ABSTRACT
Magnetic-liquid deformable mirrors (MLDMs) were introduced by our group in 2004 and numerous developments have been made since then. The usefulness of this type of mirror in various applications has already been shown, but experimental data on their dynamics are still lacking. A complete theoretical modeling of MLDM dynamics is a complex task because it requires an approach based on magnetohydrodynamics. A purpose of this paper is to present and analyze new experimental data of the dynamics of these mirrors from open-loop step response measurements and show that a basic transfer function modeling is adequate to achieve closed-loop control. Also, experimental data on the eigenmodes dynamic is presented and a modal-based control approach is suggested.
ABSTRACT
A deformable mirror made of a magnetic liquid has been used to produce conical surfaces with subwavelength (λ/4) accuracy. The surface profile of the liquid mirror is controlled by 91 small magnetic coils. The mirror exhibits a linear response with respect to the currents driving the coils, and it allows for real-time changes of its surface profile. The magnetic liquid deformable mirror has been used to produce reflected beams having a conical wavefront; the propagation of the reflected beams was verified to be consistent with that of Bessel beams in the near and far field. The large dynamic range of such a deformable mirror has made it possible to generate Bessel beams with a broad range of beam parameters.
ABSTRACT
We present the experimental performance of a 91-actuator deformable mirror made of a magnetic liquid (ferrofluid) using a new technique that linearizes the response of the mirror by superposing a uniform magnetic field to the one produced by the actuators. We demonstrate linear driving of the mirror using influence functions, measured with a Fizeau interferometer, by producing the first 36 Zernikes polynomials. Based on our measurements, we predict achievable mean PV wavefront amplitudes of up to 30 microm having RMS residuals of lambda/10 at 632.8 nm. Linear combination of Zernikes and over-time repeatability are also demonstrated.
ABSTRACT
Ferrofluids can be used to make deformable mirrors having highly interesting characteristics (e.g., extremely large strokes and low costs). Until recently, such mirrors were thought to be restricted to corrections of frequencies lower than 10 Hz, thus limiting their usefulness. We present counterintuitive results that demonstrate that the limiting operational frequency can be increased by increasing the viscosity of the ferrofluid. We tested the response of ferrofluids having viscosities as high as 494 cP, finding that they could allow an adaptive optics correction frequency as high as 900 Hz. We also demonstrate that we can counter the amplitude loss due to the high viscosity by overdriving the actuators. The overdriving technique combines high current, short duration pulses with ordinary driving step functions to deform the mirror. The integration of a FDM in a complete closed-loop adaptive optics system running at about 500 Hz thus appears to be a realistic goal in the near future.
ABSTRACT
We report the preparation of metal liquid-like films (MELLFs) of silver nanoparticles stabilized by thiolate surface ligands. These surface films, composed of particles with diameters of about 100 nm, are highly reflective and can be employed in the fabrication of liquid mirrors. A number of different thiols are considered as stabilizing ligands, including alkanethiols, aromatic thiols and dithiols. Under identical preparation conditions, some lead to the spontaneous formation of reflective surface films, whereas others do not. Shorter chain alkanethiols (C2 to C8), thiophene and thiophenol are found to be effective whereas longer chain alkanethiols (C10 and C12) and short dithiols (C2 and C3) do not produce reflective films. Ethanethiol and propanethiol protected particles form surface films with reflectivities in the near-IR that surpass those of a previous generation of MELLFs prepared with 1,10-dimethylphenanthroline as the ligand. This enhanced reflectivity is attributed to a more closely packed nanoparticle film with a higher metal volume fraction. The closer proximity of the particles, however, leads to enhanced coupling of their surface plasmon resonance and increased absorption in the visible region of the spectrum. Short chain dithiols do not produce MELLFs but rather provoke particle aggregation. In the case of 1,2-ethanedithiol, the particles are found to precipitate in a continuous organic matrix, presumably caused by oxidative polymerization of the dithiol to a polydisulfide. Finally, preliminary investigations indicate that a large variety of organic solvants can be employed in the preparation of thiol protected MELLFs.
ABSTRACT
An optical/infrared telescope of 20-100 m aperture located on the Moon would be able to observe objects 100 to 1,000 times fainter than the proposed next generation of space telescopes. The infrared region of the spectrum is particularly important for observations of objects at redshifts z > 7. The apparent simplicity and low mass of a liquid mirror telescope, compared with a traditional pointable glass mirror, suggest that the concept should be considered further. A previously proposed liquid mirror telescope, based upon a spinning liquid metallic alloy, is not appropriate for infrared applications, which will require a liquid below 130 K. Here we report the successful coating of an ionic liquid with silver. The surface is smooth and the silver coating is stable on a timescale of months. The underlying ionic liquid does not evaporate in a vacuum and remains liquid down to a temperature of 175 K. Given that there are approximately 10(6) simple and approximately 10(18) ternary ionic liquids, it should be possible to synthesize liquids with even lower melting temperatures.
ABSTRACT
This paper discusses an innovative low-cost deformable mirror made of a magnetic liquid (ferrofluid) whose surface is actuated by an hexagonal array of small current carrying coils. Predicted and experimental performances of a 37-actuator ferrofluid deformable mirror are presented along with wavefront correction examples. We show the validity of the model used to compute the actuators currents to obtain a desired wavefront shape. We demonstrate that the ferrofluid deformable mirror can correct a 11 microm low order aberrated wavefront to a residual RMS error of 0.05 microm corresponding to a Strehl ratio of 0.82.
Subject(s)
Image Enhancement/instrumentation , Lenses , Magnetics/instrumentation , Microfluidics/instrumentation , Elastic Modulus , SolutionsABSTRACT
We present a new class of magnetically shaped deformable liquid mirrors made of a magnetic liquid (ferrofluid). Deformable liquid mirrors offer advantages with respect to deformable solid mirrors: large deformations, low costs and the possibility of very large mirrors with added aberration control. They have some disadvantages (e.g. slower response time). We made and tested a deformable mirror, producing axially symmetrical wavefront aberrations by applying electric currents to 5 concentric coils made of copper wire wound on aluminum cylinders. Each of these coils generates a magnetic field which combines to deform the surface of a ferrofluid to the desired shape. We have carried out laboratory tests on a 5 cm diameter prototype mirror and demonstrated defocus as well as Seidel and Zernike spherical aberrations having amplitudes up to 20 microm, which was the limiting measurable amplitude of our equipment.
ABSTRACT
We discuss a new type of deformable mirror made from nanoengineered reflective layers deposited onto liquids. The surfaces are shaped by heating with a laser. The response times of the deformed surfaces are slow (> 1 s). Simplicity and low cost appear to be the main advantages of thermally deformable liquid mirrors.
ABSTRACT
We describe a new technology for the fabrication of inexpensive high-quality mirrors. We begin by chemically producing a large number of metallic nanoparticles coated with organic ligands. The partides are then spread on a liquid substrate where they self-assemble to give optical quality reflective surfaces. Since liquid surface can be modified by a variety of means (e.g., rotation, electromagnetic fields), this opens the possibility of making a new class of versatile and inexpensive optical elements that can have complex shapes and that can be modified within short time scales. Interferommetric measurements show optical quality surfaces. We have obtained reflectivity curves that show 80% peak reflectivities. We are confident that we can improve the reflectivity curves because theoretical models predict higher values. We expect nanoengineered liquid mirrors to be useful for scientific and engineering applications. The technology is interesting for large optics, such as large rotating parabolic mirrors, because of its low cost. Furthermore, because the surfaces of of ferrofluids can be shaped with magnetic fields, one can generate complex, time-varying surfaces that are difficult to make with conventional techniques.
