Towards very low temperatures

With the liquefaction of helium performed by Kammerling Onnes in 1908, all known gases had been liquefied. The discovery of new and unexpected physical phenomena like the superconductivity and the connection of these phenomena with the new quantum theory introduced by Planck in 1900 opened new fields of research what motivated the physicists to develop new techniques to approach more and more the absolute zero temperature (-273,15 deg C). If the refrigeration at the temperature of liquid helium (4.2 K) is used in on industrial way in particular for the medical imagery (MRI) or the production of helium, the lower temperatures remain in the field of laboratory or great scientific projects (particles collider, nuclear fusion). Thus, it is possible to approach the absolute zero today (less than 1 mK), by combining several techniques of refrigeration like evaporation, adiabatic demagnetization or the dilution of helium 3 in helium 4. (author)