The Sapphire Atomic Clock:

( located at University of Western Australia ( UWA) )

The actual sapphire atomic clock at UWA, commonly known as the 'Cryogenic Sapphire Oscillator'. The output signal is so precise that it is equivalent to a clock that would lose or gain a second every 63 million years.

The sapphire at the heart of the clock sits around 1.5m underground in the large blue dewar flask (bottom of photo) in a vacuum chamber submerged under several hundred litres of liquid helium (−268.93 °C). The large racks of equipment are the supporting microwave electronics for the clock that allow the oscillator to lock to the "whispering gallery mode" resonance of the sapphire, a temperature control system, and equipment for processing and measurement of the clock signal

The sapphire at the heart of the UWA sapphire atomic clock. A man-made, highest purity HEMEX-grade sapphire 5cm in diameter x 3 cm tall. Natural sapphires are coloured due to the presence of large concentrations of paramagnetic impurities (up to several percent by weight). Our man-made crystal is completely colourless as only parts-per-billion concentrations of these impurities are present. Interestingly, this vanishingly small population of paramagnetic impurities is crucial for the world leading performance of the clock. Technically speaking, the impurities result in a Curie Law paramagnetic susceptibility which counteracts the temperature dependence of permittivity of the sapphire. This allows the effect of temperature fluctuations in the sapphire resonator to be nullified to first order which is absolutely key to its performance.

Daniel Creedon PhD student
( in the research group at UWA that developed the sapphire clock.)