Laser spectroscopy

High-precision spectroscopy of simple atomic and molecular systems sets the benchmark for tests of bound-state Quantum Electrodynamics (QED) theory. Therefore we measured the X-EF transition in H2 at 2×202 nm using the Ramsey-comb spectroscopy technique. We have determined the transition frequency with an accuracy of 73 kHz. This result is a two orders of magnitude improvement of the previous result [1] and provides a slightly more accurate value of the dissociation energy, which is an interesting quantity for tests of QED [2]. We are currently extending our method to the extreme ultra-violet spectral region to measure the 1S-2S transition in singly ionized helium at ~30 nm, which could help resolve the proton radius puzzle. [1] S. Hannemann et al., Phys. Rev. A 74, 062514 (2006) [2] J. Liu et al., J. Chem. Phys. 130, 174306 (2009)