Figure 7: The symmetric stretching vibration of carbon dioxide (CO2) increases the size of the electron cloud. It is therefore Raman-active.

Absorption: Some of the incident wavelengths are (partially) absorbed in the sample, while other wavelengths are transmitted without much loss in intensity. (Figure 3)

Rayleigh scattering is the term used for elastic scattering of light by molecules, and is by far the most dominant scattering process. The interaction does not change the energy state of the molecule and as such the scattered photon has the same color (wavelength) as the incident photon. In a Raman spectrometer, the Rayleigh scattered light has to be removed from the collected light, otherwise it would obscure the Raman signals.

Some sources claim that certain of the original polyhedral dice used in the Dungeons & Dragons role-playing game system were obtained from Edmund Scientific.[4]

Figure 8: Raman spectrum of benzonitrile and the stretching vibration of the cyano-group (CN) of benzonitrile at 2229.4 cm-1 (red).

In 1984, the company split into Edmund Scientific and Edmund Industrial Optics, the latter taking over their optical manufacturing. Later known simply as Edmund Optics, the commercial side of the company continued to expand and now has a multinational presence. In 2001, the two companies were purchased by Boreal Science, which was in turn purchased by VWR International. Many of the science toys and kits are currently offered by the online retailer Scientifics Direct.

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The microscopic origin of this Raman interaction is an excitation or de-excitation of molecular vibrations in the matter. The characteristics of these vibrations determine the wavelength of the inelastically scattered light. From measuring the intensity distribution (spectrum) of the scattered light it is hence possible to deduce information about the vibrational structure of the substance illuminated. Therefore, Raman spectroscopy belongs to the group of vibrational spectroscopies.

The count rate is the number of events the detector registers for the respective Raman shift per second of detector integration. It is proportional to the intensity of the light imaged to the detector.

Matter can reemit absorbed light again by an independent process called fluorescence. The emitted light has a different, longer wavelength than the originally absorbed light, which will result in a perceived “amplification” of some light wavelengths.

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However, a tiny fraction of the scattered light interacts with the matter it hits in a way that it exchanges small amounts of energy, which is called inelastic scattering. The change in energy of the scattered light results in a changed frequency and wavelength.

Stokes Raman scattering is the inelastic scattering process that transfers energy from the light to a vibration of the molecule. Therefore, the scattered photon has lower energy and a higher wavelength than the incident photon. The amount of energy transferred is not arbitrary, it has to be exactly the amount required to excite one of the molecular vibrations of the molecule. The composition of the scattered light is therefore highly dependent on the exact type of molecule (like a fingerprint). Stokes scattering is the most commonly exploited process to acquire a Raman spectrum. It is, however, several orders of magnitude less likely to occur compared to Rayleigh scattering, rendering it difficult to detect.

In this way substance identification is possible within seconds and non-technical users can easily interpret the results.

Edmund Scientific Corporation, based in Barrington, New Jersey, was founded in 1942 as a retailer of surplus optical parts like lenses. It later branched out into complete systems like telescopes and microscopes, and in the 1960s, a wide variety of science toys and kits. Through the 1970s and 80s they were best known for their mail order sales and associated catalogs, although they also maintained a retail presence at their factory store.

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For historical reasons, spectroscopists also like to use the wavenumber $ṽ$, which is defined as the reciprocal of the wavelength. The wavenumber is directly proportional to the energy of the photon (Equation 3) and usually expressed in units of reciprocal centimeters (cm–1) to give easy to read numbers.

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Norman W. Edmund retired in 1975 and left the company to his son, Robert. The company continued on as before into the 1980s, but the original business model began to wane. Robert split the company into Edmund Scientifics and Edmund Optics.[2] Edmund Scientifics marketed to consumers and specialized in science-themed toys, vaguely high-tech household gadgets, and "science gifts." Edmund Optics did not have a public showroom like Edmund Scientifics, although the two organizations shared the same building. The large back room of Edmund Scientifics still sold military surplus from World War II and other wars well into the 1980s and into the mid-1990s. Some of the items in the surplus room were from German and other non-American militaries. None of these items were in the mail-order catalogs. They also sold other surplus wares of interest to hobbyists, including specialized motors and other miscellaneous electronics, parts from toys, and other household items.[citation needed]

However, obtaining a Raman spectrum is just the start: after visualizing the data, you need to interpret the Raman image.

5. Hesse, M., Meier, H. and Zeeh, B. (2005). Spektroskopische Methoden in der organischen Chemie. Stuttgart: Georg Thieme Verlag.

Figure 2: Electromagnetic spectrum: Depending on the energy of the electromagnetic radiation, different processes in atoms and molecules can be induced by the interaction between light and matter.

The transfer of energy from light to matter leads to an excitation. The following section outlines the most important excitation processes required to understand Raman spectroscopy: absorption, fluorescence, and scattering.[3]

Each of these processes can be exploited to extract information about the chemical and physical nature of the sample. The exact type and extent of molecular properties deducible depends on the type of spectroscopy used. The two main vibrational spectroscopies are infrared (IR) spectroscopy and Raman spectroscopy. Raman spectroscopy employs the Raman effect for the analysis of substances. The basics of Raman scattering are explained below.

Anti-Stokes Raman scattering is another inelastic scattering process. Here, a specific amount of energy is transferred from a molecular vibration to the photon. The scattered photon has higher energy and a lower wavelength than the incident photon. This process is even less likely to occur than Stokes scattering. Therefore, it is usually not used in Raman spectroscopy. The information extracted from anti-Stokes scattered light is mostly equivalent to the information extracted from Stokes scattered light, and only very specialized applications will require the extra effort to measure both scattering processes.

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Raman spectroscopy detects changes in the polarizability of a molecule. It therefore only detects vibrations where the polarizability changes during the movement (these are Raman-active vibrations)

Skeletal vibrations are usually found at Raman shifts below 1500 cm–1 and have a substance-specific, characteristic pattern. This region, often referred to as the “fingerprint” region of a substance, is the most important part of the spectrum for identification purposes.[5]

The most important physical parameters and their corresponding equations relevant for Raman spectroscopy are summarized in Table 1.

Among the company's best-known products were the Astroscan reflector telescope and their inexpensive bimetallic jumping disks.

Edmund ScientificAstroscan

The company became briefly famous in 1973 when Comet Kohoutek approached Earth and the company sold out of telescopes, a fact that made national news.[2] Neil deGrasse Tyson would later comment that "The Edmund Scientific catalog was a geek's paradise. At a time when no one had access to lasers, they had them for sale."[2]

Spectroscopy is the study of the interaction between matter and light. There are different types of spectroscopy, which are typically named after either the used light source (e.g. IR spectroscopy) or the process of light-matter interaction exploited. Raman spectroscopy is based on the inelastic light scattering in a substance where the incident light transfers energy to molecular vibrations. The scattered light can be detected by a Raman spectrometer and represents a “chemical fingerprint” of the substance. Based on such spectral information, a material can be identified or characterized.

The vibrations of certain distinct subunits of a molecule, called its functional groups, will appear in a Raman spectrum at characteristic Raman shifts. Such a shift is similar for all molecules containing the same functional group. These signals are particularly useful when monitoring reactions which involve these functional groups (oxidation, polymerization, etc.), since they provide a direct measure of the progress during the reaction.

Following Sputnik, Edmund was able to capitalize on a growing national interest in science and astronomy. They expanded their business into a full line of telescopes and telescope kits as well as equipment, parts, and supplies for other scientific fields such as physics, optics, chemistry, microscopy, electronics, and meteorology. They continued to grow as a supplier to teachers and schools with demonstration devices and kits which covered most fields of science.

The above description is valid for a single light wave or photon. However, a light beam consists of many light waves with different frequencies propagating in the same direction. Each frequency contributes to the beam with intensity I  (i.e. a certain number of photons per time interval). The intensity of a light beam is the quantity that is ultimately measured with the detector of a spectrometer.

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In 2000 Edmund Scientific was purchased by Science Kit and Boreal Laboratories, a western New York based science supply company. Science Kit and Boreal Laboratories is part of a group of companies that provide science supplies to elementary, middle, and high schools, as well as colleges and universities. This group falls under the unofficial umbrella "VWR Education", and its constituent enterprises are owned by VWR International, a multi-national conglomerate with offices in India, China, Europe, Canada, and the United States. They are no longer affiliated with Edmund Optics Inc.[citation needed]

Raman spectroscopy belongs to the group of vibrational spectroscopies. This article presents the fundamental principles of Raman spectroscopy and the basics of the measurement.

Raman spectroscopy is one type of vibrational spectroscopy which requires good understanding of the properties of light. It provides a chemical “fingerprint” of the substance measured and is therefore frequently used whenever unknown materials need to be identified.

Therefore, a light wave (or photon) carries more energy E the larger the frequency or, alternatively, the smaller the wavelength is (Equation 2).

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The set of vibrations is highly dependent on the exact structure of the molecule and therefore comprise a unique vibrational spectrum. This makes vibrational spectroscopy an ideal tool for substance identification. In fact, the vibrational spectrum is so unique that it (or more precisely part of it) is often referred to as the “chemical fingerprint” of the molecule.

Using these characteristic shifts makes it possible to relate the spectrum of an unknown compound to a class of substances, for example the stretching vibration of the carbonyl group in an aldehyde is always in the range of 1730 cm–1 to 1700 cm–1. Figure 8 demonstrates the Raman spectrum of benzonitrile containing the stretching vibration of the cyano-group (CN) of benzonitrile at a characteristic value of 2229.4 cm-1.[4]

Fluorescence: The incident green light is absorbed (resulting in a loss in intensity) and reemitted in different, longer wavelengths (this results in a gain in intensity or even addition of new “colors”). (Figure 4)

Beginning in 2000, Edmund Optics offered a variety of experimental grade and stock clearance items via a print catalog and online under a separate business named Anchor Optics, but this operation ceased in 2016, and the current Anchor Optics web site now redirects to a page at Edmund Optics listing clearance items.[5]

Electromagnetic radiation propagates through space carrying a certain amount of electromagnetic energy. This energy is proportional to its frequency $\nu$ of oscillation, which is connected to the wavelength $\lambda$ by the speed of light $c$ (Equation 1):

Edmund Scientific has provided items used in television shows such as House, MythBusters, 24, Modern Marvels, and motion pictures such as Star Trek, and the 1975 version of Escape to Witch Mountain. Wah Chang, the artist who designed and built several props in the 1960s for the Star Trek television show, used moiré patterns found in the Edmund Scientific Educator's and Designer's Moiré Kit for the texture used in the Starfleet communicator props.[6]

When a light beam hits matter, it will interact with it in a specific way, dependent on the interplay between the light waves and the atoms and molecules that make up the matter. The interaction may leave the energy of matter and light unchanged (e.g. refraction, reflection, elastic scattering) or lead to an energy exchange between both. The processes used in spectroscopy to characterize matter belong to the latter category.

Light is a form of electromagnetic radiation, which has both wave and particle (“photon”) properties. Light waves are usually mathematically described by a cosine function, where the two most important characteristic parameters are the wavelength (distance between two consecutive wave crests or troughs) and the amplitude (height of the waves over the baseline).

The Raman shift is the energy difference between the incident (laser) light and the scattered (detected) light. This difference is then only connected to the energetic properties of the molecular vibrations studied and hence independent of the laser wavelength. The Raman shift is usually expressed in wavenumbers.

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The business continued in the post-war era and owned so much stock that when the Korean War started the military came to him for the optics needed to repair war-era systems. One official told him, "Gee, you have more optics than the Army!"[2] In 1948 they completed a new building and warehouse in Barrington and opened a retail store at the front. Among its displays was a complete periscope from a WWII Japanese submarine.[2] The core of the company in this era remained surplus lenses. These were single-element lenses, shipped in 2.5-by-4.25-inch (64 mm × 108 mm) coin envelopes, with the approximate diameter and focal length stenciled on them. Reflecting their salvage and surplus origins, available diameters and focal lengths did not fall into regular progressions.

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Different vibrational spectroscopies can detect a different subset of the full vibrational spectrum, which is why the most common methods in this class, Raman and (FT-)IR, are often referred to as "complementary methods".[1][2]

Raman scattering: Most of the incident yellow light is scattered elastically in all directions. Small amounts of light, usually with higher wavelengths (orange, red), are also scattered inelastically after interaction with the molecules of the sample. (Figure 5)

In addition to optics, the company soon branched out into various kits and plans for optics-related systems like telescopes and microscopes. It soon changed its name to Edmund Scientific and made its name with ads in publications like Scientific American. Its advertisements caught the attention of hobbyists, amateur astronomers, high school students, and cash-strapped researchers.[1] The company also began publishing a series of pamphlets on telescopes in a do-it-yourself fashion that was popular in contemporary magazines like Popular Mechanics. These were later collected into book form in 1967, "All About Telescopes", which contained many plans for telescope systems that became a best seller and was republished repeatedly into the 1980s.[3]

2. Long, D. A. (2002). The Raman Effect – A Unified Treatment of the theory of Raman Scattering by Molecules. Chichester, UK: John Wiley & Sons.

As of 2017, Edmund Optics continued to offer brand-new stock optics, as well as offering custom and specialized optics to corporations and higher education institutions.[citation needed]

In 1942, amateur photographer Norman W. Edmund (1916–2012[1]) found it hard to find lenses he needed for his hobby. He found that the military was happy to sell off less-than-perfect optics for next to nothing and began using these. Buying in bulk, he began to sell his own surplus through advertisements in photography magazines. It was so successful he founded "'Edmund Salvage Corporation'" in 1942. Working from a card table in his home, the company soon had so much stock that they had to rent space in more than 30 separate garages.[2]

For more information on the measurement principle and uses of Raman spectroscopy, see "How can Raman spectroscopy help you?"

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Apart from the molecular vibrations of specific functional groups, vibrations of the molecular scaffolding (skeletal vibrations) can be detected in a Raman spectrum.

When an intense light source (e.g. a laser) hits a sample, part of the light will be scattered in different directions. The majority of the scattered light has the same wavelength (“color”) as the incident light – it is elastically scattered. This is why the human eye is able to “see” the spot of a laser pointer on the wall or table.

In 2001, the Barrington, New Jersey, store closed after Edmund Scientific was acquired by Science Kit and Boreal Laboratories.[citation needed]

As of 2009, online sales made up the bulk of Edmund Scientific's revenues. The company was still selling telescopes (including an updated version of their Astroscan Telescope), microscopes (mostly they have carried the Boreal brand, manufactured for their parent company Science Kit LLC), surplus optics, magnets, and Fresnel lenses. They continued to sell many of their old favorites along with new items such as the Impossiball and hand boilers as well as other science-themed toys, novelty items, gifts, and gadgets.[citation needed]

Edmund's catered to the 1960s generation by expanding and highlighting their line of projectors, color wheels, black lights, filters, and other optical devices which could be used by rock bands and in psychedelic light shows. Other items catering to the counterculture were eventually added to the catalog covering the fields of Biofeedback, ESP, Kirlian photography, Pyramid power, and alternative energy.[citation needed]

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"Edmund is the best source we know of for low-cost scientific gadgetry (including math and optics gear). [In this category,] many of the items we found independently... turned up in the Edmund catalog, so we were obliged to recommend that in this area we've been precluded."[2]

Substance identification using Raman spectroscopy is nowadays carried out by using software containing a comparison algorithm and a spectral database. The result is shown as a matching factor – the Hit Quality Index (HQI). This factor ranges from 0 (for “no match”) to 100 (for “exact match”).

The intensity distribution of all frequencies is called the spectrum of this light beam. Only a small part of the light frequencies can be seen by the human eye (“visible light”). Other spectral regions are e.g. microwave, infrared, ultra-violet (UV), or Röntgen (X-ray) radiation (Figure 2). For Raman spectroscopy, visible light or infrared (IR) light is used for the excitation.[1][2][3]

This means some light waves pass through the matter without modification (transmission), while some light is absorbed by the sample.

All vibrational spectroscopies characterize molecular vibrations and to a smaller extent also molecular rotations. Molecular vibrations are based on the movements of the individual atoms of the molecule relative to each other. The forces keeping the molecule together will act like small springs connecting the atoms as illustrated in figure 6.

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