2,319 research outputs found
Analytical description of high-aperture STED resolution with 0-2 vortex phase modulation
Stimulated emission depletion (STED) can achieve optical super-resolution,
with the optical diffraction limit broken by the suppression on the periphery
of the fluorescent focal spot. Previously, it is generally experimentally
accepted that there exists an inverse square root relationship with the STED
power and the resolution, yet without strict analytical description. In this
paper, we have analytically verified the relationship between the STED power
and the achievable resolution from vector optical theory for the widely used
0-2 vortex phase modulation. Electromagnetic fields of the focal region of
a high numerical aperture objective are calculated and approximated into
polynomials, and analytical expression of resolution as a function of the STED
intensity has been derived. As a result, the resolution can be estimated
directly from the measurement of the saturation power of the dye and the STED
power applied.Comment: (19 pages
Controlled formation and disappearance of creases
Soft, elastic materials are capable of large and reversible deformation, readily leading to various modes of instability that are often undesirable, but sometimes useful. For example, when a soft elastic material is compressed, its initially flat surface will suddenly form creases. While creases are commonly observed, and have been exploited to control chemical patterning, enzymatic activity, and adhesion of surfaces, the conditions for the formation and disappearance of creases have so far been poorly controlled. Here we show that a soft elastic bilayer can snap between the flat and creased states repeatedly, with hysteresis. The strains at which the creases form and disappear are highly reproducible, and are tunable over a large range, through variations in the level of pre-compression applied to the substrate and the relative thickness of the film. The introduction of bistable flat and creased states and hysteretic switching is an important step to enable applications of this type of instability.Engineering and Applied Science
Topological nanophotonics for photoluminescence control
Rare-earth doped nanocrystals are emerging light sources used for many
applications in nanotechnology enabled by human ability to control their
various optical properties with chemistry and material science. However, one
important optical problem -- polarisation of photoluminescence -- remains
largely out of control by chemistry methods. Control over photoluminescence
polarisation can be gained via coupling of emitters to resonant nanostructures
such as optical antennas and metasurfaces. However, the resulting polarization
is typically sensitive to position disorder of emitters, which is difficult to
mitigate. Recently, new classes of disorder-immune optical systems have been
explored within the framework of topological photonics. Here we explore
disorder-robust topological arrays of Mie-resonant nanoparticles for
polarisation control of photoluminescence of nanocrystals. We demonstrate
polarized emission from rare-earth-doped nanocrystals governed by photonic
topological edge states supported by zigzag arrays of dielectric resonators. We
verify the topological origin of polarised photoluminescence by comparing
emission from nanoparticles coupled to topologically trivial and nontrivial
arrays of nanoresonators
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Creases on the interface between two soft materials
Theory and experiment are presented to show that an interface between two soft materials under compression can form creases, a type of bifurcation distinct from wrinkles. While creases bifurcate from a state of flat interface by a deformation localized in space and large in amplitude, wrinkles bifurcate from a state of flat interface by a deformation nonlocal in space and infinitesimal in amplitude. The interfacial creases set in at a lower critical compression than interfacial wrinkles, but higher than surface creases. The condition for the onset of interfacial creases is scale-free, and is calculated in terms of elastic moduli, pre-strains and applied strains.Engineering and Applied Science
Research progress on GlnR-mediated regulation in Actinomycetes
This review constitutes a summary of current knowledge on GlnR, a global regulator, that assumes a critical function in the regulation of nitrogen metabolism of Actinomycetes. In cross-regulation with other regulators, GlnR was also shown to play a role in the regulation of carbon and phosphate metabolisms as well as of secondary metabolism. A description of the structure of the GlnR protein and of its binding sites in various genes promoters regions is also provided. This review thus provides a global understanding of the critical function played by GlnR in the regulation of primary and secondary metabolism in Actinomycetes
Contrast-enhanced fluorescence microscope by LED integrated excitation cubes
Fluorescence microscopy is a powerful tool for scientists to observe the microscopic world, and the fluorescence excitation light source is one of the most critical components. To compensate for the short operation lifetime, integrated light sources, and low excitation efficiency of conventional light sources such as mercury, halogen, and xenon lamps, we designed an LED-integrated excitation cube (LEC) with a decentralized structure and high optical power density. Using a Fresnel lens, the light from the light-emitting diode (LED) was effectively focused within a 15 mm mounting distance to achieve high-efficiency illumination. LEC can be easily designed in the shape of fluorescence filter cubes for installation in commercial fluorescence microscopes. LECs’ optical efficiency is 1–2 orders of magnitude higher than that of mercury lamps; therefore, high-quality fluorescence imaging with spectral coverage from UV to red can be achieved. By replacing conventional fluorescence filter cubes, LEC can be easily installed on any commercial fluorescence microscope. A built-in LEC driver can identify the types of LEDs in different spectral bands to adopt the optimal operating current and frequency of pulses. Moreover, high-contrast images can be achieved in pulse mode by time-gated imaging of long-lifetime luminescence
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