Alex Sulai, student of Master Programme at Fysikum

Alex tells us about himself and his future plans.

"My name is Aleksandros Sulaj (everybody calls me Alex) and I am from Greece. I was born in 28th October of 1999 and I grew up in Athens with my parents and two brothers. Right now I am enrolled for a Master's Programme in Physics in SU."

During high school, he liked math and literature and was ok with the rest of the courses but for some reason he was really bad in Physics.
"I did not love or hate the subject, I was just bad at it. To fix this, my parents got me a private tutor in order to catch up with the other students. It was during those tutor lessons that I fell in love with Physics. My teacher managed to pass on his interest to me and by the end of high school Physics was the subject that I loved the most and was best at."

Despite some difficulties, he passed his exam

The things that he learned in high school did not seem enough, thus studying Physics in university seemed like a natural option for him.
"I did really good in my admission tests and managed to get enrolled to Bachelor's Degree in Physics in the University of Athens, in September 2017. I was pretty excited at first but during my second year I failed almost every course and was on the verge of quitting altogether. My programme was one of the most difficult ones in Greece and I thought that I was not cut out for it. One of my professors even advised me to switch majors. But after talking to some friends, this feeling seemed to be common to others as well. So I said to myself to keep trying. Then, I had a really good final year and managed to graduate in December 2021 with a good grade."

In 2022 he started studying Physics at Fysikum's Master Programme

After graduation, he wanted a change of things and was welcome to the idea of living abroad and if possible maybe continue his education even further.
"I decided to move to Sweden and after a few months I also got accepted in SU for a Master's Programme. When I am done with my studies, I would like to stay in Sweden and work in the industry. I did an internship in a company last year and it has been a wonderful learning experience. In the future, I could see myself doing what I was doing in the internship."

The internship at Cobolt

"The company where I did my internship is called Cobolt and is
located in Solna Strand. It was a start-up that originated from KTH and has grown a lot over the years. It deals in Photonics and manufactures lasers for various applications.
Target clients include pharmaceutical companies, universities, other photonics companies and laboratories. The company also goes by the name of “Hübner Photonics”.

Before I started my studies in Stockholm University (September 2022), I worked briefly at Cobolt from June 2022 until August 2022. I really enjoyed working there, and we agreed with the company to continue our agreement (although part-time due to studying). I am still working there as of now. I really had the best connections one could have for an internship.

I was working within Production but I was interested to see how the skills from university are applied to the industry. I asked the R&D manager
if I could work on a project as a part of the “Internship in Physics” course in SU and he agreed. The weird thing was that I was both working and doing an internship within the same company. The way we solved this was that on Fridays, I was only doing R&D stuff.

The project we worked on was called “Wavelength tuning of a Solid-State
Laser.” A simplified version of a laser consists simply of an active medium between two reflectors. The generated light of the medium bounces back from the reflectors and causes a stimulated emission from the medium leading to an amplification of the light. These two reflectors only allow light that constructively interferes to bounce back and forth. The
condition that satisfies this is : L = mλ/2. This means that if one were to change the length of the cavity (L) one could cause the output wavelength of the laser (λ) to change as well.

The problem with lasers is that when continually operating, due to fluctuations in temperature, the cavity thermally contracts and expands leading to a random fluctuation of the output wavelength of the laser.

Internship Objectives:

1. Establish a way to tune the wavelength and describe how tuning works.
2. Develop a way to lock the laser to a specific wavelength.
3. Lock the laser to a specific absorption line of Iodine.

We used a piezoelectric crystal to tune the cavity size. The piezo crystal contracts and expands depending on the applied voltage to it. Thus by tuning the voltage one essentially gets a shift in wavelength.
My task was to do all of the above with the invaluable help of an
R&D colleague. We determined how the wavelength tunes using an Optical Spectral Analyzer. Then we wrote an algorithm to detect any frequency shifts due to temperature and using this data the algorithm could then induce a new shift to counteract the first shift rendering the frequency to be constant at all times.
When temperature causes df, we induce -df so we stay at f = f0 (constant).

Then with the algorithm, an Iodine Gas Cell and a photodetector, we were able to lock the laser frequency to a specific absorption line of Iodine.
We were more than satisfied with the results of the internship. We wanted to continue even further with laser locking using Doppler-free spectroscopy but we did not have enough time.
I would definitely recommend people to do an internship, although it
would have to be an internship within the industry. The opportunity to work in university already exists due to thesis projects, thus internships within university are rather unnecessary. I learned a lot from my time in Cobolt (and still am!). It taught me how to apply my skills in real world problems and how to be more independent when working."

Alex advice to other students

Travel abroad. In my brief time here in Sweden, I learned a lot, met many people and studied in a completely different way that I was used to. Coming here was something that I definitely do not regret.
Doing an internship. An internship can give you a taste of the industry and the thesis project a taste of academia. Having done both, one can make an informed choice between the two.

More information

Master Programme in Physics at Fysikum
Four study paths are proposed: Particles and Cosmos, Quantum matter, Atomic-Molecular-Optical physics and finally General Physics.

Hüber Photonics