Holographic gunsight was first conceived in the 1970s and prototypes were fabricated using a He-Ne laser as the illuminating source. The laser source was too costly and fragile and these prototype units were too bulky to be viable as a commercial product. With the advent of low cost laser diodes, EOTech introduced into the commercial market a compact holographic gunsight for small arms in 1996 which has since become one of the most popular gunsight in the U.S. and in Europe. In this paper, the design of the second generation holographic gunsight is described. The optical path travels predominantly in the vertical direction which reduces the length and the weight of the sight by a third. The optical design challenges include the generation of a stable holographic image with changes in the laser emission wavelength, circularization of the laser elliptical beam profile, and the production of high quality optics at low cost. The opto-mechanical design challenges include very fine angular adjustments, stability over large temperature range and the ability to withstand the recoil of powerful handguns.
The holographic sight development started as a search for a sight with improved accuracy, reduced size and greater simplicity. The main component of the sight is a hologram that generates an image of the reticle. This image can appear at any selected distance from the hologram, and can be located either in a plane or in three-dimensional space. The sight accuracy is that of the optics used in forming the hologram, which can be of excellent quality as only one set is needed for hologram recording. The field of view is unrestricted and a 'light-line,' an image of a line in space that extends from the sight to the reticle, guides the observer's eyes to the reticle. Sight designs are reviewed and designs described as the design evolved from a large 20 by 25 cm sight to the current compact sight for small arms. The latest design incorporates a laser diode light source and a pair of holographic elements to make the sight achromatic thus avoiding sighting errors due to laser diode wavelength drift.
Holographic gunsights were first demonstrated in the mid 1970s by researchers at the Environmental Research Institute of Michigan (ERIM) under contracts with the Air Force and the Army. The sights utilized He-Ne gas lasers and were designed for use with large weapons systems. With the advent of low cost visible laser diode, ERIM formed a new company, EOTech, to develop, manufacture and market a holographic gun sight for small arms. A hologram is used to reconstruct the image of a reticle pattern that appears at the target plane. Unlike red-dot sights, virtually any reticle pattern, 2D or 3D, can be formed. The design challenges include an opto-mechanical package that is compact, light weight and low cost which can withstand recoils up to 4,000 Gs and provide fine elevation/windage pointing adjustments, and optics that are aberration-free and stable over a wide temperature range. Manufacturing challenges include the mass production of high quality holographic optics at low cost and the precision alignment of the very low f/number optics.