Editing C. V. Raman (section)

== Scientific contributions ==

[[File:Raman energy levels.svg|thumb|300px|Energy level diagram showing the states involved in Raman signal]]

[[File:Nobel ceremony 1930.jpg|thumb|300px|Raman at the 1930 [[Nobel Prize|Nobel Prize Award Ceremony]] with other winners, from left C. V. Raman (physics), [[Hans Fischer]] (chemistry), [[Karl Landsteiner]] (medicine) and [[Sinclair Lewis]] (literature)]]

=== Musical sound ===

One of Raman's interests was on the scientific basis of musical sounds. He was inspired by [[Hermann von Helmholtz]]'s ''The Sensations of Tone'', the book he came across when he joined IACS.<ref name="Banerjee-2014" /> He published his findings prolifically between 1916 and 1921. He worked out the theory of [[:wikt:transverse|transverse]] vibration of [[bowed string instrument]]s based on [[Superposition principle|superposition]] of velocities. One of his earliest studies was on the [[wolf tone]] in violins and cellos.<ref>{{Cite journal|last=Raman|first=C.V.|date=1916|title=XLIII. On the "wolf-note" in bowed stringed instruments |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=32|issue=190|pages=391–395|doi=10.1080/14786441608635584}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1916|title=On the "Wolf-note" of the Violin and 'Cello|journal=Nature|language=en|volume=97|issue=2435|pages=362–363|doi=10.1038/097362a0|bibcode=1916Natur..97..362R|s2cid=3966106|url=https://zenodo.org/record/1950214|access-date=30 April 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031081442/https://zenodo.org/record/1950214|url-status=live}}</ref> He studied the [[acoustics]] of various violin and related instruments, including Indian stringed instruments,<ref>{{Cite journal|last=Raman|first=C.V.|date=1918|title=On the mechanical theory of the vibrations of bowed strings and of musical instruments of the violin family, with experimental verification of the results-Part I|url=http://repository.ias.ac.in/69871/1/69871.pdf|journal=Bulletin of the Indian Association for the Cultivation of Science|volume=15|pages=1–158|access-date=10 March 2020|archive-date=23 October 2020|archive-url=https://web.archive.org/web/20201023090928/http://repository.ias.ac.in/69871/1/69871.pdf|url-status=live}}</ref><ref>{{Cite journal|last=Raman|first=C.V.|date=1921|title=On some Indian stringed instruments|url=http://repository.ias.ac.in/69870/1/69870.pdf|journal=Proceedings of the Indian Association for the Cultivation of Science|volume=7|pages=29–33|access-date=10 March 2020|archive-date=2 January 2014|archive-url=https://web.archive.org/web/20140102200140/http://repository.ias.ac.in/69870/1/69870.pdf|url-status=live}}</ref> and water splashes.<ref>{{Cite journal|last1=Raman|first1=C.V.|last2=Dey|first2=Ashutosh|date=1920|title=X. On the sounds of splashes|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=39|issue=229|pages=145–147|doi=10.1080/14786440108636021}}</ref> He even performed what he called "Experiments with mechanically-played violins."<ref>{{Cite journal|last=Raman|first=C.V.|date=1920|title=Experiments with mechanically-played violins|url=http://repository.ias.ac.in/69866/1/69866.pdf|journal=Proceedings of the Indian Association for the Cultivation of Science|volume=6|pages=19–36|access-date=10 March 2020|archive-date=23 October 2020|archive-url=https://web.archive.org/web/20201023092236/http://repository.ias.ac.in/69866/1/69866.pdf|url-status=live}}</ref>

Raman also studied the uniqueness of Indian drums.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Kumar|first2=Sivakali|date=1920|title=Musical Drums with Harmonic Overtones|journal=Nature|language=en|volume=104|issue=2620|pages=500|doi=10.1038/104500a0|bibcode=1920Natur.104..500R|s2cid=4159476|url=https://zenodo.org/record/1429634|doi-access=free|access-date=24 August 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031083805/https://zenodo.org/record/1429634|url-status=live}}</ref> His analyses of the [[harmonic]] nature of the sounds of [[tabla]] and [[mridangam]] were the first scientific studies on Indian percussions.<ref>{{cite journal|author1=Raman, C.V.|author2=Sivakali Kumar|year=1920|title=Musical drums with harmonic overtones|journal=Nature|volume=104|issue=2620|page=500|bibcode=1920Natur.104..500R|doi=10.1038/104500a0|s2cid=4159476|url=https://zenodo.org/record/1429634|doi-access=free|access-date=24 August 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031083805/https://zenodo.org/record/1429634|url-status=live}}</ref> He wrote a critical research on vibrations of the [[pianoforte]] string that was known as Kaufmann's theory.<ref>{{Cite journal|last1=Raman|first1=C.V.|last2=Banerji|first2=B.|date=1920|title=On Kaufmann's theory of the impact of the pianoforte hammer|journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character|language=en|volume=97|issue=682|pages=99–110|doi=10.1098/rspa.1920.0016|bibcode=1920RSPSA..97...99R|doi-access=free}}</ref> During his brief visit of England in 1921, he managed to study how sound travels in the [[Whispering Gallery|Whispring Gallery]] of the dome of [[St Paul's Cathedral]] in London that produces unusual sound effects.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Sutherland|first2=G. A.|date=1921|title=Whispering-Gallery Phenomena at St. Paul's Cathedral|journal=Nature|language=en|volume=108|issue=2706|pages=42|doi=10.1038/108042a0|bibcode=1921Natur.108...42R|s2cid=4126913|doi-access=free}}</ref><ref>{{cite journal|author=Raman, C.V.|year=1922|title=On whispering galleries|url=http://repository.ias.ac.in/69841/1/69841.pdf|journal=Bulletin of the Indian Association for the Cultivation of Science|volume=7|pages=159–172|access-date=7 January 2015|archive-date=12 December 2013|archive-url=https://web.archive.org/web/20131212004223/http://repository.ias.ac.in/69841/1/69841.pdf|url-status=live}}</ref> His work on acoustics was an important prelude, both experimentally and conceptually, to his later works on optics and [[quantum mechanics]].<ref>{{cite journal|author=Banerjee, Somaditya|year=2014|title=C. V. Raman and Colonial Physics: Acoustics and the Quantum|journal=Physics in Perspective|volume=16|issue=2|pages=146–178|bibcode=2014PhP....16..146B|doi=10.1007/s00016-014-0134-8|s2cid=121952683}}</ref>

=== Blue color of the sea ===

Raman, in his broadening venture on optics, started to investigate scattering of light starting in 1919.<ref>{{Cite journal|last=Raman|first=C.V.|date=1919|title=LVI. The scattering of light in the refractive media of the eye|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=38|issue=227|pages=568–572|doi=10.1080/14786441108635985|url=https://zenodo.org/record/1554442|access-date=10 March 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031081718/https://zenodo.org/record/1554442|url-status=live}}</ref> His first phenomenal discovery of the physics of light was the [[Color of water|blue color of seawater]]. During a voyage home from England on board the ''S.S. Narkunda'' in September 1921, he contemplated the blue color of the [[Mediterranean Sea]]. Using simple optical equipment, a pocket-sized [[spectroscope]] and a [[Nicol prism]] in hand, he studied the sea water.<ref>{{Cite journal|last=Anon.|date=2009|title=This Month in Physics History: February 1928: Raman scattering discovered|url=https://www.aps.org/publications/apsnews/200902/physicshistory.cfm|journal=APS News|volume=12|issue=2|pages=online|access-date=10 March 2020|archive-date=6 March 2020|archive-url=https://web.archive.org/web/20200306100800/https://www.aps.org/publications/apsnews/200902/physicshistory.cfm|url-status=live}}</ref> Of several hypotheses on the colour of the sea propounded at the time,<ref>{{Cite journal|last=Buchanan|first=J. Y.|date=1910|title=Colour of the Sea|journal=Nature|language=en|volume=84|issue=2125|pages=87–89|doi=10.1038/084087a0|bibcode=1910Natur..84...87B|doi-access=free}}</ref><ref>{{Cite journal|last=Barnes|first=H. T.|date=1910|title=Colour of Water and Ice|journal=Nature|language=en|volume=83|issue=2111|pages=188|doi=10.1038/083188a0|bibcode=1910Natur..83..188B|s2cid=3943242|url=https://zenodo.org/record/1567754|doi-access=free|access-date=16 March 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031080914/https://zenodo.org/record/1567754|url-status=live}}</ref> the best explanation had been that of [[Lord Rayleigh]]'s in 1910, according to which, "The much admired dark blue of the deep sea has nothing to do with the color of water, but is simply the blue of the sky seen by reflection".<ref>{{Cite journal|last=Rayleigh|first=J.W.S.|date=1910|title=Colours of Sea and Sky|journal=Nature|language=en|volume=83|issue=2106|pages=48–50|doi=10.1038/083048a0|bibcode=1910Natur..83...48.|doi-access=free}}</ref> Rayleigh had correctly described the nature of the blue sky by a phenomenon now known as [[Rayleigh scattering]],<ref>{{Cite journal|last=Rayleigh|first=Lord|date=1899|title=XXXIV. On the transmission of light through an atmosphere containing small particles in suspension, and on the origin of the blue of the sky|url=https://zenodo.org/record/1431249|url-status=live|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=47|issue=287|pages=375–384|doi=10.1080/14786449908621276|archive-url=https://web.archive.org/web/20201031200404/https://zenodo.org/record/1431249|archive-date=31 October 2020|access-date=16 March 2020}}</ref> the scattering of light and refraction by particles in the atmosphere.<ref>{{Cite journal|last1=Stetefeld|first1=Jörg|last2=McKenna|first2=Sean A.|last3=Patel|first3=Trushar R.|date=2016|title=Dynamic light scattering: a practical guide and applications in biomedical sciences|journal=Biophysical Reviews|language=en|volume=8|issue=4|pages=409–427|doi=10.1007/s12551-016-0218-6|pmc=5425802|pmid=28510011}}</ref> His explanation of the blue colour of water was instinctively accepted as correct. Raman could view the water using a [[Nicol prism]] to avoid the influence of sunlight reflected by the surface. He described how the sea appears even more blue than usual, contradicting Rayleigh.<ref name="Nature1921">{{Cite journal|last=Raman|first=C. V.|date=1921|title=The Colour of the Sea|journal=Nature|language=en|volume=108|issue=2716|pages=367|doi=10.1038/108367a0|bibcode=1921Natur.108..367R|s2cid=4064467|doi-access=free}}</ref>

As soon as the ''S.S. Narkunda'' docked in Bombay Harbour (now [[Mumbai Harbour]]), Raman finished an article "The colour of the sea" that was published in the November 1921 issue of ''Nature''. He noted that Rayleigh's explanation is "questionable by a simple mode of observation" (using Nicol prism).<ref name="Nature1921" /> As he thought:{{blockquote|

Looking down into the water with a Nicol in front of the eye to cut off surface reflections, the track of the sun's rays could be seen entering the water and appearing by virtue of perspective to converge to a point at a considerable depth inside it. The question is: What is it that diffracts the light and makes its passage visible? An interesting possibility that should be considered in this connection is that the diffracting particles may, at least in part, be the molecules of the water themselves.<ref name="Mukherji-2018b" />}}
[[File:Raman-2.jpg|alt=Title page to Raman's Molecular Diffraction of Light (1922)|thumb|230x230px|Title page to Raman's ''Molecular Diffraction of Light'' (1922)]]

When he reached Calcutta, he asked his student K. R. Ramanathan, who was from the University of Rangoon, to conduct further research at IACS.<ref name="Mallik-2000">{{Cite journal|last=Mallik|first=D. C. V.|date=2000|title=The Raman Effect and Krishnan's Diary|journal=Notes and Records of the Royal Society of London|volume=54|issue=1|pages=67–83|jstor=532059|doi=10.1098/rsnr.2000.0097|s2cid=143485844}}</ref> By early 1922, Raman came to a conclusion, as he reported in the ''[[Proceedings of the Royal Society of London]]'':{{blockquote|It is proposed in this paper to urge an entirely different view, that in this phenomenon, as in the parallel case of the colour of the sky, ''molecular diffraction'' determines the observed luminosity and in great measure also its colour. As a necessary preliminary to the discussion, a theoretical calculation and experimental observations of the intensity of molecular scattering in water will be presented.<ref>{{Cite journal|last=Raman|first=C.V.|date=1922|title=On the molecular scattering of light in water and the colour of the sea|journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character|language=en|volume=101|issue=708|pages=64–80|doi=10.1098/rspa.1922.0025|bibcode=1922RSPSA.101...64R|doi-access=free}}</ref>}}True to his words, Ramanathan published an elaborate experimental finding in 1923.<ref>{{Cite journal|last=Ramanathan|first=K.R.|date=1923|title=LVIII. On the colour of the sea|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=46|issue=273|pages=543–553|doi=10.1080/14786442308634277}}</ref> His subsequent study of the [[Bay of Bengal]] in 1924 provided the full evidence.<ref>{{Cite journal|last=Ramanathan|first=K. R.|date=1 March 1925|title=The Transparency and Color of the Sea|journal=Physical Review|language=en|volume=25|issue=3|pages=386–390|doi=10.1103/PhysRev.25.386|bibcode=1925PhRv...25..386R}}</ref> It is now known that the intrinsic color of water is mainly attributed to the selective absorption of longer wavelengths of light in the red and orange regions of the [[spectrum]], owing to overtones of the [[infrared]] absorbing O-H (oxygen and hydrogen combined) stretching modes of water molecules.<ref name="Braun">{{Citation|last1=Braun|first1=Charles L.|title=Why is water blue?|url=http://inside.mines.edu/fs_home/dwu/classes/CH353/study/Why%20is%20Water%20Blue.pdf|journal=[[Journal of Chemical Education]]|volume=70|issue=8|pages=612–614|year=1993|bibcode=1993JChEd..70..612B|doi=10.1021/ed070p612|last2=Smirnov|first2=Sergei N.|access-date=27 July 2021|archive-date=1 December 2019|archive-url=https://web.archive.org/web/20191201000418/http://inside.mines.edu/fs_home/dwu/classes/CH353/study/Why%20is%20Water%20Blue.pdf|url-status=live}}</ref>

=== Raman effect ===

{{main|Raman scattering}}

==== Background ====

Raman's second important discovery on the scattering of light was a new type of radiation, an eponymous phenomenon called the Raman effect.<ref name="Singh-2018" /> After discovering the nature of light scattering that caused blue colour of water, he focused on the principle behind the phenomenon. His experiments in 1923 showed the possibility of other light rays formed in addition to the [[incident ray]] when sunlight was filtered through a violet glass in certain liquids and solids. Ramanathan believed that this was a case of a "trace of [[fluorescence]]."<ref name="Mukherji-2018b" /> In 1925, [[K. S. Krishnan]], a new Research Associate, noted the theoretical background for the existence of an additional scattering line beside the usual polarised elastic scattering when light scatters through liquid.<ref>{{Cite journal|last=Krishnan|first=K.S.|date=1925|title=LXXV. On the molecular scattering of light in liquids|journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science|language=en|volume=50|issue=298|pages=697–715|doi=10.1080/14786442508634789}}</ref> He referred to the phenomenon as "feeble fluorescence."<ref>{{Cite journal|last=Mallik|first=D. C. V.|date=2000|title=The Raman effect and Krishnan's diary|url=https://royalsocietypublishing.org/doi/10.1098/rsnr.2000.0097|journal=Notes and Records of the Royal Society of London|language=en|volume=54|issue=1|pages=67–83|doi=10.1098/rsnr.2000.0097|s2cid=143485844|access-date=13 December 2020|archive-date=24 October 2019|archive-url=https://web.archive.org/web/20191024125416/https://royalsocietypublishing.org/doi/10.1098/rsnr.2000.0097|url-status=live|url-access=subscription}}</ref> But the theoretical attempts to justify the phenomenon were quite futile for the next two years.<ref>{{Cite journal|last1=Raman|first1=C.V.|last2=Krishnan|first2=K.S.|date=1927|title=Magnetic double-refraction in liquids. part I.—benzene and its derivatives|journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character|language=en|volume=113|issue=765|pages=511–519|doi=10.1098/rspa.1927.0004|bibcode=1927RSPSA.113..511R|doi-access=free}}</ref>

The major impetus was the discovery of [[Compton scattering|Compton effect]]. [[Arthur Compton]] at [[Washington University in St. Louis]] had found evidence in 1923 that [[electromagnetic waves]] can also be described as particles.<ref name="Compton effect">{{cite journal|author=Compton, Arthur H.|date=May 1923|title=A Quantum Theory of the Scattering of X-Rays by Light Elements|journal=[[Physical Review]]|volume=21|issue=5|pages=483–502|bibcode=1923PhRv...21..483C|doi=10.1103/PhysRev.21.483|doi-access=free}}</ref> By 1927, the phenomenon was widely accepted by scientists, including Raman.<ref>{{Cite journal|last=Raman|first=C. V.|date=1927|title=Thermodynamics, Wave-theory, and the Compton Effect|journal=Nature|language=en|volume=120|issue=3035|pages=950–951|doi=10.1038/120950a0|bibcode=1927Natur.120..950R|s2cid=29489622}}</ref> As the news of Compton's [[Nobel Prize in Physics]] was announced in December 1927, Raman ecstatically told Krishnan, saying:

{{blockquote|Excellent news... very nice indeed. But look here Krishnan. If this is true of X-Rays, it must be true of Light too. I have always thought so. There must be an Optical analogue to Compton Effect. We must pursue it and we are on the right lines. It must and shall be found. The Nobel Prize must be won.<ref name="Ramdas-1973">{{Cite journal|last=Ramdas|first=L. A.|date=1973|title=Dr. C. V. Raman (1888–1970), Part II|url=http://dspace.rri.res.in:8080/jspui/handle/2289/6371|journal=Journal of Physics Education|language=en|volume=1|issue=2|pages=2–18|access-date=12 March 2020|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031071756/http://dspace.rri.res.in:8080/jspui/handle/2289/6371|url-status=live}}</ref> }}But the origin of the inspiration went further. As Compton later recollected "that it was probably the Toronto debate that led him to discover the Raman effect two years later."<ref name="Banerjee-2014" /> The Toronto debate was about the discussion on the existence of light quantum at the [[British Science Association|British Association for the Advancement of Science]] meeting held at Toronto in 1924. There Compton presented his experimental findings, which [[William Duane (physicist)|William Duane]] of [[Harvard University]] argued with his own with evidence that light was a wave.<ref>{{Cite journal|last=Singh|first=Rajinder|date=2002|title=C. V. Raman and the Discovery of the Raman Effect|journal=Physics in Perspective |volume=4|issue=4|pages=399–420|doi=10.1007/s000160200002|bibcode=2002PhP.....4..399S|s2cid=121785335}}</ref> Raman took Duane's side and said, "Compton, you're a very good debater, but the truth isn't in you."<ref name="Banerjee-2014" />

==== The scattering experiments ====

[[File:1928 Benzene Raman Spectrum.png|thumb|An early Raman spectrum of [[benzene]] published by Raman and Krishnan<ref>{{Cite journal|last1=K. S. Krishnan|last2=Raman|first2=C. V.|date=1928|title=The Negative Absorption of Radiation|journal=Nature|language=en|volume=122|issue=3062|pages=12–13|doi=10.1038/122012b0|bibcode=1928Natur.122...12R|s2cid=4071281|issn=1476-4687}}</ref>|240x240px]]

Krishnan started the experiment in the beginning of January 1928.<ref name="Mallik-2000" /> On 7 January, he discovered that no matter what kind of pure liquid he used, it always produced polarised fluorescence within the [[visible spectrum]] of light. As Raman saw the result, he was astonished why he never observed such phenomenon all those years.<ref name="Mallik-2000" /> That night he and Krishnan named the new phenomenon as "modified scattering" with reference to the Compton effect as an unmodified scattering. On 16 February, they sent a manuscript to ''Nature'' titled "A new type of secondary radiation", which was published on 31 March.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Krishnan|first2=K. S.|date=1928|title=A new type of secondary radiation|journal=Nature|language=en|volume=121|issue=3048|pages=501–502|doi=10.1038/121501c0|bibcode=1928Natur.121..501R|s2cid=4128161}}</ref>

On 28 February 1928, they obtained spectra of the modified scattering separate from the [[incident light]]. Due to difficulty in measuring the wavelengths of light, they had been relying on visual observation of the colour produced from sunlight through prism. Raman had invented a type of [[spectrograph]] for detecting and measuring electromagnetic waves.<ref name="ACS-2015" /><ref>{{cite news|url=https://www.businessinsider.in/science/news/how-is-c-v-raman-connected-with-the-national-science-day/articleshow/74371450.cms#:~:text=On%20February%2028%2C%201928%2C%20Raman,a%20couple%20of%20years%20later.|title=How is C.V Raman connected with The National Science Day|work=Business Insider|date=28 February 2020|access-date=26 February 2021|archive-date=15 April 2020|archive-url=https://web.archive.org/web/20200415053333/https://www.businessinsider.in/science/news/how-is-c-v-raman-connected-with-the-national-science-day/articleshow/74371450.cms#:~:text=On%20February%2028%2C%201928%2C%20Raman,a%20couple%20of%20years%20later.|url-status=live}}</ref> Referring to the invention, Raman later remarked, "When I got my Nobel Prize, I had spent hardly 200 [[rupees]] on my equipment,"<ref>{{Cite journal|last=Long|first=D. A.|date=1988|title=Early history of the Raman effect|url=http://www.tandfonline.com/doi/abs/10.1080/01442358809353216|journal=International Reviews in Physical Chemistry|language=en|volume=7|issue=4|pages=317–349|doi=10.1080/01442358809353216|bibcode=1988IRPC....7..317L|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101614/https://www.tandfonline.com/doi/abs/10.1080/01442358809353216|url-status=live|url-access=subscription}}</ref> although it was obvious that his total expenditure for the entire experiment was much more than that.<ref>{{Cite journal|last=Singh|first=Rajinder|date=2018|title=How costly was Raman's equipment for the discovery of Raman effect?|url=http://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol53_4_2018__Art09.pdf|journal=Indian Journal of History of Science|volume=53|issue=4|pages=68–73|doi=10.16943/ijhs/2018/v53i4/49527|access-date=27 July 2021|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728000409/https://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol53_4_2018__Art09.pdf|url-status=live|doi-access=free}}</ref> From that moment they could employ the instrument using [[monochromator|monochromatic light]] from a [[mercury arc lamp]] which penetrated transparent material and was allowed to fall on a spectrograph to record its spectrum. The lines of scattering could now be measured and photographed.<ref>{{cite web|url=https://www.youtube.com/watch?v=Beq0D5nFR00|title=Raman Effect Visualised|website=[[YouTube]]|date=8 October 2008 |access-date=15 May 2014|archive-date=22 May 2014|archive-url=https://web.archive.org/web/20140522061043/http://www.youtube.com/watch?v=Beq0D5nFR00|url-status=live}}</ref><ref name="b1">Venkataraman, G. (1988) ''Journey into Light: Life and Science of C. V. Raman''. Oxford University Press. {{ISBN|978-81-85324-00-5}}.</ref>

==== Announcement ====

The same day, Raman made the announcement before the press. The ''[[Associated Press of India]]'' reported it the next day, on 29 February, as "New theory of radiation: Prof. Raman's Discovery."<ref>{{Cite book|last1=Jagdish|first1=Mehra|author-link1=Jagdish Mehra |title=The Historical Development of Quantum Volume 6 Part 1|last2=Rechenberg|first2=Helmut| author-link2=Helmut Rechenberg |publisher=Springer|year=2001|isbn=978-0-387-95262-8|location=New York|pages=360|oclc=76255200}}</ref> It ran the story as:{{blockquote|Prof. C. V. Raman, F.R.S., of the Calcutta University, has made a discovery which promises to be of fundamental significance to physics... The new phenomenon exhibits features even more startling than those discovered by Prof. Compton with X-rays. The principal feature observed is that when matter is excited by light of one colour, the atoms contained in it emit light of two colours, one of which is different from the exciting colour and is lower down the spectrum. The astonishing thing is that the altered colour is quite independent of the nature of the substance used.<ref name="Singh-2018">{{Cite journal|last=Singh|first=Rajinder|date=2018-03-01|title=The 90th Anniversary of the Raman Effect|url=http://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol53_1_2018__Art04.pdf|journal=Indian Journal of History of Science|volume=53|issue=1|pages=50–58|doi=10.16943/ijhs/2018/v53i1/49363|doi-access=free|access-date=17 March 2020|archive-date=25 August 2020|archive-url=https://web.archive.org/web/20200825164824/https://insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol53_1_2018__Art04.pdf|url-status=live}}</ref>}}The news was reproduced by ''[[The Statesman (India)|The Statesman]]'' on 1 March under the headline "Scattering of Light by Atoms – New Phenomenon – Calcutta Professor's Discovery."<ref>{{Cite journal|last=Long|first=D. A.|date=2008|title=80th Anniversary of the discovery of the Raman effect: a celebration|journal=Journal of Raman Spectroscopy|language=en|volume=39|issue=3|pages=316–321|doi=10.1002/jrs.1948|bibcode=2008JRSp...39..316L}}</ref> Raman submitted a three-paragraph report of the discovery on 8 March to ''Nature'' and was published on 21 April.<ref>{{Cite journal|last=Raman|first=C. V.|date=1928|title=A Change of Wave-length in Light Scattering|journal=Nature|language=en|volume=121|issue=3051|pages=619|doi=10.1038/121619b0|bibcode=1928Natur.121..619R|s2cid=4102940|doi-access=free}}</ref> The actual data was sent to the same journal on 22 March and was published on 5 May.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Krishnan|first2=K. S.|date=1928|title=The Optical Analogue of the Compton Effect|journal=Nature|language=en|volume=121|issue=3053|pages=711|doi=10.1038/121711a0|bibcode=1928Natur.121..711R|s2cid=4126899|doi-access=free}}</ref> Raman presented the formal and detailed description as "A new radiation" at the meeting of the South Indian Science Association in Bangalore on 16 March. His lecture was published in the ''[[Indian Journal of Physics]]'' on 31 March.<ref name="Raman-1928" /> A thousand copies of the paper reprint were sent to scientists in different countries on that day.<ref name="Jayaraman-1989d" />

==== Reception and outcome ====

Some physicists, particularly French and German physicists were initially sceptical of the authenticity of the discovery. [[Georg Joos]] at the [[Friedrich Schiller University of Jena]] asked [[Arnold Sommerfeld]] at the [[University of Munich]], "Do you think that Raman's work on the optical Compton effect in liquids is reliable?... The sharpness of the scattered lines in liquids seems doubtful to me". Sommerfeld then tried to reproduce the experiment, but failed.<ref name="Singh-2008">{{Cite journal|last=Singh|first=Rajinder|date=2008|title=80 Years Ago – the Discovery of the Raman Effect at the Indian Association for the Cultivation of Science, Kolkata, India|url=http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/8110/1/80%20years%20ago%20-%20the%20Discovery%20of%20the%20Raman_By%20Rajinder%20Singh.pdf|url-status=dead|journal=Indian Journal of Physics|volume=82|pages=987–1001|archive-url=https://web.archive.org/web/20200606142247/http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/8110/1/80%20years%20ago%20-%20the%20Discovery%20of%20the%20Raman_By%20Rajinder%20Singh.pdf|archive-date=6 June 2020|access-date=8 March 2020}}</ref> On 20 June 1928, Peter Pringsheim at the [[University of Berlin]] was able to reproduce Raman's results successfully. He was the first to coin the terms ''Ramaneffekt'' and ''Linien des Ramaneffekts'' in his articles published the following months.<ref>{{Cite journal|last=Pringsheim|first=Peter|date=1928|title=Der Ramaneffekt, ein neuer von C. V. Raman entdeckter Strahlungseffekt|journal=Die Naturwissenschaften|language=de|volume=16|issue=31|pages=597–606|doi=10.1007/BF01494083|bibcode=1928NW.....16..597P|s2cid=30433182}}</ref><ref>{{Cite journal|last1=Carrelli|first1=A.|last2=Pringsheim|first2=Peter|last3=Rosen|first3=B.|date=1928|title=Über den Ramaneffekt an wässerigen Lösungen und über den Polarisationszustand der Linien des Ramaneffekts|journal=Zeitschrift für Physik|language=de|volume=51|issue=7–8|pages=511–519|doi=10.1007/BF01327842|bibcode=1928ZPhy...51..511C|s2cid=119516536}}</ref> Use of the English versions, "Raman effect" and "Raman lines" immediately followed.<ref>{{Cite journal|last=Ramdas|first=L. A.|date=1928|title=The Raman Effect and the Spectrum of the Zodiacal Light|journal=Nature|language=en|volume=122|issue=3063|pages=57|doi=10.1038/122057a0|s2cid=4092715|doi-access=free}}</ref><ref name="SinghR-2002" /><ref name="Brand-1989">{{Cite journal|last=Brand|first=J. C. D.|date=31 January 1989|title=The discovery of the Raman effect|journal=Notes and Records of the Royal Society of London|language=en|volume=43|issue=1|pages=1–23|doi=10.1098/rsnr.1989.0001|s2cid=120964978}}</ref>

In addition to being a new phenomenon itself, the Raman effect was one of the earliest proofs of the [[Light#Quantum theory|quantum nature of light]]. [[Robert W. Wood]] at the [[Johns Hopkins University]] was the first American to confirm the Raman effect in early 1929.<ref>{{Cite journal|last=Wood|first=R. W.|date=1929|title=The Raman Effect with Hydrochloric Acid Gas: the 'Missing Line.'|journal=Nature|language=en|volume=123|issue=3095|pages=279|doi=10.1038/123279a0|bibcode=1929Natur.123Q.279W|s2cid=4121854|doi-access=free}}</ref> He made a series of experimental verification, after which he commented, saying, "It appears to me that this very beautiful discovery which resulted from Raman's long and patient study of the phenomenon of light scattering is one of the most convincing proofs of the quantum theory".<ref>{{Cite journal|last=Wood|first=R. W.|date=1933|title=Raman Spectrum of Heavy Water (By Cable)|journal=Nature|language=en|volume=132|issue=3347|pages=970|doi=10.1038/132970b0|bibcode=1933Natur.132..970W|s2cid=4092727|doi-access=free}}</ref><ref>{{Cite web|url=https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/ramaneffect.html|title=C.V. Raman The Raman Effect - Landmark|website=American Chemical Society|language=en|access-date=11 March 2020|archive-date=4 March 2020|archive-url=https://web.archive.org/web/20200304020054/https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/ramaneffect.html|url-status=live}}</ref> The field of [[Raman spectroscopy]] came to be based on this phenomenon, and [[Ernest Rutherford]], President of the [[Royal Society]], referred to it in his presentation of the [[Hughes Medal]] to Raman in 1930 as "among the best three or four discoveries in experimental physics in the last decade".<ref name="Ramdas-1973" />

Raman was confident that he would win the Nobel Prize in Physics as well but was disappointed when the Nobel Prize went to [[Owen Richardson]] in 1928 and to [[Louis de Broglie]] in 1929. He was so confident of winning the prize in 1930 that he booked tickets in July, even though the awards were to be announced in November. He would scan each day's newspaper for announcement of the prize, tossing it away if it did not carry the news.<ref name="Venkataraman-1995">{{citation|author=Venkataraman, G.|title=Raman and His Effect|url=https://books.google.com/books?id=OjLls3eaOhEC&pg=PA50|page=50|year=1995|publisher=Orient Blackswan|isbn=978-81-7371-008-7|access-date=28 July 2016|archive-date=7 February 2021|archive-url=https://web.archive.org/web/20210207130540/https://books.google.com/books?id=OjLls3eaOhEC&pg=PA50|url-status=live}}</ref> He did eventually win that year.<ref name="Nobel-2014">{{cite web|title=The Nobel Prize in Physics 1930|url=http://nobelprize.org/nobel_prizes/physics/laureates/1930/index.html|url-status=live|archive-url=https://web.archive.org/web/20141011205133/http://www.nobelprize.org/nobel_prizes/physics/laureates/1930/index.html|archive-date=11 October 2014|access-date=9 October 2008|publisher=Nobel Foundation}}</ref>

===Later work===

Raman had association with the [[Banaras Hindu University]] in [[Varanasi]]. He attended the foundation ceremony of BHU<ref>{{cite news |last1=Singh |first1=Binay |title=BHU preserves CV Raman's association with university |url=http://timesofindia.indiatimes.com/city/varanasi/BHU-preserves-CV-Ramans-association-with-university/articleshow/25403012.cms |access-date=17 June 2015 |newspaper=The Times of India |date=8 November 2013 |archive-date=28 November 2013 |archive-url=https://web.archive.org/web/20131128010326/http://timesofindia.indiatimes.com/city/varanasi/BHU-preserves-CV-Ramans-association-with-university/articleshow/25403012.cms |url-status=live }}</ref> and delivered lectures on mathematics and "Some new paths in physics" during the lecture series organised at the university from 5 to 8 February 1916.<ref>{{cite journal |last1=Dwivedi |first1=B. N. |title=Madan Mohan Malaviya and Banaras Hindu University |url=http://www.currentscience.ac.in/Volumes/101/08/1091.pdf |journal=Current Science |volume=101 |issue=8 |pages=1091–1095 |year=2011 |access-date=17 June 2015 |archive-date=17 June 2015 |archive-url=https://web.archive.org/web/20150617123506/http://www.currentscience.ac.in/Volumes/101/08/1091.pdf |url-status=live }}</ref> He also held the position of permanent visiting professor.<ref>{{cite book |last1=Prakash |first1=Satya |title=Vision for Science Education |date=20 May 2014 |publisher=Allied Publishers |isbn=978-81-8424-908-8 |page=45}}</ref>

With [[Suri Bhagavantam]], he determined the [[Spin (physics)|spin]] of [[photons]] in 1932, which further confirmed the quantum nature of light.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Bhagavantam|first2=S.|date=1932|title=Experimental Proof of the Spin of the Photon|url=http://www.nature.com/articles/129022a0|url-status=live|journal=Nature|language=en|volume=129|issue=3244|pages=22–23|bibcode=1932Natur.129...22R|doi=10.1038/129022a0|archive-url=https://web.archive.org/web/20200316035934/https://www.nature.com/articles/129022a0|archive-date=16 March 2020|access-date=18 March 2020|hdl-access=free|hdl=10821/664|s2cid=4064852}}</ref><ref name="Brand-1989" /> With another student, Nagendra Nath, he provided the correct theoretical explanation for the [[Acousto-optics|acousto-optic effect]] (light scattering by sound waves) in a series of articles resulting in the celebrated Raman–Nath theory.<ref>C. V. Raman, N. S. Nagendra Nath, [http://dspace.rri.res.in/handle/2289/2045 "The diffraction of light by high-frequency sound waves. Part I"] {{Webarchive|url=https://web.archive.org/web/20141213022033/http://dspace.rri.res.in/handle/2289/2045 |date=13 December 2014 }}, ''Proc. Ind. Acad. Sci.'', 1935</ref> Modulators, and switching systems based on this effect have enabled optical communication components based on [[laser]] systems.<ref>{{Cite journal|last1=Cheng|first1=Qixiang|last2=Bahadori|first2=Meisam|last3=Glick|first3=Madeleine|last4=Rumley|first4=Sébastien|last5=Bergman|first5=Keren|date=2018|title=Recent advances in optical technologies for data centers: a review|url=https://www.osapublishing.org/abstract.cfm?URI=optica-5-11-1354|journal=Optica|language=en|volume=5|issue=11|pages=1354–1370|doi=10.1364/OPTICA.5.001354|bibcode=2018Optic...5.1354C|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101641/https://www.osapublishing.org/optica/fulltext.cfm?uri=optica-5-11-1354&id=399361|url-status=live|doi-access=free}}</ref>

Other investigations he carried out included experimental and theoretical studies on the diffraction of light by acoustic waves of [[Ultrasound|ultrasonic]] and [[hypersonic]] frequencies,<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Nagendra Nathe|first2=N. S.|date=1935|title=The diffraction of light by high frequency sound waves: Part I.|url=http://link.springer.com/10.1007/BF03035840|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=2|issue=4|pages=406–412|doi=10.1007/BF03035840|s2cid=198141323|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101617/https://link.springer.com/article/10.1007/BF03035840|url-status=live|url-access=subscription}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1942|title=The nature of the liquid state|url=https://www.jstor.org/stable/24213500|journal=Current Science|volume=11|issue=8|pages=303–310|jstor=24213500|access-date=27 July 2021|archive-date=27 July 2021|archive-url=https://web.archive.org/web/20210727110049/https://www.jstor.org/stable/24213500|url-status=live}}</ref> and those on the effects produced by X-rays on infrared vibrations in crystals exposed to ordinary light which were published between 1935 and 1942.<ref>{{Cite journal|last=Raman|first=C. V.|date=1941|title=Crystals and photons|url=http://link.springer.com/10.1007/BF03052526|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=13|issue=1|pages=1–8|doi=10.1007/BF03052526|s2cid=198142013|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101627/https://link.springer.com/article/10.1007/BF03052526|url-status=live|url-access=subscription}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1942|title=Reflexion of X-Rays with Change of Frequency|url=http://www.nature.com/articles/150366a0|journal=Nature|language=en|volume=150|issue=3804|pages=366–369|doi=10.1038/150366a0|bibcode=1942Natur.150..366R|s2cid=222373|access-date=27 July 2021|archive-date=27 July 2021|archive-url=https://web.archive.org/web/20210727124745/https://www.nature.com/articles/150366a0|url-status=live|url-access=subscription}}</ref>

In 1948, through studying the [[Spectroscopy|spectroscopic]] behaviour of crystals, he approached the fundamental problems of crystal dynamics in a new manner.<ref>{{Cite journal|last=Raman|first=C. V.|date=1948|title=Dynamic X-ray reflections in crystals|url=http://dspace.rri.res.in/bitstream/2289/1780/1/1948%20CS%20V17%20p65-75.pdf|journal=Current Science|language=en|volume=17|pages=65–75|access-date=27 July 2021|archive-date=27 July 2021|archive-url=https://web.archive.org/web/20210727124227/http://dspace.rri.res.in/bitstream/2289/1780/1/1948%20CS%20V17%20p65-75.pdf|url-status=live}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1948|title=X-Rays and the Eigen-Vibrations of Crystal Structures|url=http://www.nature.com/articles/162023b0|journal=Nature|language=en|volume=162|issue=4105|pages=23–24|doi=10.1038/162023b0|pmid=18939227|bibcode=1948Natur.162...23R|s2cid=4073206|access-date=27 July 2021|archive-date=27 July 2021|archive-url=https://web.archive.org/web/20210727145135/https://www.nature.com/articles/162023b0|url-status=live|url-access=subscription}}</ref> He dealt with the structure and properties of diamond from 1944 to 1968,<ref>{{Cite journal|last=Raman|first=C. V.|date=1943|title=The structure and properties of diamond|url=http://repository.ias.ac.in/69822/1/69822.pdf|journal=Current Science|volume=12|issue=1|pages=33–42|jstor=24208172|access-date=27 July 2021|archive-date=27 July 2021|archive-url=https://web.archive.org/web/20210727124226/http://repository.ias.ac.in/69822/1/69822.pdf|url-status=live}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1968|title=The diamond: Its structure and properties|url=http://link.springer.com/10.1007/BF03049362|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=67|issue=5|pages=231–246|doi=10.1007/BF03049362|s2cid=91751475|url-access=subscription}}</ref> the structure and optical behaviour of numerous [[Iridescence|iridescent]] substances including [[labradorite]],<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Jayaraman|first2=A.|date=1950|title=The structure of labradorite and the origin of its iridescence|url=http://link.springer.com/10.1007/BF03172469|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=32|issue=1|pages=1–16|doi=10.1007/BF03172469|s2cid=128235557|url-access=subscription}}</ref> pearly [[feldspar]],<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Jayaraman|first2=A.|date=1953|title=The diffusion haloes of the iridescent feldspars|url=http://link.springer.com/10.1007/BF03052851|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=37|issue=1|pages=1–10|doi=10.1007/BF03052851|s2cid=128924627|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101620/https://link.springer.com/article/10.1007/BF03052851|url-status=live|url-access=subscription}}</ref> [[agate]],<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Jayaraman|first2=A.|date=1953|title=The structure and optical behaviour of iridescent agate|url=http://link.springer.com/10.1007/BF03045221|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=38|issue=3|pages=199–206|doi=10.1007/BF03045221|s2cid=198139210|url-access=subscription}}</ref> [[quartz]],<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Jayaraman|first2=A.|date=1954|title=X-ray study of fibrous quartz|url=http://link.springer.com/10.1007/BF03047162|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=40|issue=3|pages=107|doi=10.1007/BF03047162|s2cid=135143703|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101628/https://link.springer.com/article/10.1007/BF03047162|url-status=live|url-access=subscription}}</ref> [[opal]],<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Jayaraman|first2=A.|date=1953|title=The structure and optical behaviour of iridescent opal|url=http://link.springer.com/10.1007/BF03045242|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=38|issue=5|pages=343–354|doi=10.1007/BF03045242|s2cid=198141813|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101620/https://link.springer.com/article/10.1007/BF03045242|url-status=live|url-access=subscription}}</ref> and [[pearl]] in the early 1950s.<ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Krishnamurti|first2=D.|date=1954|title=The structure and optical behaviour of pearls|url=http://link.springer.com/10.1007/BF03047140|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=39|issue=5|pages=215–222|doi=10.1007/BF03047140|s2cid=91310831|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101621/https://link.springer.com/article/10.1007/BF03047140|url-status=live|url-access=subscription}}</ref> Among his other interests were the optics of [[colloid]]s, and electrical and magnetic [[anisotropy]].<ref>{{Cite journal|last=Krishnan|first=R. S.|date=1948|title=Sir C. V. Raman and crystal physics|url=https://doi.org/10.1007/BF03170788|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=28|issue=5|pages=258|doi=10.1007/BF03170788|s2cid=172445086|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101633/https://link.springer.com/article/10.1007/BF03170788|url-status=live|url-access=subscription}}</ref><ref>{{Cite journal|last1=Raman|first1=C. V.|last2=Viswanathan|first2=K. S.|date=1955|title=The theory of the propagation of light in polycrystalline media|url=https://doi.org/10.1007/BF03047170|journal=Proceedings of the Indian Academy of Sciences, Section A|language=en|volume=41|issue=2|pages=37–44|doi=10.1007/BF03047170|s2cid=59436273|access-date=27 July 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812101621/https://link.springer.com/article/10.1007/BF03047170|url-status=live|url-access=subscription}}</ref> His last interests in the 1960s were on biological properties such as the colours of flowers and the [[Visual system|physiology of human vision]].<ref>{{Cite journal|last=Raman|first=C. V.|date=1960|title=The perception of light and colour and the physiology of vision|journal=Proceedings of the Indian Academy of Sciences, Section B|language=en|volume=52|issue=6|pages=253–264|doi=10.1007/BF03047051|s2cid=170662624}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1962|title=The role of the retina in vision|journal=Proceedings of the Indian Academy of Sciences, Section B|language=en|volume=56|issue=2|pages=77–87|doi=10.1007/BF03051587|jstor=24059723|hdl=2289/1702|s2cid=83159946|url=https://www.ias.ac.in/article/fulltext/secb/056/02/0077-0087|access-date=12 August 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812125853/https://www.ias.ac.in/article/fulltext/secb/056/02/0077-0087|url-status=live|url-access=subscription}}</ref><ref>{{Cite journal|last=Raman|first=C. V.|date=1970|title=The florachromes: Their chemical nature and spectroscopic behaviour|journal=Proceedings of the Indian Academy of Sciences, Section B|language=en|volume=72|issue=1|pages=1–23|url=https://www.ias.ac.in/article/fulltext/seca/072/01/0001-0023|doi=10.1007/BF03049697|s2cid=97395288|access-date=12 August 2021|archive-date=12 August 2021|archive-url=https://web.archive.org/web/20210812125853/https://www.ias.ac.in/article/fulltext/seca/072/01/0001-0023|url-status=live|url-access=subscription}}</ref>