Evaporative Cooling
Due to the limitations of laser cooling, another method of cooling the atoms is needed to reach absolute zero. A method of lowering the temperature past the limitation is evaporative cooling. The principle behind evaporative cooling is that the higher energy atoms will escape leaving the lower energy electrons behind. When the energetic atoms escape, they take a significant amount of heat away and the atoms left will reduce in temperature. Some energy from the atoms left behind is lost in this process.
This method works similarly to hot water in a cup where the hotter water molecules boil off as steam. The steam which escapes contain far more energy compared to the rest of the water. The overall temperature of the water left is less hot.
This method works similarly to hot water in a cup where the hotter water molecules boil off as steam. The steam which escapes contain far more energy compared to the rest of the water. The overall temperature of the water left is less hot.
For this to work on the atomic scale, the atoms have to be slowed down first by laser cooling. This is because the atoms would normally move about 1600 kilometers per hour and all will escape. The colder the atoms, the slower they move and when they are less than a millionth of a degree above Absolute Zero, the atoms slow down immensely to less than 15 kilometers per hour. The process is used to lower the temperature of atoms below the limitations of laser Doppler cooling.
This was also done in the University of Colorado in their attempt to cool rubidium to the temperature at which it turns into a Bose-Einstein Condensate. They used an instrument to form a magnetic field which could hold the atoms like a cup and slowly lower the sides to let the atom with more energy to escape. The remaining atoms were colder and contained less energy. The temperature of the rubidium atoms were 20 Nano Kelvin. The aim of this experiment is to achieve another state of matter, the Bose-Einstein Condensate.
This was also done in the University of Colorado in their attempt to cool rubidium to the temperature at which it turns into a Bose-Einstein Condensate. They used an instrument to form a magnetic field which could hold the atoms like a cup and slowly lower the sides to let the atom with more energy to escape. The remaining atoms were colder and contained less energy. The temperature of the rubidium atoms were 20 Nano Kelvin. The aim of this experiment is to achieve another state of matter, the Bose-Einstein Condensate.