National Physical Laboratory

Dimensional Laser Wavelength Standards

NPL is the home of the frequency-stabilised lasers that provide the practical realisation of the metre within the UK.

NPL is the home of the frequency-stabilised lasers that provide the practical realisation of the metre within the UK.

These lasers have a very stable vacuum wavelength (i.e. a very stable frequency) that is obtained by controlling the frequency to that of an atomic or molecular absorption. There are a number of internationally agreed laser systems that can be used to realise the metre.

For dimensional metrology, where precision measurements are generally made using laser interferometry, the laser wavelength can be calibrated using one of NPLs iodine stabilised lasers. The most commonly used reference laser operates at 633 nm. For frequency metrology in telecomms near 1550 nm, traceability is provided via one of NPLs acetylene-stabilised lasers.

The definition of the metre closely links realisation of the metre to the realisation of the second. In addition to the gas-cell stabilised lasers already discussed, NPL is undertaking research into optical frequency standards based on both ion traps and lattice clocks.

Laser Wavelength Standards products & services

  • NPL offers a routine service for the verification of interferometer system accuracy.
  • Iodine-stabilised HeNe lasers are used in many national standards laboratories and measurement institutes for the practical implementation of the SI unit of length, the metre. Such systems offer an accurate and effective means of delivering traceability for length and dimensional measurement within the precision engineering and manufacturing industries.

Laser Wavelength Standards Units

The SI unit of length is the metre. Since 1983 the metre has been defined as “the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.”

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