A5045483371- Adaptive optics and wavefront sensing
- Optical Wireless Communication Technologies
- Optical Systems and Laser Technology
- Advanced optical system design
- Advanced Image Processing Techniques
- Stellar, planetary, and galactic studies
- Optical measurement and interference techniques
- Astronomy and Astrophysical Research
- Optical Coherence Tomography Applications
- Orbital Angular Momentum in Optics
- Calibration and Measurement Techniques
- Image and Signal Denoising Methods
- Advanced Optical Sensing Technologies
- Advanced Vision and Imaging
- Image Enhancement Techniques
- Infrared Target Detection Methodologies
- Advanced Image Fusion Techniques
- Radio Wave Propagation Studies
- Meteorological Phenomena and Simulations
- Solar and Space Plasma Dynamics
- Optical Polarization and Ellipsometry
- Photoacoustic and Ultrasonic Imaging
- Optical Network Technologies
- Underwater Vehicles and Communication Systems
- Semiconductor Lasers and Optical Devices
Fraunhofer Institute of Optronics, System Technologies and Image Exploitation
2015-2024
Fraunhofer Society
2012
European Southern Observatory
2009-2011
Technion – Israel Institute of Technology
2011
Ollscoil na Gaillimhe – University of Galway
2004-2009
Small-angle coronagraphy is technically and scientifically appealing because it enables the use of smaller telescopes, allows covering wider wavelength ranges, potentially increases yield completeness circumstellar environment - exoplanets disks detection characterization campaigns. However, opening up this new parameter space challenging. Here we will review four posts high contrast imaging their intricate interactions at very small angles (within first 4 resolution elements from star). The...
We present a numerical wave propagation method for simulating imaging of an extended scene under anisoplanatic conditions. While isoplanatic simulation is relatively common, few tools are specifically designed the scenes provide complete description proposed tool, including used. Our approach computes array point spread functions (PSFs) two-dimensional grid on object plane. The PSFs then used in spatially varying weighted sum operation, with ideal image, to produce simulated image realistic...
We theoretically investigate the effectiveness of adaptive optics correction for Gaussian beams affected by oceanic turbulence. Action an idealized system is modeled as a perfect removal certain number Zernike modes from aberrated wavefront. focused on direct detection systems and we used aperture-averaged scintillation main metric to evaluate optical performances. found that, similar laser beam propagation in atmospheric turbulence, very effective improving performance communication links...
Recent advances in image processing for atmospheric propagation have provided a foundation tackling the similar but perhaps more complex problem of underwater imaging, which is impaired by scattering and optical turbulence. As result these impairments imagery suffers from excessive noise, blur, distortion. Underwater turbulence impact on light becomes critical at longer distances as well near thermocline mixing layers. In this work, we demonstrate method restoration images that are severely...
Abstract Atmospheric effects significantly influence the propagation of light. Conventional adaptive optics systems, based on Shack-Hartmann sensors (SHS), work well for vertical-path propagation. However, more challenging scenarios like horizontal-path imaging or free-space laser communications through extended-volume turbulence and strong scintillation, bandwidth SHS is insufficient. A promising alternative holographic wavefront sensor (HWFS). Our paper deals with some dependencies...
We theoretically investigate the performance of adaptive-optics correction for Gaussian beams affected by oceanic turbulence. Action adaptive optics is modeled as removal a certain number Zernike modes from aberrated wavefront. found that, similarly to atmospheric turbulence, very effective improve optical system laser communication links in weak
Over the years, there has been much interest in use of optical wavelengths for communication because potential high data rates. However, performance these systems can become significantly degraded due to turbulence-induced signal fluctuations. These fluctuations be minimized by enlarging receiving aperture, thereby averaging There is extensive developing probability density functions (PDFs) describing intensity so as accurately predict system performance. This work examines several PDF...
We have investigated the temporal variability and statistics of "instantaneous" Strehl ratio. The observations were carried out with 3.63-m AEOS telescope equipped a high-order adaptive-optics system. In this paper ratio is defined as peak intensity single short exposure. also studied behavior phase variance computed on reconstructed wavefronts. tested Maréchal approximation used it to explain observed negative skewness distribution. estimate shown fit three-parameter Gamma distribution...
This paper is an introduction to the problem of modeling probability density function adaptive-optics speckle. We show that with modified Rician distribution one cannot describe statistics light on axis. A dual solution proposed: for off-axis speckle and gamma-based core point spread function. From these two distributions we derive optimal statistical discriminators between real sources quasi-static speckles. In second part morphological difference functions used constrain a one-dimensional,...
We have performed a series of experiments aiming at understanding the statistics deep turbulence over cities. The experimental setup consisted Shack-Hartmann wavefront sensor and an imaging camera that simultaneously recorded wavefront-, focal-plane data, respectively. At same time, measurements optical were urban area interest using two large-aperture scintillometer systems to get impression strength C<sub>n</sub><sup>2</sup> above rooftops Ettlingen. Our focus is "urban" because we are...
Adaptive optics systems are used to compensate for distortions of the wavefront light induced by turbulence in atmosphere. Shack-Hartmann sensors measure this distortion before correction. However, conditions where strong scintillation (intensity fluctuation) is present, these show considerably worse performance. This partly because lenslet arrays sensor designed without regard and not adaptable changes strength. Therefore, we have developed an that can flexibly exchange its array relying on...
Adaptive optics systems are used to compensate for wavefront distortions introduced by atmospheric turbulence. The corrected an adaptable device, normally a deformable mirror. control signal of the mirror is based on measurement delivered sensor. Relevant characteristics sensor accuracy, achievable speed and robustness against scintillation. modal holographic can theoretically provide highest bandwidth compared other state art sensors it robust scintillation effects. However, accuracy...
Wind speed and sonic temperature measured with ultrasonic anemometers are often utilized to estimate the refractive index structure parameter C n 2 , a vital for optical propagation. In this work, we compare four methods from T using same temporal data streams two separated on homogenous path. Values of obtained these field trial compared those commercial scintillometer differential image motion method grid light sources positioned at end common addition comparison between methods, also...
Correction of atmospheric effects on the propagation laser light can be achieved with adaptive optics (AO) by relying adequate wavefront sensors. For free-space communications and for tracking high-speed airborne objects, conventional sensing methods e.g. those based Shack-Hartmann sensor (SHS), are not always effective. Partial obscuration saturation detector due to strong turbulence lead errors in reconstruction. Another drawback wavefront-sensing is timeconsuming readout whole subsequent...
A simple grid of 10×10 white-light LEDs allows for simultaneous measurement several characteristics atmospheric turbulence. With this device, an imaging sensor and the model tilt anisoplanatism one can determine turbulence strength, anisotropy, outer scale spectral slope We describe theory present preliminary results obtained over a 270-m path.
We propose a complete framework for the detection, astrometry, and photometry of faint companions from sequence adaptive optics corrected short exposures. The algorithms exploit difference in statistics between on-axis off-axis intensity. Using moderate-Strehl ratio data obtained with natural guide star system on Lick Observatory's 3-m Shane Telescope, we compare these methods to standard approach PSF fitting. give detection limits system, as well first expected accuracy differential...
We describe the results of a Phase A study for single field, wide band, near-infrared integral field spectrograph European Extremely Large Telescope (E-ELT).HARMONI, High Angular Resolution Monolithic Optical & Nearinfrared Integral spectrograph, provides E-ELT's core spectroscopic requirement.It is work-horse instrument, with four different spatial scales, ranging from seeing to diffraction-limited, and spectral resolving powers 4000, 10000 20000 covering 0.47 2.45 μm wavelength range.It...
The modal holographic wavefront sensor enables fast measurement of individual aberration modes without the need for time-consuming calculations. However, accuracy suffers greatly from intermodal crosstalk, caused when contains more aberrations than one to be measured. In this paper, we present optimization minimize effect and show improvement using Karhunen–Lòeve instead Zernike as basis. Finally, in simulation that an open-loop adaptive optics system based on optimized can used correct...
The direct imaging of planets around nearby stars is exceedingly difficult. Only about 14 exoplanets have been imaged to date that masses less than 13 times Jupiter. next generation planet-finding coronagraphs, including VLT-SPHERE, the Gemini Planet Imager, Palomar P1640, and Subaru HiCIAO predicted contrast performance roughly a thousand would be needed detect Earth-like planets. In this paper we review state art in exoplanet imaging, most notably method Locally Optimized Combination...
The use of remote sensing techniques such as adaptive optics and image restoration post processing to correct for aberrations in a wavefront light propagating through turbulent environment has become customary many areas including astronomy, medical imaging, industrial applications. EO imaging underwater been mainly concentrated on overcoming scattering effects rather than dealing with turbulence. However, the turbulence have crucial impact over long image-transmission ranges under extreme...
Unconventional wavefront sensing strategies are being developed to provide alternatives for measuring the deformation of a laser beam propagating through strong turbulence and/or along horizontal-path. In this paper we present results from two "wavefront-sensorless" approaches: stochastic parallel gradient descent (SPGD) and its modal version (M-SPGD). We compare performance both algorithms experimental measurements under emulated dynamic atmospheric by using coupling efficiency in single...
Two analog holographic wavefront sensors, for measurement of defocus, have been fabricated as both thin and volume phase transmission holograms in a self-developing photopolymer. This represents the first reported direct comparison hologram regimes when designed sensing. An analysis effect crosstalk presence one other aberration mode (astigmatism X (0/90°), coma (horizontal), primary spherical aberration) was carried out with each version sensor. The performance sensors characterized under...
The modal holographic wavefront sensor offers a promising alternative to established sensing techniques. Since the strengths of individual aberration modes are directly measured, there is no need for time-consuming signal processing and reconstruction. Bandwidths up three orders magnitude higher than those commercial sensors can in principle be achieved. However, practice accuracy measurements compromised by intermodal crosstalk, which arises when exhibits additional aberrations encoded...
We have investigated both the temporal and spatial structure of point spread function (PSF) produced by Lick Observatory adaptive optics (AO) system using FastSub readout mode IRCAL camera short-exposure images with exposure times 22ms at a frame rate ~ 20Hz suitable for "freezing" compensation under typical <i>K</i>-band observing conditions. These short exposures are useful diagnostic tool determining performance permit measurement instantaneous Strehl ratio. Data taken from number runs,...