“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton (but previously Bernard of Chartres) used this metaphor to express how he achieved his scientific goals thanks to the work of many previous researchers. These were also the first words that came to mind when I heard (and after a believing process) the big news: gravitational waves exist, and we are already able to detect them.

In this regard, it does not surprise me that the first two citations in the detection announcement paper (DOI: 10.1103/PhysRevLett.116.061102) are by Einstein et al. from 1916 and 1918.

But we are not here to look to the past but to the future. We already know that gravitational waves exist, that’s nice. We can detect them, which is great. And we can even make science with them, which is amazing.

However we want more: we want to do real astronomy with gravitational waves as we do with X-rays, visible light, γ-rays, etc. And it definitely requires better detectors, or to talk more accurately, a network of better detectors. However this is something we already knew in the GraWIToN network. Actually this is the reason why we (the Early Stage Researchers) are doing our PhD in this field: to study new options to enhance the detectability of the third generation of Gravitational Wave Detectors (GWDs).

In my last entry of this newsletter I wrote about the Large Mode Area (LMA) fibers and how they allow us to increase the power in fiber amplifiers and, at the same time, increase the non-linearities threshold. After that, my colleagues and I decided to study the gain and phase dynamics of erbium-doped fiber amplifiers (EDFAs). EDFAs are used to amplify laser radiation around 1.5µm, which is a promising wavelength for next generations of GWDs. For example the early design study of Einstein Telescope (ET) already contemplates the use of both, 1µm and 1.5µm laser sources, together with silicon-based optics cryogenically cooled (find it here).

Some other researchers in our group had studied gain and phase dynamics in ytterbium-doped and erbium:ytterbium-codoped fiber amplifiers as well, but pure erbium had not been studied before. It was a great challenge for me because I had to learn a lot of new concepts, measuring techniques, etc., but also very satisfying because at the end the results led (well, is still in process but hopefully it will) to my first paper as first author J.

I am not going in to technical details here, all those will be available in the paper if it is finally published, but I want to talk a bit about the stages of an experiment and process to get it done from an idea to results and conclusions. From my point of view this is one of the most important things I learnt: this process is strongly non-linear.

Everything started with an idea, actually a rough idea, of what I was about to do. My colleagues and I designed the experiments to be carried out, including setups, measurements and simulations. It is curious that, even before measuring anything, I preconceived an idea of what everything should look like, and of course it made more difficult to interpret the real results. Why? Because in my minds I already “knew” how a graph should be and the real measurement did not look like that. You should not look for a specific result. After re-measuring everything two, three and four times I started to attribute the discrepancies between what I saw and what I expected to see to noise, uncalibrated equipment, too low sensitivity in the measurements and a number of other excuses typically used to explain something when you have no clue about what’s going on. It really took some time to suspect that my preconceived idea was simply not right, and it was just after a mathematical analysis and the developing of an analytical model that I accepted it. When I decided to fit the measured data to the analytical model I saw something really strange. It was something I had never expected: the model and measurement results fitted perfectly. Now in retrospect is funny to think that my concerns at that point were “Why do they fit?”, “What can be wrong?”. The answers required strong will: the preconceived ideas were all wrong, and I was about to throw away my results because it did not look like I expected, but they were good actually!

The moral of the story is “Do not let your first thought dominate the following”. Anyway there is another important thing behind this happy ending: the group of people who I work with. Probably I would have given up before having something if I were alone. When you are in a dead end with lack of creativity there is nothing better than a brainstorming with your colleagues. This is one of the reasons why I really enjoy working at Laser Zentrum Hannover. Up to now, I have always found help when I have needed it and this speeds up my learning process and research, but at this point this should not be a surprise, after all I am standing on the shoulders of giants!

Omar de Varona Ortega

Laser Zentrum Hannover e.V.
Laser Development Department
Solid-State Lasers Group
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