How Holography Works
explanatory Essay
1688 words
To develop and understanding of how holograms work, one first needs a basic understanding of light and its wave-like properties. First, we will consider investigate the concepts of diffraction and an interference pattern. Consider, for a moment, a person threw a rock into a pond. At the point where the rock hit the water, waves would form and would move away from the source of the wave (the rock) in a spherical shape.
This is what a wave looks like when the wave is being emitted from a single point. Now, consider a water wave that is traveling through a small slit in a wall. The waves would emerge form that slit like it would from a point source (the rock). The waves travel through the slit and emerge in a spherical pattern.
Now, lets take the next step. Lets say instead of just one slit, two slits were put in the wall. Waves would emerge from each point in a spherical pattern. But this time, the system is more complicated. Because the waves are emerging in spherical patterns, the waves begin to intersect with each other and form an interference pattern. Every wave has crests and troughs. A crest can be thought of as the high point of a wave and a trough can be thought of as the low point of a wave. Every wave can be expressed a sin function, that is, it is periodic. These crests and troughs occur at regular intervals in the wave. So, when these waves from the two slits in the wall start intersecting, the crests and troughs start intersecting with each other; this is known as an interference pattern. If the periods of the waves are lined up, or rather the waves are in phase with each other, the crests and troughs of the two waves overlap and reinforce each other.
That is, it looks like there is a wave that is twice as large as one of the original waves at a particular point of intersection; this is known as constructive interference. Now, lets consider a point of intersection where the crest of one wave is present where the trough of the other wave is present. These two waves at this point are out of phase and are experiencing destructive interference. The water would actually look calm at this point, because the waves, in a sense, cancel each other out.
In this essay, the author
- Explains how holograms work by examining the concepts of diffraction and interference patterns.
- Illustrates how a wave looks when it's being emitted from one point. the waves travel through the slit in the wall and emerge in symmetrical patterns.
- Explains that the two slits in a wall form an interference pattern, which intersects with each other and forms crests and troughs.
- Explains that there is a wave that is twice as large as one of the original waves at an intersection; this is known as constructive interference.
- Explains that this interference pattern occurs with water waves and light waves, and proves it through young's double slit experiment. before looking at holograms, it is important to understand lasers.
- Explains how lasers are created and their importance in regard to holography. a rod is shaped into a flash tube, which emits short, intense bursts of broadband light.
- Explains that niels bohr suggested that the radiation of spectral lines created by atoms could be explained if the electrons moved about the nucleus in a fixed orbit.
- Explains that laser light source material provides a particular form of energy state in which the excited atoms can and do pause before returning to the ground state.
- Explains that holography is the means of storing wave information and reproducing it in such a way that none of that information is lost.
- Explains that the interference pattern is important because all of the three-dimensional information about the waves is contained in the two dimensional sample.
- Explains that if the two-dimensional surface is a finite surface, some of the original wave data, the interference pattern, is not recorded and therefore reconstructed.
- Explains that to record the interference pattern, there must be a point of reference by which all of the waves can be measured. a regular light bulb puts out light at many frequencies and wavelengths.
- Explains that the laser emits a single wavelength, that is, coherent light. coherent light waves travel in phase with each other.
- Explains that if we simply illuminate our object with laser light and take a photograph, we would only be recording the different light intensities of the object; we wouldn't have captured any information about the phase of light waves after bouncing off.
- Explains that to capture vital information, we need a standard or reference source to record the phase difference of the light waves and thus capture the information which supplies the vital dimensions and depth, to the holographic presentation.
- Explains that the reference light is emitted in what we will call a plane wave. the object beam strikes the object, and the light deviates in intensity and phase.
- Explains that the hologram, the medium that contains all the information, is nothing more than a high contrast, very fine grain, black and white photographic film.
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In this essay, the author
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- Explains that the objective lens sags due to its own weight because the lens is only supported at the edge.
- Explains that refractors and reflectors involve both refraction and reflection of light rays.
- Explains that reflector telescope can escape from chromatic aberration because wavelength does not effect reflection. the primary mirror is stable because it is located at the back of the telescope.
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- Explains that physics is vital for all musical instruments, and acoustic guitar is one of them.
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- Explains that sound is energy in the form of waves caused by vibration. the strings are stretched from the bridge of the guitar, all the way over the body and sound hole.
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823 wordsRead More - Long Shore Current and the Moving Shorelineexplanatory essayWhen waves approach shore and "feel the bottom", water piles up and breakers form. This process proves that a shoreline is not static. Primarily these waves, breaking at an angle to the shoreline, are what generate a long shore current that parallels the shore. The long shore current not only moves water in the surf zone, it also moves sediment parallel to the shoreline. Long shore current is a function of the angle of wave approach. For example, if the waves approach the shoreline from the south, long shore current moves from south to north
In this essay, the author
- Explains that waves, breaking at an angle to the shoreline, generate a long shore current that parallels it.
- Explains that long shore current and the resulting transport of sediment are only one of the dynamic processes that constantly alter the shoreline.
- Explains that waves do not form parallel to the shoreline, so beach sand has a net movement up or down the beach, depending on the direction of incoming waves.
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371 wordsRead More - Blast Wave Reflection Essayexplanatory essayoccurs, Ernst Mach shows that the incident and the reflected waves would merge together to
In this essay, the author
- Explains that is scaled time, w is the weight of the explosive charge, and t is arrival time.
- Explains that is the scaled impulse, w the weight of the explosive charge, and i the impulse.
- Explains that the fireball followed by an explosion is considered a critical consequence especially while transferring of the heat near any combustible materials.
- Explains that craters are one of the explosion consequences, and that the quantity of explosive is directly proportional to the volume and the deepness.
- Explains that r is the distance between the explosive charge and the interest point, m and w are summary.
- Explains that crawford and karagozian developed anther equation to estimate pso in psi.
- Explains that x is the distance between the explosive charge and the interest point, m and po is ambient atmospheric pressure, in psi.
- Explains that the reflected waves following the incident wave would be greater than the event wave itself, as it could reach up to eight to twenty times of its incident value.
- Assumes that the incident and reflected pressure-time history are as triangular shape with sudden rises figure.
- Explains that the initial shock wave reflects and re-reflects many times. the approximate assumption to predict the value of these reflected waves was given by baker, w.e., 1973.
- Explains the typical internal blast pressure – time history in vented structure and the quasi-static pressure.
- Explains that when the angle of incidence is greater than the critical angle, ernst mach shows that the incident and the reflected waves would merge together to form the mach stem.
- Explains how hopkinson proved the most common law "hopkinson-cranz" or "cube root" scaling, and it has verified by many experiments.
- Explains that p is the blast wave amplitude, r the distance between the center of explosive charge to the interest point, t the duration or "time history", i the impulse, d the characteristic dimension of the explosive source.
- Explains that z is the scaled distance (dimensional distance), w is mass of explosive charge which is usually expressed in kilograms, and r is actual distance between the center of the explosive.
- Explains that explosions can reach up to kilograms and spread through the air and projected with very high velocities.
- Explains that the number and weight of fragments depend on the type of explosive and the material and thickness of the explosive.
- Explains that secondary fragments result when blast waves interact with objects that are not able to resist the blast wave such as buildings, pipes, windows...
- Explains that a review of 81 accidents during 1959-1968 resulted in 78 fatalities. one of them died due to the blast over pressure, while the rest died as the result of flying fragments or the searing heat.
- Explains that the most important factors that affect the shape and size of a crater are the mass of the explosive charge (w) and the distance between it and ground surface (d).
- Explains that when an explosion occurs within a structure, the reflected blast wave from structure elements will increase due to the presence of walls external or internal and ceilings which are not able to resist the blast loads.
- Explains that the prediction of the peak over pressure has been studied for many times during (1950-1960), the first equation was introduced by brode in (1955) due to spherical blast based on the scaled
- Explains that newmark and hansen introduced another equation in bars for a high explosive.
- Explains that the quasi-static pressure is considered as the major difference between the internal and external explosion as it depends on the type and amount of explosive charges and the volume of the building.
1817 wordsRead More