School of Physics and Astrophysics

Postgraduate research profiles


Daniel Creedon

Phone: (+61 8) 6488 3443


Start date

Feb 2008

Submission date

Feb 2012

Daniel Creedon


Ultra-stable Cryogenic Whispering Gallery Mode Maser Based on Electron Spin Resonance of Paramagnetic Ions in Sapphire


This project aims to investigate and develop a new type of atomic clock based on stimulated emission of microwave radiation in a sapphire resonator. The recently discovered clock scheme exploits a spin resonance of residual paramagnetic impurities in the sapphire, in concert with sharp electromagnetic resonances which may be excited by injecting microwave radiation. These resonances, so called Whispering Gallery (WG) modes, have Q-factors on the order of several billion when the clock is operated at around 7 degrees above absolute zero. The system exhibits the potential to rival the frequency stability of current world-leading Cryogenic Sapphire Oscillators (CSO), but in a simplified way with fewer active components and control systems. Development of this novel CSO maser will potentially see a new generation of ultra-stable frequency standards at a level of simplicity never before achieved. The system requires only that we excite the sapphire at a specific ‘pump’ frequency, and stabilise the resulting maser output frequency. This is achieved by operating at the frequency-temperature turnover point of the chosen WG mode within the electron paramagnetic resonance (EPR) bandwidth. The result is an ultra-stable, high power maser output at 12.038 GHz. The project is following several avenues of investigation including the development and implementation of a Coherent Population Trapping scheme. We plan to investigate the behaviour of the system in the low temperature limit of several thousandths of a degree above absolute zero, as well as attempting to reliably implement and stabilise operation of the maser in a bimodal regime. Recent results indicate an interesting cross-relaxation process occurring in the maser, which warrants modeling and investigation of the complex spin-spin and spin-lattice interactions involved.

Why my research is important

Sources of precision signals (frequency standards) like this "clock" are indispensable in a wide range of scientific and industrial applications. Global Positioning System (GPS) satellites contain atomic clock frequency standards to provide precise position, velocity, and time information to GPS receivers anywhere in the world. This is important not only for civilian use, but for military tracking and navigation, geological surveying, and countless scientific measurement applications. Ultra-stable frequency standards are also used for high-resolution radio astronomy, performed using the Very Long Baseline Interferometry (VLBI) technique. This will be used in the Square Kilometer Array (SKA) radio telescope project, for which Western Australia is a shortlisted candidate location. In addition, atomic clock frequency standards are used to realise the official definition of the second, and a weighted average of more than 250 atomic clocks worldwide forms the basis of Coordinated Universal Time (UTC). Scientists also use frequency standards like the one developed in this project for precision tests of fundamental physics. Such high stability sources have been used in experiments which challenge and test the predictions of widely accepted scientific theories such as Einstein’s Theory of Relativity, Local Lorentz Invariance in electrodynamics, CPT Symmetry (Charge/Parity/Time) and the constancy of physical quantities such as the speed of light and the fine structure constant. Frequency is the most sensitive experimental parameter because clocks like these allow it to be measured with such exquisite accuracy. The continued development of precise frequency standards is important because it allows improved accuracy in the measurement of any effect which can be seen directly or indirectly in terms of a change in frequency.


  • Australian Postgraduate Award


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Last updated:
Thursday, 17 April, 2014 9:11 AM