Large space telescopes made of deployable and lightweight structures suffer from aberrations caused by thermal deformations, gravitational release, and alignment errors which occur during the deployment procedure. An active optics system would allow on-site correction of wave-front errors, and ease the requirements on thermal and mechanical stability of the optical train. In the course of a project funded by the European Space Agency we have developed and manufactured a unimorph deformable mirror based on piezoelectric actuation. The mirror is able to work in space environment and is designed to correct for large aberrations of low order with high surface fidelity. This paper discusses design, manufacturing and performance results of the deformable mirror.

https://www.hb.fh-muenster.de/opus4/files/822/2015_07_07_Optics_Expr_Unimorph_def_mirrors_for_space_telescopes_design_and_manufacturing.pdf

Unimorph deformable mirror for space telescopes: design and manufacturing.

Hysteresis compensation of piezoelectric deformable mirror based on Prandtl-Ishlinskii model

To solve the local optimum problem, a modified hill-climbing algorithm based on Zernike modes is presented for wavefront sensorless adaptive optics. This algorithm adopts the Zernike mode coefficients, instead of the actuators' voltages in a traditional hill-climbing algorithm, as the adjustable variables to optimize the object function. First, the prin- ciple of the algorithm is described. Then the efficiency of the modified and traditional hill-climbing algorithms are analyzed numerically and experi- mentally using a He-Ne laser beam shaping system with a 37-element unimorph deformable mirror. The results of both simulations and experi- ments demonstrate that the modified hill-climbing algorithm can eliminate the local optimum problem with a fast speed of about 100 iterations. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.OE.52.1.016601) Subject terms: wavefront sensorless; adaptive optics; hill-climbing algorithm; Zernike modes; deformable mirror.

Hill-climbing algorithm based on Zernike modes for wavefront sensorless adaptive optics

The thermal-piezoelectric deformable mirror (TPDM) is a device employed to compensate for laser-induced mirror deformation and thermal lensing in high-power optical systems. The TPDM setup is a unimorph deformable mirror with thermal and piezoelectric actuation properties. Laser-induced thermal lensing is compensated for by heating of the TPDM. We show that this mirror can be applied to high-power laser systems of up to 6.2 kW laser power and high power densities of up to 2  kW/cm2. The piezoelectric stroke of the single actuators is between 1.5 and 4 μm and is not reduced by either the absorbed laser power or mirror heating.

Performance of a thermal-piezoelectric deformable mirror under 6.2 kW continuous-wave operation

We present the realization and characterization of an active spherical diffraction grating with variable radius of curvature to be used in grazing-incidence monochromators. The device consists of a bimorph deformable mirror on the top of which a diffraction grating with laminar profile is realized by UV lithography. The experimental results show that the active grating can optimize the beam focalization of visible wavelengths through its rotation and focus accommodation.

Active diffraction gratings: development and tests.

This paper reports the development and characterization of a low-cost thin unimorph deformable mirror (DM) driven by positive voltage. The developed DM consists of both an inner actuator array and an outer ring actuator, which works two drive modes: the inner actuator array is used for aberration correction, while the outer ring actuator is used to generate an overall defocus bias. An analytical model based on the theory of plates and shells is studied for predicting the behavior of the developed DM. Measurement results indicate that dual direction maximum defocus deformations of the developed DM are −14.3 and 14.9 μm, respectively, and the resonant frequency is 1.8 kHz. The root-mean-square deformation of the mirror surface after correction is better than λ/20 for λ=633 nm. The replication of Zernike mode shapes up to the fifth order demonstrates that this developed DM is satisfactory for low-order aberration correction.

Double drive modes unimorph deformable mirror for low-cost adaptive optics

The invention discloses a single-piezoelectric patch deformable mirror and a manufacturing method thereof; the manufacturing method comprises the following step: first, a mirror layer which comprises a non-reflective surface and a reflective surface is provided; then the mirror layer is connected with a driving layer with an upper electrode layer and a lower electrode layer, wherein the non-reflective surface of the mirror layer is connected with the upper electrode layer of the driving layer; and the lower electrode layer of the driving layer is graphical to obtain an outer electrode on the periphery and an inner electrode in the middle part, wherein the outer electrode is used for correcting misfocus aberration and the inner electrode is used for correcting multi-order aberration. According to the invention, the deformable mirror has the advantages of simple structure, small size, light weight, low cost, large correction stroke and the like.

Ting He

Papers

Double drive modes unimorph deformable mirror for low-cost adaptive optics

Single-piezoelectric patch deformable mirror and manufacturing method thereof