“Believe you can and you’re halfway there”

I usually start my contributions to this newsletter with a quote that expresses or summarizes my thoughts about the main topic I write about. To be honest this time was harder to find a proper quotation because this one is, most probably, my last newsletter entry within the GraWIToN network, and no quotation can summarize all the things that are worth to say. However this one (by Theodore Roosevelt, the 26th President of the United States of America) expresses exactly how I feel about the status of my PhD: When I started to believe that I can do it, half of the work was actually done. I can’t say a date yet, but hopefully within the summer of 2018.

When I started, in 2015, I felt like every new PhD student feels: indescribably lost. Every time I tried to read a paper I had to stop and read first a different one to be able to follow the topic. It was hard at the beginning, but I have to admit that I never lost the motivation. Everything started to change when one day a department colleague came to me looking for advice. He had a lab issue and thought that I could help him! That was the first time I understood that my skills were positively evolving (although 9 from 10 of my ideas were -are- still stupid!).

Now I am happy to say that I am working on my third experiment, which will constitute the third (and last) experimental chapter in my thesis. I already wrote about the first one in the newsletter of June 2016, when I described the process I went through to interpret some results that a priori seemed wrong but resulted to be an evidence of a well-done experiment. It was a study and modelling of the gain- and phase-dynamics of erbium-doped fiber amplifiers and had a happy ending because led to my first publication (DOI: 10.1364/OE.24.024883). The second experiment was a lab prototype of high power fiber amplifier at 1.5μm pumped with a technique called “off-resonant” or “off-peak”. It basically means that the active media (e.g. the substance responsible for absorbing energy in a wavelength to reemit it in a different wavelength) is pumped at a wavelength far from its maximum absorption peak. This can sound a very inefficient way to pump an amplifier but it offers certain benefits and the results were very promising. We achieved up to 100W of optical power at 1.5μm in the linearly-polarized TEM00 mode. The noise behaviour was good, considering that the system was free-running, and we didn’t find signs of Stimulated Brillouin Scattering (SBS) nor Amplified Spontaneous Emission, which are the most limiting phenomena in this type of single-frequency amplifiers. I believe this pumping technique has good chances to be implemented in Einstein Telescope, LIGO Voyager or LIGO Cosmic Esxplorer one day, if fiber amplifiers are finally used for their interferometer at 1.5μm. This work was presented at CLEO-Europe on June 2017 and submitted to the journal Optics Express. Let’s hope it is accepted! The third experiment, which is the one I am working on at the moment, is also a lab prototype for the proof of principle of the off-resonant pumping technique, but this time using purely single-mode fibers that are core-pumped. The goal is to demonstrate whether it makes sense to keep trying crazy wavelength to pump fiber amplifiers at 1.5μm or not. The experiment is in an early stage at the moment, but preliminary results encourage us to keep investigating this topic.

But my host institution (Laser Zentrum Hannover e.V) is not the only place I have worked at. The GraWIToN network provides the opportunity to work in different institutions participating in the network. We call it secondments. These secondments enable a much higher level of cooperation and collaboration which definitely boosts the experience gain of the Early Stage Researcher (ESR). In my case I spent 4 weeks at Albert Einstein Institute working on fiber ring cavities consisting of fiber couplers to lock the frequency of a laser. Although the use fiber couplers for this task had already been demonstrated and reported, its properties and potential use as frequency reference for gravitational waves detectors has not been fully investigated. Obviously, it is impossible to carry out a real research in just 4 weeks, but enough to get introduced in this new topic, which was new for me. Also, working in a different group, with different methods and areas of expertise is a very didactic complement for a PhD candidate.

However the secondments are not the only thing the Marie Curie Actions (MCA) offers via the GraWIToN network. My 13 colleagues (distributed by institutions across Europe) and I, have access to financial support that allows us to attend to congresses, conference, trade fairs, and all these kind of events at which one has to attend to get properly involved in the scientific community and engage in networking. Additionally, up to six schools have been held in the institutions participating in GraWIToN, focusing on data analysis, optics, lasers, optical simulation, project management and outreach. Summarizing, a MCA grant is an opportunity to carry out a PhD that should not be turned down.