Title: Ultra precise atomic clocks and their applications Speaker: J.W. Thomsen, The Niels Bohr Institute, Copenhagen Time: Thursday, March 24, 15.15 to 16.00 Place: Fysisk Auditorium Abstract: Alkaline Earth elements have attracted considerable attention, theoretical as a well as experimental, over the past years. One of the main motivations for studying these atoms is their use for optical atomic clocks and high precision measurements. In the talk I will present the first results for the measurement of an alternative clock transition in magnesium the 1S_0 - 3P_2 electric-dipole forbidden transition. In the talk I will also rapport on our progress on direct spectroscopy of ultra-narrow optical transitions for laser frequency stabilization. In contrast to stabilization against a reference cavity which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from the thermal noise problem. Spectroscopy of ultra-narrow optical transitions is typically in a very highly saturated regime in which non-linear effects such as bi-stability play an important role. We predict laser linewidths below 1 mHz using current experimental techniques. Jacob Sherson and Aurélien Dantan Coffee, tea and cake will be served at 15.05 Dr. Jacob Friis Sherson Institut for Fysik og Astronomi Aarhus Universitet Ny Munkegade 120 8000 Århus C Tel.:8942 3680