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Wave-front Shaping Controls Nonlinearity in Complex Media

May 7, 2018|

Wavefront shaping can enhance imaging through turbid media such as fog, or endoscopes. A CU Boulder STROBE team led by Rafael Piestun implemented a new kind of control that enables optimization of highly non-linear interactions through fibers. Tailoring the wave-front shape at the input, the system controls the generation of nonlinear phenomena known as stimulated-Raman-scattering cascades and four-wave-mixing, generating and shaping the different colors of the light pulses at the output of the fiber. This research has implications for the understanding of so-called adaptive systems, optical communications, fiber lasers, and imaging.

O. Tzang et al., “Adaptive wavefront shaping for controlling nonlinear multimode interactions in optical fibres” Nature Photonics 12, 368–374 (2018).

Sub-ångström Cryo-EM Structure of a Prion Protofibril Reveals a Polar Clasp

January 15, 2018|

Brain dysfunction can be caused by aggregated proteins such as prions. In humans, the prion protein causes an infection by changing its shape and transforming into rope like aggregates. In this way, stable prion aggregates are immune to normal processes of destruction in an organism and bring about neuronal death and ultimately disease. There is no molecular explanation for the variable efficiency of prion spread between species. To investigate this phenomenon, STROBE scientists Rodriguez and Maio used cryo electron microscopy to reveal the atomic structures of regions within prion that have a high propensity to form structured aggregates. This made it possible to take an atomic look at structural motifs that may represent the molecular basis for a prion species barrier.

M. Gallagher-Jones et al., “Sub-ångström cryo-EM structure of a prion protofibril reveals a polar clasp,” Nature Structural &amp Molecular Biology 25, 131 - 134 (2018).

Semiconductor Voltage Sensors for Neuron Imaging

January 12, 2018|

A STROBE team led by Simon Weiss implemented semiconductor-based voltage sensors as neuronal activity imaging probes. Unlike conventional voltage sensors, these nanosensors operating via the quantum confined Stark effect are highly sensitive, bright, and fast-responding. With further optimization, these nanosensors may enable single-particle detection and facilitate monitoring of neuronal signals at the nanoscale.

Kyoungwon Park et al., “Membrane insertion of—and membrane potential sensing by—semiconductor voltage nanosensors: Feasibility demonstration”, Science Advances 12 (2018).

Multiple Beam Illumination for Large Field-of-view, High Throughput, Imaging

January 1, 2018|

The ability to record large field of view images without a loss in spatial resolution is critical for many applications of imaging science. However, for most imaging techniques, an increase in field-of-view comes at the cost of decreased resolution. STROBE scientists at CU Boulder implemented a novel extension to ptychographic coherent diffractive imaging that permits simultaneous full-field imaging of multiple simultaneous locations on a sample, by illuminating it with spatially separated, interfering beams. This technique allows for large field-of-view imaging in amplitude and phase while maintaining diffraction-limited resolution, without an increase in collected data i.e. diffraction patterns acquired.

C. Bevis, “Multiple beam ptychography for large field of view, high throughput, quantitative phase contrast imaging,” Ultramicroscopy 184, 164–171 (2018).

GENFIRE: A Generalized Fourier Iterative Reconstruction Algorithm for High-resolution 3D Imaging

September 5, 2017|

A STROBE team from the Miao group at UCLA implementated a powerful new tomographic algorithm, termed GENeralized Fourier Iterative REconstruction (GENFIRE), for high-resolution 3D reconstruction from a limited number of 2D projections. GENFIRE assembles a 3D Fourier grid with oversampling and then iterates between real and reciprocal space to search for a solution that is consistent with the measured data and physical constraints. This new algorithms has enabled many new imaging advances.

A. Pryor et al., “GENFIRE: A generalized Fourier iterative reconstruction algorithm for high-resolution 3D imaging”, Scientific Reports 7, 23: S1, (2017).

Sub-wavelength Coherent Diffractive Imaging Using a Tabletop High Harmonic Light Source

March 20, 2017|

Visible microscopes can produce crisp images with a spatial resolution on order of the illuminating wavelength, because of the availability of near-perfect lenses in this region of the spectrum. Extreme ultraviolet (EUV) and soft X-ray (SXR) light has wavelengths 10-100 times shorter than visible light: thus, it should be possible to design a powerful microscope that can image structures that are too small or too opaque to be seen with visible light. However, EUV/SXR lenses are very lossy and imperfect, limiting the advantage of using shorter wavelengths, and blurring the resulting images to >8 times the theoretical limit. Fortunately, new techniques pioneered by STROBE scientists Kapteyn, Murnane and Miao make it possible to build lensless microscopes illuminated by coherent laser-like beams — a capability that is revolutionizing X-ray imaging worldwide. Very recently, the Kapteyn-Murnane group at CU Boulder used tabletop EUV beams at a wavelength of 13nm to achieve sub-wavelength spatial resolution imaging at short wavelengths for the first time – essentially demonstrating the first near-perfect X-ray microscope. Moreover, because the EUV source produces exceedingly short, femtosecond (~10-15 sec), bursts of light, it can now be used to make stroboscopic movies to observe how the nanoworld functions. STROBE graduate student Dennis Gardner received the American Physical Society Division of Laser Science Thesis Award for this work.

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