Abstract of the invited speakers
Prof. Margaret Murnane, NSF STROBE Science and Technology Center JILA, University of Colorado Boulder (USA)
Coherent Imaging using Tabletop High Harmonic EUV Beams
We demonstrate unique, nondestructive, coherent imaging capabilities using tabletop high harmonic beams.In particular, we implemented a complex-imaging EUV reflectometer based on variable-angle ptychographic imaging that can non-destructively determine depth-dependent, spatially-resolved composition, with high sensitivity to chemical makeup, thin film layer thicknesses, interface quality and dopant profiles. This capability is critical for engineering current and next-generation quantum technologies.
Prof. Sylvain Gigan, Sorbonne Université (France)
Imaging in scattering media without wavefront shaping
Imaging in a scattering medium, where light is multiply scattered, has been tackled mostly through wavefront shaping : spatially modulating coherent input light in order to form and scan a tight focus through a multiple scattering media. However, shaping is not always necessary, and it has been shown that using suble correlations in the speckle patterns, in particular the so-called memory effect, images can be retrieved using phase-retrieval algorithms. I will show that even without such correlations, informations can be retrieved nonetheless, and show an exemple of functional neuronal activity recording at depth, using non-negative matrix factorization.
Yihui Wu, Changchun Institute of Optics, Fine Mechanics and Physics (CN)
Photonic nanojet with WGMs and Side lobes phase controlled.
Microsphere assisted with microscopy can achieve very high resolution for the imaging of nonflurescent samples or structures. The resolution is related to photonic nanojets and Whispering Gallery modes. It shows that the high-order scattering modes play the dominant role in the reconstructed virtual image when the Whispering Gallery modes exist. Furthermore, we find that the high image resolution of electric dipoles can be achieved, when the out-of-phase components exist from the illustration of Whispering Gallery modes. As for the photonic nanojets, we proposed a method for side lobes controlling photonic nanojets. A super-narrow photonic nanojet with a full width at half-maximum waist of approximately 116.6nm is obtained, with 500nm excitation wavelength. Those researchs can improve the resolution of microsphere.
Dr. Andreas Menzel, Paul Scherrer Institute (CH)
Ever since their discovery, X-rays have been used of imaging. However, for high-resolution microscopy, limitations of X-ray optics have proven to an impediment. Coherent diffractive imaging addresses this issue by replacing image-forming optics by mathematical reconstruction algorithms. Ptychography is one such technique that has gained particular attention and advances various forms of X-ray microscopy. The methodology, ongoing developments and applications will be discussed.
Dr. Stefano Bonora, NR Institute for Photonics and Nanotechnologie (IT)
Fast aberration correction with Multi-actuator adaptive lenses
Fast adaptive optics systems with deformable mirrors have been used to correct for time variant aberrations induced by air turbulence. We will show that the multi actuator adaptive lenses can replace deformable mirrors in such applications with the advantage of a simpler and more compact optical setup. We will show the results obtained on medium size telescopes and to improve the stability of complex laser systems.
Dr. Ivo Vellekop, Universty of Twente (NL)
Adaptive Optics and Wavefront Shaping, what lies in between?
Adaptive Optics (AO) and Wavefront Shaping (WFS) are both techniques to compensate the distortions of light that are caused by refractive index inhomogeneities in a medium. Where AO is mainly concerned with correcting aberrations in transparent media, WFS usually operates in the regime of highly turbid materials. As a consequence, the approaches, applications, language and even the fundamental physics of these techniques are different. I will explore how ideas from AO influence WFS and vice versa, and I will discuss recent advances in describing the cross-over regime between AO and WFS, which is particularly important in microscopy.
Paul Planken, ARCNL (NL))
Ultrafast photoacoustics for the detection of buried gratings
We present results on the photo-acoustic detection of gratings, buried underneath optically opaque layers, using two different laser systems. We find that the shape of the optically detected acoustic signals can change due to interference between diffraction from different acoustic sources, and due to interference with background scattered light. The latter is particularly important when a laser with a high repetition rate is used
Henry N. Chapman, DESY / Universtät Hamburg, (DE)
Coherent Diffractive Imaging of Macromolecules
The short wavelength of X-rays allows us to image structures at the atomic scale, giving detailed pictures of biological macromolecules. However, X-ray radiation is energetic enough to ionize matter: the very act of measurement destroys the structure being investigated. This can be overcome by outrunning radiation damage with femtosecond-duration X-ray pulses from free-electron lasers. However, even with the extreme intensities these produce, diffraction of single macromolecules is weak, and patterns must therefore be classified and averaged to build up signal. I will describe efforts of single-molecule imaging at FELs and various tricks we have been employing to boost signals.
John Rodenburg and Yangyang Mu, University of Sheffield (UK)
Illumination modes in ptychography
Ptychography is a computational imaging method that solves the phase problem using multiple diffraction patterns. Its resolution is not limited by lens apertures or aberrations: a key benefit in X-ray and electron microscopy. Here we examine how we can use ptychography to generate a compact representation of the partial coherence in the illuminating beam, and thus obtain a definitive measurement of the source coherence. We also explore limitations of the technique.
Kevin Zhou, Duke University (USA)
Improving diffraction tomography with intensity-only images
Diffraction tomography (DT) is a well-known 3D microscopic imaging method that uses variable-angle illumination to probe thick samples. While typical DT setups require phase-sensitive measurements, several recent techniques can now use phase retrieval algorithms to perform DT with standard microscope images in simple and robust setups. In this work, we show how to improve the resolution and reconstruction quality of phase-sensitive 3D image reconstruction from intensity-only images. First, we propose a unique regularization strategy to help address artifacts caused by the missing cone, and second, we demonstrate a novel setup that requires no moving parts and can illuminate the sample from nearly every transmission and reflection angle to maximize the amount of extracted information.
Shiyuan Liu,Huanzhong University of Science and Technology (CN)
Tomographic Mueller-matrix scatterometry for nanostructure metrology: Principles and opportunities
To address the challenges in conventional optical scatterometry for measuring the critical dimension and overlay of nanostructures in current semiconductor manufacturing, we recently developed a novel instrument called the tomographic Mueller-matrix scatterometer (TMS). With much more abundant scattering information, the TMS is expected to gain wide applications in the metrology of not only periodic nanostructures but also isolated or generally non-periodic structures.
Na Ji, Helen Wills NeuroScience Institute, Berkeley Neuroscience (USA)
Wavefront shaping for high-resolution high-speed imaging of the brain
Physics has long employed optical methods to probe and manipulate matter on scales from the infinitesimal to the immense. To understand the brain, we need to monitor physiological processes of single synapses as well as neural activity of a large number of networked neurons. Optical microscopy has emerged as an ideal tool in this quest, as it is capable of imaging neurons distributed over millimeter dimensions with sub-micron spatial resolution. Using concepts developed in astronomy and optics, my laboratory develops next-generation microscopy methods for imaging the brain at higher resolution, greater depth, and faster speed. By shaping the wavefront of the light, we have achieved synapse-level spatial resolution through the entire depth of the primary visual cortex, optimized microendoscopes for imaging deeply buried nuclei, and developed high-speed volumetric imaging methods. I will discuss our recent advances as well as their applications to understanding neural circuits.
Hans Peter Herzig, EPFL (CH)
Metasurfaces vs diffractive optics
Arbitrary phase structures that can shape the light propagation precisely without loss are dream structures in optics. Their fabrication has been driven by the progress in technology. In the past, such micro-optical components were called computer-generated holograms, kinoforms, binary optics, diffractive optics. Recently the term metasurface was introduced for subwavelength structures promising novel optical structures with new functionalities. Are these promises realistic?
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