Newport FSM-300, User Manual

Page: 14 / 42

14 Fast Steering Mirror Technology
Figure 2: FSM mirror head showing the eight basic components.
The voice coil actuators
1
provide the torque necessary to tilt the mirror sub-
strate. Four actuators are mounted behind the mirror, one in each quadrant.
Voice coils are connected in pairs along the diameter of the mirror and
operate in a push/pull manner, rotating the mirror about the axis that bisects
them. Two actuator pairs (four coils) plus a coordinate transformation are
used to produce two orthogonal rotations
θ
x
and
θ
y
about the
X
and
Y
axes.
The high force generated by four distributed actuators rotates large mirrors
more effectively than the one actuator used in galvanometer scanners. The
distributed force combined with thick optics enables the FSM mirror head to
preserve static and dynamic surface flatness, excellent positional resolution,
large angular range and rapid motion. The coil portion of the actuators is
placed within the support structure and contacted to a heat sink such that heat
produced in the actuator is dissipated far from the mirror surface, thus
minimizing thermal distortions.
A flexure suspension system is used to support the mirror carrier that holds
the mirror. This system allows free rotation about orthogonal
X
and
Y
-axes
while constraining side-to-side motion, rotation about the normal (
Z
) axis
and “pogo” motion along the
Z
-axis. Different types of flexure systems are
used for different FSM applications. Some flexure systems are stiff (large
spring constant) and offer a relatively stable and repeatable power-off mirror
1
Historically, voice coils were first used in loudspeakers, from which they derive their name. A linear
voice coil consists of a tubular coil of wire situated within the radially oriented magnetic field of a
permanent magnet. When current flows through the coil, a force is generated that causes axial (linear)
motion. This linear motion is then used to move the mirror.