Microscopy & Imaging News and Discussions

weatheriscool
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Getting in gear: Researchers create a slow light device with high optical quality
https://phys.org/news/2022-01-gear-devi ... ality.html
by University of Massachusetts Amherst
Researchers including a postdoc at the University of Massachusetts Amherst have created a gear-shaped photonic crystal microring that increases the strength of light-matter interactions without sacrificing optical quality. The result is an on-chip microresonator with an optical quality factor 50 times better than the previous record in slow light devices that could improve microresonators used in a range of photonics applications, including sensing and metrology, nonlinear optics and cavity quantum electrodynamics.

Optical microresonators are structures that enhance light-matter interactions through a combination of long temporal confinement (i.e., high quality factor) and strong spatial confinement of an electromagnetic wave. The device the authors have developed in many ways integrates the best attributes of two types of optical microresonators—a photonic crystal and a whispering gallery mode resonator—in one device. While combining the two has been attempted in the past, previous microring devices that have succeeded in slowing light to increase interactions (a consequence of the photonic crystal) have had to sacrifice quality factor. In this new "microgear" photonic crystal ring, researchers observed modes with group velocity slowed down by 10 times relative to conventional microring modes without any degradation in quality factor.

The study, led by first author Xiyuan Lu and principal investigator Kartik Srinivasan, both from the National Institute of Standards and Technology (NIST) and the University of Maryland, appears in the January 2022 issue of Nature Photonics. UMass Amherst's Andrew McClung, a postdoc in the photonics lab of Amir Arbabi and a former NIST colleague of Lu, provided modeling and computer simulations for the work.
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Advanced photonic radar captures images down to the centimeter scale
By Michael Irving
February 07, 2022
https://newatlas.com/electronics/advanc ... ter-scale/

Researchers at the University of Sydney have developed a new type of radar that can measure objects down to centimeters. The new technique uses a photonic system to generate much higher bandwidth signals, enabling radar that can detect smaller objects more precisely, and even be used to monitor patient vital signs in hospitals.

Radar works by beaming radiofrequency signals out and analyzing how they bounce back, revealing the location, shape and speed of an object of interest, like a plane. Frequencies of a few hundred megahertz are most commonly used, which return images with a resolution on the scale of meters. Using higher frequencies could allow radar to capture finer detail, but that also widens the bandwidth. This requires far more powerful signal processing, in turn blowing out the cost and complexity of the system.

Photonic radar can help solve that problem. This technology still beams out microwaves, but the signals are generated and processed using lasers instead, giving them a much higher frequency over a wider bandwidth.

In the new study, the researchers developed an advanced photonic radar system that produced signals with a bandwidth of 11 GHz, centered on the frequency of 34 GHz. Importantly, the electronic components driving this operate at frequencies of just 40 to 80 MHz, keeping the system’s requirements simple. The resulting radar images have a much finer resolution, down to just 1.3 cm (0.5 in).
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Researchers combine piezoelectric thin film and metasurfaces to create lens with tunable focus
https://phys.org/news/2022-02-combine-p ... -lens.html
by The Optical Society
For the first time, researchers have created a metasurface lens that uses a piezoelectric thin film to change focal length when a small voltage is applied. Because it is extremely compact and lightweight, the new lens could be useful for portable medical diagnostic instruments, drone-based 3D mapping and other applications where miniaturization can open new possibilities.

"This type of low-power, ultra-compact varifocal lens could be used in a wide range of sensor and imaging technologies where system size, weight and cost are important," said research project leader Christopher Dirdal from SINTEF Smart Sensors and Microsystems in Norway. "In addition, introducing precision tunability to metasurfaces opens up completely new ways to manipulate light."

Dirdal and colleagues describe the new technology in the journal Optics Letters. To change focal length, a voltage is applied over lead zirconate titanate (PZT) membranes causing them to deform. This, in turn, shifts the distance between two metasurface lenses.

"Our novel approach offers a large displacement between the metasurface lenses at high speed and using low voltages," said Dirdal. "Compared to state-of-the-art devices, we demonstrated twice the out-of-plane displacement at a quarter of the voltage."

Combining technologies

The researchers made the new lens using metasurfaces—flat surfaces that are patterned with nanostructures to manipulate light. They are particularly interesting because they can integrate several functionalities into a single surface and can also be made in large batches using standard micro- and nanofabrication techniques at potentially low cost.
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Researchers develop large-field-of-view and high-resolution two-photon microscope
https://phys.org/news/2022-02-large-fie ... scope.html
by Li Yuan, Chinese Academy of Sciences
Two-photon microscopy (TPM) enables the observation of cellular and subcellular dynamics and functions in deep nervous tissues, providing critical in situ and in vivo information for understanding neurological mechanisms.

However, conventional TPM retains cellular resolution imaging over only a restricted field-of-view (FOV), usually 0.5 × 0.5 mm2, depending on the optical system. FOV is usually determined by objectives.

A research team led by Prof. Zheng Wei from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences proposed a novel method to extend the FOV of objectives and achieve high-resolution and large-FOV two-photon imaging.

The study was published in Optics Letters on Feb. 14.

Although several TPM systems have been reported with custom design objectives to achieve large FOV with high-resolution imaging, these systems need sophisticated design and assembly of customized optical components, which limits their wide applications.

The nominal FOV of objectives reflects the maximum imaging area where the optical aberration is considerably corrected. The team found that the incident light still could reach the area outside the nominal FOV of objectives (the extended FOV). However, when the signals from the extended FOV were used for imaging, the images were extremely blurred and distorted.
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New optical tweezers can control luminescent color using light pressure
https://phys.org/news/2022-02-optical-t ... ssure.html
by Osaka City University
One big stumbling block in the field of photonics is that of color control. Until now, to control color, i.e. the wavelength of light emission, researchers would have to alter the chemical structure of the emitter or the concentration of the solvent—all of which require direct contact, greatly limiting their application.

"Such conditions make it impossible to change color quickly, use it as a light source in microscopic spaces like a cell, or in closed systems where exchange is not an option," says Yasuyuki Tsuboi and professor of the Department of Chemistry, Osaka City University. With "optical tweezers," a technology he developed in previous research, Prof. Tsuboi led a team of researchers to show it possible to control the luminescence color remotely, using only the effect of light pressure.

Their findings were recently published online in the German international journal Angewandte Chemie.

For years, Professor Tsuboi and his colleagues have been conducting research on a technology that can capture and manipulate nano- and micrometer-sized materials with a laser. In exploring this "optical tweezers" technology, they found that when a silicon crystal with a special needle-shaped nanostructure, called black silicon, was submerged in a sample solution, the optical field enhancement effect of the nanostructure trapped a perylene-modified polymer, causing a local concentration of the solution to increase and form an aggregate of polymers.
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Ultra-compact integrated photonic device could lead to new optical technologies
https://phys.org/news/2022-03-ultra-com ... ogies.html
by University of Chicago
Photonic integrated circuits are essential to many technologies, including fiber-optic communications, mapping systems, and biosensors.

These circuits—which use photons instead of electrons—employ optical isolators that allow photons to travel in only one direction, which prevents light from re-entering the system and destabilizing it. But guiding light in one direction often requires large magnets, making these circuits difficult to create on a small scale.

Researchers at University of Chicago's Pritzker School of Molecular Engineering (PME) have developed a new way to guide light in one direction on a tiny scale. By coupling light confined in a nanophotonic waveguide with an atomically thin, two-dimensional semiconductor, the researchers exploited the properties of both the light and the material to guide photons in one direction.

The result – a small, tunable on-chip photonic interface – could lead to smaller photonic integrated circuits that could be more easily integrated into modern technologies, including computing systems and self-driving cars.
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A stretchy display for shapable electronics
https://techxplore.com/news/2022-03-str ... onics.html
by Stanford University
No one would ever imagine crumpling up their smartphone, television or another electronic device. Today's displays—which are flat, rigid and fragile—lack the ability to reshape to interactively respond to users.

As part of an overarching quest to build "skin-inspired" electronics that are soft and stretchy, Stanford University chemical engineer Zhenan Bao and her research team have been developing a display to change that. Now, after more than three years of work, they show the proof of principle toward a stretchable, potentially reshapable display in a new paper published March 23 in Nature.

Their invention hinges on the discovery of a method to produce a high-brightness elastic light-emitting polymer, which functions like a filament in a lightbulb. The group's resulting display is made entirely of stretchy polymers—synthetic plastic materials. The device has a maximum brightness at least two times that of a cellphone and can be stretched up to twice its original length without tearing.

"Stretchable displays can allow a new way of interactive human-machine interface," said Bao, the K. K. Lee Professor in the School of Engineering and senior author of the paper. "We can see the image and interact with it, and then the display can change according to our response."

An illuminating discovery

Most light-emitting polymers are stiff and crack when stretched. Scientists can increase their flexibility by adding elastic insulating materials, such as rubber. But these additives decrease electrical conductivity, which requires the polymer to use a dangerously high voltage to generate even dim light.

About three years ago, however, postdoctoral scholar Zhitao Zhang discovered that a yellow-colored light-emitting polymer called SuperYellow not only became soft and pliable but also emitted brighter light when mixed with a type of polyurethane, a stretchy plastic.
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Quantum 'shock absorbers' allow perovskite to exhibit superfluorescence at room temperature
https://phys.org/news/2022-03-quantum-a ... -room.html
by Tracey Peake, North Carolina State University
quote]

Semiconducting perovskites that exhibit superfluorescence at room temperature do so due to built-in thermal "shock absorbers" which protect dipoles within the material from thermal interference. A new study from North Carolina State University explores the mechanism involved in this macroscopic quantum phase transition and explains how and why materials like perovskites exhibit macroscopic quantum coherence at high temperatures.

Picture a school of fish swimming in unison or the synchronized flashing of fireflies—examples of collective behavior in nature. When similar collective behavior happens in the quantum world—a phenomenon known as macroscopic quantum phase transition—it leads to exotic processes such as superconductivity, superfluidity, or superfluorescenece. In all of these processes a group of quantum particles forms a macroscopically coherent system that acts like a giant quantum particle.

Superfluorescence is a macroscopic quantum phase transition in which a population of tiny light emitting units known as dipoles form a giant quantum dipole and simultaneously radiate a burst of photons. Similar to superconductivity and superfluidity, superfluorescence normally requires cryogenic temperatures to be observed, because the dipoles move out of phase too quickly to form a collectively coherent state.

Recently, a team led by Kenan Gundogdu, professor of physics at NC State and corresponding author of a paper describing the work, had observed superfluorescence at room temperature in hybrid perovskites.

"Our initial observations indicated that something was protecting these atoms from thermal disturbances at higher temperatures," Gundogdu says.[/quote]
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A new method to form a lens for atomic-resolution electron microscopes
https://phys.org/news/2022-04-method-le ... copes.html
by Tohoku University

Electron microscopy enables researchers to visualize tiny objects such as viruses, the fine structures of semiconductor devices, and even atoms arranged on a material surface. Focusing down the electron beam to the size of an atom is vital for achieving such high spatial resolution. However, when the electron beam passes through an electrostatic or magnetic lens, the rays of electrons exhibit different focal positions depending on the focusing angle and the beam spreads out at the focus. Correcting this "spherical aberration" is costly and complex, meaning that only a select few scientists and companies possess electron microscopes with atomic resolution.

Researchers from Tohoku University have proposed a new method to form an electron lens that uses a light field instead of the electrostatic and magnetic fields employed in conventional electron lenses. A ponderomotive force causes the electrons traveling in the light field to be repelled from regions of high optical intensity. Using this phenomenon, a doughnut-shaped light beam placed coaxially with an electron beam is expected to produce a lensing effect on the electron beam.

The researches theoretically assessed the characteristics of the light-field electron lens formed using a typical doughnut-shaped light beam—known as a Bessel or Laguerre-Gaussian beam. From there, they obtained a simple formula for focal length and spherical aberration coefficients which allowed them to determine rapidly the guiding parameters necessary for the actual electron lens design.

The formulas demonstrated that the light-field electron lens generates a "negative" spherical aberration which opposes the aberration of electrostatic and magnetic electron lenses. The combination of the conventional electron lens with a "positive" spherical aberration and a light-field electron lens that offset the aberration reduced the electron beams size to the atomic scale. This means that the light-field electron lens could be used as a spherical aberration corrector.
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Researchers Demonstrate Super-Resolution Microscopy

https://www.eurekalert.org/news-releases/949971
(EurekAlert) WASHINGTON — Researchers have developed a new measurement and imaging approach that can resolve nanostructures smaller than the diffraction limit of light without requiring any dyes or labels. The work represents an important advance toward a new and powerful microscopy method that could one day be used to see the fine features of complex samples beyond what is possible with conventional microscopes and techniques.

The new method, described in Optica, Optica Publishing Group’s journal for high-impact research, is a modification of laser scanning microscopy, which uses a strongly focused laser beam to illuminate a sample. The researchers expanded on the technique by measuring not only the brightness, or intensity, of the light after it interacts with a specimen under study, but also detecting other parameters encoded in the light field.

“Our approach could help extend the microscopy toolbox used to study nanostructures in a variety of samples,” said research team leader Peter Banzer from the University of Graz in Austria. “In comparison to super-resolution techniques based on a similar scanning approach, our method is fully non-invasive, meaning it doesn’t require any fluorescent molecules to be injected into a specimen before imaging.”

The researchers show that they can measure the position and sizes of gold nanoparticles with an accuracy of several nanometers, even when multiple particles were touching.

“Our novel approach to laser-scanning microscopy could close the gap between conventional microscopes with limited resolution and super-resolution techniques that require modification of the specimen under study,” said Banzer.
Here is a link to Optica: https://opg.optica.org/
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