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103-433: Raman spectroscopy is a technique employed to identify mineral phases produced by water-related processes. RLS will help to identify organic compounds and search for microbial life by identifying the mineral products and indicators of biologic activities. RLS will provide geological and mineralogical context information that will be scientifically cross-correlated with that obtained by other instruments. Raman spectroscopy

206-418: A polarizer . The Raman scattered light collected is passed through a second polarizer (called the analyzer) before entering the detector. The analyzer is oriented either parallel or perpendicular to the polarization of the laser. Spectra acquired with the analyzer set at both perpendicular and parallel to the excitation plane can be used to calculate the depolarization ratio . Typically a polarization scrambler

309-458: A beam of filtered monochromatic light generated by a gas discharge lamp . The photons that were scattered by the sample were collected through an optical flat at the end of the tube. To maximize the sensitivity, the sample was highly concentrated (1 M or more) and relatively large volumes (5 mL or more) were used. The magnitude of the Raman effect correlates with polarizability of the electrons in

412-401: A different frequency. The importance of spectroscopy is centered around the fact that every element in the periodic table has a unique light spectrum described by the frequencies of light it emits or absorbs consistently appearing in the same part of the electromagnetic spectrum when that light is diffracted. This opened up an entire field of study with anything that contains atoms. Spectroscopy

515-417: A hyperspectral image could show the distribution of cholesterol, as well as proteins, nucleic acids, and fatty acids. Sophisticated signal- and image-processing techniques can be used to ignore the presence of water, culture media, buffers, and other interferences. Because a Raman microscope is a diffraction-limited system , its spatial resolution depends on the wavelength of light, the numerical aperture of

618-616: A light source such as a laser. The resolution of the spectrum relies on the bandwidth of the laser source used. Generally shorter wavelength lasers give stronger Raman scattering due to the ν increase in Raman scattering cross-sections, but issues with sample degradation or fluorescence may result. Continuous wave lasers are most common for normal Raman spectroscopy, but pulsed lasers may also be used. These often have wider bandwidths than their CW counterparts but are very useful for other forms of Raman spectroscopy such as transient, time-resolved and resonance Raman. Raman scattered light

721-427: A lower frequency (lower energy) so that the total energy remains the same. This shift in frequency is called a Stokes shift , or downshift. If the final state is lower in energy, the scattered photon will be shifted to a higher frequency, which is called an anti-Stokes shift, or upshift. For a molecule to exhibit a Raman effect, there must be a change in its electric dipole-electric dipole polarizability with respect to

824-500: A means to detect explosives from a safe distance using laser beams. Raman Spectroscopy is being further developed so it could be used in the clinical setting. Raman4Clinic is a European organization that is working on incorporating Raman Spectroscopy techniques in the medical field. They are currently working on different projects, one of them being monitoring cancer using bodily fluids such as urine and blood samples which are easily accessible. This technique would be less stressful on

927-432: A molecule. It is a form of inelastic light scattering , where a photon excites the sample. This excitation puts the molecule into a virtual energy state for a short time before the photon is emitted. Inelastic scattering means that the energy of the emitted photon is of either lower or higher energy than the incident photon. After the scattering event, the sample is in a different rotational or vibrational state . For

1030-426: A more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics, and astronomy. Per Fraknoi and Morrison, "Later, in 1815, German physicist Joseph Fraunhofer also examined the solar spectrum, and found about 600 such dark lines (missing colors), are now known as Fraunhofer lines, or Absorption lines." In quantum mechanical systems,

1133-407: A photon by molecules which are excited to higher vibrational or rotational energy levels. In more detail, it will collect and analyse the scattered light emitted by a laser on a crushed Mars rock sample; the spectrum observed (number of peaks, position and relative intensities) is determined by the molecular structure and composition of a compound, enabling the identification and characterisation of

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1236-440: A prism; a key moment in the development of modern optics . Therefore, it was originally the study of visible light that we call color that later under the studies of James Clerk Maxwell came to include the entire electromagnetic spectrum . Although color is involved in spectroscopy, it is not equated with the color of elements or objects that involve the absorption and reflection of certain electromagnetic waves to give objects

1339-592: A public Atomic Spectra Database that is continually updated with precise measurements. The broadening of the field of spectroscopy is due to the fact that any part of the electromagnetic spectrum may be used to analyze a sample from the infrared to the ultraviolet telling scientists different properties about the very same sample. For instance in chemical analysis, the most common types of spectroscopy include atomic spectroscopy, infrared spectroscopy, ultraviolet and visible spectroscopy, Raman spectroscopy and nuclear magnetic resonance . In nuclear magnetic resonance (NMR),

1442-441: A quantitative measure for wound healing progress. Spatially offset Raman spectroscopy (SORS), which is less sensitive to surface layers than conventional Raman, can be used to discover counterfeit drugs without opening their packaging, and to non-invasively study biological tissue. A reason why Raman spectroscopy is useful in biological applications is because its results often do not face interference from water molecules, due to

1545-549: A resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford–Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be

1648-411: A sense of color to our eyes. Rather spectroscopy involves the splitting of light by a prism, diffraction grating, or similar instrument, to give off a particular discrete line pattern called a "spectrum" unique to each different type of element. Most elements are first put into a gaseous phase to allow the spectra to be examined although today other methods can be used on different phases. Each element that

1751-428: A small change in its length such as that which occurs during a vibration has only a small resultant effect on polarization. Vibrations involving polar bonds (e.g. C-O , N-O , O-H) are therefore, comparatively weak Raman scatterers. Such polarized bonds, however, carry their electrical charges during the vibrational motion, (unless neutralized by symmetry factors), and this results in a larger net dipole moment change during

1854-423: A spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations , between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions. Spectra of atoms and molecules often consist of a series of spectral lines, each one representing

1957-403: A standard optical microscope, and adds an excitation laser, a monochromator or polychromator , and a sensitive detector (such as a charge-coupled device (CCD), or photomultiplier tube (PMT)). FT-Raman has also been used with microscopes, typically in combination with near-infrared (NIR) laser excitation. Ultraviolet microscopes and UV enhanced optics must be used when a UV laser source

2060-412: A vibrationally excited state on the ground electronic state potential energy surface. Raman scattering also contrasts with infrared (IR) absorption, where the energy of the absorbed photon matches the difference in energy between the initial and final rovibronic states. The dependence of Raman on the electric dipole-electric dipole polarizability derivative also differs from IR spectroscopy, which depends on

2163-444: Is hyperspectral imaging or chemical imaging , in which thousands of Raman spectra are acquired from all over the field of view by, for example, raster scanning of a focused laser beam through a sample. The data can be used to generate images showing the location and amount of different components. Having the full spectroscopic information available in every measurement spot has the advantage that several components can be mapped at

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2266-539: Is a light scattering technique, specimens do not need to be fixed or sectioned. Raman spectra can be collected from a very small volume (< 1 μm in diameter, < 10 μm in depth); these spectra allow the identification of species present in that volume. Water does not generally interfere with Raman spectral analysis. Thus, Raman spectroscopy is suitable for the microscopic examination of minerals , materials such as polymers and ceramics, cells , proteins and forensic trace evidence. A Raman microscope begins with

2369-417: Is an efficient and non-destructive way to investigate works of art and cultural heritage artifacts, in part because it is a non-invasive process which can be applied in situ . It can be used to analyze the corrosion products on the surfaces of artifacts (statues, pottery, etc.), which can lend insight into the corrosive environments experienced by the artifacts. The resulting spectra can also be compared to

2472-454: Is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified. Raman spectroscopy relies upon inelastic scattering of photons, known as Raman scattering . A source of monochromatic light, usually from a laser in the visible , near infrared, or near ultraviolet range is used, although X-rays can also be used. The laser light interacts with molecular vibrations, phonons or other excitations in

2575-429: Is diffracted by a prism-like instrument displays either an absorption spectrum or an emission spectrum depending upon whether the element is being cooled or heated. Until recently all spectroscopy involved the study of line spectra and most spectroscopy still does. Vibrational spectroscopy is the branch of spectroscopy that studies the spectra. However, the latest developments in spectroscopy can sometimes dispense with

2678-548: Is from Observatoire Midi-Pyrénées (LAOMP), France. The three major components are the Spectrometer Unit , the Control and Excitation Unit (includes the power converters), and Optical head . The RLS instrument provides a structural fingerprint by which molecules can be identified. It is used to analyse the vibrational modes of a substance either in the solid, liquid or gas state. The technique relies on Raman scattering of

2781-459: Is in the wavenumber range 500–1,500 cm ), Raman provides a fingerprint to identify molecules. For instance, Raman and IR spectra were used to determine the vibrational frequencies of SiO, Si 2 O 2 , and Si 3 O 3 on the basis of normal coordinate analyses. Raman is also used to study the addition of a substrate to an enzyme. In solid-state physics , Raman spectroscopy is used to characterize materials, measure temperature , and find

2884-415: Is often performed using red to near-infrared excitation (e.g., 785 nm, or 1,064 nm wavelength). Due to typically low absorbances of biological samples in this spectral range, the risk of damaging the specimen as well as autofluorescence emission are reduced, and high penetration depths into tissues can be achieved. However, the intensity of Raman scattering at long wavelengths is low (owing to

2987-413: Is placed between the analyzer and detector also. It is convenient in polarized Raman spectroscopy to describe the propagation and polarization directions using Porto's notation, described by and named after Brazilian physicist Sergio Pereira da Silva Porto . For isotropic solutions, the Raman scattering from each mode either retains the polarization of the laser or becomes partly or fully depolarized. If

3090-472: Is polarization sensitive and can provide detailed information on symmetry of Raman active modes. While conventional Raman spectroscopy identifies chemical composition, polarization effects on Raman spectra can reveal information on the orientation of molecules in single crystals and anisotropic materials, e.g. strained plastic sheets, as well as the symmetry of vibrational modes. Polarization–dependent Raman spectroscopy uses (plane) polarized laser excitation from

3193-497: Is sensitive to the composition and structure of any organic compound , making it a powerful tool for the definitive identification and characterisation of biomarkers , and providing direct information of potential biosignatures of past microbial life on Mars . This instrument will also provide general mineralogical information for igneous, metamorphous, and sedimentary processes. RST will also correlate its spectral information with other spectroscopic and imaging instruments such as

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3296-487: Is the excitation wavelength, and λ 1 is the Raman spectrum wavelength. Most commonly, the unit chosen for expressing wavenumber in Raman spectra is inverse centimeters (cm ). Since wavelength is often expressed in units of nanometers (nm), the formula above can scale for this unit conversion explicitly, giving Modern Raman spectroscopy nearly always involves the use of lasers as excitation light sources. Because lasers were not available until more than three decades after

3399-427: Is the intensity of Raman scattering when the analyzer is rotated 90 degrees with respect to the incident light's polarization axis, and I u {\displaystyle I_{u}} the intensity of Raman scattering when the analyzer is aligned with the polarization of the incident laser. When polarized light interacts with a molecule, it distorts the molecule which induces an equal and opposite effect in

3502-409: Is the key to understanding the atomic properties of all matter. As such spectroscopy opened up many new sub-fields of science yet undiscovered. The idea that each atomic element has its unique spectral signature enabled spectroscopy to be used in a broad number of fields each with a specific goal achieved by different spectroscopic procedures. The National Institute of Standards and Technology maintains

3605-506: Is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of astronomy , chemistry , materials science , and physics , allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances . Historically, spectroscopy originated as

3708-519: Is typically collected and either dispersed by a spectrograph or used with an interferometer for detection by Fourier Transform (FT) methods. In many cases commercially available FT-IR spectrometers can be modified to become FT-Raman spectrometers. In most cases, modern Raman spectrometers use array detectors such as CCDs. Various types of CCDs exist which are optimized for different wavelength ranges. Intensified CCDs can be used for very weak signals and/or pulsed lasers. The spectral range depends on

3811-409: Is used for Raman microspectroscopy. In direct imaging (also termed global imaging or wide-field illumination ), the whole field of view is examined for light scattering integrated over a small range of wavenumbers (Raman shifts). For instance, a wavenumber characteristic for cholesterol could be used to record the distribution of cholesterol within a cell culture. This technique is being used for

3914-567: Is usually necessary to separate the Raman scattered light from the Rayleigh signal and reflected laser signal in order to collect high quality Raman spectra using a laser rejection filter. Notch or long-pass optical filters are typically used for this purpose. Before the advent of holographic filters it was common to use a triple-grating monochromator in subtractive mode to isolate the desired signal. This may still be used to record very small Raman shifts as holographic filters typically reflect some of

4017-489: The MOMA analyser. The processor board carries out several key functions for the Raman spectrometer control, spectral operation, data storage, and communications with the rover. The complete instrument has a mass of 2.4 kg (5.29 lb) and consumes about 30 W while operating. The goal of RLS is to seek signs of past life on Mars ( biosignatures and biomarkers ) by analysing drilled samples acquired from 2  meters below

4120-495: The radiant energy interacts with specific types of matter. Atomic spectroscopy was the first application of spectroscopy. Atomic absorption spectroscopy and atomic emission spectroscopy involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to electronic transitions of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to

4223-560: The Indian scientist C. V. Raman , who observed the effect in organic liquids in 1928 together with K. S. Krishnan , and independently by Grigory Landsberg and Leonid Mandelstam in inorganic crystals. Raman won the Nobel Prize in Physics in 1930 for this discovery. The first observation of Raman spectra in gases was in 1929 by Franco Rasetti . Systematic pioneering theory of the Raman effect

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4326-511: The Infrared Spectrometer and MicrOmega-IR . This will be the first Raman analyser to be deployed for a planetary exploration. The first version for the rover was presented by Fernando Rull-Perez and Sylvestre Maurice in 2003. The RLS is being developed by a European consortium integrated by Spanish, French, German and UK partners. The Principal Investigator is Fernando Rull-Perez, from Spanish Astrobiology Center . The co-investigator

4429-540: The Kramers-Heisenberg-Dirac (KHD) equation using the Albrecht A and B terms, as demonstrated. The KHD expression is conveniently linked to the polarizability of the molecule within its frame of reference. The polarizability operator connecting the initial and final states expresses the transition polarizability as a matrix element , as a function of the incidence frequency ω 0 . The directions x, y, and z in

4532-530: The Martian surface by the Rosalind Franklin rover core drill . The science objectives of RLS are: Raman spectroscopy Raman spectroscopy ( / ˈ r ɑː m ən / ) (named after physicist C. V. Raman ) is a spectroscopic technique typically used to determine vibrational modes of molecules , although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy

4635-498: The Raman-shifted backscatter from laser pulses to determine the temperature along optical fibers. The orientation of an anisotropic crystal can be found from the polarization of Raman-scattered light with respect to the crystal and the polarization of the laser light, if the crystal structure ’s point group is known. In nanotechnology, a Raman microscope can be used to analyze nanowires to better understand their structures, and

4738-467: The analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom , via an oscillatory source of energy such as a photon . The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy E of a photon is related to its frequency ν by E = hν where h is the Planck constant , and so

4841-428: The atomic nuclei and are studied by both infrared and Raman spectroscopy . Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy . Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser . The combination of atoms or molecules into crystals or other extended forms leads to

4944-505: The causes behind deterioration. The IRUG (Infrared and Raman Users Group) Spectral Database is a rigorously peer-reviewed online database of IR and Raman reference spectra for cultural heritage materials such as works of art, architecture, and archaeological artifacts. The database is open for the general public to peruse, and includes interactive spectra for over a hundred different types of pigments and paints. Raman spectroscopy offers several advantages for microscopic analysis. Since it

5047-436: The characterization of large-scale devices, mapping of different compounds and dynamics study. It has already been used for the characterization of graphene layers, J-aggregated dyes inside carbon nanotubes and multiple other 2D materials such as MoS 2 and WSe 2 . Since the excitation beam is dispersed over the whole field of view, those measurements can be done without damaging the sample. The most common approach

5150-439: The chemical composition and physical properties of astronomical objects (such as their temperature , density of elements in a star, velocity , black holes and more). An important use for spectroscopy is in biochemistry. Molecular samples may be analyzed for species identification and energy content. The underlying premise of spectroscopy is that light is made of different wavelengths and that each wavelength corresponds to

5253-409: The compounds in the sample. Some advantages of RLS over other analysers are that it is nondestructive, analysis is completed in a fraction of a second, and the spectral bands provide definitive composition of the material. RLS measurements will be conducted on the resulting crushed sample powder and it will be a useful tool for flagging the presence of organic molecules for further biomarker search by

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5356-621: The context of the Laser Interferometer Gravitational-Wave Observatory (LIGO). Spectroscopy is a branch of science concerned with the spectra of electromagnetic radiation as a function of its wavelength or frequency measured by spectrographic equipment, and other techniques, in order to obtain information concerning the structure and properties of matter. Spectral measurement devices are referred to as spectrometers , spectrophotometers , spectrographs or spectral analyzers . Most spectroscopic analysis in

5459-444: The creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, i.e., broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well. Pure crystals, though, can have distinct spectral transitions, and

5562-527: The creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states ( electron paramagnetic resonance ), molecular rotations , molecular vibration , and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimetre-wave spectral regions. Rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of

5665-595: The crystal arrangement also has an effect on the observed molecular spectra. The regular lattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies. Nuclei also have distinct energy states that are widely separated and lead to gamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for nuclear magnetic resonance spectroscopy . Other types of spectroscopy are distinguished by specific applications or implementations: There are several applications of spectroscopy in

5768-537: The crystallographic orientation of a sample. As with single molecules, a solid material can be identified by characteristic phonon modes. Information on the population of a phonon mode is given by the ratio of the Stokes and anti-Stokes intensity of the spontaneous Raman signal. Raman spectroscopy can also be used to observe other low frequency excitations of a solid, such as plasmons , magnons , and superconducting gap excitations. Distributed temperature sensing (DTS) uses

5871-544: The development of quantum mechanics , because the first useful atomic models described the spectra of hydrogen, which include the Bohr model , the Schrödinger equation , and Matrix mechanics , all of which can produce the spectral lines of hydrogen , therefore providing the basis for discrete quantum jumps to match the discrete hydrogen spectrum. Also, Max Planck 's explanation of blackbody radiation involved spectroscopy because he

5974-415: The discovery of the effect, Raman and Krishnan used a mercury lamp and photographic plates to record spectra. Early spectra took hours or even days to acquire due to weak light sources, poor sensitivity of the detectors and the weak Raman scattering cross-sections of most materials. Various colored filters and chemical solutions were used to select certain wavelength regions for excitation and detection but

6077-414: The dispersion technique. In biochemical spectroscopy, information can be gathered about biological tissue by absorption and light scattering techniques. Light scattering spectroscopy is a type of reflectance spectroscopy that determines tissue structures by examining elastic scattering. In such a case, it is the tissue that acts as a diffraction or dispersion mechanism. Spectroscopic studies were central to

6180-432: The drug Cayston ( aztreonam ), marketed by Gilead Sciences for cystic fibrosis , can be identified and characterized by IR and Raman spectroscopy. Using the correct polymorphic form in bio-pharmaceutical formulations is critical, since different forms have different physical properties, like solubility and melting point. Raman spectroscopy has a wide variety of applications in biology and medicine. It has helped confirm

6283-449: The electric dipole moment derivative, the atomic polar tensor (APT). This contrasting feature allows rovibronic transitions that might not be active in IR to be analyzed using Raman spectroscopy, as exemplified by the rule of mutual exclusion in centrosymmetric molecules . Transitions which have large Raman intensities often have weak IR intensities and vice versa. If a bond is strongly polarized,

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6386-402: The excitation of inner shell electrons to excited states. Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantitation of a sample's elemental composition. After inventing the spectroscope, Robert Bunsen and Gustav Kirchhoff discovered new elements by observing their emission spectra. Atomic absorption lines are observed in

6489-499: The existence of low-frequency phonons in proteins and DNA, promoting studies of low-frequency collective motion in proteins and DNA and their biological functions. Raman reporter molecules with olefin or alkyne moieties are being developed for tissue imaging with SERS-labeled antibodies . Raman spectroscopy has also been used as a noninvasive technique for real-time, in situ biochemical characterization of wounds. Multivariate analysis of Raman spectra has enabled development of

6592-467: The fact that they have permanent dipole moments, and as a result, the Raman scattering cannot be picked up on. This is a large advantage, specifically in biological applications. Raman spectroscopy also has a wide usage for studying biominerals. Lastly, Raman gas analyzers have many practical applications, including real-time monitoring of anesthetic and respiratory gas mixtures during surgery. Raman spectroscopy has been used in several research projects as

6695-518: The fields of medicine, physics, chemistry, and astronomy. Taking advantage of the properties of absorbance and with astronomy emission , spectroscopy can be used to identify certain states of nature. The uses of spectroscopy in so many different fields and for so many different applications has caused specialty scientific subfields. Such examples include: The history of spectroscopy began with Isaac Newton 's optics experiments (1666–1672). According to Andrew Fraknoi and David Morrison , "In 1672, in

6798-486: The first paper that he submitted to the Royal Society , Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbow." Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when

6901-431: The focusing element, and — in the case of confocal microscopy — on the diameter of the confocal aperture. When operated in the visible to near-infrared range, a Raman microscope can achieve lateral resolutions of approx. 1 μm down to 250 nm, depending on the wavelength and type of objective lens (e.g., air vs. water or oil immersion lenses). The depth resolution (if not limited by the optical penetration depth of

7004-405: The frequencies of vibrations in highly symmetric molecules that may be both IR and Raman inactive. The IINS selection rules, or allowed transitions, differ from those of IR and Raman, so the three techniques are complementary. They all give the same frequency for a given vibrational transition, but the relative intensities provide different information due to the different types of interaction between

7107-810: The intense Rayleigh scattered laser light (referred to as "laser rejection"). Historically, Raman spectrometers used holographic gratings and multiple dispersion stages to achieve a high degree of laser rejection. In the past, photomultipliers were the detectors of choice for dispersive Raman setups, which resulted in long acquisition times. However, modern instrumentation almost universally employs notch or edge filters for laser rejection. Dispersive single-stage spectrographs (axial transmissive (AT) or Czerny–Turner (CT) monochromators ) paired with CCD detectors are most common although Fourier transform (FT) spectrometers are also common for use with NIR lasers. The name "Raman spectroscopy" typically refers to vibrational Raman using laser wavelengths which are not absorbed by

7210-476: The laboratory starts with a sample to be analyzed, then a light source is chosen from any desired range of the light spectrum, then the light goes through the sample to a dispersion array (diffraction grating instrument) and captured by a photodiode . For astronomical purposes, the telescope must be equipped with the light dispersion device. There are various versions of this basic setup that may be employed. Spectroscopy began with Isaac Newton splitting light with

7313-437: The low frequency bands in addition to the unshifted laser light. However, Volume hologram filters are becoming more common which allow shifts as low as 5 cm to be observed. Raman spectroscopy is used in chemistry to identify molecules and study chemical bonding and intramolecular bonds. Because vibrational frequencies are specific to a molecule's chemical bonds and symmetry (the fingerprint region of organic molecules

7416-469: The measurement parameters have to be individually optimized. For that reason, modern Raman microscopes are often equipped with several lasers offering different wavelengths, a set of objective lenses, and neutral density filters for tuning of the laser power reaching the sample. Selection of the laser wavelength mainly depends on optical properties of the sample and on the aim of the investigation. For example, Raman microscopy of biological and medical specimens

7519-537: The molecular frame are represented by the Cartesian tensor ρ and σ here. Analyzing Raman excitation patterns requires the use of this equation, which is a sum-over-states expression for polarizability. This series of profiles illustrates the connection between a Raman active vibration's excitation frequency and intensity . Spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectrum . In narrower contexts, spectroscopy

7622-422: The molecule and the incoming particles, photons for IR and Raman, and neutrons for IINS. Raman shifts are typically reported in wavenumbers , which have units of inverse length, as this value is directly related to energy. In order to convert between spectral wavelength and wavenumbers of shift in the Raman spectrum, the following formula can be used: where Δν̃ is the Raman shift expressed in wavenumber, λ 0

7725-441: The monochromatic light, which can create an induced dipole moment within the molecule based on its polarizability. Because the laser light does not excite the molecule there can be no real transition between energy levels. The Raman effect should not be confused with emission ( fluorescence or phosphorescence ), where a molecule in an excited electronic state emits a photon and returns to the ground electronic state, in many cases to

7828-488: The orientation of molecules with a single crystal or material. The spectral information arising from this analysis is often used to understand macro-molecular orientation in crystal lattices, liquid crystals or polymer samples. The polarization technique is useful in understanding the connections between molecular symmetry , Raman activity, and peaks in the corresponding Raman spectra. Polarized light in one direction only gives access to some Raman–active modes, but rotating

7931-485: The painting in cases where the pigments have degraded with age. Beyond the identification of pigments, extensive Raman microspectroscopic imaging has been shown to provide access to a plethora of trace compounds in Early Medieval Egyptian blue , which enable to reconstruct the individual "biography" of a colourant, including information on the type and provenance of the raw materials, synthesis and application of

8034-581: The patients than constantly having to take biopsies which are not always risk free. In photovoltaics , Raman spectroscopy has gained more interest in the past few years demonstrating high efficacy in delivering important properties for such materials. This includes optoelectronic and physicochemical properties such as open circuit voltage, efficiency, and crystalline structure. This has been demonstrated with several photovoltaic technologies, including kesterite-based, CIGS devices , Monocrystalline silicon cells, and perovskites devices . Raman spectroscopy

8137-531: The photographic spectra were still dominated by a broad center line corresponding to Rayleigh scattering of the excitation source. Technological advances have made Raman spectroscopy much more sensitive, particularly since the 1980s. The most common modern detectors are now charge-coupled devices (CCDs). Photodiode arrays and photomultiplier tubes were common prior to the adoption of CCDs. The advent of reliable, stable, inexpensive lasers with narrow bandwidths has also had an impact. Raman spectroscopy requires

8240-515: The pigment, and the ageing of the paint layer. In addition to paintings and artifacts, Raman spectroscopy can be used to investigate the chemical composition of historical documents (such as the Book of Kells ), which can provide insight about the social and economic conditions when they were created. It also offers a noninvasive way to determine the best method of preservation or conservation of such cultural heritage artifacts, by providing insight into

8343-411: The plane-wave, causing it to be rotated by the difference between the orientation of the molecule and the angle of polarization of the light wave. If ρ ≥ 3 4 {\textstyle \rho \geq {\frac {3}{4}}} , then the vibrations at that frequency are depolarized ; meaning they are not totally symmetric. Resonance Raman selection rules can be explained by

8446-536: The polarization gives access to other modes. Each mode is separated according to its symmetry. The symmetry of a vibrational mode is deduced from the depolarization ratio ρ, which is the ratio of the Raman scattering with polarization orthogonal to the incident laser and the Raman scattering with the same polarization as the incident laser: ρ = I r I u {\displaystyle \rho ={\frac {I_{r}}{I_{u}}}} Here I r {\displaystyle I_{r}}

8549-506: The radial breathing mode of carbon nanotubes is commonly used to evaluate their diameter. Raman active fibers, such as aramid and carbon, have vibrational modes that show a shift in Raman frequency with applied stress. Polypropylene fibers exhibit similar shifts. In solid state chemistry and the bio-pharmaceutical industry, Raman spectroscopy can be used to not only identify active pharmaceutical ingredients (APIs), but to identify their polymorphic forms, if more than one exist. For example,

8652-422: The same time, including chemically similar and even polymorphic forms, which cannot be distinguished by detecting only one single wavenumber. Furthermore, material properties such as stress and strain , crystal orientation , crystallinity and incorporation of foreign ions into crystal lattices (e.g., doping , solid solution series ) can be determined from hyperspectral maps. Taking the cell culture example,

8755-570: The sample) can range from 1–6 μm with the smallest confocal pinhole aperture to tens of micrometers when operated without a confocal pinhole. Depending on the sample, the high laser power density due to microscopic focussing can have the benefit of enhanced photobleaching of molecules emitting interfering fluorescence. However, the laser wavelength and laser power have to be carefully selected for each type of sample to avoid its degradation. Applications of Raman imaging range from materials sciences to biological studies. For each type of sample,

8858-430: The sample. There are many other variations of Raman spectroscopy including surface-enhanced Raman , resonance Raman , tip-enhanced Raman , polarized Raman, stimulated Raman , transmission Raman, spatially-offset Raman, and hyper Raman . Although the inelastic scattering of light was predicted by Adolf Smekal in 1923, it was not observed in practice until 1928. The Raman effect was named after one of its discoverers,

8961-497: The size of the CCD and the focal length of spectrograph used. It was once common to use monochromators coupled to photomultiplier tubes. In this case the monochromator would need to be moved in order to scan through a spectral range. FT–Raman is almost always used with NIR lasers and appropriate detectors must be used depending on the exciting wavelength. Germanium or Indium gallium arsenide (InGaAs) detectors are commonly used. It

9064-807: The solar spectrum and referred to as Fraunhofer lines after their discoverer. A comprehensive explanation of the hydrogen spectrum was an early success of quantum mechanics and explained the Lamb shift observed in the hydrogen spectrum, which further led to the development of quantum electrodynamics . Modern implementations of atomic spectroscopy for studying visible and ultraviolet transitions include flame emission spectroscopy , inductively coupled plasma atomic emission spectroscopy , glow discharge spectroscopy , microwave induced plasma spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include X-ray spectroscopy and X-ray fluorescence . The combination of atoms into molecules leads to

9167-416: The spectra of surfaces that are cleaned or intentionally corroded, which can aid in determining the authenticity of valuable historical artifacts. It is capable of identifying individual pigments in paintings and their degradation products, which can provide insight into the working method of an artist in addition to aiding in authentication of paintings. It also gives information about the original state of

9270-416: The study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism . Current applications of spectroscopy include biomedical spectroscopy in the areas of tissue analysis and medical imaging . Matter waves and acoustic waves can also be considered forms of radiative energy, and recently gravitational waves have been associated with a spectral signature in

9373-431: The symmetry labels of vibrational modes. In the solid state, polarized Raman spectroscopy can be useful in the study of oriented samples such as single crystals. The polarizability of a vibrational mode is not equal along and across the bond. Therefore the intensity of the Raman scattering will be different when the laser's polarization is along and orthogonal to a particular bond axis. This effect can provide information on

9476-446: The system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy typically yields similar yet complementary information. Typically, a sample is illuminated with a laser beam. Electromagnetic radiation from the illuminated spot is collected with a lens and sent through a monochromator . Elastic scattered radiation at

9579-545: The theory behind it is that frequency is analogous to resonance and its corresponding resonant frequency. Resonances by the frequency were first characterized in mechanical systems such as pendulums , which have a frequency of motion noted famously by Galileo . Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways. The types of spectroscopy are distinguished by

9682-435: The total energy of the system to remain constant after the molecule moves to a new rovibronic (rotational–vibrational–electronic) state, the scattered photon shifts to a different energy, and therefore a different frequency. This energy difference is equal to that between the initial and final rovibronic states of the molecule. If the final state is higher in energy than the initial state, the scattered photon will be shifted to

9785-418: The type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of radiative energy studied include: The types of spectroscopy also can be distinguished by the nature of the interaction between the energy and the material. These interactions include: Spectroscopic studies are designed so that

9888-465: The vibration, producing a strong IR absorption band. Conversely, relatively neutral bonds (e.g. C-C , C-H , C=C) suffer large changes in polarizability during a vibration. However, the dipole moment is not similarly affected such that while vibrations involving predominantly this type of bond are strong Raman scatterers, they are weak in the IR. A third vibrational spectroscopy technique, inelastic incoherent neutron scattering (IINS), can be used to determine

9991-413: The vibrational coordinate corresponding to the rovibronic state. The intensity of the Raman scattering is proportional to this polarizability change. Therefore, the Raman spectrum (scattering intensity as a function of the frequency shifts) depends on the rovibronic states of the molecule. The Raman effect is based on the interaction between the electron cloud of a sample and the external electric field of

10094-427: The vibrational mode involved in the Raman scattering process is totally symmetric then the polarization of the Raman scattering will be the same as that of the incoming laser beam. In the case that the vibrational mode is not totally symmetric then the polarization will be lost (scrambled) partially or totally, which is referred to as depolarization. Hence polarized Raman spectroscopy can provide detailed information as to

10197-415: The wavelength corresponding to the laser line ( Rayleigh scattering ) is filtered out by either a notch filter , edge pass filter, or a band pass filter, while the rest of the collected light is dispersed onto a detector. Spontaneous Raman scattering is typically very weak; as a result, for many years the main difficulty in collecting Raman spectra was separating the weak inelastically scattered light from

10300-554: The white light is passed through a prism. Fraknoi and Morrison state that "In 1802, William Hyde Wollaston built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the spectrum." During the early 1800s, Joseph von Fraunhofer made experimental advances with dispersive spectrometers that enabled spectroscopy to become

10403-494: The ω dependence of Raman scattering intensity), leading to long acquisition times. On the other hand, resonance Raman imaging of single-cell algae at 532 nm (green) can specifically probe the carotenoid distribution within a cell by a using low laser power of ~5 μW and only 100 ms acquisition time. Raman scattering, specifically tip-enhanced Raman spectroscopy, produces high resolution hyperspectral images of single molecules, atoms, and DNA. Raman scattering

10506-487: Was comparing the wavelength of light using a photometer to the temperature of a Black Body . Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs. The measured spectra are used to determine

10609-430: Was developed by Czechoslovak physicist George Placzek between 1930 and 1934. The mercury arc became the principal light source, first with photographic detection and then with spectrophotometric detection. In the years following its discovery, Raman spectroscopy was used to provide the first catalog of molecular vibrational frequencies. Typically, the sample was held in a long tube and illuminated along its length with

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