Lectures are too long!

I am sure this has been already investigated in scientific literature and I am probably reinventing the wheel, but it must finally come out of academic discussions – only then will the lecturers understand that we, students, need a change.

Never-ending lecture

At WrUT, a lecture normally lasts 1h30 with a 15min break in the middle. The first problem is that many lecturers consider it as optional. Some would ask the students if they want a break but people do not really want to stand out and so the lecture continues. Some do not even bother to ask.

Remaining focused on one topic for one hour is (for me) impossible, and if I loose attention for a brief moment, I also loose track of whatever the professor is saying, which makes my thoughts wander again as my brain finds it boring to listen to something I do not quite understand, and we have a vicious cycle. I know there are students whose ability to concentrate is much better than mine, but there are many more whose experiences are similar to mine. It does not mean we are bad students – I dare say it indicates that the system fails to meet our needs.

It is very easy for the lecturers to forget the student’s perspective, not only in this matter. If you are lecturing, I imagine you must stay alert all the time because otherwise you would simply forget what you were supposed to say next. I have given a few short talks on conferences and seminars – of course it was much more stressful for me than it would be for a seasoned speaker, but it was a completely different experience than being on the other side! Therefore I forgive you, dear professors on whose lectures I could hardly stay awake, and I believe in your good intentions.

A short comparison: here in Cambridge, the lectures are usually around 50min long. In the US – more or less the same, which you can check here or anywhere else – the Internet is now full of lectures recorded at various universities. I asked my friends from India and the answer was the same. However, even at the best unis they can be unreasonably long.

Now, reducing lectures’ duration by half is a good starting point, but we should not stop here. Last year we witnessed the emergence of a few on-line universities (e.g. Coursera, edX.org, Khan Academy). There, the lecture videos can be heavily edited after recording, and guess what: the sequences you are supposed to watch without pausing are between 10 and 25 minutes long! Why would they choose to cut the lecture in four pieces if they could just upload it as it is? Because it yields better results!

Two postulates

Dear deans, rectors, heads of departments: if students at your university have to sit at lectures for more than an hour then the quality of teaching there is poor. Shorten the lectures. The total time may remain the same, all you need to do is split a long lecture on Wednesday afternoon in two shorter ones on Tuesday and Friday – at the same time giving the more motivated students time to revise. Or, if it has to stay the way it is, introduce Zen training for students and we will be able to focus for as long as you want.

Dear lecturers (wherever you are from), here is a simple advice for you: every 15-25 minutes, when you finish talking about one concept and move to another, give the students a break. Ask them an interesting question about what you have just said (you will spot the best students in the class!), demonstrate an experiment, entertain them with a funny story from your life, share the latest gossip from the university, or simply walk out and let them talk for a short while. I guarantee that they will like your course much more than the others!


The viva was somewhat less stressful than some of the most important exams that I had passed (one of them being the driving exam, a fact that I still laugh about). Whether the reason laid in my poor memory (I could have forgotten how it was to be examined after six months) or overconfidence, I am not sure.

Before, there is cheering and question-guessing with your friends, but everyone knows that their time is about to come so the conversation is rather anxious. A viva lasts around half an hour. It takes certain skills to present your work in 7-10mins, especially if the topic is not yet well known amongst faculty staff. Fortunately, the three doctors seemed to listen and they did not interrupt while I was reaching the limits of my mouth’s words per second ratio.

Each examiner asked one question. For the first I was well prepared because he asked about tight binding and k·p band structure solving methods, which he taught us two years ago. The second asked about the definition of the angular momentum and its conservation law. It reminded me of my ever-returning plan to revise general physics, for my answer – albeit correct – was not as fluent as the first one. The third question was somewhat related to quantum cascade lasers. Although I knew that minibands emerge in superlattices, I had never given it a deeper thought and I only managed to answer fully with some help of the doctor who asked the question.

That was it. After a moment they called me back, announced the mark they gave me and congratulated on obtaining my first degree. I was pleased with the form of the examination: it was not black-and-white (i.e. either you know everything or you know nothing). If you struggled, they were there to point you in the right direction. They did not mean to show me how uneducated I was – which I heard was a normal attitude on a few other faculties. They smiled and were kind, for what I am grateful.

If you want to take a look at my thesis, you are welcome to do so: download link. It is published under CC BY-NC-SA 3.0 licence. I would like to upload it to arXiv.org, but I have yet to learn how.

Festival of Ideas

Another great event which I must mention here: Festival of Ideas consists of talks, panel discussions, guided tours, exhibitions, concerts – essentially anything that is stimulating your mind and imagination. It is held here every year and, I believe, they are constantly improving it.

On a panel discussion called Why Languages Die? I learned that there were about 40 languages in and around Iberian Peninsula two thousand years ago but only three survived to our times. Basque’s story is astonishing: although it has never been an official language of any political or economical power, it has always lived in literature, art and amongst people who have had a strong sense of national identity. Languages die not only because of conquers, immigrants or political reasons: climate can kill a language, as it will probably do in Greenland in a few years – Inughuit people will be forced to move to other parts of the island, communicate in Danish or Greenlandic and forget their mother tongue.

Is the future of food GM? was definitely a treat. There was no end to questions from the audience. Surprisingly, people asked them rather out of curiosity than hostility – it seemed that people who had come there were less sceptical than an average European. The general consensus of the discussion was that something has to be done, because the way the law is now, it is a pain for any farmer who wants to use genetically modified seeds.

Adventures of a palaeolinguist was the first talk that I went to – a little less exciting than panel discussions, but still very interesting. I hadn’t expected Happiness and sustainability to be purely philosophy oriented so I was struggling a bit with the unfamiliar language, but I liked the speaker’s attitude very much – he was a wise man and gave very good examples. Science and religion: friends or foes? was probably the one I liked the least, just because all four panellists were scientists and believers, which narrowed the perspective in my opinion. However, I cannot say I didn’t learn anything: I think I realized that they are neither friends nor foes as long as you understand their purpose properly. Religion does not explain chemical reactions in our bodies, science on the other hand will never tell us why we are here. It is all about the answers you need and the ones you don’t care about.

Energy policy: should scientists be in charge? was another discussion I attended. I liked the fact that the speakers had different backgrounds: there were two engineers, one scientist and one economist. Engineers had an easy task: before the discussion, the audience were asked who would they put in charge of the energy policy. 80% answered… “engineers”. Whoever it is, everyone seemed to agree it shouldn’t be politicians.

There was also a post-festival event: a screening of The Hitch-hiker’s guide to the Galaxy preceded by a popular science talk and demonstration. Albeit amusing, the talk was too chaotic and I don’t think lay people could understand anything from it. On overall, I loved the festival and I wish I had booked the most interesting events earlier (they were all free or almost free, but for some booking was necessary).


Some time ago I promised to write about my sources of funding. It took me so long just because I wasn’t entirely sure about them until the last week.

Whatever you may think about the European Union, it is helping young people to broaden their horizons. I applied for Erasmus life-long learning programme which provides students with scholarships for internships within EU. Unlike Erasmus for student exchange, this one allows you to choose a hosting company or university. After you contact them and they accept you, all you need is some paperwork which I had already described here. Initially, they said I would get around 100 euros/week for 3 months. However, just before I left, I learned that they would extend it to 6 months and raise the wage to almost 150 euros! It was great news and it consequently prevented me from spending any savings while living in the UK.

I also received significant support from my group here and I am sure I owe it to prof. Misiewicz’s correspondence with prof. Ritchie. That was the money I was waiting for until last week: 1500 pounds from SP.

The third official source of funding is Wrocław University of Technology, courtesy of prof. Misiewicz. Before I knew about additional support from EU, my budget hadn’t looked too optimistic, so I asked him if there was any other scholarship I could apply for. He just asked how much I needed and after a few days I received the exact amount (7000zł) from WrUT – apparently they have funds for students and researchers going abroad, but I imagine they use it only in special cases. Now, who will tell me my university is not great?

Last but not least, I knew that if anything went wrong, I could count on my parents’ help, a comfort for which I will always be grateful. As you can see, voloir c’est povoir - I have got enough funding to live normally - albeit modestly - in one of Europe’s most expensive countries.

Physics at work

Each September, Cavendish organizes a big event for schoolchildren: Physics at Work. Teenagers come to the Institute and spend a few hours attending demonstrations by various research groups. This year we broke the record and welcomed some 3000 kids. I say “we”, because I had an opportunity to participate, and I must admit I enjoyed it.

Firstly, I like the idea: boys and girls come to a real research institute, where they can see, touch and talk to scientists. I missed it at school: I had to use my imagination and figure out how work is like in such a place basing only on what I had read or heard. The more information you have, the better chance of making the right decision. Of course, (Polish) universities organize Open Days, but they are usually a few weeks before pupils take A-levels and are about to choose where and what to study. This is great, but it would be even better if they knew it at least one year earlier. This is exactly what Physics at Work is about: we are showing them how exciting research in physics is, but if they ask difficult questions, we are honest (I hope the other demonstrators were!). I also hope that they come back home with a much better idea of who a scientist is.

I volunteered to show our presentation to three groups of children. The slides had been already prepared – in fact, we had been recycling them for a couple of years. I think it might be slightly improved, I can’t see a point in talking about Ohm’s law and how we use it in our measurements if kids haven’t heard of it yet. However, we could as well play with liquid nitrogen for a few minutes, which always amused them. Expressions of girls’ faces in the first row when I dropped some of the liquid onto the floor was priceless. They were curious and I got questions from each group, the most difficult being Why do you do that?

Outreach is important, there is no doubt about that. There is no other way to encourage young people to study natural sciences than making them believe they really want it – if they don’t, they will be frustrated soon after they start studying. Department of Physics, keep up the good work!

Physics at Work

Our guests in cleanroom suits (source: http://www-outreach.phy.cam.ac.uk/physics_at_work)

How does a laser lase?

How do I know that my laser works properly? Obviously, I have to measure it somehow, because a human eye (or rather any eye) can’t see this radiation. In the group, we conduct a few different experiments on QCLs. The simplest one is an LIV (Light-Current-Voltage) characteristics – resulting data indicates whether the laser emits any radiation and for what current the emission is the strongest.

Firstly, I have to mount a device on a cryostat. The end of the cryostat is called a cold finger. As both names suggest, they are used to cool down whatever we place on them – we do it by filling a cryostat with liquid helium (which has a temperature of around 4.5K or -269C), but it does not fill the chamber where the sample is, because that could spoil our measurement. The cold is transferred to it (just as heat is) by a narrow, metal part, hence the name cold finger. Before I put the cryostat on an optical bench, I have to make sure there are no broken connections by simply measuring the resistance across the device using a multimeter.

Cold finger

The cryostat has four windows through which radiation is coming out. Before an LIV measurement, I remove one window and mount a thermopile in its place. No, I am not talking about Greek history here – a thermopile is in fact a pile of thermocouples, which are a kind of thermometers. When a laser is emitting radiation onto this detector, there is a small (because my lasers’ output power is only of the order of milliwatts) change in its temperature, which is then converted to voltage.

What useful information I can get from such measurement? Although I will only know my device’s power in some arbitrary units, I can determine the current at which it lases with the maximum power, i.e. when it is properly aligned (see the picture in the previous post – in other words it lases best for a particular slope of the diagram, which is controlled by the current). Also, I repeat the experiment in different temperatures to see when it is too hot for the laser to work. Finally, by looking at the features of the plot, we can learn about general behaviour of the laser: what is the range of currents for which it is working, whether there are any additional wavelengths emitted, what is its resistivity and so on. Below is an LIV plot of my first QCL. It is a two colour design, so you can see a second, much smaller hill on the right – this is where the second colour (frequency) is switched on. The upper lines pertain to current-voltage characteristics.

LIV of my laser

Quantum cascade laser in simple words

I am afraid I haven’t explained what a QCL really is. I will try to do so in simple words. Fellow physicists: please don’t blame me for simplifications.

One of the most amazing technologies invented in the last few decades is definitely Molecular Beam Epitaxy – a technique that allows us to deposit unbelievably thin layers of elements like gallium, phosphorus or antimony. To create a wafer (a sandwich made of these elements) appropriate for a QCL, we need more precision than in other devices. A typical height of one layer of our sandwiches is of order of a few nanometres, and one sandwich consists of hundreds of layers!

Why couldn’t we just use one material and don’t worry about thickness? It’s here when quantum mechanics needs to be mentioned. In the picture below you can see many rectangular shapes. These are intuitively called wells and barriers. If we consider such a well, we get a surprising result: electrons cannot increase their energy by any portion, but are confined to discrete (not continuous) set of states. We say that their energy is quantized. Hence in each well there is a ladder of states and an electron can only be on one of its steps. It’s visible when you look at the tails of orange lines – they indicate where each electron level is. I should mention that wells’ depth and barriers’ height represents energy while the real space is drawn horizontally so when electron travels through the structure, it goes from left to right.  Now, why the diagram is diagonal? Because we apply voltage to our structure and it pushes our carriers – electrons – in the right direction.

Quantum cascade structure

How does an electron go through a barrier? This is the tricky part which I don’t feel competent enough to explain here. Going through the barriers is the crucial element of QCL design and researchers around the world are constantly searching for the best solution. You could think that they jump over the barriers, but this is not the case. In quantum mechanics, it’s possible that they actually go through or tunnel. In the picture you can see wavy shapes – these are wave functions of electrons. If there are two “hills” emerging from two different lines in one well, it means that an electron can mysteriously go from one well to another.

Laser emits radiation. In this case, it is radiation of a fairly low energy (200-400 times lower than that of visible light). When is it emitted? As an electron goes from left to right, with each transition they jump down, which means they lose energy. It can be passed to the electron’s environment, but sometimes it is emitted as a photon (as radiation). The whole designing process is about controlling the widths of wells and barriers. As you can imagine it is a very complex task, because one variable (width) corresponds to many effects (emitted energy, tunnelling mechanism, thermal properties etc.).

I hope it makes sense even if you are not a physicist. Next time I will describe how to make such a structure a working device that you can plug in and turn on, provided you have some spare liquid helium around.

It’s lasing!

It took me more than a month to fully process my first quantum cascade laser. Do not think that it normally takes so long; I just had to do things slowly to learn them properly, but also I had to wait more than two weeks for one step to be done by someone else. It seems I am a bit too technical with my posts so I will try to reduce the amount of boring, meaningless words from now on.

I am sitting next to my experimental setup where a few minutes ago I saw my device lasing for the first time. It is fairly simple: a cryostat (to cool the sample down to 4K),  a thermopile (collects the radiation from the laser and converts it to voltage) and a few standard lab tools: an oscilloscope, a function generator and a lock-in. Oh, and obviously I needed pumps to evacuate the cryostat!

For the first time I saw LabVIEW being useful – I learned to use it at university but I cannot say we invented a wheel at that time and it was just a fun way of programming. Nevertheless, it is a powerful tool that allows me to do other things while it is collecting the data. I will try to make a few cosmetic improvements to the script later.

The final steps of processing are perhaps the most stressful, because you know that any false move can lead to destroying your samples. Wire bonding – connecting the laser with its package with a very thin gold thread - was the last of these. Fortunately, with a little help from Yash, my 250μm wide precious was given 11 beautiful bonds and it showed a few ohms of resistance across itself as a sign of happiness!

Now I need to measure it properly and then understand the figures, which will take me a few days. However, there are more devices to be processed so I won’t be bored at all in the nearest future. I present my little friend to you:

My first laser

The dark rectangle with golden stripes is my laser.