2010-06-22

Liquid Mirrors for Adaptive Optics

Liquid mirror

From Wikipedia, the free encyclopedia

Liquid mirrors are mirrors made with reflective liquids. The most common liquid used is mercury, but other liquids will work as well (for example, low melting alloys of gallium). The container for the liquid is rotating so that the liquid assumes a parabolic shape. A parabolic shape is precisely the shape needed for the primary mirror of a telescope. The rotating liquid assumes the parabolic shape regardless of the container's shape. To reduce the amount of liquid metal needed, and thus weight, a rotating mercury mirror uses a container that is as close to the necessary parabolic shape as possible. Liquid mirrors can be a low cost alternative to conventional large telescopes. Compared to a solid glass mirror that must be cast, ground, and polished, a rotating liquid metal mirror is much cheaper to manufacture.



Liquid Mirror Breakthrough Could Make State-of-the-Art Optics Cheap

A $120 million Earth-based telescope using brand new adaptive optics just trumped Hubble's deep space image clarity three-fold, but such high tech optics aren't just reserved for high-dollar observatories. A breakthrough in deformable liquid mirror technology could drastically reduce the price associated with adaptive optics, making the best in high-tech telescopes more widely available.
[...]
Using a ferromagnetic liquid (rather than mercury), researchers pioneered a novel way to create deformable liquid mirrors a few years back, but there were some problems. For one, the magnetic fields used to deform the liquid couldn't be cycled quickly enough to be useful in astronomy. For another, there was a non-linear disconnect between the deformation of the mirror and the magnetic field strength that required a highly complex algorithm to be built from scratch.

Now, those same researchers from the Université Laval in Quebec have published a paper saying they've resolved those problems. They now claim they can cycle their magnetic fields 100 times faster, and by applying a second uiform magnetic field atop the original one they've eliminated that disconnect between deformity and magnetic field strength.



Technology Review - Published By MIT

Deformable Liquid Mirrors Could Revolutionise Astronomy

Liquid mirrors are cheaper and easier to make than glass ones. A new prototype shows how they can also make adaptive optics systems.



Today, Brousseau and buddies reveal a next generation liquid mirror that gets around these problems. The proof-of-principle mirror is just 5 cm across but sits atop a honeycomb of 91 actuators that can deform the liquid.

The team say they've found a way to cycle their actuators at rates of up to 1 Khz, much more useful than before. And they've overcome the the non-linear control problems by superimposing a strong uniform magnetic field on top of the field created by the actuators. This has the effect of linearising the response of the liquid.

The big advantage, of course, is that instead of having to develop their own exotic control algorithms, they can now use off-the-shelf algorithms developed for conventional adaptive optics.

The result is a mirror that ought to be able to compete with the vary best conventional adaptive optics but that can be built at a fraction of the price.


Laval University

Liquid mirrors and adaptive optics group

Welcome to the Laval University liquid mirrors and adaptive optics group website. By browsing through these pages you will find valuable information on our ongoing research activities and earlier projects as well. Please note that some sections are still under work.

[...]
The Ferrofluid deformable mirrors section gives a brief overview of our ongoing research on liquid deformable mirrors based on the use of magnetic liquids called ferrofluids.

The Reflective liquids section discuss reflective liquids called MeLLFs (Metal Liquid-Like Films) that has been developped by a team of chemists working in our group. There is also a section on the vacuum deposition of reflective coatings on ionic liquids.



What is a ferrofluid?

Illustration showing the structure of the ferrofluid-mellf interface.

Photographs of a homemade ferrofluid coated with a MeLLF. The image at right
shows the liquid deformed by the presence of a magnetic field of a
permanent magnet located under the container.



Sources
Liquid mirror - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Liquid_mirror
Liquid Mirror Breakthrough Could Make State-of-the-Art Optics Cheap | Popular Science
http://www.popsci.com/technology/article/2010-06/liquid-mirror-breakthrough-could-make-state-art-optics-cheap
Technology Review: Blogs: arXiv blog: Deformable Liquid Mirrors Could Revolutionise Astronomy
http://www.technologyreview.com/blog/arxiv/25342/
Laval University Liquid Mirror Group
http://wood.phy.ulaval.ca/
Laval University Liquid Mirror Group
http://wood.phy.ulaval.ca/ferro.html

Related
[1006.2843] Linearization of the response of a 91-actuator magnetic liquid deformable mirror
http://arxiv.org/abs/1006.2843
Liquid mirror shows promise for adaptive optics - physicsworld.com
http://physicsworld.com/cws/article/news/35123
2Physics: Ferrofluidic Deformable Mirrors for Adaptive Optics
http://www.2physics.com/2009/03/ferrofluidic-deformable-mirrors-for.html
HowStuffWorks "How Lunar Liquid Mirror Telescopes Work"
http://science.howstuffworks.com/liquid-mirror-telescope.htm


Labels: , ,