Through the continual efforts of several generations of scientific researchers, the image enhancement equipment has brought the vision to the dark night. Image intensification, the idea of night-sight, may be a complex conversion of energy particles that happens within a tube. An image-intensifier system works by collecting photons through an objective lens, converting them to electrons via a photocathode, increasing the electricity with a microchannel plate (MCP), converting the electricity back to light employing a phosphor screen, and presenting the image for viewing through an eyepiece lens.
A sophisticated miniaturized power supply is employed to supply the voltages between the weather of the tube that leaves energy conversion and amplification. All of the weather within the tube are closely spaced to avoid electron scatter.
The main electron amplification occurs within the MCP, a skinny disc that contains many closely spaced channels. because the electrons undergo the channels and strike the channel walls, thousands of additional electrons are released. When these strike the phosphor screen, the increased energy is reconverted into light thousands of times brighter than that which entered. The phosphor screen emits this light within the same pattern because the light collected by the target lens, therefore the brightened, intensified image is seen within the eyepiece corresponds to the scene being viewed (or not viewed) within the dark.
Generation 0
During war II and therefore the Korean War, the art of stealth warfare had taken hold, and formal sniper training had become a neighborhood of military maneuvers. it had been during these years that the image-intensification progression began.
Early snipers used image converters (sniper scopes) that required an infrared source to illuminate their target. referred to as Gen 0, these image converters evolved from RCA’s image converter tube developed within the mid-1930s to be used in televisions. The Gen 0 image converter used an S-1 photocathode, an IR-sensor with a high-voltage electron acceleration electric field , and a phosphor screen. The S-1 cathode (AgOCs) didn’t have the maximum amount of quantum efficiency because of the cathodes used today, but it had been ready to provide images with the assistance of the IR illuminator.
The process by which the image was intensified was quite simple during this generation. The reflected IR illuminator light entered the tube and therefore the photocathode converted the sunshine to electrons. Electronic elements focused these electrons through a cone-shaped component (anode) and accelerated them using very high voltage in order that they hit the phosphor screen with greater energy, recreating a clear image. Accelerating the electrons during this manner didn’t produce much gain and caused distortion within the image.
Generation 1
The starlight scope, developed during the first 1960s and used during the Vietnam War, was made using Gen 1 image intensifier tubes. during this scope, three image-intensifier tubes were connected serial, making the unit larger and heavier than today’s night-vision goggles. This early generation produced a transparent center image with a distorted periphery. the utilization of multiple tubes connected serial allowed for much greater overall light gain because the output of the primary tube was amplified by the second and therefore the second by the third. thanks to the straightforward power supply design, the image was subject to instances of blooming — momentary image washout thanks to an overload within the intensifier tube caused by bright light sources.
The primary difference between Gen 1 and Gen 0 was the more sophisticated chemical change employed to make the photocathode. The S-20 cathode, a multi-alkali antimonide process, enhanced the sensitivity also because of the spectral response. However, Gen 1 did have a number of equivalent drawbacks of image distortion and decreased tube life as seen with Gen 0.
Generation 2
Developed within the late 1960s, Gen 2 technology brought a serious breakthrough in night-sight with the event of the microchannel plate. Additionally, the photocathode process used for Gen 1 was further refined to the S-25 cathode and produced a way higher photoresponse.
Nevertheless, it had been the introduction of the MCP that made Gen 2 unique. The MCP begins with two dissimilar pieces of glass. an outsized tube of solid glass (core) is placed within a tubular sleeve of glass (clad). the 2 glasses are then heated together and stretched to make a really small-diameter optical fiber. The fibers are ultimately compressed together to make a bundle of glass fibers called a boule. The boule is then sliced at an angle to get thin discs. Further chemical processing removes only the core glass, thus creating the channels within the MCP. During the tube operation, the electrons travel into the channels and, as they strike the channel walls, they produce secondary electron emissions which create several hundred electrons
The close spacing of the channels within the MCP, alongside the close spacing of the MCP to both the photocathode and therefore the phosphor screen, allows a picture to be created without the distortion characteristic of the Gen 0 and Gen 1 tubes. However, the channels within early MCPs were quite large compared with today’s MCPs. As such, the resolution within early Gen 2 tubes wasn’t nearly as good as that of Gen 0, Gen 1, or today’s Gen 2 and Gen 3 tubes.
The other advancement with Gen 2 was the reduction within the overall size and weight of both the tube module and therefore the power supply. This reduction allowed Gen 2 tubes to be the primary image intensifiers used within user-mounted devices like head- and helmet-mounted goggles.
Generation 3
Developed within the mid-1970s and placed into production during the 1980s, Gen 3 was mainly an advance in photocathode technology. the general appearance of Gen 2 and Gen 3 tubes is sort of similar. Gen 3 tubes use gallium arsenide (GaAs) for the photocathode. This increases the tube’s sensitivity dramatically and particularly within the near-IR. The increased sensitivity improved system performance under low-light conditions, or, to place it differently, enabled the tube to detect light at far greater distances.
However, the highly reactive GaAs photocathode might be easily degraded by the inherent chemical interactions that happen within a tube under normal operation. Most of the chemical reactions happen within the MCP thanks to the electron interactions with the walls of the MCP channels. Thus, to beat the degrading effects of the photocathode, a skinny metal-oxide coating was added to the input side of the MCP. This coating, more commonly referred to as an ion barrier film, not only prevented premature degradation of the photocathode but also enhanced the tube life by repeatedly that of the Gen 2 tubes.
This improvement continues to be a big performance difference between Gen 2 and Gen 3 tubes. The film can, however, impede the photoelectrons from entering the MCP, so intrinsically it increases the electronic noise component of the tube. a serious measure of overall performance for an image-intensifier tube is understood because of the signal-to-noise or SNR. The signal component comes directly from the photocathode sensitivity. The noise component comes from the combined effect of varied operational aspects of the tube, both physical and electrical. The substantially higher photoresponse of the Gen 3 photocathode quite offsets the increased noise component (due to the ion barrier film), providing Gen 3 with a big improvement over Gen 2.
Both Gen 2 and Gen 3 tube manufacturers have made continuous improvements through the years to extend the signal-to-noise within each respective technology. Additionally, continuous improvements are made within MCP manufacturing so on improve the general resolution also. There has been considerable effort expended in developing a Gen 3 tube without the ion barrier film. the trouble proved successful, but the manufacturing costs were excessive compared to the performance improvements.
What’s the future direction？
Image-intensifier technology has most generally been related to use in night-vision goggles (NVGs). Another major technology, unrelated to image intensification, yet mentioned as night-sight, is that of thermal or IR imaging. Image intensification and thermal imaging each have comparative strengths and weaknesses. Thermal imagers are quite good at detecting heat sources in lightlessness, like body heat of personnel or engine heat; however, they are doing not have as high a resolution as do image intensifiers (at equivalent fields of view). Such is because thermal imagers provide an electronic output and therefore the pixel size of the focal plane array (FPA) is far greater than the “effective” pixel size of the direct view optical output of the image intensifier tube. Additionally, thermal imagers had for several years been impractical for user-mounted applications, like NVGs, due to their greater size, weight, and power (SWaP) consumption. Advances in recent years with uncooled thermal imagers like vanadium oxide and amorphous silicon have greatly improved these features making them more suitable for head-mounted applications.
It is easy to imagine myriad situations during which users would greatly enjoy the attributes of both thermal and image-intensification devices at an equivalent time. Thus the logical progression would be to create one device that brings the advantages of both technologies together.
Sensor fusion
Sensor fusion combines the respective strengths of thermal and image-intensification technologies into one device. By combining the strengths of both technologies, users can view a way greater portion of the sunshine spectrum – visible to near-IR to long-wave infrared. the power to ascertain information from both the visible and thermal spectrums through one device represents a big advantage to military, security, and enforcement personnel.
The desire to fuse these two technologies – and keep the general SWaP consumption low therefore the device is often worn by an individual – is resulting in the event of the latest night-vision technologies and devices. the first device is that the enhanced night-vision goggle (ENVG) that mixes a thermal imager with a picture intensifier. within the ENVG, the image intensifier works sort of as a standard NVG. However, the image from the thermal sensor is presented on a display screen then optically overlaid with the image-intensifier output. the longer-term desire is to mix the video output of a thermal imager directly with the video output of an electronic output image intensifier. These new devices could then present an entire digitally fused image to an HMD during a device referred to as the digitally enhanced night-vision goggle (ENVG-D).
Leading the technology development in image intensifiers with direct video outputs are the MCPCMOS (microchannel plate complementary metal-oxide-semiconductor) and therefore the EBAPS (electron bombarded active pixel sensor). Both devices combine a modified CMOS imager directly into the vacuum envelope of a proximity-focused image tube. The CMOS imager replaces the phosphor screen and provides an immediate video output which will be presented to a head or helmet-mounted display. the first difference is that the EBAPS doesn’t contain a microchannel plate thus limiting its luminous gain capability. Additionally, by having an electronic output, the image are often digitally enhanced also as digitally combined with the electronic output of a thermal imager.
Having the pictures in a completely electronic format will allow users to transmit images to a command center for information verification or general intelligence gathering and observation. Considerable research and development funding has come from governmental sources to enhance the performance of image intensifiers. the first use for image intensifiers and related technologies as discussed within this text has been for the military, though as is usually found with modern technology, products developed for one purpose have proved useful for an additional .
As technology has advanced, the areas to be used have widened. Medical, scientific, industrial, and commercial imaging applications are all taking advantage of this technology. The medical imaging profession is increasingly counting on the utilization of image intensifiers as a key component in diagnostic systems. Image intensifiers are utilized in conjunction with endoscopes, x-ray imaging, and fluoroscopy equipment to help with numerous procedures. Additionally, image intensifiers are getting used with research project tools for cell and tissue evaluations related to cancer studies. Image intensifiers are also gaining popularity in numerous commercial applications like machine vision and spectroscopic equipment.
