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.
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.
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.
Specifications
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 |
| Options | |
| Detector comparator stage & software |  |
| Transfer standard detectors | |
NPL support includes the installation of the facility and training in its use
For further information, please contact: Bill Hartree