PAN Membrane Deformable Mirrors for Adaptive Optic Applications

PAN is a membrane deformable mirror suitable for adaptive optics. It is composed of a thin, reflective and conducting membrane which faces an actuator structure.

The structure acts as a set of capacitors sharing the membrane. The layout of the PAN mirror is depicted in the following figure.

As the membrane is fixed only at the borders, an electrostatic pressure can be created by applying a voltage to the actuators. This pressure can deform the membrane as per the following formula:

where
d is the distance between the membrane and the actuator
ε₀ is the dielectric constant.

This pressure pulls the membrane to the j-th actuator, which results in a local curvature of the membrane. The membrane can be deformed so as to produce desired shapes by modulating the actuator voltages and taking into account their disposition above the membrane. The shape created by one single actuator is known as influence function. The membrane shape is influenced by the set of voltages as per the Poisson equation given below:

where
M(x,y) is the membrane shape
T is the membrane mechanical tension
p is the electrostatic pressure

Advantages of PAN Deformable Membrane Mirrors

When compared to other common devices for adaptive optics such as bimorph mirrors or thermal mirrors, they have the following advantages:

• Low cost
• Large dynamic behaviour
• Achromaticity
• No hysteresis
• Relatively high optical load
• Good performance in aberrations generation
• Low power consumption.

The drawback of other devices is limited maximum stroke and high correlation within the electrodes. In terms of these drawbacks, other solutions, such as the Saturn mirror, capable of placing the actuator on the top of the membrane and thus pushing and pulling the membrane can be considered.

Optical Performance

The influence functions, that is, the deformation generated by each actuator, are illustrated in the following figure. These when arranged in a matrix will form the influence matrix. The inverted influence matrix can help generate the required wavefront.

Within a Europa P Kit, the PAN mirror is supplied with a measured influence matrix. However, for better results, the influence matrix should be measured while placing the mirror in the optical setup.

This information has been sourced, reviewed and adapted from materials provided by Adaptica.

For more information on this source, please visit Adaptica.