Lasers are not all that’s green in the photonics industry. Photonics technologies are helping to reduce energy consumption, they’re used in the manufacturing of renewable energy technologies, and many green, sustainable practices are adhered to throughout the photonics industry. And, yes, trend that it is – there is certainly green in going green. New technologies and products are developed with energy efficiency in mind. This is not only because energy savings is a buzz word or marketing tool but also because customers are trying to cut their manufacturing costs – and saving electricity is a great way to start. As an example, Power Technology (PTI) of Little Rock, Ark., has replaced inefficient gas lasers with diode lasers. The IQ Micro (IQu) laser at 488 nm produces 60 mW of light and typically requires less than 10 W of energy to operate. The argon gas laser it replaces required 1500 W to generate the same power and wavelength.
Imaging in Green Apps
Use of machine vision systems in the solar industry makes sense, as precision and high-quality output are of paramount importance. According to Gregory Hollows, director of machine vision solutions at Edmund Optics in Barrington, N.J., machine vision used in the solar industry is not just about looking for defects in wafers. “A subtle modification of one lens can be like reinventing the wheel,” Hollows said. The goal is to see with the camera what you see with the eye. It has to be done on the assembly line, and it has to be repeatable over and over. In some cases the material itself presents challenges – from highly reflective to curved to flat – “many properties come into play.”
Optics in Solar
The huge growth in solar energy installations has presented optics manufacturers with new opportunities for components that collect or focus the sun’s energy. Some of the components are similar to those made for other applications, such as homogenizing rods, light pipes or lightguides, according to Gregg Fales, product line manager at Edmund Optics. In some cases, solutions are customized for specific photovoltaic applications. For example, concentrated photovoltaics (CPV) requires a square aperture at one end of a concentrated parabolic concentrator (CPC) that’s bigger than the square aperture at the other end.
Optics engineers and other lighting experts are hard at work trying to improve solid-state lighting, driven in part by government mandates. According to a report by the US Department of Energy, 22 percent of the electricity generated in the US goes toward lighting applications. If light sources were converted to more energy-efficient LEDs, electrical use would be significantly reduced. To that end, governments are promoting research and development in the area of LEDs so that the technology can catch up with the demand for lighting applications. The US Department of Energy, for example, set a research goal of 160 lumens per watt by 2025.
Adhering to Green
Companies are also embracing sustainability efforts such as “lean” manufacturing, adoption of the Waste Electrical and Electronic Equipment (WEEE) initiative, compliance with RoHS standards and the REACH initiative. And many are taking a myriad of smaller measures that add up to a great amount of energy saved, such as recycling manufacturing byproducts, installing energy-efficient lighting and more.
For more information: https://www.photonics.com/Articles/Green_Photonics_/a41461
A team of researchers in Germany and Australia report using photopolymerization to coat upconverting nanoparticles (UCNPs) with a “stealth cap” that increases nanoparticle stability and biocompatibility. The work, the researchers believe, could increase the usefulness of UCNPs in medical applications. Results from in vitro demonstrations showed that the UCNPs with the hydrophilic cap maintain photoluminescence when submerged in water, do not interact with biomolecules in human blood serum, and are also capable of carrying other molecules, like drugs or radioactive labels, within the cap via bioconjugation. The researchers, led by Holger Stephan of Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany, say these stealth qualities could someday prove useful in targeted drug delivery for cancer treatment and biomedical imaging.
Traveling incognito through the body
UCNPs are of great interest for biomedical imaging because they absorb infrared (IR) light, which is typically safe for the human body, and convert it into detectable, tunable ultraviolet (UV) light signals. However, UCNPs are usually produced with a hydrophobic oleate coating. This hydrophobic coating repels water molecules, which prevents the UCNPs from traveling unencumbered throughout the body (which is more than 50 percent water by weight). The HZDR team solved this problem by synthesizing a hydrophilic cap for UCNPS that can in principle allow the particles to travel more freely within biological systems. The method uses UV irradiation to first crosslink diacetylenes on the surface of UCNPs, creating a hydrophilic polydiacetylene (PDA) coating about 2-nm thick. Next, the researchers overcoat the PDA layer with mixed-diyne phospholipids, to give the UCNPs a neutral surface charge that prevents biomolecules from sticking to them as they move through the body.
In vitro demonstrations
The researchers demonstrated UCNP fluorescence by exciting the particles with IR light. They recorded emissions between 550 nm and 750 nm, with a maximum emission at 625 nm, and found that the UCNPs only lost a small amount of luminescence intensity when submerged in water. To test the surface-charge-neutrality “invisibility cloak,” the researchers incubated UCNPs with and without a phospholipid overcoat in human blood serum at 37 °C for one hour. Results from gel electrophoresis showed the phospholipid-coated UCNPs had almost no biomolecules from the serum adhered to their surfaces, while the uncoated UCNPs picked up a substantial amount of biomaterial.
The team also discovered that the phospholipid overcoat gave the UCNPs’ surface-exposed amino groups to which other molecules—for example, radioactive labels or drugs—could be attached using bioconjugation methods. To demonstrate the ability to stow away molecules of interest, the researchers successfully crosslinked a radioactive copper label to the surface of the UCNPs.
Stephan and his group say that results from these preliminary demonstrations are encouraging, and they hope to further investigate their UCNPs with in vivo studies.
For more information: doi: 10.1002/anie.20181100
Congratulations for the publication of paper “The electronic and optical properties of armchair germanene nanoribbons”
By Arash Karaei Shiraz, Arash Yazdanpanah Goharrizi, Seyedeh Mehri hamidi
The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n=3P, n=3P+1, n=3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG(3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.
The DESY accelerator facility in Hamburg, Germany, goes on for miles to host a particle making kilometer-long laps at almost the speed of light. Now researchers have shrunk such a facility to the size of a computer chip.
A University of Michigan team in collaboration with Purdue University created a new device that still accommodates speed along circular paths, but for producing lower light frequencies in the terahertz range of applications such as identifying counterfeit dollar bills or distinguishing between cancerous and healthy tissue. “The more terahertz sources we have, the better. This new source is also exceptionally more efficient, let alone that it’s a massive system created at the millimeter scale,” said Vlad Shalaev, Purdue’s Bob and Anne Burnett Distinguished Professor of Electrical and Computer Engineering. The device that Michigan and Purdue researchers built generates so-called “synchrotron” radiation, which is electromagnetic energy given off by charged particles, such as electrons and ions, that are moving close to the speed of light when magnetic fields bend their paths.
Several facilities around the world, like DESY, generate synchrotron radiation to study a broad range of problems from biology to materials science. But past efforts to bend light to follow a circular path have come in the form of lenses or spatial light modulators too bulky for on-chip technology. A team led by Merlin and Meredith Henstridge, now a postdoctoral researcher at the Max Planck Institute for the Structure and Dynamics of Matter, substituted these bulkier forms with about 10 million tiny antennae printed on a lithium tantalite crystal, called a “metasurface,” designed by the Michigan team of Anthony Grbic and built by Purdue researchers.
The researchers used a laser to produce a pulse of visible light that lasts for one trillionth of a second. The array of antennae causes the light pulse to accelerate along a curved trajectory inside the crystal. Instead of a charged particle spiraling for kilometers on end, the light pulse displaced electrons from their equilibrium positions to create “dipole moments.” These dipole moments accelerated along the curved trajectory of the light pulse, resulting in the emission of synchrotron radiation much more efficiently at the terahertz range.
Lung infections due to Gram-negative bacteria are notoriously difficult to diagnose rapidly for prompt treatment. A new procedure involving an optical probe and a fluorescent marker could make those pulmonary predators pop out on a display screen, leading to rapid diagnosis of potentially deadly pneumonia.
Engineering a fluorescent marker
So-called Gram-negative bacteria—the name comes from their lack of reaction to a crystal violet stain—have an outer cell membrane that contains an endotoxin with a component called lipid A. In small amounts, lipid A can provoke an attacking response from the human body’s immune system, but higher concentrations during an infection by Gram-negative bacteria can lead to septic shock, and even death, in the patient. Traditional methods for diagnosing Gram-negative pulmonary infections, from lung-tissue biopsy to sputum cultures that take days to produce results, have significant drawbacks. To get around those drawbacks, the Edinburgh team sought a fluorescent marker that would adhere specifically to Gram-negative bacteria. They found that an antimicrobial peptide called polymyxin selectively binds to the lipid A in the outer membrane of Gram-negative bacteria. Then, they attached the polymyxin to a fluorophore molecule. By testing the combination marker on several species of disease-causing bacteria, the scientists found that the marker produced fluorescent amplification with good signal-to-noise ratios when it hooked up with Gram-negative bacteria, but not with Gram-positive pathogens. The marker also distinguished between bacteria and mammalian cells in vitro.
Animal and human testing
After toxicology tests to make sure that the fluorescent marker did not damage animal tissues, the team hooked up ex vivo sheep lungs to a mechanical ventilator. The researchers then tested the ability of their optical endomicroscope with an optical-fiber probe to detect the bacteria’s fluorescence within tissues. The fluorescence confocal endomicroscope captured images at 12 frames/s and used a 488-nm laser as the illumination source. Finally, the researchers used their system on two small groups of humans: six patients with bronchiectasis, a chronic condition of airway enlargement with mucus production leading to frequent infections, and seven mechanically vented patients who were in the intensive care unit with suspected pneumonia. The clinical version of the optical endomicroscope had a circular field of view roughly 600 μm in diameter. Image-processing algorithms made the Gram-negative bacteria appear as bright spots.
For more information: doi:10.1126/scitranslmed.aal0033
A team led by OSA Fellow Sharon Weiss of Vanderbilt University, USA, has demonstrated an all-dielectric “bowtie” structure that combines the tight spatial light confinement of plasmonic resonators with the ultralow losses and long cavity lifetimes of photonic crystals.
A long-standing conundrum of nanophotonics has been how to achieve deep-subwavelength light confinement (measured by a parameter called the mode volume, Vm) while holding the light in place in a cavity for long periods (an ability characterized by the cavity’s quality factor, Q). Plasmonics—the enhancement of optical fields at metal-dielectric interfaces, using nanoscale metallic resonators or antennas—can give you very tight spatial confinement (low Vm). But plasmonic devices tend to be lossy, with anemic Q factors, and thus the spatially confined light energy quickly dissipates.
In a theoretical study in late 2016, Weiss, along with OSA member and then-grad-student Shuren Hu (now with the semiconductor fabrication firm GlobalFoundries), proposed an answer: combine the subwavelength-confinement properties of nanoscale dielectrics with the near-legendary Q values of photonic-crystal cavities. The process works in two steps. Incident light becomes localized in the photonic-crystal cavity air hole. Then, the cavity’s bowtie geometry, and the energy concentration at the bowtie tips, funnels and squeezes the optical energy into the nanoscale dielectric bar. The result is deep subwavelength confinement of the light energy, combined with the photonic crystal’s long cavity lifetime.
The result was a silicon photonic-crystal cavity consisting of unit-cell bowties with a radius of 150 nm, and with mirror unit cells of 187 nm radii on either end, arrayed in a 700-nm-wide waveguide. To put the structure through its paces, the team tied it, via lensed optical fiber, to a 1500-to-1630-nm tunable continuous-wave laser, and measured the field distribution using near-field scanning optical microscopy.The quality factor, on the order of Q = 105
Realizing those possibilities will take a significant amount of work to scale up from these initial experiments, and to reproducibly create the exquisitely precise photonic-crystal structures required. Hu, at GlobalFoundries, is now co-P.I. with Weiss on a new project, funded by a U.S. National Science Foundation GOALI (Grant Opportunities for Academic Liaison with Industry) award, to work toward scale-up and proof-of-concept applications. Weiss notes that Hu began the work as a grad student in her lab under another GOALI grant, with IBM.
For more information: doi: 10.1126/sciadv.aat2355
Using nanochip technology and a targeted beam of light, scientists have devised a real-time, label-free way to monitor biofilms, an important component in the search for alternatives to bacteria-resistant antibiotics. The team from the Okinawa Institute of Science and Technology (OIST) wanted to gain a better understanding of the biochemical reactions that allow bacteria to produce biofilms, which are slimy linked matrix structures. Finding no tools available that would allow them to monitor biofilm growth according to their requirements, the researchers modified an existing tool.
“We created little chips with tiny structures for E. coli to grow on,” said researcher Nikhil Bhalla. “They are covered in mushroom-shaped nanostructures with a stem of silicon dioxide and a cap of gold. When the researchers exposed the nanomushrooms to a beam of light, the nanostructures absorbed light through a localized surface plasmon resonance (LSPR) sensor. The sensor was able to capture the signatures of biofilm formation in real time by measuring the wavelength shift in the LSPR resonance peak with high temporal resolution. The researchers could observe the E. coli growing around the mushroom structures without damaging the sample.
A nanomushroom chip undergoing testing with an localized surface plasmon resonance (LSPR) device. Courtesy of OIST and CC 2.0.
The researchers used the LSPR sensor to investigate how biofilm formation is affected by different drugs, including conventional antibiotics. To enable a constant stream of data from the LSPR-based tool, the researchers developed a program to automate the data analysis and processing so they could monitor biofilm growth in real time.The team believes that its benchtop tool could be used on a variety of clinically relevant bacteria for biofilm characterization and drug screening. It plans to miniaturize the technology to create a portable device that could be used in a range of biosensing applications.
For more information: (doi: 10.1021/acssensors.8b00287).
Researchers from Japan have taken a step toward faster and more advanced electronics by developing a a better way to measure and manipulate conductive materials through scanning tunneling microscopy. The team published their results in July in Nano Letters, an American Chemical Society journal. Scientists from the University of Tokyo, Yokohama National University, and the Central Research Laboratory of Hamamatsu Photonics contributed to this paper.
Scanning tunneling microscopy (STM) involves placing a conducting tip close to the surface of the conductive material to be imaged. A voltage is applied through the tip to the surface, creating a “tunnel junction” between the two through which electrons travel. The shape and position of the tip, the voltage strength, and the conductivity and density of the material’s surface all come together to provide the scientist with a better understanding of the atomic structure of the material being imaged. With that information, the scientist should be able to change the variables to manipulate the material itself. The researchers designed a custom terahertz pulse cycle that quickly oscillates between near and far fields within the desired electrical current.
“The characterization and active control of near fields in a tunnel junction are essential for advancing elaborate manipulation of light-field-driven processes at the nanoscale,” said Jun Takeda, a professor in the department of physics in the Graduate School of Engineering at Yokohama National University. “We demonstrated that desirable phase-controlled near fields can be produced in a tunnel junction via terahertz scanning tunneling microscopy with a phase shifter.”
According to Takeda, previous studies in this area assumed that the near and far fields were the same—spatially and temporally. His team examined the fields closely and not only identified that there was a difference between the two, but realized that the pulse of fast laser could prompt the needed phase shift of the terahertz pulse to switch the current to the near field.
More information: Katsumasa Yoshioka et al, Tailoring Single-Cycle Near Field in a Tunnel Junction with Carrier-Envelope Phase-Controlled Terahertz Electric Fields, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b02161
Coherent coupling between plasmons and transition dipole moments in emitters can lead to two distinct spectral effects: vacuum Rabi splitting at strong coupling strengths, and induced transparency (also known as Fano interference) at intermediate coupling strengths. Achieving either strong or intermediate coupling between a single emitter and a localized plasmon resonance has the potential to enable single-photon nonlinearities and other extreme light–matter interactions, at room temperature and on the nanometer scale. Both effects produce two peaks in the spectrum of scattering from the plasmon resonance, and can thus be confused if scattering measurements alone are performed. Here we report measurements of scattering and photoluminescence from individual coupled plasmon–emitter systems that consist of a single colloidal quantum dot in the gap between a gold nanoparticle and a silver film. The measurements unambiguously demonstrate weak coupling (the Purcell effect), intermediate coupling (Fano interference), and strong coupling (Rabi splitting) at room temperature.
As shown in Fig. , however, a measurement of the photoluminescence (PL) spectrum can distinguish between the two regimes. Unlike scattering, PL is an incoherent process, and thus does not display Fano interference. Splitting in the PL spectrum thus occurs only in the strong-coupling regime, and has therefore been recognized as the definitive signature of Rabi splitting. So far, there has been only one report of PL splitting for a single emitter (a QD) coupled to a plasmonic metal nanostructure, but the PL spectrum showed an unexpected four-peak structure.
Fabrication of coupled quantum-dot / gap-plasmon systems. a Illustration of the synthesis process. Quantum dots (red) are linked to gold nanoparticles (yellow) through their capping molecules. The linked assemblies are then deposited on a silver film. b Electron-microscope images of linked assemblies. Quantum dots are colored in red and indicated by arrows. The left image was obtained by scanning transmission electron microscopy, and the right image was obtained by transmission electron microscopy. The scale bars are 100 nm
For more information: https://www.nature.com/articles/s41467-018-06450-4