One middle infrared imaging system researched and accomplished by Ma Xiaolong, Yan Jianfeng and other scientific researchers of our institute obtained the authorization of national patent for invention recently, patent number of which is ZL200910218528.5.
In a broad sense, electromagnetic radiation with wavelength from 0.9 micron to 1000 microns can all be called infrared radiation. Transmissivity of atmosphere for infrared radiation with different wavebands is various. Generally, transmissivity for infrared radiation is relatively high for two wavebands, of which one is 3 microns to 5 microns which is called middle infrared band, while the other is 8 microns to 12 microns which is called thermal infrared band. Just like the radiation of visible light, infrared radiation is also one kind of electromagnetic wave, what’s different is that wavelength of the latter is longer. Infrared radiation also follows the law of reflection and the law of refraction, so it is the same as visible light making imaging through optical system available. However, there are distinct differences between infrared imaging and imaging of visible light. First of all, in terms of target characteristics, infrared radiation is from radiation of the target itself which is an passive imaging system, while visible radiation is from radiation reflected from other light source (such as the sun) which is an active imaging system; second, the detector of infrared imaging system often needs refrigeration with cold light aperture internally installed. Refrigeration of detector can reduce considerably dark current and increase sensitivity thereof. The function of cold light aperture of the detector is to filter out stray radiation outside field of view.
The purpose of the invention of the said middle infrared imaging system is to provide an optical imaging system which can work in middle infrared waveband, specifically speaking, it is an optical system which can work in middle infrared waveband with finite object distance and telecentric of the object, and possesses 100% efficiency of cold light aperture and tiny little distortion. The imaging system contains camera lens and detector which are located at the same optical axis. And the detector includes, successively from the side near the camera lens, window of the detector, cold light aperture and the imaging focal plane. The special point lies in that the camera lens is composed of six pieces of lenses, which include, successively from the side far away from the detector, the first lens, the second lens, the third lens, the fourth lens, the fifth lens and sixth lens: the first lens is a meniscus lens with positive optical power and bending to the object; the second lens is a meniscus lens with positive optical power and bending to the image; the third lens is a meniscus lens made and grinded from germanium with negative optical power and bending to the object; the fourth lens is a meniscus lens with positive optical power and bending to the image; the fifth lens is a meniscus lens made and grinded from germanium with negative optical power and bending to the image and the sixth lens is a meniscus lens with positive optical power and bending to the image. The imaging system is an ideal coupled apparatus which is suitable to enable to transfer the middle infrared optical fiber bundle to dot signal and is telecentric of the object and with distortion less than five per ten thousand.
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