The invention discloses an
infrared filter with a
broadband of 3.65 to 5 microns, and a manufacturing method for the
infrared filter. The
infrared filter with the
broadband of 3.65 to 5 microns is characterized in that: monocrystalline
germanium Ge with the size of phi 18*1.0mm is used as a base plate 1, wherein the surface aperture N of the monocrystalline
germanium Ge is less than or equal to 5, and the local aperture
delta N is less than or equal to 0.5, the depth of parallelism theta is less than or equal to 1', and the
surface finish is more than 60 / 40;
coating materials are
silicon monoxide SiO and the monocrystalline
germanium Ge, and multiple
layers of interference films are deposited on two surfaces of the base plate; Sub 1.33(.5HL.5H)<5>3.39(.5LH.5L)<5> Air is adopted by the design of a first
surface film system interference film 2; Sub 0.92(.5HL.5H)<3> 1.1(.5HL.5L)<4> Air is adopted by the design of a second
surface film system interference film 3; and according to the infrared filter with the
broadband of 3.65 to 5 microns, gradient of two sides is less than 3 percent, namely the
wavelength of a transition area from the transmissivity of 5 percent to the transmissivity of 80 percent is less than 20nm, the transmissivity of a high-transmissivity area is more than or equal to 90 percent, the
cut-off depth in a
cut-off area is less than or equal to 0.1 percent, the transmissivity reaches more than 92 percent in the range of thermal imager
wavelength of 3.7 to 4.9mu m, excellent
signal-to-
noise ratio is achieved, and the requirements of sensitivity and accuracy of a high-performance thermal imager can be met.