© 2021 Thorlabs
2 Operating Principle
8
2.4 Hysteresis of Piezoelectric Materials
Hysteresis is a well known effect in ferromagnetic and ferroelectric materials.
Due to the hysteresis of the PZT (lead zirconate titanate) material used for the Deformable Mir-
ror, the mirror stroke depends not only on the actual applied control voltages, but also on the
"history" of recent changes. This "memory effect" is caused by internal states of the material
that differ for increasing and decreasing voltages.
Due to the hysteresis effect, the mirror stroke does not follow the same track each time the con-
trol voltage is increased or decreased. The diagram below shows a typical hysteresis curve of
the spherical deformation at a voltage oscillation between 0 V and 300 V (i.e., the same voltage
change is applied to all 40 mirror segments).
DMH40 Hysteresis Curve
The hysteresis is expressed as the maximum difference divided by the maximum stroke
between the two tracks. For this particular sample the hysteresis is 3.5 µm or 14% related to
the total stroke range of 24.5 µm. The max hysteresis of the used material for the DMH40 is
25%.
For this reason, a control voltage of 150 V (half of the maximum control voltage) will not always
produce a flat mirror (zero spherical deformation); the previous control voltage needs to be
taken into account. For instance, a flat shape is achieved when the voltage is increased from
0V towards 171V and the same shape is achieved when decreasing the voltage from 300V
down to 123V.
Note
The maximum concave and the maximum convex stroke may differ slightly as well!
Hysteresis Compensation
The Thorlabs Deformable Mirror software incorporates a hysteresis compensation. The driver
software monitors all consecutive voltage changes for each segment individually and applies a
corrected voltage, calculated based on a mathematical algorithm, to the mirror segments.
Consequently, when controlling the DMH40 via the Thorlabs Deformable Mirror software, the
mirror behaves almost like a mirror without a hysteresis effect. Both tracks of the hysteresis
curve will collapse to a straight line.
Summary of Contents for DMH40-F01
Page 1: ...Piezoelectric Deformable Mirror 2021 DMH40 M F01 DMH40 M P01 Operation Manual...
Page 2: ...Version Date 1 1 15 Apr 2021 Copyright 2021 Thorlabs...
Page 56: ...2021 Thorlabs 51 DMH40 7 4 Dimensions DMH40 xxx Imperial...
Page 59: ...2021 Thorlabs 7 Appendix 54 7 8 Certifications and Compliances...
Page 66: ...www thorlabs com...