New silicon resonator keeps the frequency of a laser more stable than ever before - Important for even better optical atomic clocks.
A laser with a frequency stability so far unequalled: This is the result of a research cooperation of the Physikalisch-Technische Bundesanstalt (PTB) within the scope of the Excellence Cluster QUEST (Centre for Quantum Engineering and Space-Time Research) with colleagues from the American NIST (National Institute of Standards and Technology)/JILA. Their development, about which they report in the scientific journal "Nature Photonics", is important for optical spectroscopy with highest resolution, e.g. of ultra-cold atoms. But, above all, an even more stable interrogation laser is now available for use in optical atomic clocks.Optical atomic clocks require laser sources that radiate light with an extremely constant frequency. Commercial laser systems are not suited for this purpose without additional measures. However, this can be achieved by stabilizing them, for example, with the aid of optical resonators.
These are composed of two highly reflecting mirrors which are kept at a fixed distance by means of a spacer. The decisive aspect is the following: In analogy to an organ pipe, the resonator length determines the frequency with which light can begin to oscillate in the resonator. Consequently, a resonator with a high length stability is required for a stable laser, i.e. the distance between the mirrors must be kept as constant as possible.