Laser Cooling
Laser cooling is an effective method of cooling matter to the brink of absolute zero. It utilizes a laser to slow down the individual particles nearing to a halt. This was first theorized in 1975 but was only functional in 1997 led by Steven Chu, Claude Cohen-Tannoudji and William D. Phillips who were all rewarded the Nobel Prize in Physics. They achieved the temperature of 240 micro kelvins with a cloud of sodium atoms.
As temperature is also the speed at which an atom moves by converting the kinetic energy present in the atom, scientists are able to lower the temperature further than they could before with laser cooling. The photons emitted from the laser bounce off the atoms slowing down the speed of the atoms repeatedly with every bounce. This works similarly to trying to slow down a bowling ball with table tennis balls. The bowling ball represents the atoms as it is significantly heavier and larger compared to photons which are represented by the table tennis balls. If enough of the table tennis balls bounce against in bowling ball, the bowling ball will eventually come to a stop.
As temperature is also the speed at which an atom moves by converting the kinetic energy present in the atom, scientists are able to lower the temperature further than they could before with laser cooling. The photons emitted from the laser bounce off the atoms slowing down the speed of the atoms repeatedly with every bounce. This works similarly to trying to slow down a bowling ball with table tennis balls. The bowling ball represents the atoms as it is significantly heavier and larger compared to photons which are represented by the table tennis balls. If enough of the table tennis balls bounce against in bowling ball, the bowling ball will eventually come to a stop.
The light emitted from the laser also has to be of a specific frequency as atoms react differently to each wavelength of light. The laser also needs to have the ability to change the wavelength of the light emitted as the frequency of light needed to react and bounce off each atom changes according to the speed of the atom due the Doppler Effect. This shift caused by the Doppler Effect means that the slower the atoms move, light of lower frequency is needed. If the light emitted have incorrect wavelengths, the photons will go right by the atoms and not affect the atoms.
The atoms also have to be placed in the center of several beams of lights for this to work. A cloud of atoms are placed in something called a “laser trap”. The six lasers are aimed at 90 degrees from each other facing towards the middle where the cloud of particles is situated. The atoms which fall into the “laser trap” cannot escape as the beams will push them back to the middle. The atoms cannot be placed in a conventional container to those used for liquefying the natural gasses as the heat of the container, though minute would heat the atoms back up. As the laser trap doesn't physically touch the atoms, no heat is transferred from the laser trap to the atoms.
Unfortunately, this method can only cool matter to 240 micro kelvins as the photons which bounce off the particles are absorbed by others. This limitation means that another method is needed to lower the temperature of matter at the final steps to absolute zero. Another cooling method used to overcome this is magnetic evaporative cooling.
The atoms also have to be placed in the center of several beams of lights for this to work. A cloud of atoms are placed in something called a “laser trap”. The six lasers are aimed at 90 degrees from each other facing towards the middle where the cloud of particles is situated. The atoms which fall into the “laser trap” cannot escape as the beams will push them back to the middle. The atoms cannot be placed in a conventional container to those used for liquefying the natural gasses as the heat of the container, though minute would heat the atoms back up. As the laser trap doesn't physically touch the atoms, no heat is transferred from the laser trap to the atoms.
Unfortunately, this method can only cool matter to 240 micro kelvins as the photons which bounce off the particles are absorbed by others. This limitation means that another method is needed to lower the temperature of matter at the final steps to absolute zero. Another cooling method used to overcome this is magnetic evaporative cooling.