Showing posts with label scattered light. Show all posts
Showing posts with label scattered light. Show all posts

November 7 - Nobel Winners Born

Posted on November 7, 2018

Marie Curie's birthday is today - and she not only won a Nobel Prize, she won two! So far she is the only woman to have been awarded two Nobels.

I've already written about Curie (see "Also on this date" below)...but there have been five other Nobel Laureates born on this date! That's...impressive.

Two of these Nobel-Prize-winning birthday-peeps came from two very different places and won for two very different areas of study: Sir Chandrasekhara Venkata Raman was born on this date in 1888, in India, and won for work in physics; and Konrad Lorenz was born on this date in 1904, in Austria, and won for his work in zoology.

C.V. Raman won a Nobel for his work on light scattering. We all know that light is scattered in a willy-nilly sort of way by particles (atoms or molecules) that are smaller than the wavelength of the light. That kind of scattering affects the short-wavelength light (the blue wavelengths) the most - and that's why the sky often appears blue. BUT that's not the sort of light scattering that Raman studied. The kind we all know and love is called Rayleigh scattering after the British physicist, Lord Rayleigh, who provided the first theoretical explanation of the effect.

Rayleigh scattering is called "elastic scattering," and the energy of the light (photon) stays the same but the direction changes. C.V. Raman studied "inelastic scattering" in liquids (and also gases and solids). In this kind of scattering, some of the energy of the light (photon) is lost or increased. This kind of scattering is called Raman scattering. Scientists use this Raman effect to figure out what is in a substance without necessarily touching and therefore without damaging the substance.


Konrad Lorenz's work is probably easier for most of us to understand. He is one of the founders of ethology, the study of animal behavior. He investigated how geese and some other birds imprint - which means that they bond instinctively with the first moving object that they see after hatching. 

When Lorenz was a young person and a student, he accumulated a lot of animal pets - including some more exotic not-usually-pet animals such as a capuchin monkey. What gets me about that is that his pets lived in his parents' apartment - and if they hadn't allowed such a thing, the world might not have gained all the knowledge about animals that Lorenz discovered.

Lorenz had to interrupt his work during World War II, when he was used as a medic and as a military psychologist for the German army. (After the war, Lorenz stated that he regretted being part of the Nazi Party, the Nazi Army, or the Nazi anything!) While the war was raging, Lorenz became a prisoner of war in Russia, and he continued to serve as a medic even as a POW. He actually started writing a book while he was a Russian prisoner, and he tamed a starling (a bird) and so had yet another pet!

The ugliness of Lorenz's life and science was the ways in which he may or may not have helped the hateful and untrue bigotry of the white supremacy and white nationalism that characterize the Nazi party.

The beauty of Lorens's life and science was that he was able to discuss animal behavior within the theory of evolution by natural selection. He asked questions like - How did behavior X benefit the animal? How did the behavior make the animal better adapted to its environment and therefore better able to pass on its genes?



Thus animal behavior became more than just cute and funny anecdotes or "believe it or not" oddities - it became a scientific study.



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(First full week of November)



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February 28 – National Science Day in India

Posted on February 28, 2016

One of India's most recognized and respected scientists is C.V. Raman.

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

On the other hand, like Charles Darwin and Albert Einstein, at least spell check know's Raman's full name and didn't allow me to accidentally type something like Chardrasekhara or Chandrasakhara or....whatever else my flying fingers blundered out.

And since 1929, Raman's full name ALSO included “Sir,” because he was knighted by Britain.

So, why am I bringing up Sir Chandrasekhara Venkata Raman today? Just because he was an Indian scientist and today is National Science Day in India?

Actually, it is because of Raman that today was chosen to celebrate and promote science in India – because today is the anniversary of his most important, Nobel-Prize-worthy discovery: the Raman effect.


So...what's the Raman effect?

Simply stated, the Raman effect is the inelastic scattering of light.

You probably know that visible light is a form of electromagnetic radiation, along with infrared, microwaves, X-rays, radio waves, and ultra-violet light. All electromagnetic radiation travels in little “packets” called photons.

I bet you have heard that, on a clear day, the sky looks blue because of scattering. But what is being scattered by what?

Air is not empty space – it's full of lots of different particles and molecules, most of which are invisible to us. When light from the Sun hits particles or molecules, some of the photons's paths are disrupted, and the various photons scatter about randomly. And blue photons have the tiniest wavelengths of all visible light, so they tend to get scattered more than green or yellow photons, and especially more than orange or red photons.

This is called Raleigh scattering, or elastic scattering. The photons that scatter shoot off on other, random paths, but they don't change their frequency and wavelength. In other words, a photon of blue light stays a photon of blue light.

In 1923, a physicist predicted that a few photons would scatter in another way. They would scatter by excitation – in other words, they would change frequency and wavelength, either gaining or losing energy. A photon of blue light might become a photon of red, or vice versa.

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).


On this date in 1928, Raman and K. S. Krishnan discovered the predicted behavior. Only about one photon in 10 million changes wavelength as it scatters, but they were able to observe it as light passed through a liquid.

(Actually, two Soviet scientists discovered this same sort of scattering as light traveled through crystals about a week before Raman and Krishnan's discovery! The reason that the “effect” is named after Raman – and the reason that Raman and Krishnan share a Nobel Prize for the discovery – is that the Indian scientists published their findings before the Russian scientists did.)

In 1928, the Raman effect seemed important to scientists, especially those in the field of spectroscopy (the study of light that has been emitted from, reflected from, or shone through a gas, liquid, or solid). But I don't know that the Raman effect had much...um...effect on the rest of us. However, these days there are a lot of utilities in many different fields. Here's a practical one: a Raman scanner is a hand held device used to detect drugs, explosives, hazardous chemicals, gases, and so forth. It is used by narcotics squads, airport security, forensic detectives, and security experts.


For more...

Check out this article on other Indian scientists.



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