A new approach to wideband scene projection

Research on DMD infrared scene projector with a high contrast ratio infrared prism design

“…Therefore the contrast of IRSP monotonically increases with scene temperature. When the scene temperature is 600 K, IR source temperature reaches as high as about 2400 K. The contrast for this DMD IRSP with a three-element TIR prism design of illumination optics is 108 at 600 K, which is better than other DMD based IRSPs using a two element TIR prism group [9,10].…”

“…3(a), it is easily to get the following formula with Snell's law sin 13 • sin  r1 = n prism n air (9) where n air stands for refractive index of the air, which equals to 1 generally,n prism stands for refractive index of the Prism 1, r1 stands for the refracted angle for the 13 • ray at the prism surface near the DMD. Then, we could deduce that  r1 = arcsin 13 • n prism (10) And the incident angle of the 13 • ray that reached at surface 2 is  1 plus  r1 . Using the Snell's law, we could get sin( 1 + arcsin 13 • n prism ) sin 90 • = n air n prism (11)…”