Suppressing meta-holographic artifacts by laser coherence tuning
2021-05-26
(Press-News.org) Metasurface holograms (meta-holograms) are ultra-thin artificial surfaces designed to shape incident light and project it to extremely wide angles. Meta-holograms have opened up numerous possibilities such as light multiplexing, information processing, 3D display, high-density data storage, and optical encoding. Despite of these remarkable advances, the road to practical applications of meta-holograms is hindered by artifacts that originate from strong interactions between the building blocks of the meta-holographic surface and inevitable fabrication defects, ultimately causing distortion and degradation to the holographic image. The small dimensions of the meta-hologram, together with the random nature of fabrication defects, make the artifacts problem extremely difficult to correct.
In a new paper published in Light Science & Application, a team of scientists, led by Hui Cao from Yale University, USA, Qinghai Song and Shumin Xiao from Harbin Institute of Technology (Shenzhen), China, and co-workers have developed an efficient method to suppress the holographic artifacts while maintaining the image quality. Their method is based on fine-tuning of the coherence of illumination, implemented with a degenerate cavity laser, a unique class of lasers which allows a precise and continuous tuning of the spatial coherence of emission with little change in total power and temporal coherence.
The majority of lasers operates with a single or a few spatial modes, and produces highly coherent emission. When the laser light is used to illuminate a meta-hologram, the interference of scattered waves produce coherent artifacts and severely distort the images. The scientists gradually decrease the coherence of laser illumination to amend the holographic artifacts. However, if the coherence is too low, the fine details of the holographic image will blur. Thus it is essential to find the optimal degree of coherence to suppress artifacts without a significant loss of spatial resolution. This was realized with a novel laser source whose spatial coherence of emission can be tuned gradually, accurately and efficiently.
The scientists summarize the operational principle of their novel technique:
"We design a bright laser source with a precise and continuous tuning of the spatial coherence. The tuning is remarkably energy efficient with low power variation. The laser is then used to illuminate a meta-hologram. The precise tuning allows reaching the right level of coherence required to suppress the coherent artifacts without significant blurring of the holographic image."
"Compared to the existing methods of lowering the coherence of conventional lasers, our degenerate cavity laser exhibits extremely fast decoherence, thus enabling high-speed artifact-free meta-holography with no pre- or post-processing of any kind." they added.
"The new method can be used to dramatically enhance the image quality of compact, dynamical holographic projection displays. This breakthrough will open a new venue for future applications of meta-holograms in augmented reality, optical storage, beam multiplexing, nonlinear holography and optical manipulation." the scientists forecast.
INFORMATION:
[Attachments] See images for this press release:
ELSE PRESS RELEASES FROM THIS DATE:
2021-05-26
GEOLOGY There has long been controversy about whether the world's highest region, Tibet, has grown taller during the recent geological past. New results from the University of Copenhagen indicate that the 'Roof of the World' appears to have risen by up to 600 meters and the answer was found in underwater lava. The knowledge sheds new light on Earth's evolution.
Tibet is referred to as the Roof of the World for good reason. With an average altitude of 4,500 meters above sea level and the world's two highest peaks, Mount Everest and K2, the vast Himalayan mountain range towers higher than anywhere else on Earth.
But the Tibetan plateau's height has been ...
2021-05-26
The goal of Kaare Hartvig Jensen, Associate Professor at DTU Physics, was to reduce the need for harvesting, transporting, and processing crops for the production of biofuels, pharmaceuticals, and other products. The new method of extracting the necessary substances, which are called plant metabolites, also eliminates the need for chemical and mechanical processes.
Plant metabolites consist of a wide range of extremely important chemicals. Many, such as the malaria drug artemisinin, have remarkable therapeutic properties, while others, like natural rubber or biofuel from tree sap, have mechanical properties.
Harvesting cell by cell
Because most plant metabolites are isolated in individual cells, the method ...
2021-05-26
When do bees sting and how do they organise their collective defence behaviour against predators? An interdisciplinary team of researchers from the Universities of Constance and Innsbruck has provided new insights into these questions. Their study, published in BMC Biology, combined behavioural experiments with an innovative theoretical modelling approach based on "Projective Simulation". It shows that individual bees decide whether to sting - or not - based on the presence and concentration of an alarm pheromone. The scientists suggest that each bee has a likelihood of stinging that is not constant, but shows at least two internal thresholds for the concentration of the pheromone: one to start stinging and one to stop stinging. The computational modelling also revealed how several environmental ...
2021-05-26
A long-standing theory assumes that terrestrial plants could only have developed by entering into a symbiosis with fungi, whereby the two organisms exchange resources in a mutually beneficial way. A new study by an international group of scientists has now confirmed this theory. By studying a liverwort species (a bryophyte related to mosses), the scientists succeeded in demonstrating that a lipid transfer takes place between the plant and the fungus similar to that already known to exist in plants with stems and roots - so called vascular plants. The study was led by French researchers from the Centre national de la recherche scientifique (CNRS) and the Université de Toulouse III - Paul Sabatier, in collaboration with the ...
2021-05-26
Researchers at Aalto University in Finland have found strong evidence that warm ice - that is, ice very close in temperature to zero degrees Celsius - may fracture differently than the kinds of ice typically studied in laboratories or nature. A new study published in The Cryosphere takes a closer look at the phenomenon, studied at the world's largest indoor ice tank on Aalto's campus.
Understanding how ice breaks is crucial for ensuring safe harbours and bridges in cool climates, as well as transportation through historically ice-heavy regions. As global warming brings changes to once-predictable seasonal conditions, the rules underpinning infrastructure ...
2021-05-26
A paper published in the Journal of Clinical Medicine presents the results from a study which examined the use of an infrared thermal imaging camera as a novel non-invasive point-of-care tool for lymphatic filariasis lower-limb lymphoedema.
Thermal imaging has been used for several decades in a wide range of medical disciplines, but this is the first time it has been used for filariasis or any skin neglected tropical disease (NTD).
LSTM's Dr Louise Kelly-Hope led the research. She said: "Infrared thermal imaging presents an innovative and objective method for quantifying clinical change in filarial lymphoedema status by using naturally emitting infrared radiation to capture skin surface temperatures. This ...
2021-05-26
A recent study finds that the vast majority of Black adolescents have experienced racism, that they experience anticipatory stress about experiencing racism again, and that their racial identity can influence that stress in a variety of ways.
"We know that racism is stressful," says Elan Hope, corresponding author of the study and an associate professor of psychology at North Carolina State University. "Part of that stress is anticipatory - waiting for the next racist thing to happen. But not everyone experiences this stress the same way. We wanted to know how racial identity may influence ...
2021-05-26
Non-parents expand the range of their facial expressions in caring for infants among primates, a team of anthropologists has found. The study shows the ability, among non-relatives, to both decipher facial expressions and to be attuned to others' emotional states, revealing the evolutionary nature of communication.
The research, which appears in the journal Evolution, focused on the relationship between alloparenting, or infant care by non-parents, and the adoption of detailed facial expressions across more than 30 species of primates.
"Our results confirm previous work indicating ...
2021-05-26
FinBIF, which is coordinated and developed by the Finnish Museum of Natural History Luomus of the University of Helsinki:
digitises natural history specimens and produces digital DNA barcodes
collects born-digital observation records of professionals and amateurs alike
integrates data collated from different sources
distributes the data mass as open data
offers data management services, such as platforms for recording and publishing monitoring data and for reporting observations, to researchers, the environmental administration and the public
Typically, different types of species data and the different stages of the data life cycle, that is, digitisation, collection, ...
2021-05-26
Whether in desalination, water purification or CO2 separation, membranes play a central role in technology. The Helmholtz-Zentrum Hereon has been working for several years on a new variant: it consists of special polymers that form pores of the same size on the nanometer scale. The materials to be separated, such as certain proteins, can literally slip through these pores. Because these separation layers are very thin and thus very fragile, they are bound to a spongey structure with much coarser pores, providing the structure with the necessary mechanical stability.
"A special aspect is that these structures form in an act of self-organization," says Prof. Volker Abetz, director of the Hereon Institute of Membrane Research and professor of physical chemistry at the University ...
LAST 30 PRESS RELEASES:
[Press-News.org] Suppressing meta-holographic artifacts by laser coherence tuning
