National Physical Laboratory

Iodine-Stabilised HeNe Reference Lasers

Robust laser head

Iodine-stabilised 633 nm
He-Ne reference laser head

Green Iodine

Iodine-stabilised 543 nm
He-Ne Standard
Reference Laser

  • Available at 633 nm (red) or 543 nm (green)
  • Fully compliant with the International Committee of Weights and Measures CIPM 1997/2001 'Mise en pratique' recommendations for the realisation of the metre
  • Frequency uncertainties (1 sigma):
    • 2 × 10-10 at 633 nm
    • 2.5 × 10-10 at 543 nm
  • Primary laser reference standards for realisation of the metre and precision length metrology
  • Calibration references for stabilised lasers
  • Optical frequency references for high resolution spectroscopy

Iodine stabilised He-Ne 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. NPL has long standing research and development experience of iodine stabilised lasers, going back over 30 years, and operates a number of systems in house as the UK national standard of length.

The robust iodine-stabilised 633 nm reference system is a new product that has a range of user-friendly properties:

  • Laser locks to an iodine component automatically within about 20 minutes after turn-on. Automatic lock monitoring without the need of a PC and logic output indicates whether laser is in lock
  • Output power > 0.3 mW
  • Unmodulated frequency output
  • Frequency lock not sensitive to acoustic or ground-borne noise and can lock in a much noisier environment

NPL has provided 633 nm red and 543 nm green iodine stabilised HeNe reference lasers to national measurement institutes and precision metrology companies worldwide. NPL can install and commission the lasers, and provide full training for system operators. Software is also available for automatic calibration and certification of test lasers.

Laser beat frequency monitoring systems for calibration of industrial stabilised lasers are also available.

System Wavelength 633 nm (provisional) 543 nm
Frequency stability
(10 s averaging time)
Typically 2 × 10-11 <5 × 10-11
Frequency uncertainty (1s) 2 × 10-10 2.5 × 10-10
Active stabilisation Iodine saturation using FM signal recovery Iodine saturation using FM signal recovery
Accessible 127I2 hyperfine components b21 of the 6-3 P(33) transition b11-b15 of the 28-0 R(106) transition
Iodine absorption cell NPL high purity NPL high purity
Iodine cell sidearm temperature Room temperature 0 ± 2 °C Peltier cooled
Single frequency tuning range Not applicable (tunes to only one iodine component) 500 MHz
Output power 300 µW 30 µW
Output polarisation Linear, horizontal Linear, horizontal
Plasma tube Internal mirror Internal mirror
Continuous frequency lock over 24 hours for ambient temperature 20 ± 5 °C YES YES
Automatic lock-in YES YES
Manual tune/lock-in NO YES
Stabilisation electronics Standard 19” rack Standard 19” rack
AC line voltages 110-120 V, 220-240 V 110-120 V, 220-240 V


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Last Updated: 25 Mar 2010
Created: 11 Aug 2007


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