Monthly Archives: June 2021

Metals useful in photonics?

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Researchers at the University of Ottawa have debunked a myth, one involving metals and light according to a March 1i, 2021 news item on phys.org (Note: Links have been removed),

Researchers at the University of Ottawa have debunked the decade-old myth of metals being useless in photonics—the science and technology of light—with their findings, recently published in Nature Communications, expected to lead to many applications in the field of nanophotonics.

“We broke the record for the resonance quality factor (Q-factor) of a periodic array of metal nanoparticles by one order of magnitude compared to previous reports,” said senior author Dr. Ksenia Dolgaleva, Canada Research Chair in Integrated Photonics (Tier 2) and Associate Professor in the School of Electrical Engineering and Computer Science (EECS) at the University of Ottawa.

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A March 18, 2021 University of Ottawa news release (also on EurekAlert), which originated the news item, introduced me to the word ‘lossy’ and discussed the decade-long myth in more detail,

“It is a well-known fact that metals are very lossy when they interact with light, which means they cause the dissipation of electrical energy. The high losses compromise their use in optics and photonics. We demonstrated ultra-high-Q resonances in a metasurface (an artificially structured surface) comprised of an array of metal nanoparticles embedded inside a flat glass substrate. These resonances can be used for efficient light manipulating and enhanced light-matter interaction, showing metals are useful in photonics.”

“In previous works, researchers attempted to mitigate the adverse effect of losses to access favorable properties of metal nanoparticle arrays,” observed the co-lead author of the study Md Saad Bin-Alam, a uOttawa doctoral student in EECS.

“However, their attempts did not provide a significant improvement in the quality factors of the resonances of the arrays. We implemented a combination of techniques rather than a single approach and obtained an order-of-magnitude improvement demonstrating a metal nanoparticle array (metasurface) with a record-high quality factor.”

According to the researchers, structured surfaces – also called metasurfaces – have very promising prospects in a variety of nanophotonic applications that can never be explored using traditional natural bulk materials. Sensors, nanolasers, light beam shaping and steering are just a few examples of the many applications.

“Metasurfaces made of noble metal nanoparticles – gold or silver for instance – possess some unique benefits over non-metallic nanoparticles. They can confine and control light in a nanoscale volume that is less than one quarter of the wavelength of light (less than 100 nm, while the width of a hair is over 10 000 nm),” explained Md Saad Bin-Alam.

“Interestingly, unlike in non-metallic nanoparticles, the light is not confined or trapped inside the metal nanoparticles but is concentrated close to their surface. This phenomenon is scientifically called ‘localized surface plasmon resonances (LSPRs)’. This feature gives a great superiority to metal nanoparticles compared to their dielectric counterparts, because one could exploit such surface resonances to detect bio-organisms or molecules in medicine or chemistry. Also, such surface resonances could be used as the feedback mechanism necessary for laser gain. In such a way, one can realize a nanoscale tiny laser that can be adopted in many future nanophotonic applications, like light detection and ranging (LiDAR) for the far-field object detection.”

According to the researchers, the efficiency of these applications depends on the resonant Q-factors.

“Unfortunately, due to the high ‘absorptive’ and ‘radiative’ loss in metal nanoparticles, the LSPRs Q-factors are very low,” said co-lead author Dr. Orad Reshef, a postdoctoral fellow in the Department of Physics at the University of Ottawa.

“More than a decade ago, researchers found a way to mitigate the dissipative loss by carefully arranging the nanoparticles in a lattice. From such ‘surface lattice’ manipulation, a new ‘surface lattice resonance (SLR)’ emerges with suppressed losses. Until our work, the maximum Q-factors reported in SLRs was around a few hundred. Although such early reported SLRs were better than the low-Q LSPRs, they were still not very impressive for efficient applications. It led to the myth that metals are not useful for practical applications.”

A myth that the group was able to deconstruct during its work at the University of Ottawa’s Advanced Research Complex between 2017 and 2020.

“At first, we performed numerical modelling of a gold nanoparticle metasurface and were surprised to obtain quality factors of several thousand,” said Md Saad Bin-Alam, who primarily designed the metasurface structure.

“This value has never been reported experimentally, and we decided to analyze why and to attempt an experimental demonstration of such a high Q. We observed a very high-Q SLR of value nearly 2400, that is at least 10 times larger than the largest SLRs Q reported earlier.”

A discovery that made them realize that there’s still a lot to learn about metals.

“Our research proved that we are still far from knowing all the hidden mysteries of metal (plasmonic) nanostructures,” concluded Dr. Orad Reshef, who fabricated the metasurface sample. “Our work has debunked a decade-long myth that such structures are not suitable for real-life optical applications due to the high losses. We demonstrated that, by properly engineering the nanostructure and carefully conducting an experiment, one can improve the result significantly.”

Here’s a link to and a citation for the paper,

Ultra-high-Q resonances in plasmonic metasurfaces by M. Saad Bin-Alam, Orad Reshef, Yaryna Mamchur, M. Zahirul Alam, Graham Carlow, Jeremy Upham, Brian T. Sullivan, Jean-Michel Ménard, Mikko J. Huttunen, Robert W. Boyd & Ksenia Dolgaleva. Nature Communications volume 12, Article number: 974 (2021) DOI: https://doi.org/10.1038/s41467-021-21196-2 Published 12 February 2021

This paper is open access.

Fish DJ makes discoveries about fish hearing

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A March 2, 2021 University of Queensland press release (also on EurekAlert) announces research into how fish brains develop and how baby fish hear,

A DJ-turned-researcher at The University of Queensland has used her knowledge of cool beats to understand brain networks and hearing in baby fish

The ‘Fish DJ’ used her acoustic experience to design a speaker system for zebrafish larvae and discovered that their hearing is considerably better than originally thought.

This video clip features zebrafish larvae listening to music, MC Hammer’s ‘U Can’t Touch This’ (1990),

Here’s the rest of the March 2, 2021 University of Queensland press release,

PhD candidate Rebecca Poulsen from the Queensland Brain Institute said that combining this new speaker system with whole-brain imaging showed how larvae can hear a range of different sounds they would encounter in the wild.

“For many years my music career has been in music production and DJ-ing — I’ve found underwater acoustics to be a lot more complicated than air frequencies,” Ms Poulsen said.

“It is very rewarding to be using the acoustic skills I learnt in my undergraduate degree, and in my music career, to overcome the challenge of delivering sounds to our zebrafish in the lab.

“I designed the speaker to adhere to the chamber the larvae are in, so all the sound I play is accurately received by the larvae, with no loss through the air.”

Ms Poulsen said people did not often think about underwater hearing, but it was crucial for fish survival – to escape predators, find food and communicate with each other.

Ms Poulsen worked with Associate Professor Ethan Scott, who specialises in the neural circuits and behaviour of sensory processing, to study the zebrafish and find out how their neurons work together to process sounds.

The tiny size of the zebrafish larvae allows researchers to study their entire brain under a microscope and see the activity of each brain cell individually.

“Using this new speaker system combined with whole brain imaging, we can see which brain cells and regions are active when the fish hear different types of sounds,” Dr Scott said.

The researchers are testing different sounds to see if the fish can discriminate between single frequencies, white noise, short sharp sounds and sound with a gradual crescendo of volume.

These sounds include components of what a fish would hear in the wild, like running water, other fish swimming past, objects hitting the surface of the water and predators approaching.

“Conventional thinking is that fish larvae have rudimentary hearing, and only hear low-frequency sounds, but we have shown they can hear relatively high-frequency sounds and that they respond to several specific properties of diverse sounds,” Dr Scott said.

“This raises a host of questions about how their brains interpret these sounds and how hearing contributes to their behaviour.”

Ms Poulsen has played many types of sounds to the larvae to see which parts of their brains light up, but also some music – including MC Hammer’s “U Can’t Touch This”– that even MC Hammer himself enjoyed.

The March 3, 3021 story by Graham Readfearn originally published by The Guardian (also found on MSN News), has more details about the work and the researcher,

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As Australia’s first female dance music producer and DJ, Rebecca Poulsen – aka BeXta – is a pioneer, with scores of tracks, mixes and hundreds of gigs around the globe under her belt.

But between DJ gigs, the 46-year-old is now back at university studying neuroscience at Queensland Brain Institute at the University of Queensland in Brisbane.

And part of this involves gently securing baby zebrafish inside a chamber and then playing them sounds while scanning their brains with a laser and looking at what happens through a microscope.

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The analysis for the study doesn’t look at how the fish larvae react during Hammer [MC Hammer] time, but how their brain cells react to simple single-frequency sounds.

“It told us their hearing range was broader than we thought it was before,” she says.

Poulsen also tried more complex sounds, like white noise and “frequency sweeps”, which she describes as “like the sound when Wile E Coyote falls off a cliff” in the Road Runner cartoons.

“When you look at the neurons that light up at each sound, they’re unique. The fish can tell the difference between complex and different sounds.”

This is, happily, where MC Hammer comes in.

Out of professional and scientific curiosity – and also presumably just because she could – Poulsen played music to the fish.

She composed her own piece of dance music and that did seem to light things up.

But what about U Can’t Touch This?

“You can see when the vocal goes ‘ohhh-oh’, specific neurons light up and you can see it pulses to the beat. To me it looks like neurons responding to different parts of the music.

“I do like the track. I was pretty little when it came out and I loved it. I didn’t have the harem pants, though, but I did used to do the dance.”

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How do you stop the fish from swimming away while you play them sounds? And how do you get a speaker small enough to deliver different volumes and frequencies without startling the fish?

For the first problem, the baby zebrafish – just 3mm long – are contained in a jelly-like substance that lets them breathe “but stops them from swimming away and keeps them nice and still so we can image them”.

For the second problem, Poulsen and colleagues used a speaker just 1cm wide and stuck it to the glass of the 2cm-cubed chamber the fish was contained in.

Using fish larvae has its advantages. “They’re so tiny we can see their whole brain … we can see the whole brain live in real time.”

If you have the time, I recommend reading Readfearn’s March 3, 3021 story in its entirety.

Poulsen as Bexta has a Wikipedia entry and I gather from Readfearn’s story that she is still active professionally.

Here’s a link to and a citation for the published paper,

Broad frequency sensitivity and complex neural coding in the larval zebrafish auditory system by Rebecca E. Poulsen, Leandro A. Scholz, Lena Constantin, Itia Favre-Bulle, Gilles C. Vanwalleghem, Ethan K. Scott. Current Biology DOI:https://doi.org/10.1016/j.cub.2021.01.103 Published: March 02, 2021

This paper appears to be open access.

There is an earlier version of the paper on bioRxiv made available for open peer review. Oddly, I don’t see any comments but perhaps I need to login.

Related research but not the same

I was surprised when a friend of mine in early January 2021 needed to be persuaded that noise in aquatic environments is a problem. If you should have any questions or doubts, perhaps this March 4, 2021 article by Amy Noise (that is her name) on the Research2Reality website can answer them,

Ever had builders working next door? Or a neighbour leaf blowing while you’re trying to make a phone call? Unwanted background noise isn’t just stressful, it also has tangible health impacts – for both humans and our marine cousins.

Sound travels faster and farther in water than in air. For marine creatures who rely heavily on sound, crowded ocean soundscapes could be more harmful than previously thought.

Marine animals use sound to navigate, communicate, find food and mates, spot predators, and socialize. But since the Industrial Revolution, humans have made the planet, and the oceans in particular, exponentially noisier.

From shipping and fishing, to mining and sonar, underwater anthropogenic noise is becoming louder and more prevalent. While parts of the ocean’s chorus are being drowned out, others are being permanently muted through hunting and habitat loss.

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[An] international team, including University of Victoria biologist Francis Juanes, reviewed over 10,000 papers from the past 40 years. They found overwhelming evidence that anthropogenic noise is negatively impacting marine animals.

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Getting back to Poulsen and Queensland, her focus is on brain development not noise although I imagine some of her work may be of use to researchers investigating anthropogenic noise and its impact on aquatic life.