Two technologies are referenced as night vision; image intensification and thermal imaging (see definitions). Because of cost and the fact that image intensifier scenes are easier to interpret than thermal (thermal images show targets as black or white – depending upon temperature – making it more difficult to recognize objects), the most widely used night vision aid in law enforcement is image intensification (l²) equipment. To date, there have been four generations of l² devices, identified as Gen 0, Gen 1, Gen 2, and Gen 3. Developmental laboratory work is on-going, and the U.S. military may designate the resulting as Gen 4. However, no definition for Gen 4 presently exists.
The first night vision aids (also called Generation Zero or Gen 0) were sniper scopes that came into use during World War II and the Korean conflict. These were not true image intensifiers, but rather image converters, which required a source of invisible infrared (IR) light mounted on or near the device to illuminate the target area.
The “starlight scopes” developed during the early 1960’s for use in Vietnam were the first Generation (Gen 1) of image intensifier devices. In Gen 1 night vision units, three image intensifiers were connected in a series, making the units longer and heavier than future night vision units would be. Gen 1 equipment produced an image that was clear in the center of the field of view but suffered from large optical distortion around the periphery. Gen 1 equipment was also subject to “blooming”. Most low-cost imported night vision units use Gen 1 technology, though often under the guise of a higher “generation”.
The development of the microchannel plate, or MCP, in the late 1960s brought on the second generation (Gen 2) in l² night vision. The MCP accelerated and multiplied electrons which provided the gain previously supplied by coupling three image intensifiers together (Gen 1). The introduction of the MCP significantly reduced size and weight for image intensifier tubes, enabling design of smaller night vision goggles and hand-held devices. The MCP also provided much more robust operation when bright lights entered the field of view. The Gen 2 tubes used the same tri-alkali photocathode as the Gen 1 devices. This generation was implemented to reflect the change in how the light was amplified (MCP versus three-stage coupling).
Third-generation (Gen 3) image intensifiers were developed in the mid-1970s and became available during the early 1980s. Gen 3 introduced two major technological improvements: the gallium arsenide (GaAs) photocathode and the ion barrier coating to the microchannel plate. The GaAs photocathode increases the tube’s sensitivity to light from the near-infrared range of the spectrum, enables it to function at greater detection distances, and improves system performance under low-light conditions. Application of a metal-oxide ion barrier to the MCP increases the life of the image tube. The operational life of Gen 3 tubes is in excess of 10,000 hours, compared to that of Gen 2 tubes which is about 2,000 to 4,000 hours. This generation was implemented to reflect the change in the photocathode (tri-alkali replaced with GaAs).
Gated Filmless Technology
Gated filmless technology was created in 1998, but without the reliability required for military delivery. By removing the ion barrier film and “gating” the system power supply, the technology demonstrated substantial increases in target detection range and resolution. In the process, however, it was discovered by ITT, that the same performance results could be achieved using a Generation 3 tube, but with a thinner ion barrier film and an auto-gated power supply, without sacrificing reliability and life-span of the intensifier tube. See also: Myth vs. Fact: Generation 4 directly below.
Myth vs. Fact: Generation 4
Some say that generation (Gen) 4 is the most advanced night vision you can buy. This is not the case. To dispel this myth, let’s start with the basics. There are four Generations of night vision; however, they are Gen 0-3, not Gen 1-4. Historically, the U.S. Army has defined each Generation of night vision. In the late 90’s the Army did define Gen 4 as the removal of the ion barrier film creating a “filmless” tube. This new advancement was to reduce halos while increasing sensitivity, signal-to-noise ratio (SNR) and resolution, for overall improved performance. While performance was improved, the lack of an ion barrier in Gen 4 tubes led to high failure rates, ultimately leading the U.S. Army to recant the existence of Gen 4 definition. Recognizing the high failure rates of Gen 4 tubes, ITT chose to improve upon the existing Gen 3 technology and create a “thin-filmed” tube. By keeping the protective ion barrier, but greatly reducing its thickness, ITT was able to maintain the reliability of Gen 3 while—at the same time—delivering on the Army’s performance requirements intended for Gen 4. This innovation resulted in the production of the Gen 3 thin-filmed tube, which is now the highest performing Gen 3 tube available.