1 Development of holographic technology

In 1947, British Dennis Gable pioneered the idea of holographic technology. According to the principle of light interference and diffraction, holographic technology reproduces light waves under specific conditions to form a three-dimensional image. This image records the shape, amplitude, brightness, phase, etc. of the subject, and contains all the information, so it is called holography. However, due to the limited recording equipment at the time and the poor quality of holographic imaging, a large number of researchers spent nearly ten years still not making great progress.

In 1962. Based on the theory of basic holography and the theory of "side-viewing radar" in the communications industry, American scientists Apatnicks and Liss invented a brand-new off-axis holographic technology, advancing holographic technology to another new historical period. This technology records and reproduces the subject through a reference beam with a deflection angle, so that the real image and the virtual image deviate from each other in direction, effectively overcoming problems such as poor imaging quality, and obtaining clear images that can be used by people.

In 1969, Benton proposed the rainbow holography technology, and its advent brought holography into the third stage of development. This technology enables holography to obtain three-dimensional images visible to the naked eye even under white light. Rainbow holography breaks the limitation of the extremely small distance between the photosensitive recording panel and the imaging surface in the traditional holographic technology, so that the observation range of the recorded hologram is relatively large, and at the same time, the use of a suitable optical path can more efficiently use energy. However, the recording process of rainbow holography technology is relatively cumbersome, and requires the naked eye to observe the wavefront reproduction results, and it is difficult to quantitatively analyze the light wave information. The hologram is noisy and cannot form a sufficiently accurate and clear holographic image.

In the late 1960s, the concept of digital holographic technology was put forward by scientists such as Lawrence and Goodman, which realized the digitization of holographic technology. From then on, holographic technology entered the era of precision.

2 Features of holographic technology

Holography technology can be divided into many types, the common divisions are: coaxial holography and off-axis holography; amplitude holography and phase holography; Fresnel holography and Fraunhofer holography. But no matter what kind of classification, holographic technology has the following remarkable characteristics:

(1) Three-dimensionality. The three-dimensionality of holographic technology is essentially different from the three-dimensionality of 3D movies. The three-dimensional images of 3D movies that the human eye can see are due to the action of two polarizers. The polarization directions of the two polarizers are different, and the left and right eyes see different images. Such frequent switching allows the eyes to obtain slightly different images, and a 3D stereo image is generated in the brain. The holographic technology accurately records the amplitude and phase information of the object light, and can see exactly the same three-dimensional image as the real object during reproduction, and can be directly observed by the naked eye.

(2) Severability. The hologram records the interference fringes of the object light and the reference light, and any point records the amplitude and phase information of each point in space, so it is separable. Any fragment can completely reproduce the three-dimensional image of the object, which is a huge advantage of holographic technology.

(3) Large amount of information storage. A holographic photosensitive plate can repeatedly expose multiple times and completely reproduce different images, so the ability to store information is stronger, and the cost of holographic storage is lower.

3 Status Quo of Holographic Technology

3. 1 Application of holographic technology in life

Holographic technology, as a technology that can observe 3D effects with naked eyes, is widely used in projection. Holographic projection can be used to show all kinds of things. The stereoscopic illusions that we often see in movies are the result of holographic technology. Holographic projection equipment is widely used in museums, science museums and various theme parks. Holographic display cabinets also appear in all corners of life. Through the reflection of the glass on the surface of the display cabinet, the observer can see the product images floating in the air from all angles. The details and internal structure of the product can also be clearly presented to the observer through the holographic display cabinet. 360-degree phantom imaging also uses holographic technology to form phantoms. Three-dimensional images are suspended in the mid-air of the real scene, which realizes the combination of real objects and images, which are mostly used in holographic phantom stages to present strange visual effects to the audience.

Because holographic technology has the characteristic of large amount of information storage, holographic storage also brings convenience to human life. Information can be stored through holography. The coupling of object light and reference light can also realize information processing, effectively combining information storage and information processing. In addition, the use of holographic dry boards with strong corrosion resistance, such as silver salt dry boards, can permanently store information. Holographic storage has a large storage capacity and a high reading rate. More importantly, local defects will not cause information loss. These advantages make holographic storage occupy an increasingly important position.

The holographic photosensitive plate has the advantage of being reusable, so the cost of mass copying holograms is very low, and holographic printing is also widely used in daily life. The production process of holographic printing is also relatively simple. Firstly, the holographic relief image on the surface of the sample is obtained through holographic technology, and then the upper nickel plate is made by coating technology, and finally the corresponding hologram is pressed through the press mold. Because holographic images can record three-dimensional information, holographic printing can also achieve three-dimensional printing, printing out three-dimensional images. Holographic printing can be processed on a large scale and has been applied in product promotion and packaging. Currently, ID cards, passports, credit cards and trademarks also use stamped holograms as anti-counterfeiting signs.

3.2 Application of holographic technology in the medical field

With its unique advantages, holographic technology has solved some problems in the medical field, the most prominent being its application in the treatment of ophthalmic diseases. The amount of information recorded by a holographic photograph is large, and the amount of information provided by a holographic photograph of the eye is much greater than that of an ordinary fundus photograph. When diagnosing ophthalmic diseases, holographic technology can present three-dimensional information of the entire eye, and various parts of the eye, such as the cornea, lens, and vitreous body, can be clearly observed layer by layer, which is convenient for doctors to check.

The holographic technology can also be used for three-dimensional recording of human organs. The vibration and deformation of human organs can be measured by interference fringes on the hologram. The second exposure of laser holography can also analyze the deformation of human organs to find out the location of the lesion and the size of the lesion. For example, the use of holographic technology can detect the location of malignant tumors and contribute to the early diagnosis and treatment of cancer. Because of the non-destructive nature of holographic photos, it is currently considered to be the best method to detect human internal organs, and holographic technology is also widely used in clinical examinations.

3.3 Application of holographic technology in the military field

Holographic technology has also been widely used in the military field in recent years. Holographic surveillance systems, holographic 3D maps, holographic missile guidance systems, and holographic display equipment have greatly promoted the development of the military field.

Holographic images play an important role in surveillance systems due to their advantages in all-round recording of three-dimensional information, which greatly compensates for the deficiencies of underwater and aerial surveillance systems. The traditional radar detection system can only detect the position and distance of the target through the radar signal, and cannot accurately identify the specific target. The holographic monitoring system can reproduce the three-dimensional image of the target, and then accurately identify the target, so as to take different countermeasures in time.

Holographic 3D maps can be realized using holographic technology. A holographic 3D map can be prepared through the processing of satellite aerial photography and laser scanning pictures through computer technology. The particularity of the prepared material allows the observer to clearly see the map information and zoom in and out only under the illumination of the LED light. In addition, the holographic 3D map is also recorded three-dimensional information, so it can truly display the features and environment of the landforms, which provides help for the formulation of tactics and planning.

Holographic zoom objectives, holographic filters and holographic correction plates are used in holographic missile guidance systems. Compared with traditional optical systems, holographic missile guidance systems have many advantages. Holographic elements can realize functions that ordinary optical elements cannot, such as three-dimensional information. In addition, the holographic system can replace the traditional complicated optical guidance system with very few holographic elements, which greatly reduces the weight of the system, and the holographic elements are easy to replicate and cost less.

Holographic display equipment also plays an important role in the military field. The holographic lens can selectively pass light waves of different wavelengths, so it can achieve high requirements for both transmittance and reflectivity in a wide band. It is difficult for traditional optical elements to have high reflection at the same time. Rate and transmittance. When the transmittance and reflectance of the element are both high, a better display effect can be achieved, and the holographic lens can achieve a good display effect. If the holographic lens is applied to the helmet display, the pilot can see the outside scenery clearly even at night or in low visibility conditions. After the holographic lens is added to the night vision goggles, the holographic night vision goggles are formed. Compared with ordinary night vision goggles, the holographic night vision goggles can observe the target under any light conditions. The application of holographic helmets and holographic night vision goggles will provide great help for military operations.

4 summary

With the continuous development of holographic technology, holographic technology is now developing in the direction of digitization and integration of optomechanics. More and more products made with holographic technology are on the market. At the same time, it also gave birth to the emergence of microwave holography and acoustic holography. It can be seen that holographic technology occupies an important position in life, medicine and military fields, and has a very broad market. We have reason to believe that in the future, holographic technology will become an irreplaceable and important part of society, economy, and national defense.