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| | | Optical Immersion of the Detectors Optical immersion of infrared detectors to high refraction microlenses is used to improve performance of the devices but it also limits maximal acceptance angle and minimal f# of the external optics. Action and properties of hemispheric and hyperhemispheric lenses are illustrated in the drawings and tables below. Table 1. Immersed device parameters | | |
| | | The focal plane position of the detectors is dependent on the diameter of the immersion lens which in turn is varied with the optical area of the detector. | | |
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| | | position of external lens | | |
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| | | hemispherical lens _ ggne | | |
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| | | _015.2±O.O5_ VIGO TO-S style 2-stage TE-cooler package with GaAs immersion lens. F- focal length of the external lens, if any n -index of reflection, which for GaAs is approximately 3.3; values vary with X due to dispersion | | |
| | | hyperhemispherical | | |
| | | acceptance angle O | | |
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| | | lens | | |
| | | objective focal plane | | |
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| | | Some examples | | |
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| | | | | | | | | | | lxl | 2x2 | 2x2 and 3x3 | | | | 1.6 | 2.5 | 3.2 | | | | 2.4 | 3.75 | 4.8 | | | | 92x92 | 184x184 | 184x184 and 276x276 | | | | | | | | | | |
| | | Optical size of detector Lopt * Lopt> mm * mm Diameter of the immersion lens 2r, mm Distance d=r(n2-1)/n from the base of the immersion lens to the apparent plane of the detector, mm Physical size of detector Lph=Lopt/n2 Mm X urn | | 0.5x0.5 and smaller To | | |
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| | | 1.5 | | |
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| | | 46x46 and smaller | | |
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| | | | | | | | | | | Parameter | Hemisphere | Hype rhe mis phe re | | | | Distance, L | L = R | L = R(n+l) | | | | d/d' | n | n2 | | | | D*- /D* nrim non-imm | n | n2 | | | | Acceptance angle, 0 | 0 = 180° | 0 = 2 arcsin(l/n) | | | | | 0 5 | 1 | | | | | | | | | | |
| | | of external lens | | |
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| | | l_l_I_I_II—I_I—I_ | | |
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| | | Parameters of thermoelectric cooler:_ I = 1.4 mA max U = 1.9 V max_ Qmx = 0.4 W AT = 110°C | | |
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| | | n - index of refraction (approx. 3.3 for GaAs and 2.7 for CdTe) The values in table 1 show the relative change of a given parameter comparing to a non-immersed detector of the same optical size. Detectors with custom acceptance angles are available on request. Immersion technology is described in "Infrared Detectors and Systems", E.L. Dereniak and G.D. Boreman, Wiley Interscience 2000. | | |
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| | | VIGO TO-8 style 3-stage TE-cooler package with GaAs immersion lens. | | |
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| | | Infrared Detectors from VIGO System S.A. | | |
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