Laser wavelength standards

Practical realisation of the metre

NPL maintains frequency-stabilised lasers that provide the practical realisation of the metre within the UK. The light from these lasers is locked to a molecular absorption, resulting in an accurate and stable optical frequency (i.e. vacuum wavelength) output. 

The NPL frequency stabilised lasers are used to calibrate the optical frequency of lasers used in dimensional metrology, such as laser interferometers. A 10 m laser rail and 30 m tapebench can then be used to verify the performance of laser interferometer systems.

Calibration services

NPL offers several calibration measurement services using the frequency stabilised lasers:

• Calibration of the optical frequency (vacuum wavelength) of red (633 nm) He-Ne lasers (or similar).
• Calibration of the optical frequency (vacuum wavelength) of green (543 nm) He-Ne lasers (or similar).
• Verification of interferometer systems up to 10 m (laser rail) or 30 m (tapebench).
• Calibration of environmental compensation transducers.
• Compensated interferometer system calibration to 1.4 parts in 10⁷ (laser rail) or 2 parts in 10⁷ (tapebench).

These calibration services have been accredited by the UK Accreditation Service (laboratory No. 0478). NPL is certified to ISO 9001. A rapid, one week turnaround is possible by prior agreement.

For laser systems outside of these wavelengths bespoke measurements using the NPL femtosecond comb facilities can be arranged.

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