive area of study that deals with surface modifications of coatings in respect to the bulk. Thin film technology covers a wide variety of thicknesses, ranging from a few nanometers to a few microns. Optical thin films embrace the interaction of electromagnetic radiation with the underlying multilayer thin-film structure. A thin film must be within a particular thickness range, often a few tens of nanometers, in order to be used in optics. Depending on the application, optical thin films can have a broad range of compositions, ranging from metallic to dielectric materials such as oxide, oxynitrides, or nitrides. In the realm of light management, optical thin films are frequently used in products that operate in the ultraviolet, visible and infrared wavelength range, such as mirrors, lenses, optical windows, beamsplitters, filters, etc. In this case, the role of the thin film is to alter the reflection, transmission, and refraction of light with respect to the behaviour of the bare substrate. In this thesis, I am only intrigued by the use of thin film in optics, primarily optical thin-film for electro-optical (EO) systems. I emphasized on the application of thin film in the development of optical filters such as linear variable optical filters and dichroic coatings for beam splitters for different EO systems. In the military, paramilitary, intelligence, security, aerospace, and space applications, electrooptic sensors are frequently utilized. The use for visible and infrared imaging technology includes telescopes, satellite imaging systems, laser processing systems, missile seekers, infrared cameras. The optical, electronic, and mechanical modules constitute the electro-optical systems. The electrical module is made up of detectors, an electronics card, a power supply, etc., whereas the optical module is consisting of an entire optical system. Engineers simulate how a sensor can detect and identify objects at a distance under varied optical conditions while designing electro-optic systems. Environmental variables such atmospheric interference, background temperature, obscurants on the battlefield, and visible and invisible light levels are taken into account when modelling performance for object detection and recognition. The optical module consists of large number of optical components, and the performance of the optical system depends upon the performance of thin film coating for individual components. If we consider an EO system which has a visible sensor only and consists of ten optical components made of borosilicate glass. The transmission output of the optical module with uncoated optics will be only 43% of the input radiance There is a loss of 57% in the transmission output. Now if we perform anti-reflection coating on all the surface of optics, with a maximum transmission of 99% on single optics. The performance of the optics module will now be 90% of the input radiance. The performance of the optics module in the infrared region become more worst when using uncoated optics. If we consider an EO system which has only two silicon optics components. The uncoated single silicon optics will transmit 54% of the input radiation. The performance of the infrared optics module will be only 29% of the input radiance. Only 29% of the input radiance reaches the infrared sensor. The anti-reflection coating on the silicon optics in the mid-wave infrared (MWIR) region can improve the transmission from 54% to 97%. Thus, the performance of the same system will now be 94%. There are different kind of filters where optical thin film places an important role in the performance of the imaging or detection systems. In the present thesis we have highlighted two different kinds of filters where thin film plays an important role in defining the performance of the EO systems. The first one is linear variable optical filter and another important filter for any EO system is beam-splitter.