Electron lens Cathode (al b Fig.4.Theoriginal IP25image co mmoverall andhas7pins. rated by koller and Campbell 1301 had a guantum efficie Press.2000 [101.The Biher an's mon ph describes the trendsofinfraedoptoelectronicsde elopment in th ed [21 missive devices many.Seven yea Asao and M.Suzuki reported a method for enhancing the ing the book Infrared Techmigues and Electro-Opnicsin with useful response in the near infrared.out to an USSR and russia 1331 In the early ed detectors bega the Inited States during 1930's was the radio Co er at th d sulphid pho conductive an rter.With visible to about 3 um. PpS.Work directed by Kutzscher.initially at the Uni the tube w the Electr Fig.4).This was one of the tubes used during World War as a part of the which tion of the most sensitive German detectors.These work arious photocathodes have dev eloped including bialkali ph cathod for the visible were brought to the m region, about Le des intnded for e detecto. s during the war.The most notable was the The early concepts of image intensification ere not V.an airbo and poor coupling Late develop of both e The image intensification by cas cading stag sted detectors concentrnatedhiseforisomleadsulphidelee dently by numb of worke the United state and in german to elect man found that other semiconductors of the lead salt family shown in Fis.5. Opto-Electron.Rev.20.no.3.2012 A.Rogalski 283 rated by Koller and Campbell [30] had a quantum efficiency two orders of magnitude above anything previously studied, and consequently a new era in photoemissive devices was inaugurated [31]. In the same year, the Japanese scientists S. Asao and M. Suzuki reported a method for enhancing the sensitivity of silver in the S−1 photocathode [32]. Consisted of a layer of caesium on oxidized silver, S−1 is sensitive with useful response in the near infrared, out to approxi− mately 1.2 μm, and the visible and ultraviolet region, down to 0.3 μm. Probably the most significant IR development in the United States during 1930’s was the Radio Corporation of America (RCA) IR image tube. During World War II, near−IR (NIR) cathodes were coupled to visible phosphors to provide a NIR image converter. With the establishment of the National Defence Research Committee, the develop− ment of this tube was accelerated. In 1942, the tube went into production as the RCA 1P25 image converter (see Fig. 4). This was one of the tubes used during World War II as a part of the ”Snooperscope” and ”Sniperscope,” which were used for night observation with infrared sources of illumination. Since then various photocathodes have been developed including bialkali photocathodes for the visible region, multialkali photocathodes with high sensitivity ex− tending to the infrared region and alkali halide photocatho− des intended for ultraviolet detection. The early concepts of image intensification were not basically different from those today. However, the early devices suffered from two major deficiencies: poor photo− cathodes and poor coupling. Later development of both cathode and coupling technologies changed the image in− tensifier into much more useful device. The concept of image intensification by cascading stages was suggested independently by number of workers. In Great Britain, the work was directed toward proximity focused tubes, while in the United State and in Germany – to electrostatically focused tubes. A history of night vision imaging devices is given by Biberman and Sendall in monograph Electro−Opti− cal Imaging: System Performance and Modelling, SPIE Press, 2000 [10]. The Biberman’s monograph describes the basic trends of infrared optoelectronics development in the USA, Great Britain, France, and Germany. Seven years later Ponomarenko and Filachev completed this monograph writ− ing the book Infrared Techniques and Electro−Optics in Russia: A History 1946−2006, SPIE Press, about achieve− ments of IR techniques and electrooptics in the former USSR and Russia [33]. In the early 1930’s, interest in improved detectors began in Germany [27,34,35]. In 1933, Edgar W. Kutzscher at the University of Berlin, discovered that lead sulphide (from natural galena found in Sardinia) was photoconductive and had response to about 3 μm. B. Gudden at the University of Prague used evaporation techniques to develop sensitive PbS films. Work directed by Kutzscher, initially at the Uni− versity of Berlin and later at the Electroacustic Company in Kiel, dealt primarily with the chemical deposition approach to film formation. This work ultimately lead to the fabrica− tion of the most sensitive German detectors. These works were, of course, done under great secrecy and the results were not generally known until after 1945. Lead sulphide photoconductors were brought to the manufacturing stage of development in Germany in about 1943. Lead sulphide was the first practical infrared detector deployed in a variety of applications during the war. The most notable was the Kiel IV, an airborne IR system that had excellent range and which was produced at Carl Zeiss in Jena under the direction of Werner K. Weihe [6]. In 1941, Robert J. Cashman improved the technology of thallous sulphide detectors, which led to successful produc− tion [36,37]. Cashman, after success with thallous sulphide detectors, concentrated his efforts on lead sulphide detec− tors, which were first produced in the United States at Northwestern University in 1944. After World War II Cash− man found that other semiconductors of the lead salt family (PbSe and PbTe) showed promise as infrared detectors [38]. The early detector cells manufactured by Cashman are shown in Fig. 5. Opto−Electron. Rev., 20, no. 3, 2012 A. Rogalski 283 Fig. 4. The original 1P25 image converter tube developed by the RCA (a). This device measures 115×38 mm overall and has 7 pins. It opera− tion is indicated by the schematic drawing (b)