February 28 – National Science Day in India

nPostednon February 28, 2016

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Onenof India’s most recognized and respected scientists is C.V. Raman. n

nInlike referring to him as “C.V.” because his full name isnChandrasekhara Venkata Raman. Which is a lot to type.

nOnnthe other hand, like Charles Darwin and Albert Einstein, at leastnspell check know’s Raman’s full name and didn’t allow me tonaccidentally type something like Chardrasekhara or Chandrasakharanor….whatever else my flying fingers blundered out.

nAndnsince 1929, Raman’s full name ALSO included “Sir,” because he wasnknighted by Britain.

nSo,nwhy am I bringing up Sir Chandrasekhara Venkata Raman today? Justnbecause he was an Indian scientist and today is National Science Daynin India?

nActually,nit is because of Raman that today was chosen to celebrate and promotenscience in India – because today is the anniversary of his mostnimportant, Nobel-Prize-worthy discovery: the Raman effect. n

nSo…what’snthe Raman effect?

Simplynstated, the Raman effect is the inelastic scattering of light.

nYounprobably know that visible light is a form of electromagneticnradiation, along with infrared, microwaves, X-rays, radio waves, andnultra-violet light. All electromagnetic radiation travels in littlen“packets” called photons.

nInbet you have heard that, on a clear day, the sky looks blue becausenof scattering. But what is being scattered by what?

nAirnis not empty space – it’s full of lots of different particles andnmolecules, most of which are invisible to us. When light from the Sunnhits particles or molecules, some of the photons’s paths arendisrupted, and the various photons scatter about randomly. And bluenphotons have the tiniest wavelengths of all visible light, so theyntend to get scattered more than green or yellow photons, andnespecially more than orange or red photons.

nThisnis called Raleigh scattering, or elastic scattering. The photons thatnscatter shoot off on other, random paths, but they don’t change theirnfrequency and wavelength. In other words, a photon of blue lightnstays a photon of blue light. n

nInn1923, a physicist predicted that a few photons would scatter innanother way. They would scatter by excitation – in other words,nthey would change frequency and wavelength, either gaining or losingnenergy. A photon of blue light might become a photon of red, or vicenversa.

In the diagram above, the incoming Sun’s light is yellow,
as is the Raleigh-scattered light. The two pink arrows
show the Raman-scattered light.

In the diagram above, the green laser shines through a crystal.
Some of the light is scattered. Most of the scattered light is
still green (Raleigh – elastic), but a bit of it is now pink
(Raman – inelastic).

nOnnthis date in 1928, Raman and K. S. Krishnan discovered the predictednbehavior. Only about one photon in 10 million changes wavelength asnit scatters, but they were able to observe it as light passed throughna liquid.

n(Actually,ntwo Soviet scientists discovered this same sort of scattering asnlight traveled through crystals about a week before Raman andnKrishnan’s discovery! The reason that the “effect” is named afternRaman – and the reason that Raman and Krishnan share a Nobel Prizenfor the discovery – is that the Indian scientists published theirnfindings before the Russian scientists did.)

Inn1928, the Raman effect seemed important to scientists, especiallynthose in the field of spectroscopy (the study of light that has beennemitted from, reflected from, or shone through a gas, liquid, ornsolid). But I don’t know that the Raman effect had much…um…effectnon the rest of us. However, these days there are a lot of utilitiesnin many different fields. Here’s a practical one: a Raman scanner isna hand held device used to detect drugs, explosives, hazardousnchemicals, gases, and so forth. It is used by narcotics squads,nairport security, forensic detectives, and security experts.

nFornmore…

nChecknout this articlenon other Indian scientists.