If you don't know what ESR is, click here.

Conventional ESR systems tend to operate at frequencies below about 10 GHz. In theory, systems operating at higher frequencies are just the same, but simply 'scaling up' conventional instruments to the mm-wave region leads to serious practical problems.

The main problems are:

Circuit diagram of simple mm-wave ESR system.

The St. Andrews system gets around the problems by employing the Quasi-Optical Circuit methods which our group specialise in. The instrument we have developed was built in conjunction with Prof. P. C. Riedi's ESR group at St. Andrews. They contributed considerable experience in ESR and in the use of the superconducting magnets required to reach the high applied fields needed for mm-wave ESR.

In the St. Andrews MM-Wave ESR system the sample is placed inside a supercooled (to 4 Kelvins) magnet which we can use to apply H-fields up to 8 Teslas. Using Quasi-Optics we can illuminate the sample with a controlled signal in the 80 GHz to 300 GHz frequency range. This field and frequency are much higher than conventional ESR, hence this type of system is often called a 'high-field ESR' instrument. The high field/frequency allows the instrument to have a sentivity and resolution which is between 100 times and 100,000 times better than conventional instruments.

The system is used for 'in house' research on magnetic materials and thin films. It is also available for use by external researchers who wish to make measurements on other samples. The system is of particular value to chemists and biologists who wish to analyse small samples of weakly interacting materials, and materials whose resonant details are too fine to be resolved by conventional commercial instruments.

The QO arrangement means the same basic system can be used over the whole frequency range of interest. It has losses, etc, which are much lower than in competing instruments which try to use ordinary waveguide at these frequencies. As a result, it is comparatively easy to use and gives very clear results. The optical approach also means it can employ a novel polarisation discrimination approach which significantly improves its performance.

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University of St. Andrews, St Andrews, Fife KY16 9SS, Scotland.