National Physical Laboratory

Laser Stabilisation Facility

This facility will work in conjunction with a variety of lasers from the ultraviolet to the infrared to provide a well-collimated, stable beam of monochromatic radiation.

Laser Stabilisation Facility
Laser Stabilisation Facility 

NPL's laser stabilisation facility can be used to externally stabilise a variety of laser sources at known wavelengths, for radiant intensity. The system is used in conjunction with the primary standard cryogenic radiometer, filter radiometer calibration facility and laser-based spectral responsivity systems.

At the heart of the laser stabilisation system is a pockels electro-optic modulator working in conjunction with a monitoring photodiode and a servo control unit. The pockels cell acts as a variable retardation plate on light from a polarised laser source. Rotation of the polarisation axis increases with the control voltage across the cell, whilst the transmission of the cell is dependent on the angle between the beam polarisation axis after leaving the cell and the axis of the output coupler.

Laser Stabilisation Facility Diagram

The beam is imaged via a spatial filter onto a pinhole to reduce any discrepancies in the profile of the radiation. A further iris selects the required beam diameter. A beam splitter is used to direct 8% of the beam towards the monitoring diode. The output of the monitoring diode is compared to a reference voltage in the control unit, which in turn provides proportional control of the pockels cell, which reacts to maintain constant power output. In this way the power at the beam splitter point is stabilised.

The laser beam stabiliser can be thought of as acting like a noise rejection filter, rejecting radiant power fluctuations present in a laser beam.

The laser stabilisation facility, with appropriate modulators, can be used with lasers covering the spectrum from the ultraviolet to the far-infrared, 250nm to 11µm.


The specific laser stabilisation facility provided would depend on the customer spectral requirements, which in turn will select the appropriate optics, modulator and spatial filtering.

UV, Vis, Near IR facility
For use in range 250 nm to 1100 nm
Clear aperture 5 mm x 5 mm
Noise reduction 26 dB @ 1 Hz
Helium Neon laser > 10 mW at 632.8 nm
Nd YAG laser > 10 mW at 1064 nm
Krypton ion laser Fixed wavelengths 350 nm to 800 nm
Mid-Infrared facility
For use in range 3 µm to 5 µm
Clear aperture 4 mm x 4 mm
Helium neon laser 6 mW at 3.39 µm
Far-Infrared facility
For use in range 9 µm to 11 µm
Clear aperture 4 mm x 4 mm
Noise reduction 18 dB @ 1 Hz
Grating tuned CO2 laser Fixed wavelengths from 9 µm to 11 µm
Detector comparator stage & software Transfer Standard Detectors
Transfer standard detectors 
Transfer standard detectors

NPL support includes the installation of the facility and training in its use.

Contact us for further information

Call the Instruments team on: 020 8943 6539

Last Updated: 10 Apr 2017
Created: 31 Jul 2007


Please note that the information will not be divulged to third parties, or used without your permission