Sensing molecules with light

Multiple types of micrometer-sized particles are simultaneously illuminated by a far-infrared laser and a green laser beam. Absorption of the infrared laser energy by the particles increases their temperatures, causing them to expand and slightly altering their visible-light optical properties. These changes are unique to the material composition of each particle and can be measured by examining the modulation of scattered green light from each particle. Credit: Ryan Sullenberger, MIT Lincoln Laboratory

At MIT researchers have invented a new type of spectroscopy that is both cheaper and easier to perform.

With spectroscopy (see clip) we are able to investigate the structure of matter by studying the interference of the atoms with an electromagnetic beam. The beam is absorbed by the atoms (their electrons) and then is released in a way that is specific to each type of atom. The emitted radiation is providing the signature of the atoms and by reading that signature we know what atoms (molecules) are there.

Spectroscopy requires some costly and bulky equipment, hence it needs to take place in a lab.

At MIT they have found a way to get the atoms signature by using two laser beams, one in the infrared and the other in the green wavelength. 

The atoms are "illuminated" by the infrared beam and this increases their temperature and this leads to a sort of "swelling" that alters the optical characteristics of the material. The swelling depends on the type of atoms and in turns this creates a specific optical signature that is captured by the green laser beam.

The advantage of this method is in its simplicity and the fact that the required set up is very small, making the apparatus portable. It is like having a microscope that can identify micrometer size particles telling you their atomic composition. It is quite sensitive, being able to detect particle as small as 1 µm (usual infrared spectroscopy has a limit around 10 µm).

A straightforward application would be in security controls at airports to detect potential explosive compounds.

This is yet another technology that provides sensing capabilities and we keep seeing a increasing variety of them, generating more and more data.

Author - Roberto Saracco

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