Adaptive optics

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Adaptive optics
Using Ferro-fluids Mathieu De Goer-de Herve and
Raphael-David Lasseri (ENS Cachan)
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Resolution in optics

• Two limitant factors
• ? Diffraction
• ? Atmosphere turbulences speckle patterns.

Characteristic length D Airy disc  Ø?xf/D
D
Characteristic length dc (correlation) dc10cm Di
sc  Ø?xf/dc
Ø
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What solution?

• High places
• Adaptive optics

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How?

• Mechanics deformation of a usual mirror using
  piezoelectric devices

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How?

• Mechanics deformation of a usual mirror using
  piezoelectric devices
• Shack-Hartmann wavefront sensor

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Ferrofluids

• General definition
• Colloidal suspensions of magnetic nanoparticles
  conferring super-paramagnetic properties to the
  fluid.
• When a magnetic field is applied to the system
  their magnetic moments tend to align along the
  applied field, leading to a net magnetization.

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Field of the study
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Rosenweig instability

• Domain of Stability
• Smooth surface

• Domain of the RW Instability
• Hedgehog surface

BgtBc
BltBc
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MHD Fundamentals Equations

• Approximations We will neglect the influence
  of the capillary forces in this stable domain,
• 3 Major Factors
• - Gravity
• Magnetostrictive Pressure
• Laplace Forces
• When the Equilibrium is reached
• -gt Bernouilli Generalised Equation (1)

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Numerical Resolution

• Finite Element Method applied to model the
  interaction of the field and the fluid.
• Field of a cylindric shaped magnet
• Height of the ferrofluid sample (From Top)

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Experiment VS Theory
Numerical approach
Physical Experiment

• Deformation of the fluid above the magnet

• Ferrofluid sample subjected to a strong magnet

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Validation of the model
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Classic methods

• Mechanics deformation of a usual mirror using
  piezoelectric devices

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Applications to adaptive optics

• Generic principle of adaptive optics

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Some examples

• Results using classic adaptive
• Final Results (NGC 7469 Galaxy)

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Liquid Mirror

• A well-know Patent (Ernesto Capocci -1856)