Editing Raman spectroscopy (section)

=== 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>