75 Years of EPR. EPR Milestones in 60 Years Bruker History

After the discovery of EPR by E.K. Zavoiski 1944 in Kazan (E.K. Zavoiski Zhurn Eksperimentalnoi i teoreticheskoi fiziki 15:344, 1945; E.K. Zavoiski J Phys USSR 9:211-245, 1945) EPR spectrometers were home-built and mostly dedicated to a special application. But commercial instruments in the contrary must be universal and cover a broad range of methods and applications. Therefore they should be compatible with any valuable accessory and offer optimal sensitivity and resolution and they should be easily convertible to other frequency bands and new methods of investigation. The sensitivity of the EPR has increased in consecutive steps, from a S/N of 200 for the week pitch in 1970 up to 3000 with a new microwave source and a new super highQcavity (SHQE). So far all the main requirements for a universal cw-EPR spectrometer for scientific applications have been met successfully. In 1987 with the ESP380 the first commercial pulse EPR spectrometer was introduced. This was no more an improvement of the previous EPR, this was a revolution in EPR instrumentation. Some necessary microwave-components were not available on the market and had to be developed and produced by the company itself. To cope with the extremely short relaxation times, necessitating high bandwidths, a new range of resonators had to be developed. In cooperation with the Eaton-group Bruker has introduced a rapid scan accessory for the ELEXSYS spectrometers increasing sensitivity for almost two orders of magnitude. The rapid scan may also give new possibilities for EPR imaging in the much less sensitive S- and L-bands for biomedical research.