 While every implementation of each kind of ALF is different, the vapor cell in each is relatively similar. The thermodynamic properties of vapor cells in filters are carefully controlled because they determine important qualities of the filter, for instance the necessary strength of the magnetic field. Light is let into and out of this vapor chamber by way of two low-reflection windows made of a material such as magnesium fluoride. The other sides of the cell may be of any opaque material, though generally a heat-resistant metal or ceramic is used as the vapor is usually kept at temperatures upwards of 100°C.
