National Physical Laboratory

Frequency and Laser Wavelength Calibration

Beat SystemBeat frequency monitoring systems of
a stabilised laser against an NPL iodine stabilised laser 
The frequency of single mode frequency stabilised lasers can be calibrated by reference to iodine stabilised reference lasers. Measurements are made by a beat frequency comparison between the test and reference lasers. With this technique, the beams from the reference and test lasers are combined (see below) and focussed onto a fast detector. The resulting beat frequency signal is the difference frequency between the two lasers, and allows calibration of the test laser. This calibration service is available for frequency stabilised HeNe lasers at 633 nm and 543 nm. We can also calibrate optical frequency standards between 1510 nm and 1550 nm using our acetylene stabilised diode lasers. Calibration of other visible laser wavelengths is also possible using our femtosecond comb systems.

frequency stabilised laser calibration
Schematic showing the calibration of a frequency stabilised laser

An accuracy of comparison of better than one part in 1010 of the optical frequency is possible for the most stable 633 nm HeNe lasers. However, most commercially available lasers have short-term stabilities of 1 part in 109, and can be significantly worse than this. The calibration uncertainty therefore generally reflects the short-term reproducibility of the test laser.

Calibration of unstabilised (multi-mode) HeNe lasers at 633 nm and 543 nm is also possible, with a typical accuracy of comparison a few parts in 108 of the optical frequency.


Customer Service tel: +44 20 8943 6796

Last Updated: 25 Mar 2010
Created: 12 Aug 2007


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