Wave interaction
Holograms.
Interference.
Diffraction
The movement of waves is spiral, spindle-shaped, and pulsating! In this article, we delve into various phenomena related to the interaction and propagation of waves.
Interference occurs as a result of the superposition of two or more waves. It’s essential for the waves to be in the same region of space to interact with each other. Consequently, the amplitude of the resultant wave increases at some points and decreases at others (interfering maxima and minima). This forms an interference pattern that remains stable over time if the waves are generated by a source that continues to oscillate in the same way. An example of such a pattern is the phenomenon observed when two stones are thrown onto a calm water surface. After they touch the water, two series of waves are generated, expanding and passing through each other. Some areas exhibit higher waves, while others exhibit quiescence. Interference also arises when a light beam is split into two rays as it passes through a thin layer. When the layer has a specific thickness, the beam is reflected twice – from its internal and prior to that, its external surface, and the reflected beams can interfere.
Wave-like objects can create an interference pattern. For a comprehensive understanding of interference (interaction), it’s necessary to consider a specific case – diffraction. Diffraction is the bending of waves from their straight-line propagation in space. An example of diffraction is the change in the direction of wave propagation when passing through an opening.
Diffraction is observed in all waves, regardless of their nature. The combination of both phenomena – interference and diffraction – can, under certain conditions, lead to the formation of a hologram. In simple terms, a hologram is created through the interaction of waves that create an interference pattern on a film with a photosensitive layer. The resulting image resembles concentric circles, similar to those formed when you toss pebbles onto a water surface. When the holographic plate is illuminated with a laser beam, diffraction occurs, resulting in the “emergence” of a three-dimensional image of the “recorded” object. The illusion of three-dimensionality and reality is extremely convincing. You can move around a hologram and view it from different angles – just like a real object. However, there is no material substance in the way we know it. The image is illusory but visible. If you were to pass your hand through it, you would realize that it’s just an illusion.
Holography - the science of creating three-dimensional images.
Holography (Greek: όλος (holos) – whole + γραφή (graphe) – write) is the science that deals with creating holograms – a form of imaging that allows the recording and reproduction of three-dimensional images using laser light. Holographic technology can also be used for information storage and processing.
The theory of holography was developed in 1947 by Hungarian scientist Dennis Gabor during research aimed at improving electron microscopy. At the core of this discovery is the methodology for reconstructing the wavefront of light, either reflected or passed through the object of imaging. Practical holography only began to evolve in the early 1960s after the invention of lasers, which provide powerful sources of coherent light necessary for obtaining and reconstructing holographic images. The laser was invented by Theodore Maiman. The concentration and emission of intense and pure (coherent) light are used across various fields. It can replace a scalpel, record and read sound and images from optical media, ignite the “fire” for nuclear fusion, reproduce relief images, and more. Sunlight, known as “white” light, is a combination of several monochromatic lights in the range from red to blue, complementing each other. Laser light is monochromatic. The waves differ from each other by their wavelengths, which are specific for each color. White light consists of multiple wavelengths, while laser light consists of only one. This light is coherent, meaning all waves that compose it are in phase. White light is incoherent, similar to a moving crowd. Laser light is concentrated, directed, and more powerful than other sources of light.
When an atom receives energy from an external stimulator, such as heat, its electrons absorb this energy by changing their orbits – this is referred to as “excited” electrons. They have altered their energy state and become unstable (non-equilibrium). Upon returning to an equilibrium state, they release (emit, while also transforming it) the energy received from the external stimulator as light (also energy). Depending on the material used, the laser light can have different colors. Typically, holograms are in the color of the laser light itself. Its true colors are difficult to perceive. The first practically usable holograms of a modern type (“thick plate”) were created by Yuri Denisyuk, a Soviet physicist. With these holograms, the real colors of the object are observed.
The principle scheme of a hologram involves splitting laser light into two beams. The first beam is directed toward the object (the one we want to holograph (capture)), and it reflects off this object. The second beam, directed toward and reflected by a mirror (referred to as a “reference”), interacts with the light reflected from the object. The resulting interference pattern is “recorded” onto the carrier with a light-sensitive layer (holographic plate). The hologram becomes the “memory” of the interaction of electromagnetic waves from the main beam and those reflected from the object.
An enormous amount of information on a small surface.
Besides three-dimensionality, holograms possess other important characteristics. If the plate is made of glass and contains an image of an object, when the plate is broken and illuminated with a laser, each piece of the glass will contain the entire image of the object. Even if the fragments are repeatedly separated, the image of the entire object can be reconstructed from each part, although it becomes increasingly unclear with the reduction in the pieces. Unlike normal photographs, every small fragment of the holographic layer contains the complete information recorded on the plate. In other words, the principle here is that the part contains the whole, and the whole is contained in the part.
Another significant property of holograms is their ability to store a vast amount of information on a particularly small surface. By changing the angle, it becomes possible to “seal” numerous different images on the same surface. The image created in this way can be restored by illuminating the photographic plate with a beam at the same angle at which it was recorded. Applying this method, researchers have calculated that as much information as is contained in fifty Bibles can be stored on a square inch of film (6.45 square centimeters).
This is also the reason why Karl Pribram turned to holography when explaining the brain’s ability to store many memories in a small space. On the other hand, the fact that every fragment of a hologram contains the complete information explains why the removal of parts of the brain does not result in the loss of specific memories. John von Neumann (a physicist and mathematician of Hungarian origin) calculated that over an average lifespan, the brain stores information on the order of 280 x 10^18 bits. This is a staggering amount, and many researchers are trying to discover the mechanism that explains such capabilities. Holograms provide an answer to this mechanism.
In summary: Holograms possess three-dimensionality, and visually, we cannot determine whether a hologram is a real object or an image. Only when we pass our hand through it do we understand that it is not a “real” object. But what if there is an energy field around the hologram that prevents the hand from passing through it? The hand stops at the boundary of the field. This triggers corresponding impulses (pressure, temperature, pressure) in the receptors of the hand, which transmit to the brain that there is an obstacle at that location. The impulses vary depending on the properties of the “touched” field. However, they are interpreted as density – “matter” with corresponding characteristics – soft, hard, elastic, smooth, warm, etc. And the “touched” field is interpreted by the brain as matter. The eyes also send an impulse that they “see” a reflection, interpreted as color. The hologram is transformed into physically existing “matter,” with specific characteristics, parameters, and properties…
