Refine
Year
Publication Type
- Article (19)
- Conference Proceeding (17)
- Contribution to a Periodical (2)
- Part of a Book (1)
Language
- English (32)
- German (6)
- Multiple languages (1)
Keywords
- adaptive optics (3)
- deformable mirror (3)
- active optics (2)
- active optics, adaptive optics, sharpness metrics, aberration compensation, algorithm design (2)
- deformable mirrors (2)
- laser machining (2)
- space optics (2)
- space telescopes (2)
- Active or adaptive optics (1)
- Deformable mirror, adaptive mirror, unimorph mirror, high-power laser (1)
- Photoluminescence (1)
- Pr3+ luminescence (1)
- Single crystal (1)
- Space instrumentation (1)
- Space optics (1)
- Telescopes (1)
- Temperature-dependent spectroscopy (1)
- Up-conversion (1)
- active optics, metrics, aberration compensation (1)
- active or adaptive optics (1)
- adaptive optics; image-sharpness (1)
- beam steering (1)
- diode lasers (1)
- diode-pumped laser (1)
- laser beams (1)
- laser crystal (1)
- laser materials processing (1)
- optical components (1)
- praseodymium (1)
- radiation (1)
- refractive index change (1)
- sensor performance (1)
- solid-state laser (1)
- space instrumentation (1)
- space qualification (1)
- telescopes thermal effects vibration analysis (1)
- thermal expansion coefficient (1)
- unimorph (1)
- vibration damping (1)
- ytterbium laser (1)
- yttrium lithium fluoride (1)
Faculty
With a view to the next generation of large space telescopes, we investigate guide-star-free, image-based aberration correction using a unimorph deformable mirror in a plane conjugate to the primary mirror. We designed and built a high-resolution imaging testbed to evaluate control algorithms. In this paper we use an algorithm based on the heuristic hill climbing technique and compare the correction in three different domains, namely the voltage domain, the domain of the Zernike modes, and the domain of the singular modes of the deformable mirror. Through our systematic experimental study, we found that successive control in two domains effectively counteracts uncompensated hysteresis of the deformable mirror.
Active optics is an enabling technology for future large space telescopes. Image-based wavefront control uses an image-sharpness metric to evaluate the optical performance. A control algorithm iteratively adapts a corrective element to maximize this metric, without reconstructing the wavefront. We numerically study a sharpness metric in the space of Zernike modes, and reveal that for large aberrations the Zernike modes are not orthogonal with respect to this metric. The findings are experimentally verified by using a unimorph deformable mirror as
corrective element. We discuss the implications for the correction process and the design of control algorithms.
It has been shown that the beam quality and the efficiency of high-power solid-state lasers could be enhanced by the use of deformable mirrors in order to compensate for optical aberrations. An intracavity compensation requires a deformable mirror which is capable of handling very high laser intensities. The active diameter of the deformable mirror should be a few millimeters in order to match typical fundamental mode laser beam diameters. There is a wide variety of commercially available deformable mirrors, but neither meets all requirements.
With a view to future large space telescopes, we investigate image-based wavefront correction with active optics. We use an image-sharpness metric as merit function to evaluate the image quality, and the Zernike modes as control variables. In severely aberrated systems, the Zernike modes are not orthogonal to each other with respect to this merit function. Using wavefront maps, the PSF, and the MTF, we discuss the physical causes for the non-orthogonality of the Zernike modes with respect to the merit function. We show that for combinations of Zernike modes with the same azimuthal order, a flatter wavefront in the central region of the aperture is more important than the RMS wavefront error across the full aperture for achieving a better merit function. The non-orthogonality of the Zernike modes with respect to the merit function should be taken into account when designing the algorithm for image-based wavefront correction, because it may slow down the process or lead to premature convergence.
Image-sharpness metrics can be used to optimize optical systems and to control wavefront sensorless adaptive optics systems. We show that for an aberrated system, the numerical value of an image-sharpness metric can be improved by adding specific aberrations. The optimum amplitudes of the additional aberrations depend on the power spectral density of the spatial frequencies of the object.
On-the-fly remote laser processing plays an increasingly important role in modern fabrication techniques. These processes require guiding of the focus of a laser beam along the contours of the workpiece in three dimensions.
State-of-the-art galvanometer scanners already provide highly dynamic and precise transverse x−y beam steering. However, longitudinal focus shifting (“z-shifting”) relying on conventional optics is restricted to a bandwidth of a few hundred Hz. We have developed and manufactured a fast piezo-based z-shifting mirror with diffraction-limited surface fidelity providing a focus shift of 1z> 60 mm with an actuation rate of 2 kHz.