PhD Defense by Stefan Alaric Schäffer

Cavity-enhanced optical clocks

Optical atomic clocks are extremely good time-keepers as well as highly accurate sensors. By using optical cavities to enhance the interaction between light and atoms, we investigate novel approaches to improving current optical atomic clocks. We use ultra-cold strontium atoms to act either as a highly sensitive frequency discriminator, or as an active medium emitting coherent laser light. Both approaches are investigated experimentally, and their ultimate frequency precision is discussed. In addition, state-of-art performance of an optical lattice clock based on ytterbium is presented, showing absolute measurements of gravitational potential corresponding to 1.3 cm in height difference over the surface of the earth.