Wolfgang Haensel

Absolute frequency measurement of 40 Ca + in a Paul trap

We report on an absolute frequency measurement of a single ⁴⁰Ca⁺ ion in a linear Paul trap at the 10^-15 level. A Cs-referenced frequency comb is used to measure the probe laser exciting the 4s²S_1/2 to 3d²D_5/2 quadrupole transition at 411 THz. A careful analysis of the estimated systematic shifts is given as well as an outlook on possible improvements.

Hidden correlation in the CEP noise of mode-locked lasers

Stabilizing the carrier-envelope phase (CEP) of mode-locked laser sources has made tremendous progress in recent years, enabling the generation of isolated attosecond pulses and precision frequency metrology at the 10−18 uncertainty level. While some laser types can be very well stabilized, other interesting laser materials have proven notoriously difficult or even impossible to be CEP stabilized. The exact mechanisms behind these problems are poorly understood. Here, we present a novel diagnostic method that provides unprecedented insight into the inner workings of noise generating mechanisms in laser oscillators.

Ultra-low phase noise frequency-comb-based microwave generation and characterization

We report on the generation of ultra-low phase noise microwave signals at 12GHz by photodetecting the pulse train of an Erbium-doped fiber-based optical frequency comb phase locked to a ultra-narrow linewidth ultra-stable laser at With advanced photodetection techniques and homemade phase noise measurement apparatus, our experiment demonstrates generation of a microwave source with absolute phase noise below -170dBc/Hz at 10kHz and above, and below -100dBc/Hz at 1Hz from a 12GHz carrier, which pushes even further the best results reported so far.