The past few months have been very eventful - it almost feels like I spent more time away from my desk than at it! This started towards the end of April, when I left for Italy for the first GraWIToN school.

The first in a series of schools in the GraWIToN program, the initial lecture week fulfilled multiple purposes: we were to gather a foundation of knowledge in the field of gravitational physics, which not only our research but also the more specialised later schools would build upon. We were also instructed on the topics of presentation and outreach, aiming to prepare us for explaining our research and field to the general public by means of written and spoken word. Last but not least, this was the first time the twelve of us ESRs got to meet each other!

Some of us had already met by virtue of working in the same academic and/or geographic location, but here we finally had the opportunity to get to know each other properly. It was great to have this ample opportunity for both personal and academic exchange, and be able to put into perspective our own work with all its highs, lows, challenges and outlooks. While the days were filled to the rim with lectures by some of the leading experts in all aspects of gravitational physics, workshops and practical work, the nights were ours to explore the wonderful city of Pisa together as spring inexorably brought Tuscany back to life from its brumal hibernation. I can't say that I wasn't exhausted as we returned to Germany after three weeks, but it was a time well spent, with many new perspectives gained and friendships begun.

Even so, the return to Hanover was only temporary. Only a few weeks later, a similar event took place organised by the Max Planck Institute instead - all first year PhD students were relocated to Scotland for a week for another set of lectures. As fate would have it, we were joined in this school by students and staff from the University of Glasgow, some of which were already familiar from time spent together in Italy! And so, among the scientific and cultural exchange, there was also a reunion of sorts. Having returned from Scotland recently, however, I am gladly looking forward to the German summer, and to finally spending some uninterrupted quality time with my own research project: the fiber ring resonator.

According to the title of my PhD thesis, I will be working on stabilising high power fiber lasers. Hence, it isn't unexpected that my first research project is fundamentally based on optical fiber. In optics, cavities are an essential tool. From the simple Fabry-Perot consisting of just two mirrors opposing each other, to ring or bowtie cavities consisting of three, five or even more mirrors - they are everywhere. Although they fundamentally all fulfill the same task in providing a resonant space for light to circulate in, their applications are varied, from providing frequency references in order to stabilise a system to storing power as is done in the arms of Virgo and LIGO. However, most cavities in use today are air based and consist of mirrors fixed in space. As we are moving toward designing completely fiber-based lasers, however, we are aiming to find fiber-based alternatives to the components found in today's lasers. Hence, I am investigating how fiber cavities might be useful for designing the next generation of lasers for gravitational wave astronomy.

A fiber cavity is also called a fiber ring resonator. The name betrays the design - it is, fundamentally, a fiber ring in which light resonates. The ring is formed by joining the two ends of a length of fiber together. Light can enter this ring by coupling into it from another fiber. Optical fibers consist of a small core guiding the light, surrounded by cladding of a different refractive index. Ordinarily, the light is confined to the core - however, when the cores of two fibers are brought close enough together, light can couple from one fiber into the other by means of evanescent waves. Using this method to couple light into our fiber ring resonator, we can also observe the light coupling back out of the resonator to investigate the properties of the cavity, for example by comparing the output of it to that of a reference cavity of very high quality.

However, numerous challenges await before this stage is reached! In producing the fiber ring, the ends are joined by a process called fusion splicing. The fiber ends are heated to very high temperatures so the glass softens and liquefies, then are pushed together so that they melt into one another and form a connection indistinguishable from the rest of the fiber. In order to produce a working fiber cavity, this splice connection needs to be of a very high quality, minimising the light that is lost passing through the joint. However, splicing fibers is an art of its own and involves many parameters to be adjusted, that differ depending on the fiber and equipment used. Another process that needs to be mastered is coupling light from a laser source into the fiber - the core is only a few thousandths of a millimeter in diameter, so focusing a spot of light just right to enter the fiber is no easy task either. These challenges are not new, and have been conquered by many scientists and engineers before us. Nonetheless, we have to find our own way to emerge victorious on our way to scientific insight.

Simulation of gravitational radiation produced by the merger of equal mass black holes. Simulations carried out by the NASA Goddard Space Flight Center Numerical Relativity Group; visualization by Chris Henze at NASA Ames.

Hello, my name is Rudy Nahed and I am the Early Stage Researcher 2 of the GraWIToN Project. Two institutes in France, both partners in GraWIToN, are hosting me: the private company Boostec and the Engineering University of Production LGP INP/ENIT.

I started my PhD a bit late (10 April 2015) and my first trip was to EGO-VIRGO, Italy, to attend the 1st GraWIToN school. On one hand, it was really exciting and outstanding to meet my colleagues and to be introduced to them; on the other hand, I liked so much interacting and learning from the experts of Astrophysical domain and other domains as well (Laser, Optics, etc…).

The subject of my thesis is about studying and developing a material called “Silicon Carbide SiC”. The purpose of this study is to identify and set the suitable requirements of baffles fabricated from this material, for blocking and absorbing stray light in the optical cavity.

This material is of great interest to VIRGO, due to its physical and chemical properties. Therefore, my main work in Italy is going to be the characterization of this material, while in France it is going to be modeling and designing the suitable model that best fits in the interferometer as baffles.

Currently, I am back to VIRGO, for a GraWIToN secondment period. I’m just beginning to work with the simulation programs used to model the optical cavities in Virgo and its components; I have been introduced by Dr. Antonino Chiummo on stray light issues, on the apparatuses I will use for measuring Reflectivity, Bidirectional Reflectance Distribution Function (BRDF) and Total Integrating Scattering (TIS) of optical elements. I hope that I have some interesting results from different characterizations to share with you in the next newsletter.

Lightweight Silicon Carbide Mirror, Polished side

"Don’t tell me how educated you are, tell me how much you traveled"

This sentence has been said by the Muslim prophet Muhammad. Actually, it is supposed to be so but I couldn't find any proper reference about that... Anyway, whoever has said that, it speaks to me... and not only to me: this is the philosophy of our European project! Ease the interactions between people from everywhere to share knowledge and different points of view in order to go further together.
Why do I speak about that? Because since the beginning of the 2015 I had the opportunity to enjoy this philosophy and to travel a lot.

At the beginning of February I went to my first international conference in...Tokyo!!! The 3rd ELiTES meeting which is another Marie Curie Action consisting in exchanges between European and Japanese researchers. I made a presentation about my PhD, obviously after 3 months I did not have yet any good results to present. It was more about presenting what are the goals of my thesis and more generally to present the GraWIToN project. There I had the opportunity to listen to the presentation and to discuss with others people involved in GW detection.

Two weeks after having come back to EGO I was already gone away, to Germany this time, and for one full month! I went to Hannover at the Laser Zentrum of Hannover (LZH), which is another partner of the GraWIToN project. I was working with Omar, the ESR working there, and his colleagues. They were very nice with me but I have to admit that at the beginning I was wondering what was I doing there. I did know what I wanted to know: how are they doing to inject high power into optical fibers, what are the difficulties that they encountered, what are the solutions they found... However, I did not know how to acquire this knowledge. On the one hand one month was a bit too short to start a whole project on high power injection, on the other hand it was too long to just wandering around asking people questions and watch them doing their experiments.
We finally found a way together: I started to ask questions, to talk with people about what I wanted to do and know, reading papers that they were advising me, I was also working with Omar on his experiments. With all that we figure out some experiments that I could carry out: testing our components/optical fibers with one of the single frequency medium power (10W) that they have at LZH but we don't at EGO. Unfortunately, the components arrived only few days before the day I was leaving... I had the time to do some experiments but I had so many others in mind that I could not have done... Next time! But anyways I learned a lot and it was definitely a good experience!

And when I'm not traveling the world? The world is traveling to me! Two weeks after my stay in Germany the first GraWIToN school began! All the others ESR, but also some others PhD from many different places, came to EGO for a three weeks summer school. It was a great moment of our formation! We learnt to know each other, to know what each of us is working on.
It was also very nice to meet all these researchers involved in GW detection who were giving us those good quality lectures in all these various domains. I would be lying if I said that I understood everything that we have been taught and that I am now an expert in all the fields of GW detection. Going back to school for 8 hours a day was sometimes a bit difficult. However, I think that becoming experts in all the fields was not the goal of this school, it was more about allowing us to get the basis in all the fields so we can have a good overview of what we are all working for.
At that point you may wonder about the practical work that I am supposed to do, isn't it? It is not in traveling all the time that the fibered Electro Optic Modulator will be finished by the end of the year.... True! I was thinking the same. But it's better to acquire knowledge before and then work using this knowledge than the inverse, no!?
Actually between all these activities I had some time to prepare the future developments of my thesis: working on the design of the mechanics and electronics parts of the modulator with the dedicated departments of EGO. However since Advance Virgo is supposed to work by the end of the year, they have lots of works to do and not too much time for me. It will not go as fast as I was expected.
Since the end of the school and for the next coming months, I don't have many sides activities so I can concentrate on my main work and have a continuity in what I am doing. Currently I am trying to get a good coupling between the two collimators which will be on both sides of the modulator as you can on the right side of the picture. I try to improve it little by little by testing new settings. We have already reach 90% of coupling which is nice but not enough! We would like to have at least 95%.

However these 5 last percents are much more difficult to gain than the 90 previous ones! Actually, I am wondering if 90% is not the maximum that can be reach with our components and I have started to look for other solutions. But while writing this newsletter I am trying a new way to improve it, and I am quite confident with it. I will let you know next time if it will have worked. I am also preparing the transfer of the experiment on the high power bench. It is quite challenging to deal with such high densities of power. I wish I will not start the next newsletter saying that I have burnt everything!

The 1st GraWIToN school has been held at EGO from the 20th of April to the 8th of May. If we describe the school by “numbers”, the depicted scenario is quite impressive: beside the 12 GraWIToN ESRs, other 13 students participated to the school. 24 teachers, coming from all Europe, have contributed with about 100 hours of lessons distributed in the three weeks of the school. The spectrum of the subjects presented during the school has been really wide: the basic notions of the gravitational wave (GW) research, elements of general relativity and astrophysics, basic concepts of optics and laser technology, a first approach to the simulation environments in GW research, notions of digital signal processing and science communications tools. Team building has been a self-organised activity, having the students completely shared their spare time during the school (and the idea to have hosted them in the same hotel in Pisa has been quite positive). Between the most “sparkling” sessions it is possible to cite the science communication lessons and the activities with the Arduino micro-controller during the digital signal processing session, where the students had to play with hardware, software and algorithms.

Now the comments of the GraWIToN students are collected to evaluate the quality of the school and to improve the next school, that will be organised in November 2015, hosted by the Gran Sasso Science Institute (GSSI, L’Aquila), and focused on astrophysics and data analysis aspects.
In parallel to the school other events have been organised: the LIGO-Virgo electromagnetic follow-up meeting, with the participation of tens of Astrophysicists and astronomer coming mainly (but not exclusively) from the whole Europe and the Virgo Week, the periodic meeting of the Virgo collaboration. This overlap exposed the students to a really international environment and demonstrated a quite good capability of the EGO infrastructures and services to support international events.
A special thank should be given to the persons that made all that possible: Erika Morucci, who anticipated or solved all the administration, organisation and logistic problems; Elena Cuoco, who has been main builder of the scientific content and structure of the school; the whole EGO computing department, and in particular Andrea Matteini and Giuseppe di Biase, that supported the school and its needs during these three long weeks.

Dr. Michele Punturo

Additional information