Editing Image intensifier (section)

===Generation 0: early infrared electro-optical image converters===
Development continued in the US as well during the 1930s and mid-1930, the first inverting image intensifier was developed at [[RCA]]. This tube used an electrostatic inverter to focus an image from a spherical cathode onto a spherical screen. (The choice of spheres was to reduce off-axial aberrations.) Subsequent development of this technology led directly to the first Generation 0 image intensifiers which were used by the military during [[World War II]] to allow vision at night with infrared lighting for both shooting and personal night vision. The first military [[night vision device]] was introduced by the German army{{citation needed|date=April 2019}} as early as 1939, developed since 1935. Early night vision devices based on these technologies were used by both sides in World War II. 

Unlike later technologies, early Generation 0 night vision devices were unable to significantly amplify the available ambient light and so, to be useful, required an infrared source. These devices used an S1 photocathode or "[[silver]]-[[oxygen]]-[[caesium]]" photocathode, discovered in 1930, which had a sensitivity of around 60 μA/lm (Microampere per Lumen) and a [[quantum efficiency]] of around 1% in the [[ultraviolet]] region and around 0.5% in the infrared region. Of note, the S1 photocathode had sensitivity peaks in both the infrared and ultraviolet spectrum and with sensitivity over 950&nbsp;nm was the only photocathode material that could be used to view infrared light above 950&nbsp;nm.