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Quantitative Atomic Gas Spectroscopy for the Determination of the Boltzmann Constant and Primary Thermometry
This project aims to enhance a newly developed technique using high-resolution quantitative spectroscopy to directly measure the thermal energies carried by atoms in a gas. A frequency-stabilised, tunable laser source is used to probe electronic transitions in alkali metal atom vapours (like rubidium and cesium). The spectral properties, like the optical frequency width, of the transition contains information about the speed and energy of the atoms, which can be used to derive the gas temperature and the Boltzmann constant. Since beginning in 2009, we have been able to determine the Boltzmann constant with an accuracy of 4 parts in 10 000.
The Boltzmann constant is a fundamental physical quantity that relates the concepts of energy and temperature. Currently, there is a global scientific effort to measure this constant with greater precision than has ever been done before, with the target of reaching errors as low as 1 part in 1 million. This degree of precision is motivated by the desire to redefine the kelvin (the unit of temperature) to more closely reflect its physical relation to energy. This is in contrast to the current situation, where temperature is referenced to an arbitrarily chosen, special state of a particular substance (known as the triple-point of water). This represents a continuation of an international effort to tie the definitions of base units (like that for time, length, mass, etc.) to more fundamental quantities like physical constants.