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Physics in the pandemic: ‘Our habit of combining theory and experiments was an advantage for the lockdown’

Photo of Tiphaine Kouadou, Nicolas Treps and Thibault Michel, wearing masks and separated by ~2m, in a corridor at the LKB — **The new lab safety** PhD student Tiphaine Kouadou (front) and colleagues in the multimode quantum optics group at the LKB return to experimental work on 18 May. (Courtesy: Tiphaine Kouadou)

Mattia Walschaers: I lead the group’s theoretical activities, which means that my days are usually split between doing calculations on the blackboard, running simulations, and meetings with students, postdocs and other colleagues (many of whom are mainly working on experiments). On most days, the coffee machine is the most important piece of machinery I encounter. However, I regularly venture down the lab to check up on experimental progress, and at one point I even tried to learn to align some of the optics.

Ironically, the lockdown hit us exactly during the week when I was supposed to make one of my notorious ventures into the lab to help with tomography of a new type of photon detector. We often joke about things going wrong when a theorist goes down to the lab, but in this case, it really seems to have gotten out of hand.

Tiphaine Kouadou: I am an experimentalist, so my work revolves around my laboratory. Before the lockdown was announced, we were building a new experiment. My working days included lab work and developing projects with our lab’s mechanical and electronic workshops.

The COVID-19 crisis forced us to stop all our experimental activities so, as a final-year PhD student, I started writing my thesis instead. I had regular video meetings with my supervisors, during which we discussed my work and how we might resume our experiments once the lockdown’s terms and conditions were relaxed.

MW: We are based in Paris, and thus all of us went into a quite strict lockdown in the middle of March. On a personal level, this has been a harsh couple of months for many of us, because we have barely been allowed to go out on the streets. Some members of our group have been confined alone in an apartment measuring less than 20m². Clearly, these conditions also put people’s mental health at risk, which is something we tried to be vigilant about.

Physics-wise, most of our theory work continues as usual. With paper, a pen, and a computer that has access to a computational grid, I can perform my own work in a normal way. However, supervising students has gotten more complicated now that we can no longer meet in person, and discussing theoretical physics without a shared blackboard is not always practical. We manage to get a lot of work done via video calls, where we discuss notes, papers, project proposals, and even future experiments. It’s a bit strange to spend most of your day talking to a screen, but we have somehow gotten used to it. We try to organize a coffee break over video call once a week, and we have a shared Mattermost (an open-source alternative to the Slack collaboration software) for the whole LKB.

Even so, I think we are all feeling the need for some face-to-face discussions, and now that (as of 11 May) the lockdown is officially over, we have regained a bit of freedom to circulate. It is clear that many people were longing for that.

A cautious return

TK: On 18 May, it became possible for us to restart experimental work. However, for the researchers allowed to work on-site, access to the university campus is restricted to a maximum of two or three days per week. Administrative services are limited, and mechanical and electronic workshops are closed, as is the IT department. This situation is supposed to run until the end of this month and we do not know what the plan will be for June.

As our team is mainly composed of experimentalists, we are alternating the days when people come in to work, and also following new safety rules. For the moment, our main goal is to restart our experimental work safely and to limit contaminations via the experimental equipment. So, in addition to wearing masks, we placed a bottle of hand sanitizer at the lab entrance with the instruction that everyone should use it before touching the experiment.

Photo of a smiling Mattia Walschaers standing in front of a whiteboard filled with equations and diagrams — **Happier times** Mattia Walschaers doing calculations at the whiteboard before the pandemic. (Courtesy: Quentin Glorieux, Laboratoire Kastler Brossel)

MW: Across the university, roughly 15% of the normal research personnel have been allowed to return to their labs since 18 May. We hope that this percentage will be increased in June, but there are still a lot of unknowns. Getting everything organized has been a complicated exercise. We had to make choices about who was allowed to go back to the lab, and who has to continue working from home.

The university and the LKB direction committee have worked hard to instate a series of safety measures. At most, two people at a time are allowed in the same lab space or meeting room; disinfectant gel is available to everyone; everyone has to wear a mask at all times; and at lunch people are supposed to eat alone in their offices, or outside. There are even rules for going up and down staircases to uphold social distancing. We had long discussions about whether to recommend gloves while touching the optical elements in our labs, but we finally decided that it is more important to encourage people to wash their hands frequently. We are also planning to set up some sort of live-stream to allow people in the lab to communicate directly with those who are working from home.

There is a fine line to walk here, though, since several of the new requirements pose challenges for other safety regulations. After all, people should not be alone in the lab in case of accidents. Therefore, the LKB set up an ad-hoc system where people can use Mattermost to register their physical presence at the LKB facilities. They have to sign out when they leave, and they have to make sure that no one is left alone. Since the LKB includes many different research groups, with more than 100 members in total, this system will clearly impose many communication challenges in the days and weeks to come.

Uncertain timeline

As for our theoretical activities, not much will change in the foreseeable future. I am actually interacting more with some of the experimentalists who are not allowed to return to the lab, since many of them have turned to doing some theory to keep making advances in their work. I am secretly hoping to convert them by introducing them to the joys of theoretical physics, but sadly I can see that they are longing to get back to their shiny lasers. I am also hoping to get back to having some blackboard discussions with my colleagues, but I am quite pessimistic about the timeline. I hope to be able to return at some point in July, but it is not unlikely that I will have to wait until the end of summer.

A photo of Daisy Shearer with a magnet in the background

Physics in the pandemic: ‘Returning to the lab will be hugely beneficial for me’

I am a bit worried about when I will be able to see my family again. I am Belgian, and as an EU citizen, the border between France and Belgium has never been a barrier before, but this changed drastically due to COVID-19. However, there is also a very clear silver lining, since I managed to go into lockdown together with my partner, who (for professional reasons) lives 700km away in Montpellier. We usually see each other only every two weeks, but the pandemic means that we have spent much more time together.

My biggest concern is the health and safety of the people around me, and I try to keep that in mind when the social distancing measures are starting to weigh. Professionally, I have managed to remain productive, and our group is still moving forward, so I am optimistic for the future. I think our habit of combining theory and experiments was an advantage for the lockdown. Our theoretical activities got a big boost during this time, which imposed some organizational challenges for me as a young permanent member of the group, but it was a good occasion to learn.

‘Molecular movie’ shows how electrons rearrange to kick-off a chemical reaction

Scientists in the US and UK are the first to observe electrons rearrange their positions in molecules during the early stages of a light-driven chemical reaction. They did so by firing ultrashort light and X-ray pulses at the molecules to create “movies” of electron motion. The technique promises to shed further light on chemical processes such as bond making and breaking. Their method could also be used to study other ultrafast processes in physics, chemistry, and biology.

There are many chemical reactions that are driven by light. Some, such as photosynthesis in plants and vitamin D production in skin are desirable, while others such as the fading of paint in sunlight are not. Chemists have long predicted that the first step in light-driven reactions is the rapid rearrangement of electrons, while the atomic nuclei move much more slowly.

“Once the electrons have changed their positions, the forces acting on the nuclei will change, leading to atomic motion and further physical processes such as energy or charge transport,” explains Adam Kirrander at the University of Edinburgh. Now, Kirrander along with colleagues at Edinburgh, Brown University and the SLAC National Accelerator Laboratory have used X-ray scattering to track this rearrangement in real time.

Electron distribution

X-ray scattering is a popular technique for determining the positions of atoms within crystals and molecules. But the X-rays interact mostly with the atomic electrons – rather than the atomic nuclei – so X-ray scattering actually reveals the distribution of electrons within a material or molecule. This distinction does not usually matter for a sample at equilibrium, but during a chemical reaction the fast-moving electrons will begin rearranging themselves well before the lethargic and much heavier atoms start to move. As a result, ultrashort X-ray pulses can be used to observe this electronic motion.

Doing so involves firing an ultrashort light pulse at sample of molecules – which sets the reaction in motion. This is followed almost immediately by an ultrashort X-ray pulse, which takes a snapshot of the electron distribution of the molecules as the reaction progresses. By varying the delay between the light and X-ray pulses, a movie of the changing distribution of electrons can be made.

To see this motion, the lengths of the two pulses and the delay between must be on the order of tens of femtoseconds. However, is not possible to have complete control of the delay between the light and X-ray pulses. “We can get the time delay between the pulses roughly right,” explains Kirrander. “But after this we rely on something called “timestamping”, which is a diagnostic tool that records the exact time delay between the optical and the X-ray pulse”.

Five years ago, the team performed such an experiment using pulses from the X-ray Free-Electron Laser at the Linac Coherent Light Source at SLAC. They were able to follow the movement of atoms in 1,3-cyclohexadiene molecules as a function of time, but the time resolution of the experiment was not good enough to see the electrons move independently of the atoms.

Interesting molecule

The species 1,3-cyclohexadiene was used because it undergoes a large change in electronic structure and is therefore favourable for making X-ray movies. However, Kirrander points out that it is an “interesting molecule that serves as an important model for more complex biological reactions like the one that produces vitamin D when sunlight hits your skin”.

Now, the team has improved the experiment and data-analysis techniques and are now able to watch the preliminary motion of the electrons as light pulses hit 1,3-cyclohexadiene. They found that the electron distribution ballooned in size over a period of 30 fs (see figure).

SLAC senior staff scientist Michael Minitti explains, “We’re imaging these electrons as they move and shift around. This paves the way to watching electron motions in and around bond breaking and bond formation directly and in real time”.

Kirrander points out that the technique could be used to study a range of systems – however it could be tricky to apply it to situations where the electrons and atoms move on the same timescale. “With further improvements in the experiments and the data analysis, we anticipate that we will be able to simultaneously capture changes in electronic structure and atomic positions throughout complex dynamic processes.”

The research is described in Nature Communications.

Astronomers see first evidence of a new planet being born

A distinctive twist in the disk of gas and dust surrounding a newly formed star likely indicates that a new planet is currently forming in the system. This discovery by researchers in France, Belgium, USA and Taiwan, led by Anthony Boccaletti at PSL University’s Paris Observatory, makes them the first astronomers to witness such an event.

For the first few million years of their lives, newly born stars are surrounded by dense disks of gas and dust. These structures don’t stay around for long; driven by gravitational instabilities, they will quickly collapse under their own gravity to form new planets. Astronomers are now well aware of this process, but the precise mechanisms that unfold as it occurs have so far remained far from certain.

Recent simulations have suggested that as they develop, young planets will kick up waves of densely packed gas that contort into spirals as they orbit their host stars; with one arm falling into the star, and the other expanding outwards. These structures provide paths for disk material to accrete onto the planet, allowing it to grow. Until now, however, no evidence for these dynamics had ever been gathered through actual observations.

In 2017, the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, operated by the European Southern Observatory (ESO), observed two of these spiral arms within a large gap of the inner disk surrounding newly formed star AB Aurigae. As the simulations suggested, they appeared to be connected to the iconic dusty spirals in the star’s outer disk.

In their study, Boccaletti and colleagues combined these measurements with the latest observations of AB Aurigae made by the SPHERE instrument at the Very Large Telescope (VLT), also operated by the ESO. Compared with previous observations, SPHERE’s measurements are able to detect far fainter light in the near-infrared range.

With this combined data, the researchers were able to produce images of AB Aurigae’s disk with unprecedented levels of detail. Within one of the spiral arms first detected by ALMA, they spotted a further twisted spiral that couldn’t be resolved in previous observations. When checking back to their density wave simulations, they found that this twist was reproduced almost perfectly.

The researchers believe that their discovery provides strong evidence that a new giant planet is currently forming around AB Aurigae – the first time that astronomers have ever witnessed such a process. Tentatively from their observations, they estimate that the planet is between four and 13 times the mass of Jupiter, and orbits at a similar distance to its host star as Neptune does to the Sun.

Boccaletti’s team now hopes to soon be able to observe these dynamics in more detail using the 39 m Extremely Large Telescope (ELT), which is due to begin operation in 2025. Drawing on the work made possible with ALMA and SPHERE, the instrument will also enable astronomers to study other newly formed systems, potentially enabling them to draw crucial new insights into the dynamics of planet formation.

The research is described in Astronomy & Astrophysics.

Women of science posters for you to colour, marshmallow LINACs, iridescent chocolate

This week’s Red Folder focuses on things you can do at home.

There is something therapeutic about colouring in pictures. Perhaps it takes some of us back to a childhood before the Internet and smartphones existed. If you fancy a bit of physics-related colouring, the Perimeter Institute for Theoretical Physics (PI) in Canada has just created colouring versions of its “Forces of Nature” poster series featuring influential women in physics. The posters feature Emmy Noether, Annie Jump Cannon, Canadian Nobel Prize-winner Donna Strickland, and more.

You can find more details about how to get the PDFs from the PI here.

A few weeks ago I mentioned a gingerbread radiation therapy LINAC that had been baked by a medical physicist in Australia. Since then, people have been tweeting photos of edible LINACs that they have made. There’s a bread LINAC and even one with flashing lights in the icing. But my favourite is the rice crispy square and marshmallow versions made (I think) by the children of Laurence Court, a medical physicist in the US.

Here at Physics World we love a good story about structural colour, so when we heard that the tech entrepreneur Samy Kamkar has made iridescent chocolate we had to learn more. According to the New York Times, he has devised a way to create micron-sized structures on the surface of the chocolate so that the colour of the chocolate changes depending on the viewing angle. It turns out that Kamkar is not alone – Swiss chocolatiers have also made iridescent confections and are trying to come up with a way to mass produce them.

My challenge to you, Physics World reader, is can you make your own iridescent chocolate?

Cryogenic temperature sensors: installation techniques for success

Want to learn more on this subject?

Watch now

This webinar will cover helpful, practical tips on how to choose the right type of sensor and packaging for the specific application and then summarize best practice for minimizing installation errors and ensuring superior thermalization in a cryogenic thermometry installation.

Topics include:

Considerations for choosing a sensor (including resistance to magnetic fields, ionizing radiation, UHV and others).
The role of packaging and adapters for shielding, mounting, stability and optimal thermal contact.
Considerations for sensor installation (placement, mounting method, materials, electrical connections, heat sinking, thermal contact medium, etc).
A look at the choices for fastening materials, wire leads, thermal mediums and adhesives.

The webinar presented by Scott Courts will help the audience to:

Understand the advantages/disadvantages of various temperature sensor types in different situations.
Gain a detailed understanding of how correct installation minimizes measurement error.
Learn about avoiding common installation errors that can disrupt your experiments.

Want to learn more on this subject?

Watch now

Scott Courts has been active in the field of cryogenics for more than 30 years. He received his BSc in physics from Marshall University and his PhD in experimental solid state physics from The Ohio State University. In 1989, he joined Lake Shore as a senior scientist in the company’s Sensor R&D Division, focusing on developing thin-film thermometer materials exhibiting high ionizing radiation tolerance and low magnetoresistance offsets for use in accelerator applications.

This work led to the development of Lake Shore Cernox^® sensors. He has also served as technical director for Lake Shore’s thermometer calibration facility, and he currently serves as a senior scientist/metrologist, maintaining Lake Shore’s traceable thermometry scales.

A member of the American Physical Society and the Cryogenic Society of America, Scott has published more than 35 articles on cryogenics/thermometry and served as a reviewer for various journals and proceedings. He has also taught short courses on cryogenic thermometry and instrumentation in both public and private settings for the past 20+ years.

Physics in the pandemic: ‘Returning to the lab will be hugely beneficial for me’

In March, everyone in our research institute was advised to work from home if possible, and our labs shut down soon after. Although my PhD project is mostly experimental, I am lucky in that I had already started incorporating some computational modelling into my work. The reason I did this is because, as an autistic person, I am not always able to physically go to campus: I sometimes find the myriad of sensations there overwhelming, and social interactions can leave me fatigued. So, I was already searching for ways to make meaningful progress on my research while working remotely for longer periods.

Despite this preparation, though, I have struggled. Big changes and unpredictable circumstances can be incredibly difficult for autistic people like me, and although there is a wide diversity of autistic experiences – we all have our own challenges and strengths – I think most of us have felt the impact of the pandemic to a heightened degree. The current global situation has also taken a huge toll on my already poor mental health. I’ve found that I can only take things a day at a time right now. Otherwise, things feel way too overwhelming and I get paralysed by anxiety. Like many others, I have had to temporarily withdraw from work over the last few months to look after myself. It is a very difficult time for us all and I think it’s important to acknowledge this.

Regaining control

I ended up moving back in with my parents due to a variety of factors. In the end this was for the best as I was no longer able to live independently, but it does mean that I am living in a very different and less controllable sensory environment. Because of this, I experienced a huge increase in autistic shutdowns (an internal response to sensory overwhelm, during which I may become unresponsive, non-verbal, vacant and floppy) and meltdowns (an external response where I may lose behavioural control and engage with behaviours such as yelling, crying, lashing out or hitting myself). I’ve also had my fair share of panic attacks.

Luckily, I’m now recovering, and I should be able to return to my rented house near my lab soon. This is great news, as I will then be in a much more controllable environment, reducing my sensory overwhelm and enabling me to work on my research more consistently (now that I am no longer withdrawn from my PhD programme). It will also mean that I can walk to the lab once we have implemented social-distancing protocols and I have booked a session to carry out new experiments there.

Returning to the lab will be hugely beneficial for me. The lab is usually my “safe space”, a place where I feel inspired, and my inability to do experimental work has led to feelings of stagnancy and uselessness. I miss the thrill of fabricating a beautiful nanostructure, collecting new data from a device, learning a new technique from a colleague, and that wonderful moment when you finally finish troubleshooting your experiment. It’s not quite the same when you’re debugging code or proofreading your writing!

Accessibility and inclusion

Although the pandemic has had a huge negative impact on everyone’s lives, I do see some positives that could come out of it, particularly in relation to accessibility and disability inclusion. Many assistive technologies and “reasonable adjustments” have now become useful for everybody. In some ways, I think able-bodied individuals have been forced to learn from people with disabilities, since we have always had to adapt and be flexible in order to work in environments that are largely inaccessible to us. There is some truth in the idea that the pandemic supports the social model of disability, which holds that attitudes and structures in society are what make people “disabled”, rather than their medical conditions, and that appropriate adjustments and accessibility aids can help overcome this.

Daisy Shearer wearing gloves and ear defenders in an office — Adaptive technology: Daisy Shearer wears sensory aids – ear defenders and compression gloves – to help her manage sensory stimuli in an open-plan office.

Here’s an example. Before the pandemic, I regularly worked from home on Fridays, and I often found that my productivity increased considerably when I did. This is probably because home working eliminates the sensory stresses of travelling to campus, while also giving me one day a week when I don’t have to socialize in person. Working from home also enables me to be non-verbal for a day, which helps me process experiences and information. Finally, when I am at home, I am much more likely to tap into an aspect of autism (and other neurodivergent conditions) that is, I think, a great asset: hyperfocus. When I’m in a hyperfocused state, my brain can concentrate intently on a task for a long period of time, but I’ve never been able to enter hyperfocus in an office (particularly an open office).

As well as facilitating home working, the pandemic has also given me the chance to experiment with different ways of communicating. Because I experience some delays in my auditory processing when I’m under stress, in-person one-to-one meetings are incredibly difficult for me. I get nothing out of them apart from very high anxiety levels and a probable sensory overload. The same is true of phone or video calls. Even before the pandemic struck, I was trying to find solutions to this, such as communicating more through e-mail. Now, I have the option of meeting with my supervisor using instant messaging and screen sharing, which has led to several incredibly engaging and useful discussions.

Hopes for a new normal

Of course, I appreciate that my supervisor prefers in-person meetings, and I will endeavour to have them again once things are back to normal. But the thought that we will still be able to meet through instant messaging even if I am unable to go onto campus for some reason is amazing. The fact is that some people, particularly those of us who are neurodivergent, communicate differently, so it makes sense that we should have different options for sharing our ideas and learning from others’ perspectives.

I also hope that the pandemic will make it easier for disabled people to work from home, without having to go through the degrading process of “evidencing” our conditions and proving that such adjustments are “reasonable”. This kind of self-advocacy can be incredibly draining. It takes a lot of time to access the support and adjustments you need to work to the best of your abilities — and that’s without taking into account the challenges faced by undiagnosed people, who often don’t have adequate “evidence” of their disability. The high cost and time required for a diagnostic assessment mean that many people just don’t get assessed and are thus denied the support and adjustments they need. Now that we’ve proved that, for example, it’s possible to carry out one-to-one meetings remotely, there isn’t any excuse to deny anyone that reasonable adjustment in the future.

In summary, I hope that there will be a shift towards accommodating individual needs in the workplace – particularly for disabled people, but also for anyone who finds that they work better in a certain place or in a certain way. There’s no reason why we shouldn’t try to maximize everyone’s wellbeing and ability to work to the best of their capabilities.

Test your knowledge of art, space and science in this trivia quiz

1 What was the name of the physicist in Hergé’s Tintin comics? A. Professor Calculus B. Dr Maths C. Prof. Angle D. Dr Division

2 Who played Nikola Tesla in the 2006 film The Prestige? A. Hugh Jackman B. Christian Bale C. David Bowie D. Michael Caine

3 Which band had a visual representation of the pulsar CP 1919 as the cover image for their debut album? A. Oasis B. Joy Division C. The Happy Mondays D. The Smiths

4 Which artist painted a special instrument calibration chart for the Beagle 2 lander? A. David Hockney B. Tracey Emin C. Sarah Lucas D. Damien Hirst

5 Which famous physicist makes an appearance in Steve Martin’s 1993 play Picasso at the Lapin Agile? A. Albert Einstein B. Paul Dirac C. Richard Feynman D. Erwin Schrödinger

6 Who first discovered the 35P/Herschel–Rigollet comet? A. William Herschel B. Roger Rigollet C. Caroline Herschel D. Nevil Maskelyne

7 What number reactor was the site of the Chernobyl disaster in 1986? A. Reactor 1 B. Reactor 2 C. Reactor 3 D. Reactor 4

8 Which famous physicist once said: “The good thing about science is that it’s true whether or not you believe in it.”? A. Brian Cox B. Carl Sagan C. Neil deGrasse Tyson D. Jocelyn Bell Burnell

9 Who wrote about the Big Bang in their 1846 prose poem Eureka? A. Edgar Allen Poe B. Walt Whitman C. William Carlos Williams D. Emily Dickinson

10 Which Kurt Vonnegut Jr. novel features the fictional Nobel-prize-winning physicist Felix Hoenikker? A. The Sirens of Titan B. Timequake C. Cat’s Cradle D. Galápago

Want to know the answers? We’ll reveal all next week on Friday 29 May.

This week’s questions have been set by IOP ebooks author Sam Illingworth, who is senior lecturer in science communication at the University of Western Australia. His book Effective Science Communication is a must-read for anyone preparing funding applications, publishing scientific papers, presenting at conferences or engaging with the public. This second edition brings the text up to date and includes additional material, yet retains the clear insight and practical advice that made the first edition so essential.

Update: the answers are 1. A 2. C 3. B 4. D 5. A 6. C 7. D 8. C 9. A 10. C

Optical phased array steers blue light

A new chip-based device that can shape and steer blue light could significantly reduce the size of the light projection components used in emerging applications such as augmented and virtual reality, autonomous vehicles, optogenetics and even trapped-ion quantum computers. So say researchers at Columbia University in New York led by Michal Lipson who have made an optical phased array (OPA) with a wide field of view that contains no moving parts.

Phased arrays consist of multiple connected antennas that produce an electronically steerable beam of electromagnetic waves. The beam is steered by applying different phases of light at each antenna such that the output waves interfere constructively in one direction and destructively in the other. To change the beam’s direction, light is delayed in one emitter or a phase is shifted relative to another.

Such antennas have long been used to transmit radio and television signals, but in the last decade or so researchers have begun to extend the phased-array concept to visible wavelengths. Since antennas work by oscillating charges along their structure, the size of the antenna must match the resonant mode of the wavelength of the electromagnetic radiation it supports. For visible light, that means shrinking the antenna down to the nanoscale.

OPAs offer an alternative to bulky devices

The light-projection components currently used to shape and steer visible light are bulky and have a limited field of view. While OPAs are smaller, they are usually made from silicon, which can only be used at longer, near-infrared wavelengths. Blue wavelengths (488 nm) require different semiconducting materials, such as silicon nitride (SiN), that can operate at visible wavelengths. However, these less-common semiconductors present additional challenges for fabrication and development.

Lipson’s team developed their SiN platform three years ago, and have now optimized it to operate at blue light wavelengths. One of the main difficulties they had to overcome was that blue wavelength light scatters more than other colours since it travels as shorter, smaller waves. This greater scattering leads to higher light losses if the device fabrication is not perfect, says the study’s co-lead author Min Chul Shin. Another challenge was to make a blue light beam that they could steer over a wide, 50-degree field of view.

Now that they have demonstrated an OPA that operates at blue wavelengths, the researchers say they could easily adapt their device design for longer red and green wavelengths. This broader wavelength range would open up applications such as optogenetic neural stimulation, in which visible light combines with genetic engineering to control neurons and other cells in living tissues. As an example, co-lead author Aseema Mohanty says the group’s chip-scale technology could be used to control an array of micron-scale beams to stimulate light-sensitive tags on neurons in animal models of brain disease.

Reducing power consumption

As well as optogenetics, the new blue OPA could come in useful in trapped ion quantum computers, which require lasers in the visible spectral range for micron-scale optical stimulation. It might also be used in ultra-small solid-state lidar on autonomous vehicles and for making significantly smaller and lighter AR/VR displays.

The researchers, who report their work in Optics Letters, now plan to reduce the electrical power consumption of their OPAs. Low-power operation will be crucial for the above-mentioned applications, they explain.

Shedding light on the interfaces

Karen Syres is a scientist who operates at the interfaces: between physics and chemistry; between big science and fundamental molecular studies; and between her chosen academic specialism and the wider public understanding of that science. As a lecturer in physics at the Jeremiah Horrocks Institute at the University of Central Lancashire (UCLan) in Preston, UK, Syres fits the template of many early-career researchers. She juggles a significant teaching load alongside the treadmill of grant applications and the daily challenge of scaling her research programme in the emerging field of liquid surfaces. What works for Syres at the interfaces may also hold lessons for other early-career physicists and educators.

You focus on the physics and chemistry of surfaces. What are the drivers here?

I’m interested in how molecules bond to a surface, how they are orientated, how charge is transferred across interfaces. Most of my research is carried out in ultrahigh-vacuum (UHV) conditions at pressures of 10^–10 mbar or thereabouts. That’s because we’re trying to detect electrons, for example, using X-ray photoelectron spectroscopy and we need to get our surfaces “atomically clean” before depositing the molecules we want to study. Fundamental studies such as this are important because what happens at the interface often dictates if a device will succeed. In solar cells, for example, the energy-band alignment between material layers determines how effectively charge is transferred, while the surface chemistry in biomedical implants can affect the healing time in patients.

Does your research have commercial implications?

Ionic liquids are a big part of my work. This class of salts shows great promise for transforming industrial processes such as gas-capture and separation, catalysis, corrosion protection and lubrication. They’re also attracting significant industry interest from developers of next-generation batteries and photovoltaic technologies.

In some respects, ionic liquids are similar to ionic solids – such as sodium chloride – but instead of simple ions they consist of bulky, asymmetric ions. Because those constituent ions don’t pack nicely, they tend to be liquid at room temperature – though they are more structured than most molecular liquids, and exhibit ordering at interfaces. There are millions of possible combinations of cations and anions that can be tuned to achieve various desired properties – liquid temperature range, conductivity, viscosity and hydrophilicity to name just a few. They can also be functionalized to perform a given task, such as reacting with carbon dioxide.

What attracted you to do physics at UCLan?

I love research and have always wanted to follow the academic path. After my MPhys and PhD in physics at the University of Manchester, I did a postdoc in the chemistry department at the University of Nottingham before my move to UCLan. What I like about UCLan is that it’s a small and supportive physics department with a real sense of community. It’s also great for the undergraduates, who get more one-to-one attention than they would in a larger department.

How do you balance your roles as lecturer and research scientist?

During term-time, most of my working week is focused around undergraduate teaching. I lecture in condensed-matter physics, nuclear physics and foundation-level maths, plus there’s supervision of final-year undergraduates and their research projects. My role as year-one tutor means that I have an additional responsibility to support and mentor our new-intake physics students (20 in the current academic year).

The teaching dovetails with intense bursts of research activity during holiday periods – typically three or four visits every year to various big-science facilities across Europe. Like all academics, I sometimes need to work evenings and weekends to keep on top of other things – writing and marking exams, for example, and putting together grant proposals. Last year, I also had my first PhD student completion. It was a brilliant feeling, though I think I was more nervous than she was on the day of her viva.

How does that arrangement work in terms of efficiency and research outcomes?

Most of my research is carried out at European synchrotron facilities – including the Diamond Light Source in the UK, ASTRID in Denmark, BESSY II in Germany and MAX IV in Sweden – and generally on beamlines that support X-ray photoelectron spectroscopy and X-ray absorption techniques. More recently, I’ve also been using near-ambient-pressure beamlines that can accommodate these techniques in the millibar regime rather than UHV, where we normally work.

It’s an attractive way to do research because somebody else has the job of maintaining all the expensive equipment, while my colleagues and I just turn up for a week and use it. If the experiment goes as planned, you can easily get enough data for a chapter of a student’s thesis – hopefully enough for a journal paper as well. It’s always a team effort and is good training for the PhD students, in particular, to work with the resident beamline scientists and technicians.

It’s an attractive way to do research because somebody else has the job of maintaining all the expensive equipment

Beyond UCLan, you’re an active member of the UK surface-science community. How has this helped your research?

I joined the Thin Films and Surfaces Group of the Institute of Physics (which publishes Physics World) in 2014, when I was still a postdoctoral researcher at the University of Nottingham. I’m now vice-chair of the group and it’s provided all manner of opportunities to develop my broader skill set, expand my contacts network and build wider recognition in the field of surface science.

Not long after I took up my lectureship at UCLan, for example, I chaired a four-day conference called the Summer School on Nanoscience@Surfaces. It’s always stressful to organize and run an event, but this one proved a big success, attracting 85 delegates from 13 countries as well as many prominent speakers from the UK and overseas. We’re now running the summer school every two years as one of our flagship events. I’ve also been involved in starting up a new one-day meeting called Surface Science Day, which runs every year at a different UK university.

What about public outreach?

I enjoy getting involved in outreach activities, although planning them can be time-consuming. That said, I think we have a responsibility to communicate to the public what we are doing with taxpayers’ money and to try our best to inspire the next generation of scientists. At UCLan, for example, we hold the Lancashire Science Festival every year, pulling in around 13,000 visitors – school children for the first two days and then the general public for the final day. Since I’ve been in Preston, I’ve organized the physics stand for the festival, including a popular magnetic-levitation railway demonstration that I designed and built with the help of my PhD student. I’ve also taken some students to our UCLan Cyprus campus for the Cyprus Science Festival – an activity made doubly interesting by the language barrier. Sometimes with outreach activities I find myself trying to control a bunch of unruly children and I wonder why I thought it was a good idea. Then you speak to a young person who’s really excited about physics and it makes it all worthwhile.

What’s next for your research career?

I’m currently director of studies for two first-year PhD students – including one studentship I won through the DTA3/COFUND Marie Skłodowska-Curie programme – so the short-term goal is to supervise them to completion. Beyond that, the priority is to win some bigger grants, add a few postdocs to my team and gain wider international recognition for my research. I’m also keen to forge interdisciplinary and industry collaborations to see how my fundamental studies can complement more applied research efforts.

What happened to all the plastic we released into the oceans?

Plastics in our oceans have something in common with dark matter in the universe. Our models tell us there should be loads of it out there, but it’s proving difficult to track it down. The big difference with marine plastic, however, it that whenever we do look for it we tend to find it – and the effect on marine wildlife can be devastating. The challenge for scientists is surveying and modelling the vast world oceans to figure out precisely where the majority of this plastic pollution is ending up.

To find out more, read ‘The search for the missing plastic‘, a feature originally published in the May 2020 issue of Physics World – a special edition on plastic waste.

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