Novel high-sensitivity Z-scan technique based on a Hartmann-Shack wavefront sensor

2010 ◽  
Author(s):  
Diego Rativa ◽  
Brian Vohnsen ◽  
Anderson S. L. Gomes ◽  
Renato E. de Araujo
Keyword(s):  
High Sensitivity ◽  
Wavefront Sensor

scholarly journals The AOLI low-order non-linear curvature wavefront sensor: a method for high sensitivity wavefront reconstruction

2012 ◽  
Author(s):  
Jonathan Crass ◽  
Peter Aisher ◽  
Bruno Femenia ◽  
David L. King ◽  
Craig D. Mackay ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Wavefront Sensor ◽  
Wavefront Reconstruction ◽  
Non Linear ◽  
Low Order

An interferometric wavefront sensor for high-sensitivity low-amplitude measurements

2012 ◽  
Author(s):  
Nazim A. Bharmal ◽  
Richard M. Myers ◽  
Alastair G. Basden ◽  
Andrew P. Reeves
Keyword(s):  
High Sensitivity ◽  
Wavefront Sensor ◽  
Low Amplitude

scholarly journals High-Sensitivity X-ray Phase Imaging System Based on a Hartmann Wavefront Sensor

2021 ◽  
Vol 7 (1) ◽  
pp. 3
Author(s):  
Ginevra Begani Provinciali ◽  
Martin Piponnier ◽  
Laura Oudjedi ◽  
Xavier Levecq ◽  
Fabrice Harms ◽  
...  
Keyword(s):  
Imaging System ◽  
High Sensitivity ◽  
Test Sample ◽  
Wavefront Sensor ◽  
Reference Image ◽  
High Angular Resolution ◽  
Phase Imaging ◽  
X Ray ◽  
Laboratory Setup ◽  
The Impact

The Hartman wavefront sensor can be used for X-ray phase imaging with high angular resolution. The Hartmann sensor is able to retrieve both the phase and absorption from a single acquisition. The system calculates the shift in a series of apertures imaged with a detector with respect to their reference positions. In this article, the impact of the reference image on the final image quality is investigated using a laboratory setup. Deflection and absorption images of the same sample are compared using reference images acquired in air and in water. It can be easily coupled with tomographic setups to obtain 3D images of both phase and absorption. Tomographic images of a test sample are shown, where deflection images revealed details that were invisible in absorption. The findings reported in this paper can be used for the improvement of image reconstruction and for expanding the applications of X-ray phase imaging towards materials characterization and medical imaging.

scholarly journals A telescope-ready approach for modal compensation of pyramid wavefront sensor optical gain

2019 ◽  
Vol 629 ◽  
pp. A107 ◽  
Author(s):  
V. Deo ◽  
É. Gendron ◽  
G. Rousset ◽  
F. Vidal ◽  
A. Sevin ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Optical Gain ◽  
High Sensitivity ◽  
Wavefront Sensor ◽  
Scientific Instrument ◽  
Nonlinearity Error ◽  
Operation Conditions ◽  
Gain Variation ◽  
Compensation Technique ◽  
Large Telescopes

The pyramid wavefront sensor (PWFS) is the currently preferred design for high-sensitivity adaptive optics (AO) systems for extremely large telescopes (ELTs). Yet, nonlinearities of the signal retrieved from the PWFS pose a significant problem for achieving the full correction potential using this sensor, a problem that will only worsen with the increasing dimension of telescopes. This paper investigates the so-called optical gain (OG) phenomenon, a sensitivity reduction and an overall modification of the sensor response induced by the residual wavefront itself, with considerable effects in standard observation conditions for ELT-sized AO systems. Through extensive numerical analysis, this work proposes a formalism to measure and minimize the first-order nonlinearity error caused by optical gain variation, which uses a modal compensation technique of the calibrated reconstructor; this enables a notable increase in performance in faint guide stars or important seeing scenarios, for example from 16 to 30% H-band Strehl ratio for a sixteenth magnitude star in r0 = 13 cm turbulence. Beyond the performance demonstrated by this compensation, a complete algorithm for realistic operation conditions is designed, which from dithering a few deformable mirror modes retrieves the optimal gains and updates the command matrix accordingly. The performance of this self-updating technique – which successfully allows automatic OG compensation regardless of the turbulent conditions, and its minimal interference with the scientific instrument are demonstrated through extensive end-to-end numerical simulations, all at the scale of an ELT instrument single-conjugate AO system.

scholarly journals Highly Sensitive Shack–Hartmann Wavefront Sensor: Application to Non-Transparent Tissue Mimic Imaging with Adaptive Light-Sheet Fluorescence Microscopy

2019 ◽  
Vol 2 (3) ◽  
pp. 59 ◽  
Author(s):  
Brajones ◽  
Clouvel ◽  
Dovillaire ◽  
Levecq ◽  
Lorenzo
Keyword(s):  
Adaptive Optics ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Light Sheet ◽  
Wavefront Sensor ◽  
Spatial Frequencies ◽  
Living Tissues ◽  
Guide Star ◽  
Two Photon Fluorescence ◽  
Subcellular Resolution

High-quality in-depth imaging of three-dimensional samples remains a major challenge in modern microscopy. Selective plane illumination microscopy (SPIM) is a widely used technique that enables imaging of living tissues with subcellular resolution. However, scattering, absorption, and optical aberrations limit the depth at which useful imaging can be done. Adaptive optics (AOs) is a method capable of measuring and correcting aberrations in different kinds of fluorescence microscopes, thereby improving the performance of the optical system. We have incorporated a wavefront sensor adaptive optics scheme to SPIM (WAOSPIM) to correct aberrations induced by optically-thick samples, such as multi-cellular tumor spheroids (MCTS). Two-photon fluorescence provides us with a tool to produce a weak non-linear guide star (NGS) in any region of the field of view. The faintness of NGS; however, led us to develop a high-sensitivity Shack–Hartmann wavefront sensor (SHWS). This paper describes this newly developed SHWS and shows the correction capabilities of WAOSPIM using NGS in thick, inhomogeneous samples like MCTS. We report improvements of up to 79% for spatial frequencies corresponding to cellular and subcellular size features.

scholarly journals Modelling of Phase Contrast Imaging with X-ray Wavefront Sensor and Partial Coherence Beams

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6469 ◽  
Author(s):  
Ginevra Begani Provinciali ◽  
Alessia Cedola ◽  
Ombeline de La Rochefoucauld ◽  
Philippe Zeitoun
Keyword(s):  
Spatial Coherence ◽  
High Sensitivity ◽  
Propagation Model ◽  
Partial Coherence ◽  
Wavefront Sensor ◽  
Contrast Imaging ◽  
Material Density ◽  
X Ray ◽  
Experimental Parameters ◽  
Precise Simulation

The Hartmann wavefront sensor is able to measure, separately and in absolute, the real δ and imaginary part β of the X-ray refractive index. While combined with tomographic setup, the Hartman sensor opens many interesting opportunities behind the direct measurement of the material density. In order to handle the different ways of using an X-ray wavefront sensor in imaging, we developed a 3D wave propagation model based on Fresnel propagator. The model can manage any degree of spatial coherence of the source, thus enabling us to model experiments accurately using tabletop, synchrotron or X-ray free-electron lasers. Beam divergence is described in a physical manner consistent with the spatial coherence. Since the Hartmann sensor can detect phase and absorption variation with high sensitivity, a precise simulation tool is thus needed to optimize the experimental parameters. Examples are displayed.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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