Catcher in the Rye Essay: Levels of Meaning -- Catcher Rye Essays

Levels of Meaning in The Catcher in the Rye Protected by a cocoon of naivetà ©, Holden Caulfield, the principal character in the novel, The Catcher in the Rye, therapeutically relates his lonely 24 hour stay in downtown New York city, experiencing the "phony" adult world while dealing with the death of his innocent younger brother. Through this well-developed teenage character, JD Salinger, uses simple language and dialogue to outline many of the complex underlying problems haunting adolescents. With a unique beginning and ending, and an original look at our new society, The Catcher in the Rye is understood and appreciated on multiple levels of comprehension. The book provides new insights and a fresh view of the world in which adolescents live. One way for readers to measure their level of comprehension in this story, is to explore the meaning of the title, it's effect on the book's theme and how it provides a deep look into Holden's character. Being an attention demanding tool, the title also can provide a mystery to which the reader can understand by pulling together the clues, hidden in the text. To an experienced reader, who may be familiar with the book, imagery of a catcher in the rye is apparent throughout the story. However, for a new reader the journey begins past the middle of the book. While analyzing the city around him, Holden sees a kid walking in the street "singing and humming." As Holden nears he realizes the child is signing that song, "If a body catch a body coming through the rye" in a very pretty voice, making traffic come to a screeching halt, and making Holden feel "not so depressed."(116) So far, the title's words are just a catchy song, though their repetition, at a key mo... ...ginal tune, by Robert Burns, has the line "If a body meet a body comin thro' the rye," not "If a body catch a body comin thro' the rye." This is not the first time Holden has distorted something, though this lie has meaning. The original poem talks of the love of two people meeting each other, while Holden's image is that of falling children being caught. Love is replaced by Holden protecting children, who are facing a death-like situation, a change showing how much of an impact Allie's death made on Holden's life. One might also see that Holden himself is falling out of innocence and needs a Catcher in the Rye himself, the book's central paradox. In the end any reader could say that "The Catcher in the Rye" is Holden Caulfield, though this title opens up a door into understanding his deep personality, the books theme, while exploring the central paradox.

The Concepts Of Knowledge And Happiness In Mary Shelleys Frankenstein

â€Å"Learn from me, if not by my precepts, at least by my example, how dangerous is the acquirement of knowledge, and how much happier that man is who believes his native town to be the world, than he who aspires to become greater than his nature will allow† (Shelley 60). In Mary Shelley’s Frankenstein, she expresses her beliefs regarding the danger of pursuing happiness through the attainment of knowledge, because true happiness is found in the emotional connections established between people. The pursuit of knowledge is not necessarily an evil thing, but it can cause destruction when it is pursued beyond natural limits. Victor Frankenstein becomes a slave to his passion for learning in more than one way; first his life is controlled by his obsession to create life, and later he becomes a slave to the monster he has created.   Ã‚  Ã‚  Ã‚  Ã‚  Frankenstein describes the beginning of his life as a happy time with his family. During his childhood, Frankenstein was passionate about learning, but his emotional connection with Elizabeth kept him from completely engrossing himself in his studies (Shelley 38). When Frankenstein left home to study at the university of Ingolstadt, he became intent on his quest to uncover the mystery of life. He tells of working in the laboratory until sunrise and being indifferent to the beauty of the world around him (Shelley 56-63). These changes in Frankenstein’s way of life represent Shelley’s belief that one’s passions must be controlled or the passions wi...

The Tapestry Metaphor Essay -- Intercultural Communication Cultural Es

The Tapestry Metaphor We have all heard or used the tapestry metaphor at one time or another: â€Å"It's like a tapestry —with many delicate threads all woven together to make a whole.† Yes, we have heard it again and again. But why not repeat it? Well, after contemplating on the sociocultural experiences I chose to study—attending a Sunday worship service at the local Nazarene church and arraignments at the Juneau Court House—I believe that a person's idea of her or his cultural self is like a tapestry. One's own life experiences and communications with others are the threads. And woven together, the experiences of one's life create a unique cultural being. The Juneau Church of the Nazarene conducts its Sunday services much like many other churches I have attended. A pastor, associate pastor, or music director leads the service from the front of the sanctuary, each taking turns standing at the pulpit when speaking. Also up in front sits the musicians, two pianists and a guitarist. In the main part of the sanctuary sit the congregation in rows of pews. The service usually begins with a reading of scripture, church announcements, or a hymn. Then there are small orders of business, like prayer concerns, special music sung by church members, or other scripture readings. The climax of the hour-long service is the pastor's sermon, in which he preaches about some specific topic centering on the Christian doctrine. The two services I attended followed this basic outline, with little to no deviation from the bulletin. Rather than a bulletin, the Juneau Court House conducts its arraignments according to a calendar, which is posted outside the door to indicate which cases will be addressed on a particular day. A judge or, in this case... ...Well, we could go with Lustig and Koester's definition: â€Å"Culture is a learned set of shared interpretations about beliefs, values, and norms, which affect the behaviors of a relatively large group of people† (27). But why not use a timeless analogy? Cultural identity is a tapestry, a tapestry of one's social interactions, traditions, values, philosophy on life, and so on. Culture is not purely family or ethnicity or location or religion; it is an amalgam of these things—a unique weaving of what makes up our everyday lives. Works Cited and Consulted Jandt, Fred E. An Introduction to Intercultural Communication: Identities in a Global Community. 4 th ed. Thousand Oaks, CA: Sage Publications Inc., 2004. Lustig, Myron W., and Jolene Koester. Intercultural Competence: Interpersonal Communication across Cultures. 4 th ed. Boston: Pearson Education Inc., 2003.

Expect more, get more

Finding the perfect match online promises to become simpler with the September 21 launching of moreProfiles.com, a website that hopes to become the hub of online dating services. With the help of powerful Web 2.0 software, moreProfiles’ president John Dahl and his associates have created a site that makes it easier for singles to search profiles, upload their own, do side-by-side comparisons—everything necessary find their perfect match. The website enlarges the selection pool by bringing together such major players in the online dating industry as Yahoo Personals, Match, American Singles, Love Happens, and True. moreProfiles.com gives the public free access to the 30 million profiles held separately by each of these dating websites, but all from one central web location. The charm and ingenuity of moreProfiles.com is the simplicity that comes with having to do only One Searchâ„ ¢ and to submit only One Profileâ„ ¢. Previously, singles interested in online dating have found that choosing a dating website often locks them into the relatively stagnant pool of users that belong to that one site. Simultaneously, it has effectively locked them out of several competing sites, any one of which has the potential to contain the one person that could match them completely. moreProfiles’ One Profileâ„ ¢ and One Searchâ„ ¢ solutions propose to remove the guesswork from choosing a dating service, as it brings all the top ones directly to the searcher. Just one search command probes the vaults of several of the most prominent dating websites, giving singles free and complete access to the profiles of millions and making it easier for them to find their match. In addition, the submission of just one profile gets singles’ information out to all the top dating websites, making it easier for matches to find them. Information integration is at the heart of moreProfiles’ mission. The key component of the One Searchâ„ ¢ and One Profileâ„ ¢ aspects of moreProfiles is its meta-search capability that reaches across company lines to bring all relevant information to searchers. It has been Dahl’s concern that singles should not be distracted by decisions about which online dating service to use.   He says, â€Å"The question shouldn't be ‘Which dating website is right for me?’ The question should be ‘Which person is right for me?’† He believes that it should be as simple to search online for a dating partner as it is has been to search for any thing else. In keeping with this, Dahl and his team have used meta-search technology to create a website that integrates all the browsing, searching, and comparison capabilities necessary for making perhaps the most important decision in a person’s life. To moreProfiles and its users, this unique service represents a long-overdue development in online dating services. The president and staff of moreProfiles.com are confident that the site fills a gaping hole in the world of online dating, and are sure that this will become evident in the coming months through an expected influx of singles to the site. Dahl says, â€Å"By offering a way to easily and intuitively browse all the top online dating websites simultaneously, we think a lot more people are going to take advantage of online dating to reach out and find that special someone.†   

Othello protagonist Essay

The protagonist of the play, Othello is a man trapped by his own weaknesses rather than a victim of circumstance. Even though the situations that Othello finds himself in are not ideal and contribute to his downfall, it is his own fatal flaws that end up destroying him. In act 3 scene 3 Iago starts to plant a seed of doubt in Othello’s mind about his wife Desdemona and her infidelity. Iago proceeds to ask Othello, â€Å"Did Michael Cassio, when you wooed my lady, know of you love? † This question immediately causes Othello to become suspicious. Iago then follows with a series of rhetorical questions that enrage Othello as well increase the doubt that is building up in his mind. By the end of this scene we see one of Othello’s weaknesses present itself, jealousy. This particular flaw becomes one of the major contributions to Othello’s downfall. By the end of the play jealousy has clouded his judgment and taken over his perspective on everything. At first Othello insists that he needs proof of the alleged affair but quickly changes his mind. â€Å"Must be to loathe her. O curse of marriage.Act 4 scene 1, Iago informs Othello that Desdemona and Cassio have slept together and he has seen that she has given Cassio the handkerchief Othello gave her when they first fell in love. All this news that Iago keeps telling him sends Othello off into a rant, â€Å"Is’t possible? – Confess? Handkerchief? O devil! †After this his falls into a trance. This is the moment when all Othello’s insecuriti es, fears and aversions as well as the obvious lack of judgment that a leader is assumed to have combine to create this kind of epileptic fit. In this scene stage directions are used to help the reader understand what is going on for a dramatic effect. Two of Othello’s flaws that cause this downfall are passion and gullibility. These feelings enabled Iago fill his head with lies that caused him to get so worked up that he lost control. In act 5 scene 1 Iago had convinced Othello that he would kill Cassio and that Othello had to kill Desdemona. Othello begins this scene with a soliloquy, reflecting and attempting to justify his decision to kill her. Othello refers to Desdemona as light. â€Å"Put out the light and then put out he light†. So sweet we ne’er so fatal. †Othello describes how she was so sweet but her actions caused so much pain. Before he kills her, Othello makes sure she has prayed or confessed so that she will go to heaven. â€Å"I will not kill thy unprepared spirit. †Othello’s blind faith in Iago is the flaw that leads all his other weaknesses to rise to the surface an d in the end the inevitable happens. Othello, once a great man, falls. Desdemona speak for one last time in the play. â€Å"A guiltless death I die. † This quote enforces the reality of what has just taken place. This innocent woman was a victim because of another man’s weakness. In this play it is clear what jealousy and misguided trust can do to a person. These weaknesses, along with others, are the reason for Othello’s downfall. Each flaw produced another weakness or doubt. The fact that Othello was manipulated to be part of Iago’s plan for revenge only accelerated the speed of his demise. The fatal mix of passion, jealousy, insecurity as well as how easily he could be manipulated caused Othello to be a man snared by his own weaknesses.

Community Colleges Essay

Does everyone that attends community colleges know the role of them? Most people don’t know the achievement gaps or knows the importance of them. Many teens today are so excited about attending college the last decision on their mind is commuting. This is because most are ready for the dorm life, freedom, and partying. Education does cross their mind, but other times it isn’t until the hard work kicks in. This also goes for charter schools. Charter schools and community colleges are very beneficial and helpful. The two are very similar when it comes to academic reasons. Today many people work hard to close achievements gaps for people coming from high and low income families who want a better education. Many people face obstacles due to family income. Whether it’s high or low income, children fight for available educational opportunities. Everyone deserves a chance at being successful and achieving goals. It is said to be that people living in poverty won’t have the same benefits as others living on the â€Å"brighter side†. People that live on the brighter side have easier chances at getting successful. This refers back to school system, and how education is involved. (1st link) The education law center stated that the Christie administration has been moving too slow. It is suggested that they build more schools for children in struggling cities. Recently, the state of Department of Education failed to move as quickly as they should, now there are many different ranges of requests for many school repairs and fix other things in some of the poorest cities. Charter schools are very different from schools such as private and public schools. In Newark, children are grouped by ages consisting children five and younger that live in poverty. Schools are trying to help these children. Charter schools are private schools that give everyone a chance. For example, in the book Outliers, KIPP was a middle school that Marita attended. KIPP was a middle school that has a high standard of academic conduct and achievement. The success of this school is continuous with its low-income students. These students end up going to college in overwhelming numbers. (2ndlink) Gladwell has questions children being given the opportunity of getting too much schooling. (book) Gladwell compares that theory to agriculture. Rice paddies are planted multiple times a year and they follow a steady schedule. In other countries, students attend school for countless numbers of days. KIPP is introduced to the same strategy for their students. They attend school from 7a. m until 7p. m. Even on Saturdays and in the Summer they are in school learning. Marita lived in poverty and decided to change her cultural legacy by attending KIPP to better herself. Most if not all of her time is spent going to school and doing homework. This allows Marita to get out of poverty. Her grade level increases tremendously. More than half of the students will graduate, including being the first to do so. (book) Charter schools focus their studies on the children. Compared to community colleges, time is spent on the people more. Universities and public schools do not receive the same attention. New Jersey’s high school students receive less standardized test based on their education system. This made charter schools easier to open. Christopher Cerf, an education commissioner, considers the state options on allowing students who take standardized testing to get into colleges to be substituted for high school proficiency test. Also, he feels that the community college entrance exam and high school test be the same. He believes in this so the test could be based on individual subjects. Cerf is trying a new system where a charter can be in Elizabeth, but children in Newark can attend. Community colleges try to close this gap by allowing the opportunity for anyone to attend. Professors interact with students more at community colleges. For community colleges do not have to have any special talents, income, or anything to attend a community college. People fail to realize they have many benefits attending these schools. These colleges aren’t for anyone of a specific age. Everyone is treated equally. The gaps are being closed because you are worked with unlike other school where you’re more independent. For example, in Outliers, the University of Michigan only enrolled 10% of minorities’ entrance chance, when their chance was just as good as the whites. Also, Christopher Logan dropped out of Montana State because the professor showed no interest in helping him. Charter schools close these gaps by allowing them to learn equally but based on a higher level than the same grades as public schools. Christie wants to replace many of the school contract performances and set specific standards. Focusing more on test results than regulatory compliance. (4th link). In the cities with the most poverty, children fail because they haven’t had anything new. The Urban Hope Act will allow private nonprofit to build new schools in Camden, Trenton, and Newark. This will only happen if they can prove experience in education. No state or other public bond dollars will be used on these schools. They will receive 5% less per student state funding than regular district schools. They do plan on promising to do much better with less. (link 5) In conclusion, enough work is being provided. It doesn’t have to always involve money. The financial issues are slowly but surely taken care of. Attention wise, these bridges are being close with enough time and patience to help children learn in charter schools and others in community colleges. Government needs to expand to allow everyone the same opportunity, instead of allowing high incomed people have certain opportunities and advantages rather than others. It is said that prodigies have a less creative mind than a student with a lower IQ. It is not true that certain people need to be smart enough to succeed in the real world. Hard work, dedication and the right education gives low incomed people the same advantage as everyone else. http://weblib. ucc. edu:2188/iw-search/we/InfoWeb? p_product=NewsBank&p_theme=aggregated5&p_action=doc&p_docid=1449450EEA63BEE0&p_docnum=4&p_queryname=2. http://weblib. ucc. edu:2188/iw-search/we/InfoWeb? p_product=NewsBank&p_theme=aggregated5&p_action=doc&p_docid=1445F9C7B95F9388&p_docnum=5&p_queryname=2 http://weblib. ucc. edu:2188/iw-search/we/InfoWeb? p_product=NewsBank&p_theme=aggregated5&p_action=doc&p_docid=139BE64F7B69B398&p_docnum=4&p_queryname=2 http://weblib. ucc. edu:2188/iw-search/we/InfoWeb? p_product=NewsBank&p_theme=aggregated5&p_action=doc&p_docid=134F1CD19D623F50&p_docnum=7&p_queryname=2 http://weblib. ucc. edu:2188/iw-search/we/InfoWeb? p_product=NewsBank&p_theme=aggregated5&p_action=doc&p_docid=13C7A18781A29440&.

3 D Optical Storage

3-D OPTICAL DATA STORAGE TECHNOLOGY * *ABSTRACT 3D optical data storage is the term given to any form of optical data storage in which information can be recorded and/or read with three dimensional resolution (as opposed to the two dimensional resolution afforded, for example, by CD). Current optical data storage media, such as the CD and DVD store data as a series of reflective marks on an internal surface of a disc. In order to increase storage capacity, it is possible for discs to hold two or even more of these data layers, but their number is severely limited since the addressing laser interacts with every layer that it passes through on the way to and from the addressed layer. These interactions cause noise that limits the technology to approximately 10 layers. 3D optical data storage methods circumvent this issue by using addressing methods where only the specifically addressed voxel (volumetric pixel) interacts substantially with the addressing light. This necessarily involves nonlinear data reading and writing methods, in particular non linear optics. 3D optical data storage is related to (and competes with) holographic data storage. Traditional examples of holographic storage do not address in the third dimension, and are therefore not strictly â€Å"3D†, but more recently 3D holographic storage has been realized by the use of microholograms. Layer-selection multilayer technology (where a multilayer disc has layers that can be individually activated e. g. electrically) is also closely related. This innovation has the potential to provide terabyte-level mass storage on DVD-sized disks. Data recording and readback are achieved by focusing lasers within the medium. However, because of the volumetric nature of the data structure, the laser light must travel through other data points before it reaches the point where reading or recording is desired. Therefore, some kind of nonlinearity is required to ensure that these other data points do not interfere with the addressing of the desired point. 1. Overview: Current optical data storage media, such as the CD and DVD store data as a series of reflective marks on an internal surface of a disc. In order to increase storage capacity, it is possible for discs to hold two or even more f these data layers, but their number is severely limited since the addressing laser interacts with every layer that it passes through on the way to and from the addressed layer. These interactions cause noise that limits the technology to approximately 10 layers. 3D optical data storage methods circumvent this issue by using addressing methods w here only the specifically addressed voxel (volumetric pixel) interacts substantially with the addressing light. This necessarily involves nonlinear data reading and writing methods, in particular nonlinear optics. 3D optical data storage is related to (and competes with) holographic data storage. Traditional examples of holographic storage do not address in the third dimension, and are therefore not strictly â€Å"3D†, but more recently 3D holographic storage has been realized by the use of microholograms. Layer-selection multilayer technology (where a multilayer disc has layers that can be individually activated e. g. electrically) is also closely related. Schematic representation of a cross-section through a 3D optical storage disc (yellow) along a data track (orange marks). Four data layers are seen, with the laser currently addressing the third from the top. The laser passes through the first two layers and only interacts with the third, since here the light is at a high intensity. As an example, a prototypical 3D optical data storage system may use a disk that looks much like a transparent DVD. The disc contains many layers of information, each at a different depth in the media and each consisting of a DVD-like spiral track. In order to record information on the disc a laser is brought to a focus at a particular depth in the media that corresponds to a particular information layer. When the laser is turned on it causes a photochemical change in the media. As the disc spins and the read/write head moves along a radius, the layer is written just as a DVD-R is written. The depth of the focus may then be changed and another entirely different layer of information written. The distance between layers may be 5 to 100 micrometers, allowing >100 layers of information to be stored on a single disc. In order to read the data back (in this example), a similar procedure is used except this time instead of causing a photochemical change in the media the laser causes fluorescence. This is achieved e. g. by using a lower laser power or a different laser wavelength. The intensity or wavelength of the fluorescence is different depending on whether the media has been written at that point, and so by measuring the emitted light the data is read. It should be noted that the size of individual chromophore molecules or photoactive color centers is much smaller than the size of the laser focus (which is determined by the diffraction limit). The light therefore addresses a large number (possibly even 109) of molecules at any one time, so the medium acts as a homogeneous mass rather than a matrix structured by the positions of chromophores. 2. History: The origins of the field date back to the 1950s, when Yehuda Hirshberg developed the photochromic spiropyrans and suggested their use in data storage. [3] In the 1970s, Valeri Barachevskii demonstrated that this photochromism could be produced by two-photon excitation, and finally at the end of the 1980s Peter T. Rentzepis showed that this could lead to three-dimensional data storage. [5] This proof-of-concept system stimulated a great deal of research and development, and in the following decades many academic and commercial groups have worked on 3D optical data storage products and technologies. Most of the developed systems are based to some extent on the original ideas of Rentzepis. A wide range of physical phenomena for data reading and recording have been investigated, large numbers of chemical systems for the medium have been developed and evaluated, and extensive work has been carried out in solving the problems associated with the optical systems required for the reading and recording of data. Currently, several groups remain working on solutions with various levels of development and interest in commercialization. *3. Processes for creating written data*: Data recording in a 3D optical storage medium requires that a change take place in the medium upon excitation. This change is generally a photochemical reaction of some sort, although other possibilities exist. Chemical reactions that have been investigated include photoisomerizations, photodecompositions and photobleaching, and polymerization initiation. Most investigated have been photochromic compounds, which include azobenzenes, spiropyrans, stilbenes, fulgides and diarylethenes. If the photochemical change is reversible, then rewritable data storage may be achieved, at least n principle. Also, multilevel recording, where data is written in ‘grayscale’ rather than as ‘on’ and ‘off’ signals, is technically feasible. 3. 1 Writing by non*-*resonant multiphoton absorption Although there are many nonlinear optical phenomena, only multiphoton absorption is capable of injecting into the media the significant energy required to electronically excite molecular species and cause chemical reactions. Two-photon absorption is the strongest multiphoton absorbance by far, but still it is a very weak phenomenon, leading to low media sensitivity. Therefore, much research has been directed at providing chromophores with high two-photon absorption cross-sections. Two photon absorption (TPA) is the simultaneous absorption of two photons of identical or different frequencies in order to excite a molecule from one state (usually the ground state) to a higher energy electronic state. The energy difference between the involved lower and upper states of the molecule is equal to the sum of the energies of the two photons. Two-photon absorption is a second-order processes several orders of magnitude weaker than linear absorption. It differs from linear absorption in that the strength of absorption depends on the square of the light intensity, thus it is a nonlinear optical process Writing by 2-photon absorption can be achieved by focusing the writing laser on the point where the photochemical writing process is required. The wavelength of the writing laser is chosen such that it is not linearly absorbed by the medium, and therefore it does not interact with the medium except at the focal point. At the focal point 2-photon absorption becomes significant, because it is a nonlinear process dependent on the square of the laser fluence. Writing by 2-photon absorption can also be achieved by the action of two lasers in coincidence. This method is typically used to achieve the parallel writing of information at once. One laser passes through the media, defining a line or plane. The second laser is then directed at the points on that line or plane that writing is desired. The coincidence of the lasers at these points excited 2-photon absorption, leading to writing photochemistry. 3. 2 Writing by sequential multiphoton absorption Another approach to improving media sensitivity has been to employ resonant wo-photon absorption (also known as â€Å"1+1† or â€Å"sequential† 2-photon absorbance). Nonresonant two-photon absorption (as is generally used) is weak since in order for excitation to take place, the two exciting photons must arrive at the chromophore at almost exactly the same time. This is because the chromophore is unable to interact with a single photon alone. However, if the chromophore has an ene rgy level corresponding to the (weak) absorption of one photon then this may be used as a stepping stone, allowing more freedom in the arrival time of photons and therefore a much higher sensitivity. However, this approach results in a loss of nonlinearity compared to nonresonant 2-photon absorbance (since each 1-photon absorption step is essentially linear), and therefore risks compromising the 3D resolution of the system. 3. 3 Microholography In microholography, focused beams of light are used to record submicrometre-sized holograms in a photorefractive material, usually by the use of collinear beams. The writing process may use the same kinds of media that are used in other types of holographic data storage, and may use 2-photon processes to form the holograms. . 4 Data recording during manufacturing Data may also be created in the manufacturing of the media, as is the case with most optical disc formats for commercial data distribution. In this case, the user cannot write to the disc – it is a ROM format. Data may be written by a nonlinear optical method, but in this case the use of very high power lasers is acceptable so media sensitivity becomes less of an issue. The fabrication of discs containing data molded or printed into their 3D structure has also been demonstrated. For example, a disc containing data in 3D may be constructed by sandwiching together a large number of wafer-thin discs, each of which is molded or printed with a single layer of information. The resulting ROM disc can then be read using a 3D reading method. 3. 5 Other approaches to writing Other techniques for writing data in three-dimensions have also been examined, including: Persistent *spectral** **hole burning* (PSHB), which also allows the possibility of spectral multiplexing to increase data density. However, PSHB media currently requires extremely low temperatures to be maintained in order to avoid data loss. Void* formation, where microscopic bubbles are introduced into a media by high intensity laser irradiation. [7] Chromophore poling, where the laser-induced reorientation of chromophores in the media structure leads to readable changes. *4. Processes for reading data*: The reading of data from 3D optical memories has been carried out in many different ways. While some of these rely on the nonlinearity of the light-matter interaction to obtain 3D resolution, others use methods that spatially filter the media's linear response. Reading methods include: Two photon absorption (resulting in either absorption or fluorescence). This method is essentially two-photon-microscopy. Linear excitation of fluorescence with confocal detection. This method is essentially confocal laser scanning microscopy. It offers excitation with much lower laser powers than does two-photon absorbance, but has some potential problems because the addressing light interacts with many other data points in addition to the one being addressed. Measurement of small differences in the refractive index between the two data states. This method usually employs a phase contrast microscope or confocal reflection microscope. No absorption of light is necessary, so there is no risk of damaging data while reading, but the required refractive index mismatch in the disc may limit the thickness (i. e. number of data layers) that the media can reach due to the accumulated random wavefront errors that destroy the focused spot quality. Second harmonic generation has been demonstrated as a method to read data written into a poled polymer matrix. Optical coherence tomography has also been demonstrated as a parallel reading method. *5. Media *design: The active part of 3D optical storage media is usually an organic polymer either doped or grafted with the photochemically active species. Alternatively, crystalline and sol-gel materials have been used. 5. 1 Media form factor Media for 3D optical data storage have been suggested in several form factors: Disc. A disc media offers a progression from CD/DVD, and allows reading and writing to be carried out by the familiar spinning disc method. Card. A credit card form factor media is attractive from the point of view of portability and convenience, but would be of a lower capacity than a disc. Crystal, Cube or Sphere. Several science fiction writers have suggested small solids that store massive amounts of information, and at least in principle this could be achieved with 3D optical data storage. 5. 2 Media manufacturing The simplest method of manufacturing – the molding of a disk in one piece – is a possibility for some systems. A more complex method of media manufacturing is for the media to be constructed layer by layer. This is required if the data is to be physically created during manufacture. However, layer-by-layer construction need not mean the sandwiching of many layers together. Another alternative is to create the medium in a form analogous to a roll of adhesive tape. *6. Drive design*: A drive designed to read and write to 3D optical data storage media may have a lot in common with CD/DVD drives, particularly if the form factor and data structure of the media is similar to that of CD or DVD. However, there are a number of notable differences that must be taken into account when designing such a drive, including: Laser. Particularly when 2-photon absorption is utilized, high-powered lasers may be required that can be bulky, difficult to cool, and pose safety concerns. Existing optical drives utilize continuous wave diode lasers operating at 780 nm, 658 nm, or 405 nm. 3D optical storage drives may require solid-state lasers or pulsed lasers, and several examples use wavelengths easily available by these technologies, such as 532 nm (green). These larger lasers can be difficult to integrate into the read/write head of the optical drive. Variable spherical aberration correction. Because the system must address different depths in the medium, and at different depths the spherical aberration induced in the wavefront is different, a method is required to dynamically account for these differences. Many possible methods exist that include optical elements that swap in and out of the optical path, moving elements, adaptive optics, and immersion lenses. Optical system. In many examples of 3D optical data storage systems, several wavelengths (colors) of light are used (e. g. eading laser, writing laser, signal; sometimes even two lasers are required just for writing). Therefore, as well as coping with the high laser power and variable spherical aberration, the optical system must combine and separate these different colors of light as required. Detection. In DVD drives, the signal produced from the disc is a reflection of the addressing laser beam, and is therefore very intense. For 3D optical storage however, the signal mus t be generated within the tiny volume that is addressed, and therefore it is much weaker than the laser light. In addition, fluorescence is radiated in all directions from the addressed point, so special light collection optics must be used to maximize the signal. Data tracking. Once they are identified along the z-axis, individual layers of DVD-like data may be accessed and tracked in similar ways to DVD discs. The possibility of using parallel or page-based addressing has also been demonstrated. This allows much faster data transfer rates, but requires the additional complexity of spatial light modulators, signal imaging, more powerful lasers, and more complex data handling. *7. Development issues*: Despite the highly attractive nature of 3D optical data storage, the development of commercial products has taken a significant length of time. This results from limited financial backing in the field, as well as technical issues, including: Destructive reading. Since both the reading and the writing of data are carried out with laser beams, there is a potential for the reading process to cause a small amount of writing. In this case, the repeated reading of data may eventually serve to erase it (this also happens in phase change materials used in some DVDs). This issue has been addressed by many approaches, such as the use of different absorption bands for each process (reading and writing), or the use of a reading method that does not involve the absorption of energy. Thermodynamic stability. Many chemical reactions that appear not to take place in fact happen very slowly. In addition, many reactions that appear to have happened can slowly reverse themselves. Since most 3D media are based on chemical reactions, there is therefore a risk that either the unwritten points will slowly become written or that the written points will slowly revert to being unwritten. This issue is particularly serious for the spiropyrans, but extensive research was conducted to find more stable chromophores for 3D memories. Media sensitivity. 2-photon absorption is a weak phenomenon, and therefore high power lasers are usually required to produce it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to achieve excitation, but these instruments are not suitable for use in consumer products. *8. Academic development*: Much of the development of 3D optical data storage has been carried out in universities. The groups that have provided valuable input include: Peter T. Rentzepis was the originator of this field, and has recently developed materials free from destructive readout. *Watt W. Webb* co developed the two-photon microscope in Bell Labs, and showed 3D recording on photorefractive media. Masahiro Irie developed the diarylethene family of photochromic materials. [13] Yoshimasa Kawata, *Satoshi Kawata* and Zouheir Sekkat have developed and worked on several optical data manipulation systems, in particular involving poled polymer systems. 14] Kevin C Belfield is developing photochemical systems for 3D optical data storage by the use of resonance energy transfer between molecules, and also develops high 2-photon cross-section materials. Seth Marder performed much of the early work developing logical approaches to the molecular design of high 2-photon cross-section chromophores. Tom Milster has made many contributions to the theory of 3D optical data storage. Robert McLeod has examine d the use of microholograms for 3D optical data storage. Min Gu has examined confocal readout and methods for its enhancement. 9 Commercial development*: In addition to the academic research, several companies have been set up to commercialize 3D optical data storage and some large corporations have also shown an interest in the technology. However, it is not yet clear whether the technology will ever come to market in the presence of competition from other quarters such as hard drives, flash storage, holographic storage and internet-based storage. Examples of 3D optical data storage media. Top row – Written Call/Recall media; Mempile media. Middle row – FMD; D-Data DMD and drive. Bottom row – Landauer media; Microholas media in action. Call/Recall was founded in 1987 on the basis of Peter Rentzepis' research. Using 2-photon recording (at 25 Mbit/s with 6. 5 ps, 7 nJ, 532 nm pulses), 1-photon readout (with 635 nm), and a high NA (1. 0) immersion lens, they have stored 1 TB as 200 layers in a 1. 2 mm thick disk. [23] They aim to improve capacity to >5 TB and data rates to up to 250 Mbit/s within a year, by developing new materials as well as high-powered pulsed blue laser diodes. Mempile are developing a commercial system with the name TeraDisc. In March 2007, they demonstrated the recording and readback of 100 layers of information on a 0. mm thick disc, as well as low crosstalk, high sensitivity, and thermodynamic stability. [25] They intend to release a red-laser 0. 6-1. 0 TB consumer product in 2010, and have a roadmap to a 5 TB blue-laser product. [26] *Constellation 3D* developed the Fluorescent Multilayer Disc at the end of the 1990s, which was a ROM disk, manufactured layer by layer. The company failed in 200 2, but the intellectual property (IP) was acquired by D-Data Inc. who are attempting to introduce it as the Digital Multilayer Disk (DMD). Storex Technologies has been set up to develop 3D media based on fluorescent photosensitive glasses and glass-ceramic materials. The technology derives from the patents of the Romanian scientist Eugen Pavel, who is also the founder and CEO of the company. First results, 40 nm marks recorded into 3D virtual layers separated by 700 nm, were presented in October 2009 at the ISOM2009 conference. Landauer inc. are developing a media based on resonant 2-photon absorption in a sapphire single crystal substrate. In May 2007, they showed the recording of 20 layers of data using 2 nJ of laser energy (405 nm) for each mark. The reading rate is limited to 10 Mbit/s because of the fluorescence lifetime. Colossal Storage aim to develop a 3D holographic optical storage technology based on photon induced electric field poling using a far UV laser to obtain large improvements over current data capacity and transfer rates, but as yet they have not presented any experimental research or feasibility study. Microholas operates out of the University of Berlin, under the leadership of Prof Susanna Orlic, and has achieved the recording of up to 75 layers of microholographic data, separated by 4. micrometres, and suggesting a data density of 10 GB per layer. [33] 3DCD Technology Pty. Ltd. is a university spin-off set up to develop 3D optical storage technology based on materials identified by Daniel Day and Min Gu. Several large technology companies such as Fuji, Ricoh and Matsushita have applied for patents on 2-photon-responsive materials for applications including 3D optical data storage, however they have not giv en any indication that they are developing full data storage solutions.