Holograms as explained earlier are a kind of method which is a photographic technique that records light dispersed from the object and then presents it in a 3 dimensional or 2 dimensional way. Now how this 3-dimensional hologram of an object is created in the last post we saw about the history of the hologram this time we will be looking through the overall science behind the holograms and the future of the holograms as well.

By now we all know that Dennis Gabor was the first to create 3D holograms using a mercury vapor lamp that produces a monochromatic blue light that is filtered and is more coherent than the normal laser used to produce holograms. For this Gabor was awarded the Nobel prize. So now what actually is the science behind this whole hologram producing process. 

How are 3D holograms produced? -  

In holography, red lasers, mainly helium-neon (HeNe) lasers, are prevalent. Some home holography studies use red laser pointer diodes, however, the light from a laser pointer is less coherent and steady, making it difficult to obtain a clear image. Some holograms make use of lasers that emit a variety of hues of light. You may also require a shutter to adjust the exposure depending on the sort of laser you're using. Although holography is sometimes referred to as "lensless photography," it does involve the use of lenses. The lens of a camera, on the other hand, concentrates light, but the lenses employed in holography spread the beam out. A beam splitter is a device that splits a single beam of light into two beams using mirrors and prisms. Light rays are directed to the right destinations via mirrors. The mirrors, like the lenses and the beam splitter, must be spotless. The final image might be degraded by dirt and smudges.

The holographic film is a type of film that can capture light at a very high resolution, which is required to make a hologram. It's a translucent surface with a coating of light-sensitive chemicals on it, similar to photographic film. The distinction between holographic and photographic film is that holographic film must be capable of recording minute changes in light across tiny distances. To put it another way, it must have a very fine grain. Holograms that employ a red laser can rely on emulsions that respond well to red light.

Just like in-camera which works like this.

1. The shutter opens.

2. The light passes through the lens and hits the photographic emulsion on the piece of film.

3. A component called silver halide reacts to the light recording to its amplitude, intensity as it reflects off the scene in front of you. 

4. Then the shutter closes.

5. The scene is then brought to you as a picture in front of you. 

The same as the camera this method too produces a piece of film that has recorded the incoming light, just like a photograph. However, when you examine the holographic plate after it has been developed, you will see something unexpected. A camera's developed film gives you a negative image of the original scene, with parts that were light becoming dark and vice versa. You may still get a feel of what the original scene looked like if you look at the negative. However, there is nothing that resembles the actual scene when looking at a developed piece of film used to create a hologram. Instead, a dark film frame or a random pattern of lines and swirls may appear. The appropriate lighting is required to turn this frame of film into a picture. Monochromatic light shines through the hologram to create a picture in a transmission hologram. Monochromatic or white light bounces off the hologram's surface to create an image in a reflection hologram. The light streaming through or reflecting off the hologram is interpreted by your eyes and brain as a three-dimensional object. Reflection holograms are the holograms you see on credit cards and stickers. To observe a hologram, you'll need the correct light source since it stores the phase and amplitude of the light like a code. It captures the interference between the reference beam and the object beam, rather than a simple pattern of reflected light from a scene. This is accomplished by a pattern of small interference fringes. Each fringe can be a fraction of the wavelength of the light that created it. It needs a key to decode these interference fringes, and that key is the appropriate sort of light. 

Similar to the camera how holograms are captured - 

1. The shutter moves away from the path of the incoming laser.

2. The light from the object reflects off from the object. 

3. Both the beam come to the point of photographic emulsion and the compounds of it then react to the beam.

4. Shutter blocks the path of the laser beam.

Now we will be looking at how the light creates interference fringes. 

    Video credit-science.howstuffworks.com

To comprehend how interference fringes arise on film, a basic understanding of light is required. The electromagnetic spectrum includes light, which is made up of high-frequency electrical and magnetic waves. These waves are quite complicated, yet they may be compared to waves on the ocean. They have peaks and troughs and move in a straight path until they hit something. Light can be absorbed or reflected by obstacles, and most things do both. Reflections from perfectly smooth surfaces are specular (mirror-like), but reflections from uneven surfaces are diffuse (scattered).

Fringes -  The light-touchy emulsion used to make multi-dimensional images makes a record of the obstruction between the light waves in the reference and article radiates. At the point when two wave tops meet, they enhance one another. This is useful obstruction. Whenever a pinnacle meets a box, they counteract each other. This is horrendous impedance. You can consider the pinnacle of a wave a positive number and the box as a negative number. At each place where the two pillars meet, these two numbers add up, either leveling or intensifying that piece of the wave.

This is a ton like what happens when you communicate data utilizing radio waves. Insufficiency adjustment (AM) radio transmissions, you join a sine wave with a flood of shifting amplitudes. In recurrence balance (FM) radio transmissions, you join a sine wave with a flood of fluctuating frequencies. In any case, the sine wave is the transporter wave that is overlaid with a second wave that conveys the data.

The two intersecting light wavefronts in a hologram generate a pattern of hyperboloids, which are three-dimensional patterns that resemble hyperbolas rotated around one or more focal points. Wolfram has further information on hyperboloidal forms. The holographic plate, which rests where the two wavefronts intersect, catches a cross-section of these three-dimensional forms, or a narrow slice of them. Consider staring through the side of a transparent aquarium full of water if this seems perplexing. Waves will spread in concentric circles toward the center if two stones are dropped into the water at opposing ends of the aquarium. When the waves contact, they will cause both constructive and destructive interference. A cross-section showing the interference between two sets of waves in one specific spot might be seen if you snapped a photo of this aquarium and covered up all save a narrow slice in the center. The waves in the aquarium are similar to the light that hits the holographic emulsion. It features peaks and troughs, with some waves being taller and others being shorter. The emulsion's silver halide reacts to these light waves in the same way as it reacts to light waves in a regular image. Parts of the emulsion that get more powerful light becomes darker as the emulsion develops, while those that receive less strong light remain a bit brighter. Interference fringes are formed by these darker and brighter patches. 

Bleaching -

     The contrast between the fringes correlates to the magnitude of the waves. The form of each fringe is determined by the wavelength of the waves. The laser beam's reflection off the object is responsible for both the spatial coherence and the contrast. Light is required to transform these fringes back into pictures. The problem is that the hologram might get so black as a result of all the tiny, overlapping interference fringes that it absorbs most of the light, allowing just a little amount to pass through for picture reconstruction. As a result, holographic emulsion processing frequently necessitates bleaching using a bleach bath. Another option is to record the interference fringes with a light-sensitive material other than silver halides, such as dichromate gelatin. When a hologram is bleached, instead of becoming black, it becomes transparent. It still features interference fringes, but instead of being darker in color, they have a different index of refraction. The index of refraction is the difference between how fast light travels through a medium and how fast it travels in a vacuum. As it passes through the air, water, glass, different gases, and various types of film, a wave of light, for example, can change its speed. This can cause visible distortions, such as a spoon bending in a half-full glass of water.

Future Use of Holograms - 

What is the future of holograms?

1. For the very first the hologram method can be used by the military for mapping due to the holograms they can view the map in-depth and contour it. This can also help them to set the military base to help the boundary and the nearby areas. 

2. The next branch which can get help from holograms is the medical sector and this will help many professionals as well as the learning medical students to look at things and learn them in depth.

3. Other fields like Sports Engineering too can get help from the hologram method which will be discussed in the next post with that we can also lookin that, can holograms be the same as the ones we see in Iron Man movies?