Author: Akshat Rathi

Akshat Rathi is a senior reporter for Bloomberg News. He has previously worked at Quartz, The Economist and The Conversation. His writing has appeared in Nature, The Guardian and The Hindu. He has a PhD in chemistry from Oxford University and a BTech in chemical engineering from the Institute of Chemical Technology, Mumbai.

A revolution in lens-making

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Understanding of optics has changed no end since the world’s oldest known lens was ground nearly 3,000 years ago in modern-day Iraq. Yet its Assyrian maker would instantly recognise today’s lenses, which continue to be made much as they were then: by fashioning a piece of transparent material into a solid with curved surfaces. Just as invariably, the curves introduce optical aberrations whose correction requires tweaking the lens’s geometry in complicated ways. As a consequence, lenses remain bulky, especially by the standards of modern electronics.

Enter Federico Capasso, of Harvard University. He and his colleagues have created a lens that is completely flat and the width of two human hairs. It works because its features, measured in nanometres (billionths of a metre), make it a “metamaterial”, endowed with some weird and useful properties.

According to the laws of quantum mechanics, a particle of light, called a photon, can take literally any possible path between source A and point B. However, those same laws stipulate that the path of least time is the most likely. When a photon is travelling through a uniform medium, like a vacuum, that amounts to a straight line. But although its speed in a vacuum is constant, light travels at different (lower) speeds in different media. For example, it moves more slowly in glass than it does in air. So in a medium composed of both air and glass, light’s most likely path from A to B will depend on the thickness of glass it needs to traverse, as well as the total distance it needs to cover. That means that the light may sometimes prefer to bend. This is the quantum-mechanical basis of refraction.

In order to maximise the probability that photons from A will end up precisely at B, those going in a straight line need to be slowed down relative to those taking a more circuitous route, so that, in effect, all hit B the same time. This can be done by forcing the former to pass through more glass than the latter. The result is a round piece of glass that is thick in the middle, where the straight-line path crosses, and tapers off towards the edge, where the less direct routes do—in other words, a focusing lens, with its focal point at B.

Dr Capasso’s lens, described in Nano Letters, also slows photons down. But instead of using varying thickness of glass to do the job, he and his team created an array of antennae which absorb photons, hold on to them for a short time and then release them. In order for this trick to work, though, the distance between the antennae has to be smaller than the wavelength of the light being focused. In Dr Capasso’s case that means less than 1,550 nanometres, though he thinks that with tweaking it could be made to work with shorter-wavelength visible light, too.

Creating the array involved coating a standard silicon wafer, 250 microns thick, with a 60-nanometre layer of gold. Most of this layer was then stripped away using a technique called electron-beam litography, leaving behind a forest of V-shaped antennae arranged in concentric circles. By fiddling with their precise shape, after much trial and error, antennae lying on different circles could be coaxed into holding on to the photons for slightly different lengths of time, mimicking an ordinary glass lens. The whole fragile system can be sandwiched between two sheets of transparent material to make it more robust.

At present the new-fangled lens only works for monochromatic light and so is unlikely to replace the glass sort in smartphone cameras anytime soon. But it could revolutionise instruments that rely on single-colour lasers, by making further minaturisation possible while eliminating the optical aberrations inherent to glass lenses. Such devices include laser microscopes, which are used to capture high-resolution images of cells, or optical data storage, where a more accurate and smaller lens could help squeeze more information into ever less space.

First published on economist.com.

References: 

  1. Capasso et al., Aberration-Free Ultrathin Flat Lenses and Axicons at Telecom Wavelengths Based on Plasmonic Metasurfaces, Nano Letters, 2012.
  2. Capasso et al., Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction, Science, 2011.

Also appeared in The Economist. Also available in audio here.

Image credit: Francesco Aieta

Smells of hell

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In 1991 a volcanic eruption occurred on the island of Luzon, near the Philippines. In a short period of time Mount Pinatubo had injected into the atmosphere 10 billion tonnes of magma and 20 million tonnes of sulfur dioxide. In the months that followed, global temperature had fallen by 0.5 °C. The cooling occurred because of the formation of a thin layer of sulfuric acid that reflected the sun’s radiation.

Sulfur: Smells of hell, Ionic Magazine, 1 December 2012.

Illustration by Carlos D Toledo-Suárez.

Why not to do a PhD if you want to become a writer

Akshat Rathi9 Comments

I got an email from a friend who is a chemical engineer that said: “I am considering doing a PhD in marketing”. The last I spoke to him he wanted to pursue a career in science writing. So I inquired whether he had changed his mind.

To which he said no. “I want to stay in academia so that I’ll get the time to read and write as much as I really want to. Getting into grad school seems like the only way. I really don’t want to get sucked into a corporate job that I would hate doing.” On reading that alarm bells started ringing in my head and I couldn’t not stop myself from telling him that what he is thinking of doing could go horribly wrong.

Too many people end up doing a PhD because it is an easy option. Leaving the academic bubble is hard when the grad school cookie is on the plate. There are also perverse incentives for universities to let its undergrads stay on to a PhD and even a postdoc. You could read all about it here. I’ll focus on my friend’s aim to become a writer, and why getting a PhD in the sciences or social sciences is not the best route to do that.

I feel the urge to share the conversation I had with my friend because, if I had known before choosing to go grad school that science writing is what I would like to do, then I would have taken a different path. Also because my friend has this romantic notion that academia gives you the freedom to pursue things beyond what you study, and that that is the key to becoming a good writer. Both those assumptions have a grain of truth in them but they are far from the ideal solution to where my friend wants to get to.

First, I can see why a PhD in marketing might have seemed tempting. He said: “The interesting thing about marketing is that you can operate from literally any area: communications, cognitive behavior, or decision making”. Second, given his scientific background and his goals I can also relate to it when he says: “I couldn’t stand the thought of doing a PhD in chemical engineering”.

But I suspect that few science students understand what a social sciences PhD entails. Some of my closest friends have pursued a PhD in social sciences, so I know.

First, there is rarely a “research group”. Most supervisors have only a handful of students who work on very different areas of a subject. So you lack the support network that science grad students have. Only when you spend day after day in a library, most of the time alone, trying to get through tons of reading do you realise the value of having friends standing by you all day in a lab.

Second, supervision in the social sciences is usually quite light. What I mean by that is that a social sciences student has a lot of freedom about how to approach the chosen subject. This is fantastic if you love your subject, you can dive in to different areas and emerge with many ways in which you could reach the end point.

That is not how a science PhD works. In most cases, a science PhD starts with a project that your supervisor has in mind and has already charted out the possible route to start with.

Also, the number of times a grad student’s work is reviewed in the social sciences tends to be, on average, much less than the number of reviews that happen in the sciences. For instance, I’ve never heard of a “group meeting” in the social sciences. Whereas I’ve never not heard of group meetings in the sciences.

This is important because it allows a science student to direct their work on a much more regular basis than a social sciences student gets to.

Third, social sciences students end up not including months and months of work in their final thesis. While that may happen to science students too, at least in their case, a negative result is a result after all. Despite negative results not being reported in academic publications, few fear not reporting legitimate negative results in their PhD theses.

I’ve spent a chunk of this post comparing a social sciences PhD with a science PhD because I feel that it is nuts to believe that a social sciences PhD will give you the time to do other things that will help you become a writer compared to an all-consuming science PhD.

The other belief that needs to be crushed is that academia is a cushy job, that academics get the time to pursue things beyond their subject area as much as they like, and that the university atmosphere is the only way to pursue the intellectual curiosity of a writer.

There is a grain of truth in all that but it is not a realistic picture. Well-established academics indeed may be in that position, but not young academics. While many academics do end up writing hugely enjoyable books, it is rare that a young academic does that. Academia today is more competitive than it has ever been, not least because there far too many PhDs and post-docs wanting that illusive tenure-track position.

This brings me to the most important point: In my opinion no one should pursue a PhD if they don’t love the subject. To be able to successfully get a PhD from a good university, you really need to know what you are doing. It takes dedication, perseverance and patience. PhD in any subject area requires you to dive deep into what you do. This is why it takes the 3 to 7 years (or more than that) to get a PhD. This is especially true if you want to become an academic at the end of it.

So, my friend asks, how do you become a writer then? I heed the words of Ed Yong:

1) Pull your finger out and work really hard. Stay up late. Practice. Sacrifice your social time. Churn out a crazy amount of output. Practice. Enter competitions. Practice.

2) Give people a reason to read you. There are plenty of competent writers and not enough time to read them. Maybe you are the go-to person for a topic. Maybe you write like an angel. If you want to stand out, stand out.

3) Tell people about yourself. Promote your work. If you want to be recognised, then it’s not enough to be good and shout into the ether. And I don’t mean in a narcissistic, self-aggrandising way. You don’t even have to directly point to your work. Just let people know you exist.

4) If you are lucky enough to be given an opportunity, grasp it as quickly as possible because the momentum fades. If you haven’t been given opportunities, maybe you should try to create some. If you’re not part of a network (and want to be; loads don’t), are you sitting around waiting to be invited or did you cold-call and ask for feedback?

5) If it’s been several years and you’re not getting anywhere… that’s about right. Building a reputation takes time. It is demotivating and miserable in the meantime. Suck it up. Do what you do because it makes you personally fulfilled. Don’t expect a windfall; that will come after a lot of work.

6) Go to 1.

But to be able to do what Ed is suggesting requires you to have a source of income to pay your rent and bills. And so my final advice to my friend was to get a day job that will allow him to pursue writing as a night job. That day job should not be a PhD. It may pay enough to sustain you, but it isn’t easy to balance writing with a PhD (although some can!). While a PhD can give you many valuable skills to be a science writer, you might be able to gain those skills on your own through practice (many have demonstrated that).

In short, a PhD is not the answer to becoming a science writer. A PhD is a hugely satisfying (stuffed with a lot of frustration in the middle) endeavour and must be pursued only if you love the subject. While quitting a PhD and doing something else is always an option, it is not as easy as quitting a job and getting another one.

Disclaimer:

1. My opinions are based on a limited sample size. What I’ve written is based on the experience of spending four years as a graduate student at Oxford. Thus, it is quite possible that I’ve got many things wrong.

2. I wrote this in response to the email from my friend. So the advice is quite tailored to his case. Just keep that in mind before you draw any general conclusions from it.