Holographic weapon sight
A holographic weapon sight or holographic diffraction sight is a non-magnifying gunsight that allows the user to look through a glass optical window and see a holographic reticle image superimposed at a distance on the field of view. The hologram of the reticle is built into the window and is illuminated by a laser diode.
History
The first-generation holographic sight was introduced by EOTech—then an ERIM subsidiary—at the 1996 SHOT Show, under the trade name HoloSight by Bushnell, with whom the company was partnered at the time, initially aiming for the civilian sport shooting and hunting market. It won the Optic of the Year Award from the Shooting Industry Academy of Excellence.EOTech was the only company that manufactured holographic sights until early 2017, when Vortex introduced the Razor AMG UH-1 into the market as a competing product. As Vortex introduced the Gen II model on mid July, 2020 which later replaced the original UH-1. In 2025, DOT entered the holographic sight market with the release of the EHS-1, adding another competitor to the field.
Design
Holographic weapon sights use a laser transmission hologram of a reticle image that is recorded in three-dimensional space onto holographic film at the time of manufacture. This image is part of the optical viewing window. The recorded hologram is illuminated by the collimated light of a laser diode built into the sight. The sight can be adjusted for range and windage by simply tilting or pivoting the holographic grating. To compensate for any change in the laser wavelength due to temperature, the sight employs a holography grating that disperses the laser light by an equal amount but in the opposite direction as the hologram forming the aiming reticle.The optical window in a holographic weapon sight looks like a piece of clear glass with an illuminated reticle in the middle. The aiming reticle can be an infinitely small dot whose perceived size is given by the acuity of the eye. For someone with 20/20 vision, it is about 1 minute of arc.
Holographic sights can be paired with "red dot magnifiers" to better engage farther targets.
Working Principle
A laser diode pulses a concentrated laser beam of light onto a convex diverging mirror, this spreads out the beam into a wider surface area. The diverged beam lands onto a collimating reflector, this reflects and blocks light along unwanted paths, causing only a parallel column of light to land on the holographic grating. The holographic grating is a blazed diffraction grating designed to diffract only the particular required wavelength of light correctly onto the reticle image hologram glass. The reticle image hologram thus receives collimated light, filtered by the diffraction grating to specific wavelength.The workings of transmission holography is briefly explained, as required to understand how the collimated light that falls upon the reticle image hologram will diffract to finally produce the holographic image seen by the viewer. The reticle image hologram is a piece of photo-sensitive glass that has been burned with holographic diffraction gratings due to the interference of a reference beam and the source beam. The reference beam used for the burn is equivalent to the aforementioned collimated light landing on the reticle image hologram. The source beam is light that is sourced from the reference beam that takes an alternative path, reflecting off a reticle-shaped object and finally incident upon the reticle image hologram. Once the diffraction grating is burned, the source beam can be removed. With just the original reference beam incident onto the reticle image hologram, the newly formed diffraction gratings on the glass diffracts the reference beam light in such a manner that the viewer perceives it as light from the original source beam. The viewer, no matter the eye position, will see diffracted light that apparently originates from the original object position.