NPL has an extensive programme of research into the development of new optical frequency standards for applications to time, frequency and length metrology.
Frequency standards based on narrow optical transitions in single trapped ions or neutral atoms confined in an optical lattice are being developed as the next generation of primary frequency standards. Other optical frequency standards provide high accuracy working standards for particular applications. These include iodine-stabilised helium-neon lasers for use in dimensional metrology and acetylene-stabilised lasers for applications in the telecommunications industry.
Optical 'flywheel' oscillators based on lasers stabilised to high finesse optical cavities are being studied to provide high stability short-term frequency references. These form a critical component of any high accuracy optical frequency standards. In addition this technology is being applied in experiments to measure fundamental physical constants such as the Rydberg constant.
Techniques for optical-microwave frequency intercomparison using femtosecond optical frequency combs are being developed and evaluated. These techniques are used to measure optical frequencies relative to the caesium primary frequency standard and allow optical frequency standards to be operated as optical clocks. The potential of installed fibre networks for remote comparison of optical frequency standards at the highest level of accuracy is also being investigated.