When cooling however was many years ago and

When we think of lasers, we often
think of them as hot or high energy. We usually associate them with things
cosmetic uses such as removing tattoos or other instances where intense heat is
needed. However, did you know they can also be used to cool atoms?

atoms have a relative velocity and as a result a relative momentum. When you
fire a laser photon with a specific momentum as calculated from the De Broglie
equation, the atom will then absorb the photon as seen in the image. When the
photon is absorbed, due to the random motion of the atom, it will reemit a
photon. This overall decreases the velocity and hence the kinetic energy of the
atom. And as kinetic energy decreases, so does the temperature. This cool
method was one of three used in creating the first Bose-Einstein Condensate! 1

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History of Laser

There are in fact many methods of
laser cooling. This includes methods such as: Sisyphus cooling, resolved
sideband cooling and a wide range of other fun methods. The most common method
however, is Doppler cooling. This was also the first method. The idea of this
originally stemmed from Maxwell’s theory of electromagnetism, and his idea that
E.M waves can exert a force on atoms but this was not experimentally
demonstrated until much later by Lebedev, Hull and Nicholas. 2 This is where the
idea of manipulating atoms with photons first began.

Then, closer to the late 70s, an
American scientist named Arthur Ashkin proposed the idea that these forces
produced by electromagnetic radiation can be used to not only trap an atom, but
also cool them.  His original idea, was
to use this technique to trap atoms in order to be able to closely study the
different interactions of atoms. From this interesting idea, several scientists
(one in particular called Wineland) were inspired to create a new and improved
method of cooling atoms using this idea. Their method involved using an
electromagnetic trap in order to contain the atoms; there the atoms would
collide with incoming photons from lasers. This was one of the early methods of
laser cooling and through this process; they managed to reach temperatures
around 40 Kelvin. 3

The Improvement
of Laser Cooling:

This original design of cooling
however was many years ago and since then, the capabilities of methods such as
Doppler Cooling have increased exponentially. The modern day methods are able
to cool atoms down to temperatures such as 150 MICROkelvin, absolutely towering
over the old techniques. Doppler Cooling, a method with this incredible result,
is used to cool atoms down to their Doppler cooling limit through the use of a
magnetic trapping force and an optical laser.