When light explores matter

Illustration : Aurélie Bordenave

What happens when light is shone at a sample? What techniques and applications are available at SOLEIL? Find some answers in this illustrated video, very accessible and didactic.

All the illustrated videos:
 
- SOLEIL, a light source for research  
- The lights of SOLEIL
- When light explores matter

When light explores matter

Audio Transcription

To probe the sample of a material at SOLEIL, the scientist exposes it to a light beam. But how can light provide information on the sample? We see the objects around us because they reflect some of the light they receive. Our eyes detect the reflected light.
Matter does not reflect all the light; it also absorbs part of it. For example, a blue object absorbs the light waves corresponding to colors red and green, but it reflects the blue ones.
If you try to light a blue object with red light, you will see that it can only reflect blue light, and red light contains none of it. So the object will appear as black.

This absorption phenomenon also exists at the scale of atoms composing matter.
That relates to every single atom, such as hydrogen, carbon and oxygen.
Each atom always absorbs the same colors, or in other words, the same “wavelengths”. It is kind of like its own footprint.

So we can understand the composition of a sample by shedding light on it and measuring the absorbed wavelengths, even when those are not visible light.
This phenomenon occurs with atoms as well as with groupings of atoms, or in other words, molecules. And if, on top of this, we use a microscope to see which wavelengths are absorbed by the various parts of the investigated sample, we can find out where each molecule is located, and work out an actual map.

Other properties of light are used to observe specific materials. For example, we can know how the atoms are arranged next to one another through a method called "X-ray diffraction".
This is how, in the 1950s, scientists exposed DNA strands to X-rays, recorded the scattered X-rays and discovered the very specific double-helix shape of the DNA molecule. Today, and at SOLEIL in particular, researchers study the structure of much more complex samples using this method.It makes it possible, for instance, to know the exact structure of the molecules in a virus' envelope, and such information allows the researchers to manufacture powerful drugs against this specific virus.

There is still so much to explore using light. Especially when the light is very intense, focused in very thin beams, and that it has many other assets…

As in the SOLEIL synchrotron facility!