How Things Work Night Vision Clayton Dordu

Outline Different “Generations” Conclusion References Background Types of Night Vision Design & Operation Overview Design -Photocathode -Micro Channel Plate -Phosphors Screen -Ocular Lens Different “Generations” Conclusion References

Night Vision Background Originally designed for military uses Kálmán Tihanyi created night vison camera The German army had the first live action NVDs The US army had created NVDs used in WWII and the Korean Four different “generations” of NVDs

We will be looking at image enhancement night vision optics Types of Night Vision There are two different kinds of night vision: Image Enhancement Thermal Imaging We will be looking at image enhancement night vision optics

Design Overview Need to amplify light Done using a transducer and electron multiplier Amplify new electric signal and project to screen

Operation Overview Light enters into NVD via objective lens Photons strike photocathode Electric signal is amplified by a Micro Channel Plate Image is created on phosphorus screen from electrons striking it Phosphorus screen is viewed using an ocular lens

Operation Overview Image from: http://electronics.howstuffworks.com/gadgets/high-tech-gadgets/nightvision3.htm

Photocathode Transducer used in night vision Convert the photons from object into electrons Photons strike an emissive surface that releases an electron Made possible via the Photoelectric Effect Similar implementation as solar panels Surface is vacuumed sealed for better performance

Micro Channel Plate (MCP) Similar to secondary electron multipliers Electrons enter channels, collide, emit creating avalanche effect Electric field used for accelerating electrons in channels Two MCPs in series can create ~108 electrons Night vision optics have multiple MCPs cascaded together

Micro Channel Plate (MCP) Made of low resistive material L/d between 40 and 80, Between 0.4 mm and 3 mm thick OAR typically 70 to 80% Channels tilted at angles ranging from 5° to 15 ° Transit time of electrons ~100 ps

Micro Channel Plate (MCP Image from: http://www.dmphotonics.com/MCP_MCPImageIntensifiers/microchannel_plates.htm

Phosphors Screen Cloud of electrons collide with a screen coated in phosphors Electrons excite the phosphors and a photon is released This photon is what is seen by the user Electrons hold same relative pattern as photons had

Ocular lens The enhanced image is viewed using an ocular lens Focuses the image Magnifies the image Can be connected to an external screen

Night Vision Images Images from: http://www.kennymester.com/category/night-vision/ (left) https://en.wikipedia.org/wiki/Night_vision (right)

Different Generations of Night Vision Generation I Generation II Generation III

Generation 0 First NVDs introduced in the 30’s and 40’s Had an infrared source to illuminate objects Uses S-1 photocathode AgOCs (Silver-Oxygen-Cesium)

Generation I First Introduced in the Vietnam War No infrared source, relied on ambient light of stars and moon Didn’t work well on cloudy nights and were unreliable Uses S-20 photocathode NaKSbCs (sodium-potassium-antimony- cesium)

Generation II Had image-intensifier tube ~20,000x light amplification There are Gen II+ devices as well Uses S-25 photocathode – same materials as S-20 just thicker layers

Generation III Still use micro channel plate Micro channel plate is coated with an ion barrier 30,000-50,000x light amplification Use photocathode made of GaAs

Comparison of Different Night Vision Generations Image from: https://www.nightvision4less.com/education-center-night-vision-generations.aspx (left) http://night-vision0.tripod.com/about.html (right)

Conclusion Photons enter objective lens Photocathode converts photons to electrons Electrons are multiplied via multiple micro channel plates Electron cloud strikes phosphors coated screen Photons are released from excitation creating enhanced image Ocular lens focusses and magnifies enhanced image 4 different generations

References Slides by Clayton Dordu Photocathode.https://www.hamamatsu.com/eu/en/technology/innovation/photocat hode/index.html (accessed 10 10, 2017). Micro Channel Plates. http://www.dmphotonics.com/MCP_MCPImageIntensifiers/microchannel_plates.htm (accessed 10 10, 2017). History of Nigth Vision. http://www.nightoptics.com/history-of-night-vision.htm (accessed 10 10, 2017). Tyson, Jeff. Night Vision. http://electronics.howstuffworks.com/gadgets/high-tech- gadgets/nightvision3.htm (accessed 10 10, 2017). Woodford, Chris. How Night Vision Works. 4 12, 2017. http://www.explainthatstuff.com/hownightvisionworks.html (accessed 10 10, 2017). Photocathode. https://en.wikipedia.org/wiki/Photocathode (accessed 10 10, 2017). Night Vision Device. https://en.wikipedia.org/wiki/Night_vision_device (accessed 10 10, 2017).

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