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Holographic Sight
Apr 25, 2018

Holographic diffraction sights appeared relatively late, and commercialized products were introduced in 1996. However, its aiming principle has already been applied to the fourth-generation head-up display (HUD) of fighters.

The operation method and display effect of the holographic diffraction collimator are similar to those of the reflex collimator, and the red dot can be aimed at the target, but the production principle and internal structure of the “red dot” are quite different.

The red dot seen on the reflex sight is a virtual image formed by the light of the light source hitting the reticle and then reflected by the curved surface of the spectroscope into the human eye. The red dot seen on the holographic diffraction collimator is a holographic image of a reticle created using holographic imaging/imaging technology.

The screen of a holographic telescope is actually a hologram (or film is more appropriate), and the information on the amplitude and position of transmitted light waves passing through the reticle is recorded on the screen. Of course, this reticle is not installed in the scope. It is only used when the factory produces holograms for holograms. The screen of the hologram is a laser hologram taken on the reticle.

During shooting, the laser is emitted from the laser and split into two beams by a beam splitter. One of the beams passes through the lens group and collimates into parallel light. The reference light is directly irradiated onto the hologram film; After the beam is irradiated as illumination light onto the reticle, the transparent portion of the reticle is transmitted through, and then the lens is corrected to be parallel light, and finally the holographic photosensitive film is also irradiated, and the hologram to the reticle is completed. Image shooting. In the shooting process, there is a strict requirement on the position, angle, and shooting environment vibration of each original component of the entire light path system (minimize vibration as much as possible).

 The hologram was shot, but how can we see the hologram? This is not the same as ordinary film. As shown in Fig. 11, in order for the hologram to be developed, a parallel ray having the same wavelength as that of the reference light at the time of shooting is required as the reproducing light to have the same incident angle as that of the reference light irradiated on the hologram when photographing. Irradiated on the hologram, after diffraction and then emitted from the back of the hologram. The light emitted from the rear of the hologram can reproduce the information when the light irradiated on the reticle falls on the holographic film at the time of shooting, including frequency, direction, etc.


When the human eye receives the diffracted light behind the hologram, it is tricked into thinking that he saw the image of the reticle, but in reality it is the +1 divergence of the hologram. Virtual image, and the human brain will make up its brain image in the reverse direction of the light that enters the human eye.

Also, since the light emitted from the rear of the hologram when the hologram is developed is the light path that can completely reproduce the light that was shot on the hologram film at the time of shooting, the light passing through the reticle after the photographic film is shot is adjusted to be parallel by the lens. After the light hit the holographic film, the light path was reproduced and the human eye received a beam of parallel light. Therefore, the human brain also felt a "straight beam of light emitted from the human eye." Image.

Because the light received by the human eye is parallel light, the aiming operation is the same as that of ordinary reflex sights. The virtual image (that is, the light spot) is first adjusted to zero, and then only the light is seen when aiming. The point falls on the target, which means that the sighting line of the mechanical sight parallel to the bundle of virtual rays is now aligned with the target.

 When the reflection scope is inside, the curved surface of the beam splitter can reflect the light from the illumination source into parallel light, so the human eye can see the red dot from which direction. The hologram is just a plane. It is How do you see the spot from any direction?

This is another feature of the hologram because each light-sensitive spot on the holographic film records the information of the light of the original scene. In principle, the entire scene can be restored by using a part of a hologram of any size. When the human eye focuses on the light spot, it actually receives only the information of the original reticle carried by a part of the diffracted light on the hologram, and the light diffracted from any part of the hologram can be Bring the same information. So the human eye can see the reticle image regardless of the location.

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