ULO Optics manufacture beam-delivery modules, based on the use of Brewster plates, for two
(1) Attenuators, intended to control the transmitted power of CO2 laser beams,
(2) Isolators, for stopping unwanted back-reflections from reaching the laser.

The units described in data sections 79.xx may, in general, be used in either role.
Each consists of two ZnSe Brewster plates mounted in a ‘Vee’ configuration to eliminate lateral
beam deviation, and to allow internal dumping of unwanted laser power.

Product types
Attenuator/isolator products divide into three broad classes:
(A) Manually Controlled Attenuators for use with low and medium power lasers. These units
overcome a processing problem often encountered with smaller CO2 lasers, in that electronic control
of emitted power takes place only by altering a ‘mark/space’ ratio when the laser is being run in
pulsed mode. Models SA15 and SA20 attenuators may be used with lasers such as Synrad and Coherent Diamond’
to control the transmitted power either in cw mode (Synrad) or without changing the mark/space of
the pulse.

(B) Motorized Attenuators work on the same principles as the manually controlled type, but are motor
driven and have electronic feedback.
The motor-driven type of attenuator may be used for power stabilization or as part of a system to
ramp/control transmitted power under instruction from a CNC controller or computer.

(C) Isolators are manually controlled units similar in most respects to the manually controlled
attenuators, but larger and having more sophisticated internal (water-cooled) beam dumps.
The Umicore Laser Optics isolators may be used in high power laser systems, and are especially useful where
competitive products (isolator or ‘AFTR’ mirrors) will not withstand high or prolonged exposure to
back-reflected radiation.

Manually controlled attenuators see data sections 79.10, 79.20
Motorized attenuators see data sections 79.30, 79.40
Isolators/Attenuators see data sections 79.80, 79.81, 79.82, 79.83

Operational notes
There are certain technical features which apply to all attenuators/isolators based on the use of
Brewster plates. Also see general technical section 79.80.
(1) Attenuators based on polarization principles rotate the emitted plane of polarization into the
azimuth of the plane of incidence/reflection of the plates.
The transmitted plane of polarization will rotate as the Brewster plates are rotated. If maintenance
of plane of polarization is critical in a system, then a second, fixed orientation (set of) plate(s) will
be needed to restore the original orientation of polarization.
(2) Brewster plates will ‘dump’ any cross-polarized radiation in the incident laser beam. This means
that the isolator (HPA) units may not transmit 100% of the incident radiation, even when correctly
set to maximum transmission, if the incident laser beam is not truly linearly polarized.
(3) When used to dump back-reflected power, the azimuth of the plates needs to be set for maximum
outgoing transmission. In this case the incident laser polarization will not be rotated.
A phase-retarder unit must be used after the isolator unit.
(The back-reflected beam will be cross-polarized to the outgoing beam, and will be internally