Editing Raman spectroscopy (section)

== Variants ==
At least 25 variations of Raman spectroscopy have been developed.<ref name="Long">{{cite book |last1=Long |first1=Derek A. |title=The Raman Effect |date=2002 |publisher=John Wiley & Sons, Ltd |isbn=978-0471490289 |doi=10.1002/0470845767 }}</ref> The usual purpose is to enhance the sensitivity (e.g., [[Surface-enhanced Raman spectroscopy]] (SERS)), to improve the spatial resolution (Raman microscopy), or to acquire very specific information (resonance Raman).

=== Spontaneous (or far-field) Raman spectroscopy ===
[[File:AFM vs Raman imaging of GaSe.jpg|thumb|Correlative Raman imaging: Comparison of topographical ([[atomic force microscopy|AFM]], top) and Raman images of [[Gallium(II) selenide|GaSe]]. Scale bar is 5 μm.<ref>{{cite journal|doi=10.1038/srep05497|pmid=24975226|pmc=4074793|title=Controlled Vapor Phase Growth of Single Crystalline, Two-Dimensional Ga ''Se'' Crystals with High Photoresponse|journal=Scientific Reports|volume=4|pages=5497|year=2014|last1=Li|first1=Xufan|last2=Lin|first2=Ming-Wei|last3=Puretzky|first3=Alexander A.|last4=Idrobo|first4=Juan C.|last5=Ma|first5=Cheng|last6=Chi|first6=Miaofang|last7=Yoon|first7=Mina|last8=Rouleau|first8=Christopher M.|last9=Kravchenko|first9=Ivan I.|last10=Geohegan|first10=David B.|last11=Xiao|first11=Kai|bibcode=2014NatSR...4.5497L}}</ref>]]
Terms such as ''spontaneous Raman spectroscopy'' or ''normal Raman spectroscopy'' summarize Raman spectroscopy techniques based on Raman scattering by using normal [[near and far field|far-field]] optics as described above. Variants of normal Raman spectroscopy exist with respect to excitation-detection geometries, combination with other techniques, use of special (polarizing) optics and specific choice of excitation wavelengths for resonance enhancement.
* ''[[Raman microscope#Correlative Raman imaging|Correlative Raman imaging]]'' – Raman microscopy can be combined with complementary imaging methods, such as [[atomic force microscopy]] (Raman-AFM) and [[scanning electron microscope|scanning electron microscopy]] (Raman-SEM) to compare Raman distribution maps with (or overlay them onto) topographical or morphological images, and to correlate Raman spectra with complementary physical or chemical information (e.g., gained by SEM-[[Energy-dispersive X-ray spectroscopy|EDX]]).
* ''[[Resonance Raman spectroscopy]]'' – The excitation wavelength is matched to an electronic transition of the molecule or crystal, so that vibrational modes associated with the excited electronic state are greatly enhanced. This is useful for studying large molecules such as [[polypeptide]]s, which might show hundreds of bands in "conventional" Raman spectra. It is also useful for associating normal modes with their observed frequency shifts.<ref>{{cite journal| author= Chao RS| author2= Khanna RK| author3= Lippincott ER | title = Theoretical and experimental resonance Raman intensities for the manganate ion| journal=Journal of Raman Spectroscopy | date = 1974| doi = 10.1002/jrs.1250030203| volume= 3| issue= 2–3| pages= 121–131|bibcode = 1975JRSp....3..121C }}</ref>
* ''Angle-resolved Raman spectroscopy'' – Not only are standard Raman results recorded but also the angle with respect to the incident laser. If the orientation of the sample is known then detailed information about the phonon dispersion relation can also be gleaned from a single test.<ref>{{cite journal| author= Zachary J. Smith| author2= Andrew J. Berger| name-list-style= amp| title= Integrated Raman- and angular-scattering microscopy| journal= Opt. Lett.| date= 2008| doi= 10.1364/OL.33.000714| volume= 3| issue= 7| pages= 714–716| pmid= 18382527| bibcode= 2008OptL...33..714S| url= http://www.optics.rochester.edu/workgroups/berger/IRAM_OptLetters_manuscript.pdf| citeseerx= 10.1.1.688.8581| access-date= 2017-11-01| archive-date= 2021-02-24| archive-url= https://web.archive.org/web/20210224190207/http://www2.optics.rochester.edu/workgroups/berger/IRAM_OptLetters_manuscript.pdf| url-status= dead}}</ref>
* ''Optical tweezers Raman spectroscopy (OTRS)'' – Used to study individual particles, and even biochemical processes in single cells trapped by [[optical tweezers]].<ref>{{Cite journal|last1=Li|first1=Yong-qing|last2=William Li|last3=Ling|first3=Lin|last4=Ling|first4=Dong-xiong|last5=Wu|first5=Mu-ying|date=2017-02-17|title=Stable optical trapping and sensitive characterization of nanostructures using standing-wave Raman tweezers|journal=Scientific Reports|volume=7|pages=42930|doi=10.1038/srep42930|pmid=28211526|issn=2045-2322|pmc=5314326|bibcode=2017NatSR...742930W}}</ref><ref>{{Cite journal |last1=Esat |first1=Kivanç |last2=David |first2=Grègory |last3=Theodoros |first3=Poulkas |last4=Shein |first4=Mikhail |last5=Ruth |first5=Signorell |author-link5=Ruth Signorell |date=2018 |title=Phase transition dynamics of single optically trapped aqueous potassium carbonate particles |journal=Phys. Chem. Chem. Phys. |volume=20 |issue=17 |pages=11598–11607 |bibcode=2018PCCP...2011598E |doi=10.1039/c8cp00599k |pmid=29651474 |hdl-access=free |hdl=20.500.11850/268286}}</ref><ref>{{Cite journal |last1=Zhiyong |first1=Gong|last2=Yong-Le|first2=Pan|last3=Gorden |first3=Videen|last4=Chuji|first4=Wang|date=2018|title=Optical trapping-Raman spectroscopy (OT-RS) with embedded microscopy imaging for concurrent characterization and monitoring of physical and chemical properties of single particles|journal=Anal. Chim. Acta|volume=1020|pages=86–94|doi=10.1016/j.aca.2018.02.062|pmid=29655431|s2cid=4886846 |doi-access=free|bibcode=2018AcAC.1020...86G }}</ref>
* ''[[Spatially offset Raman spectroscopy]] (SORS)'' – The Raman scattering beneath an obscuring surface is retrieved from a scaled subtraction of two spectra taken at two spatially offset points.
* ''[[Raman optical activity]] (ROA)'' – Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or, equivalently, a small circularly polarized component in the scattered light.<ref>{{cite journal | author = Barron LD | author2 = Hecht L | author3 = McColl IH| author4 = Blanch EW| title = Raman optical activity comes of age | journal = Mol. Phys. | date=2004 | issue = 8 | pages = 731–744 | volume = 102 | doi=10.1080/00268970410001704399|bibcode = 2004MolPh.102..731B | s2cid = 51739558 }}</ref>
* ''[[Transmission raman|Transmission Raman]]'' – Allows probing of a significant bulk of a [[turbid]] material, such as powders, capsules, living tissue, etc. It was largely ignored following investigations in the late 1960s ([[Bernhard Schrader|Schrader]] and Bergmann, 1967)<ref>{{cite journal|last1=Schrader|first1=Bernhard|last2=Bergmann|first2=Gerhard|title=Die Intensität des Ramanspektrums polykristalliner Substanzen|journal=Fresenius' Zeitschrift für Analytische Chemie|volume=225|issue=2|year=1967|pages=230–247|issn=0016-1152|doi=10.1007/BF00983673|s2cid=94487523| author-link = Bernhard Schrader}}</ref> but was rediscovered in 2006 as a means of rapid assay of [[pharmaceutical]] [[dosage forms]].<ref>{{cite journal | author = Matousek, P. | author2 = Parker, A. W. | title = Bulk Raman Analysis of Pharmaceutical Tablets | journal = Applied Spectroscopy | date = 2006 | volume = 60 | pages = 1353–1357 | doi = 10.1366/000370206779321463 | pmid = 17217583 | issue = 12|bibcode = 2006ApSpe..60.1353M | s2cid = 32218439 }}</ref>  There are medical diagnostic applications particularly in the detection of cancer.<ref name="autogenerated1"/><ref>{{cite journal | title = Prospects for the diagnosis of breast cancer by noninvasive probing of calcifications using transmission Raman spectroscopy | journal = Journal of Biomedical Optics | volume = 12 | date = 2007 | page = 024008 | author = Matousek, P. | author2 = Stone, N. | doi = 10.1117/1.2718934 | pmid = 17477723 | issue = 2|bibcode = 2007JBO....12b4008M | s2cid = 44498295 | doi-access = free }}</ref><ref>{{cite journal|display-authors=4|last1=Kamemoto|first1=Lori E.|last2=Misra|first2=Anupam K.|last3=Sharma|first3=Shiv K.|last4=Goodman|first4=Hugh Luk|last5=Dykes|first5=Ava C.|last6=Acosta|first6=Tayro|title=Near-Infrared Micro-Raman Spectroscopy for in Vitro Detection of Cervical Cancer|pmid=20223058|pmc=2880181|journal=Applied Spectroscopy|date=December 4, 2009|volume=64|issue=3|pages=255–61|doi=10.1366/000370210790918364|bibcode=2010ApSpe..64..255K}}</ref>
* ''Micro-cavity substrates'' – A method that improves the detection limit of conventional Raman spectra using micro-Raman in a micro-cavity coated with reflective Au or Ag. The micro-cavity has a radius of several micrometers and enhances the entire Raman signal by providing multiple excitations of the sample and couples the forward-scattered Raman photons toward the collection optics in the back-scattered Raman geometry.<ref>{{cite journal|display-authors=4|last1=Misra|first1=Anupam K.|last2=Sharma|first2=Shiv K.|last3=Kamemoto|first3=Lori|last4=Zinin|first4=Pavel V.|last5=Yu|first5=Qigui|last6=Hu|first6=Ningjie|last7=Melnick|first7=Levi|title=Novel Micro-Cavity Substrates for Improving the Raman Signal from Submicrometer Size Materials|pmid=19281655|journal=Applied Spectroscopy|date=December 8, 2008|volume=63|issue=3|pages=373–7|doi=10.1366/000370209787598988|bibcode=2009ApSpe..63..373M|s2cid=9746377}}</ref>
* ''Stand-off remote Raman'' – In standoff Raman, the sample is measured at a distance from the Raman spectrometer, usually by using a telescope for light collection. Remote Raman spectroscopy was proposed in the 1960s<ref>{{cite journal|last1=Cooney|first1=J.|journal= Bulletin of the American Meteorological Society|volume=46|issue=10|pages=683–684|date=1965|title= International symposium on electromagnetic sensing of the earth from satellites|doi=10.1175/1520-0477-46.10.683|bibcode=1965BAMS...46..683.|doi-access=free}}</ref> and initially developed for the measurement of atmospheric gases.<ref>{{cite journal|doi=10.1038/216142a0|title=Observation of Raman Scattering from the Atmosphere using a Pulsed Nitrogen Ultraviolet Laser|journal=Nature|volume=216|issue=5111|pages=142–143|year=1967|last1=Leonard|first1=Donald A.|bibcode=1967Natur.216..142L|s2cid=4290339}}</ref> The technique was extended In 1992 by Angel et al. for standoff Raman detection of hazardous inorganic and organic compounds.<ref>{{Cite journal|last1=Vess|first1=Thomas M.|last2=Kulp|first2=Thomas J.|last3=Angel|first3=S. M.|date=1992-07-01|title=Remote-Raman Spectroscopy at Intermediate Ranges Using Low-Power cw Lasers|url=https://www.osapublishing.org/as/abstract.cfm?uri=as-46-7-1085|journal=Applied Spectroscopy|volume=46|issue=7|pages=1085–1091|doi=10.1366/0003702924124132|bibcode=1992ApSpe..46.1085A|s2cid=95937544}}</ref>
* ''[[X-ray Raman scattering]]'' – Measures electronic transitions rather than vibrations.<ref>{{cite book|last=Schülke|first=W|title=Electron dynamics studied by inelastic x-ray scattering|year=2007|publisher=[[Oxford University Press]]}}</ref>

=== Enhanced (or near-field) Raman spectroscopy ===
Enhancement of Raman scattering is achieved by local electric-field enhancement by optical [[near and far field|near-field]] effects (e.g. localized [[surface plasmon]]s).
* ''[[Surface Enhanced Raman Spectroscopy|Surface-enhanced Raman spectroscopy]] (SERS)'' – Normally done in a silver or gold colloid or a substrate containing silver or gold. Surface [[plasmons]] of silver and gold are excited by the laser, resulting in an increase in the electric fields surrounding the metal. Given that Raman intensities are proportional to the electric field, there is large increase in the measured signal (by up to 10<sup>11</sup>). This effect was originally observed by [[Martin Fleischmann]] but the prevailing explanation was proposed by Van Duyne in 1977.<ref>{{cite journal |author = Jeanmaire DL |author2 = van Duyne RP | title = Surface Raman Electrochemistry Part I. Heterocyclic, Aromatic and Aliphatic Amines Adsorbed on the Anodized Silver Electrode |journal = [[Journal of Electroanalytical Chemistry]] | volume = 84 | pages =1–20  | date = 1977 | doi = 10.1016/S0022-0728(77)80224-6 }}</ref> A  comprehensive theory of the effect was given by Lombardi and Birke.<ref>{{cite journal|author=Lombardi JR|author2=Birke RL|title= A Unified Approach to Surface-Enhanced Raman Spectroscopy |journal = [[Journal of Physical Chemistry C]]| volume=112|issue=14|pages= 5605–5617 | date = 2008 | doi = 10.1021/jp800167v}}</ref>
* ''Surface-enhanced resonance Raman spectroscopy (SERRS)'' – A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity, and excitation wavelength matched to the maximum absorbance of the molecule being analysed.
* ''[[Tip-enhanced Raman spectroscopy]] (TERS)'' – TERS combines the chemical sensitivity of SERS with the high spatial resolution of scanning probe microscopy techniques, enabling chemical imaging of surfaces at the nanometre length-scale with high detection sensitivity.<ref>{{Cite journal |last1=Shi |first1=Xian |last2=Coca-López |first2=Nicolás |last3=Janik |first3=Julia |last4=Hartschuh |first4=Achim |date=2017-02-17 |title=Advances in Tip-Enhanced Near-Field Raman Microscopy Using Nanoantennas |url=http://dx.doi.org/10.1021/acs.chemrev.6b00640 |journal=Chemical Reviews |volume=117 |issue=7 |pages=4945–4960 |doi=10.1021/acs.chemrev.6b00640 |pmid=28212025 |issn=0009-2665}}</ref> It uses a metallic (usually silver-/gold-coated AFM or STM) tip to enhance the Raman signals of molecules situated in its vicinity. The spatial resolution is approximately the size of the tip apex (20–30&nbsp;nm). TERS has been shown to have sensitivity down to the single molecule level <ref>{{Cite journal|last1=Hou|first1=J. G.|last2=Yang|first2=J. L.|last3=Luo|first3=Y.|last4=Aizpurua|first4=J.|last5=Y. Liao|last6=Zhang|first6=L.|last7=Chen|first7=L. G.|last8=Zhang|first8=C.|last9=Jiang|first9=S.|date=June 2013|title=Chemical mapping of a single molecule by plasmon-enhanced Raman scattering|journal=Nature|volume=498|issue=7452|pages=82–86|doi=10.1038/nature12151|pmid=23739426|issn=1476-4687|bibcode=2013Natur.498...82Z|s2cid=205233946}}</ref><ref>{{Cite journal|last1=Lee|first1=Joonhee|last2=Tallarida|first2=Nicholas|last3=Chen|first3=Xing|last4=Liu|first4=Pengchong|last5=Jensen|first5=Lasse|last6=Apkarian|first6=Vartkess Ara|date=2017-10-12|title=Tip-Enhanced Raman Spectromicroscopy of Co(II)-Tetraphenylporphyrin on Au(111): Toward the Chemists' Microscope|journal=ACS Nano|volume=11|issue=11|pages=11466–11474|doi=10.1021/acsnano.7b06183|pmid=28976729|issn=1936-0851|doi-access=free}}</ref><ref>{{Cite journal|last1=Tallarida|first1=Nicholas|last2=Lee|first2=Joonhee|last3=Apkarian|first3=Vartkess Ara|date=2017-10-09|title=Tip-Enhanced Raman Spectromicroscopy on the Angstrom Scale: Bare and CO-Terminated Ag Tips|journal=ACS Nano|volume=11|issue=11|pages=11393–11401|doi=10.1021/acsnano.7b06022|pmid=28980800|issn=1936-0851|doi-access=free}}</ref><ref>{{Cite journal|last1=Lee|first1=Joonhee|last2=Tallarida|first2=Nicholas|last3=Chen|first3=Xing|last4=Jensen|first4=Lasse|last5=Apkarian|first5=V. Ara|date=June 2018|title=Microscopy with a single-molecule scanning electrometer|journal=Science Advances|volume=4|issue=6|pages=eaat5472|doi=10.1126/sciadv.aat5472|pmid=29963637|pmc=6025905|issn=2375-2548|bibcode=2018SciA....4.5472L}}</ref> and holds some promise for [[bioanalysis]] applications <ref>{{cite journal | last1 = Hermann | first1 = P | last2 = Hermeling | first2 = A | last3 = Lausch | first3 = V | last4 = Holland | first4 = G | last5 = Möller | first5 = L | last6 = Bannert | first6 = N | last7 = Naumann | first7 = D | year = 2011 | title = Evaluation of tip-enhanced Raman spectroscopy for characterizing different virus strains | journal = Analyst | volume = 136 | issue = 2| pages = 1148–1152 | doi = 10.1039/C0AN00531B | pmid = 21270980 | bibcode = 2011Ana...136.1148H }}</ref> and DNA sequencing.<ref name="He 753–757"/> TERS was used to image the vibrational normal modes of single molecules.<ref>{{Cite journal|last1=Lee|first1=Joonhee|last2=Crampton|first2=Kevin T.|last3=Tallarida|first3=Nicholas|last4=Apkarian|first4=V. Ara|date=April 2019|title=Visualizing vibrational normal modes of a single molecule with atomically confined light|journal=Nature|volume=568|issue=7750|pages=78–82|doi=10.1038/s41586-019-1059-9|pmid=30944493|issn=0028-0836|bibcode=2019Natur.568...78L|s2cid=92998248}}</ref>
* ''[[Surface plasmon polariton]] enhanced Raman scattering (SPPERS)'' – This approach exploits apertureless metallic conical tips for near field excitation of molecules. This technique differs from the TERS approach due to its inherent capability of suppressing the background field. In fact, when an appropriate laser source impinges on the base of the cone, a TM0 mode<ref>{{cite journal|last1=Novotny|first1=L|last2=Hafner|first2=C|title=Light propagation in a cylindrical waveguide with a complex, metallic, dielectric function|journal=Physical Review E|volume=50|issue=5|pages=4094–4106|date=1994|doi=10.1103/PhysRevE.50.4094|pmid=9962466|bibcode = 1994PhRvE..50.4094N }}</ref> (polaritonic mode) can be locally created, namely far away from the excitation spot (apex of the tip). The mode can propagate along the tip without producing any radiation field up to the tip apex where it interacts with the molecule. In this way, the focal plane is separated from the excitation plane by a distance given by the tip length, and no background plays any role in the Raman excitation of the molecule.<ref>{{cite journal|display-authors=4|last1=De Angelis|first1=F|last2=Das|first2=G|last3=Candeloro|first3=P|last4=Patrini|first4=M|last5=Galli|first5=M|last6=Bek|first6=A|last7=Lazzarino|first7=M|last8=Maksymov|first8=I|last9=Liberale|first9=C|title=Nanoscale chemical mapping using three-dimensional adiabatic compression of surface plasmon polaritons|journal=Nature Nanotechnology|volume=5|issue=1|pages=67–72|date=2010|doi=10.1038/nnano.2009.348|pmid=19935647|bibcode = 2010NatNa...5...67D |last10=Andreani|first10=Lucio Claudio|last11=Di Fabrizio|first11=Enzo}}</ref><ref>{{cite journal|display-authors=4|last1=De Angelis|first1=F|last2=Proietti Zaccaria|first2=R|last3=Francardi|first3=M|last4=Liberale|first4=C|last5=Di Fabrizio|first5=E|title=Multi-scheme approach for efficient surface plasmon polariton generation in metallic conical tips on AFM-based cantilevers|journal=Optics Express|volume=19|issue=22|pages=22268–79|date=2011|doi=10.1364/OE.19.022268|pmid=22109069|bibcode = 2011OExpr..1922268D |doi-access=free}}</ref><ref>{{cite journal|display-authors=4|last1=Proietti Zaccaria|first1=R|last2=Alabastri|first2=A|last3=De Angelis|first3=F|last4=Das|first4=G|last5=Liberale|first5=C|last6=Toma|first6=A|last7=Giugni|first7=A|last8=Razzari|first8=L|last9=Malerba|first9=M|title=Fully analytical description of adiabatic compression in dissipative polaritonic structures|journal=Physical Review B|volume=86|issue=3|page=035410|date=2012|doi=10.1103/PhysRevB.86.035410|bibcode = 2012PhRvB..86c5410P |last10=Sun|first10=Hong Bo|last11=Di Fabrizio|first11=Enzo}}</ref><ref>{{cite journal|display-authors=4|last1=Proietti Zaccaria|first1=R|last2=De Angelis|first2=F|last3=Toma|first3=A|last4=Razzari|first4=L|last5=Alabastri|first5=A|last6=Das|first6=G|last7=Liberale|first7=C|last8=Di Fabrizio|first8=E|title=Surface plasmon polariton compression through radially and linearly polarized source|journal=Optics Letters|volume=37|issue=4|pages=545–7|date=2012|doi=10.1364/OL.37.000545|pmid=22344101|bibcode = 2012OptL...37..545Z }}</ref>

=== Non-linear Raman spectroscopy ===
Raman signal enhancements are achieved through non-linear optical effects, typically realized by mixing two or more wavelengths emitted by spatially and temporally synchronized pulsed lasers.
* ''Hyper Raman'' – A [[non-linear optics|non-linear]] effect in which the vibrational modes interact with the [[second harmonic generation|second harmonic]] of the excitation beam. This requires very high power, but allows the observation of vibrational modes that are normally "silent". It frequently relies on SERS-type enhancement to boost the sensitivity.<ref>{{cite journal | author = Kneipp K | author2 = Knelpp H| title=Surface-Enhanced Non-Linear Raman Scattering at the Single Molecule Level | journal = Chem. Phys. | volume = 247 | issue = 1| date = 1999 | pages = 155–162 | doi = 10.1016/S0301-0104(99)00165-2 |bibcode = 1999CP....247..155K | display-authors = 1 | last3 = Itzkan | first3 = Irving | last4 = Dasari | first4 = Ramachandra R. | last5 = Feld | first5 = Michael S. }}</ref>
* ''[[Stimulated Raman spectroscopy]]'' ''(SRS)'' – A [[Pump-probe spectroscopy|pump-probe]] technique, where a spatially coincident, two color pulse (with polarization either parallel or perpendicular) transfers the population from ground to a [[rotational–vibrational coupling|rovibrationally]] excited state. If the difference in energy corresponds to an allowed Raman transition, scattered light will correspond to loss or gain in the pump beam. 
* ''[[Inverse Raman effect|Inverse Raman spectroscopy]]'' – A synonym for stimulated Raman loss spectroscopy.
* ''[[Coherent anti-Stokes Raman spectroscopy]] (CARS)'' – Two laser beams are used to generate a coherent anti-Stokes frequency beam, which can be enhanced by resonance.

=== Morphologically-Directed Raman spectroscopy ===
Morphologically Directed Raman Spectroscopy (MDRS) combines automated particle imaging and Raman microspectroscopy into a singular integrated platform in order to provide particle size, shape, and chemical identification.<ref name="MalvernMDRS">{{Cite web|url=https://www.malvernpanalytical.com/en/products/technology/image-analysis/morphologically-directed-raman-spectroscopy|title=MDRS Morphologically Directed Raman Spectroscopy|author=[[Malvern Panalytical]]}}</ref><ref name="QualitycontrolMDRS">{{cite magazine |author=<!--Staff writer(s); no by-line.--> |title=Introducing morphologically directed Raman spectroscopy: A powerful tool for the detection of counterfeit drugs|magazine=Quality Control|publisher=Manufacturing Chemist |date=October 2016}}</ref><ref name="SpectroscopyOnlineMDRS">{{cite news |url=https://core.ac.uk/download/pdf/214330323.pdf |title=Morphologically Directed Raman Spectroscopic Analysis of Forensic Samples|date=January 2018 |work=Spectroscopy Onlinet}}</ref> Automated particle imaging determines the particle size and shape distributions of components within a blended sample from images of individual particles.<ref name="QualitycontrolMDRS" /><ref name="SpectroscopyOnlineMDRS" /> The information gathered from  automated particle imaging is then utilized to direct the Raman spectroscopic analysis.<ref name="MalvernMDRS" /> The Raman spectroscopic analytical process is performed on a randomly-selected subset of the particles, allowing chemical identification of the sample’s multiple components.<ref name="MalvernMDRS" /> Tens of thousands of particles can be imaged in a matter of minutes using the MDRS method, making the process ideal for forensic analysis and investigating counterfeit pharmaceuticals and subsequent adjudications.<ref name="QualitycontrolMDRS" /><ref name="SpectroscopyOnlineMDRS" />