The NPL’s optical reference cavity is used to realise the most stable laser in the UK and one of the most stable in the world. It is made in ultralow expansion glass and has one of the most stable lengths ever realised, with a residual length fluctuation 50 times smaller than the diameter of a proton over a macroscopic length of 48.5 cm! For instance, fractionally this is equivalent to a wobble of the distance between the earth and the sun of less than the width of a human hair! This exceptional length stability is transferred into frequency stability, realising a so called ultrastable laser.
Constantly improving the stability of lasers has an impact on a variety of fields, in particular on the measurement precision of time and frequency. This measurement precision is at the base of critical sectors of our modern society, such as communication, synchronisation, localisation and navigation. We all rely on these critical systems in our everyday life, their performance affects our quality of life and sets the pace of the technological development and economic growth of our society.
These state-of-the-art ultrastable lasers can also serve as benchmark systems for the laser industry to measure frequency stability, spectral linewidth and phase noise power spectral density of commercial lasers.
The definition of the SI second is today based on frequency standards operating in the microwave domain. The measurement of time and frequency has experienced an incredible improvement in the last few decades thanks to the development of new frequency standards operating in the optical domain. The work on ultrastable lasers contributes to this development and to a wider use of these new optical time and frequency standards. It will lead to an international redefinition of the SI second with consequent new possibilities of scientific discovery, and technological and economic progress for our society.
NPL is the natural environment for the development and evolution of the next generation of standards such as optical time and frequency standards. NPL’s focus on metrology strategically strengthens the foundations of our modern society with benefits to our wider community.
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