Introductionlaser attenuator
The SA20 laser attenuator is intended to control the transmitted power of small/medium CO2 lasers
in order to assist in processing.
The attenuator uses Brewster plates mounted in a ‘Vee’ configuration to eliminate lateral beamoffset.
The plates may be of standard (uncoated) or enhanced type.
SA20 attenuators work only with linearly polarized laser beams.
Rotation of the plate pair about the optical axis causes the ‘unwanted’ power to be reflected and
dumped into the main body of the unit.
Available models
SA20 incorporates 2 standard Brewster plates, and transmits 11% to 100% of incident linearly
polarized radiation.
SA20-E incorporates 2 enhanced Brewster plates, and transmits <0.5% up to >98% of incident
linearly polarized radiation.
Accessory SA15-WJ external water jacket, allows use of the SA20 unit to higher power levels.
(NB: model SA20 is the same physical size as the SA15 unit, and the water jacket accessory fits both

Technical specifications
Dimensions : See figure 79.201.
Method of operation : Rotation of Brewster plate pair.
Calibration : Engraved T% (assumes linear pol input)
Lateral beam offset : Nil
Angular deviation : <2 arcminutes
Cooling : Air cooled (water-cooled with SA15-WJ)
Construction : Al. alloy body, black anodised, with
ZnSe Brewster plates. End bearings (2).
Connection : Via ULO Optics coupling rings,
52.0mm dia x 1.5mm pitch at each end.
Max power : 100W air-cooled. (250W with SA15-WJ)
Clear aperture : 20.0mm diameter.

Associated equipment
SA20 units fit directly to ULO Optics ‘OPG’ piping (data 61.1) and to lateral adjustment units
LAU25 and LAM25 (section 72).
The accessory water-cooling jacket SA15-WJ is factory-fitted if required, and cooling is via 6/4 size
Applications note
Small/medium power lasers often have, as the only means of ‘average’ power control, a method of
changing the mark/space ratio when run in pulsed mode. This is unsatisfactory in some laser
SA20 attenuators allow control of transmitted power with cw lasers and with no change of
mark/space ratio for pulsed operation. Model SA20 is often chosen for use with an expanded laser
beam, usually up to a full beam diameter of about 16mm).
Quality note
Brewster-based systems can be extremely sensitive to errors of plate flatness on a scale of fractions
of one visible fringe of error.
ULO Optics 2-plate systems are tested to ensure no more than 10% beam ovality (at 10.6μm)
at 4 metres from the unit.