%0 Journal Article
%T Infrared: A Key Technology for Security Systems
%A Carlo Corsi
%J Advances in Optical Technologies
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/838752
%X Infrared science and technology has been, since the first applications, mainly dedicated to security and surveillance especially in military field, besides specialized techniques in thermal imaging for medical diagnostic and building structures and recently in energy savings and aerospace context. Till recently the security applications were mainly based on thermal imaging as surveillance and warning military systems. In all these applications the advent of room temperature, more reliable due to the coolers avoidance, low cost, and, overall, completely integrable with Silicon technology FPAs, especially designed and tailored for specific applications, smart sensors, has really been impacted with revolutionary and new ideas and system concepts in all the infrared fields, especially for security applications. Lastly, the advent of reliable Infrared Solid State Laser Sources, operating up to the Long Infrared Wavelength Band and the new emerging techniques in Far Infrared Submillimeter Terahertz Bands, has opened wide and new areas for developing new, advanced security systems. A review of all the items with evidence of the weak and the strong points of each item, especially considering possible future developments, will be reported and discussed. 1. Historical Introduction Infrared, as part of e.m. spectrum, was discovered by Sir William Herschel as a form of radiation beyond red light. These ¡°calorific rays¡± renamed infrared rays or infrared radiation (the prefix infra in latin means ¡°below¡±) were mainly devoted to thermal measurement and for a long time the major advances were due to infrared thermal imaging based on radiometric measurements [1]. The basic laws of IR radiation (Kirchhoff¡¯s law, Stefan-Boltzmann¡¯s law, Planck¡¯s law, and Wien¡¯s displacement law) have been developed many years after the discovery of IR radiation. In 1859, Gustave Kirchhoff found that a material that is a good absorber of radiation is also a good radiator. Kirchhoff¡¯s law states that the ratio of radiated power and the absorption coefficient (1) is the same for all radiators at that temperature, (2) is dependent on wavelength and temperature, and (3) is independent of the shape or material of the radiator. If a body absorbs all radiation falling upon it, it is said to be ¡°black.¡± For a blackbody the radiated power is equal to the absorbed power and the emissivity (ratio of emitted power to absorbed power) equals one. In 1884, L. E. Boltzmann, starting from the physical principles of thermodynamics, derived the theoretical formula of Black Body Radiation Law, stated
%U http://www.hindawi.com/journals/aot/2012/838752/