"We have detected gravitational waves, we did it!". I was sitting in a room, filled with enthusiastic physicists and journalists, at the Albert Einstein Institute in Hannover, Germany, listening to these winged words from David Reitze via a live stream of the press conference taking place in Washington, DC. For me it was a very happy and emotional moment.

As the advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) upgrade was already finished and the two observatories were in commissioning mode when I started to work in the field, I cannot say I contributed anything to this achievement. But my emotions were not rooted in any personal work or success, but in the long journey the field of gravitational waves and the LSC-Virgo collaboration had gone through to finally step over the threshold where the observatories were astronomically useful. In particular, I was moved by thinking about the many individuals in the collaboration that have founded the field, spent decades building and improving gravitational wave observatories, and managed to convince fund raisers that they were able to build these modern wonders of high precision length measurement devices. Now their creation was evidently successful, and their believes and hard work were proven correct and worthwhile. However, I must admit that I was partly happy for personal reasons as well. I was happy for having the fortunate honour of being a member of the team making this historical first direct detection of gravitational waves. I was happy for the opportunity of being a part of the collaboration for the interesting time to come. And I was happy for finally being allowed to talk about the detection we kept a secret for so long while the data was being thoroughly analysed.

Since I were working in Hannover, Germany, at the time of the announcement, and since I do not speak German, I missed out on most real life outreach opportunities. Instead, I tried to be active on social media, and I was also interviewed over Skype by a Swedish local newspaper, which was a new and interesting experience for me.

With the first direct detection of gravitational waves, one huge milestone is reached, but the era of gravitational wave astronomy has just begun. To observe gravitational wave events more frequently, and to better locate the sources on the sky, we need to improve the current observatories, have more observatories in operation simultaneously (Virgo and KAGRA are soon operational, and LIGO-India is hopefully operational in a few years), and keep working towards building even better ones in the future.

This is where my work comes in, which is aiming at improving the current gravitational wave observatories, as well as contributing to the design of future observatories. One technique that will be used for improving future detectors is frequency dependent squeezed light, which offers an increased sensitivity in the whole frequency band where the current detectors are designed to look for gravitational waves. The name squeezed light can be a bit misleading, as the light itself is not squeezed, but its quantum noise. If the phase noise (noise in photon arrival times) is squeezed (reduced phase noise), the amplitude noise (noise in photon energy) is anti-squeezed (increased amplitude noise), and vice versa. Since gravitational wave detectors are limited by amplitude noise for low frequencies, and phase noise for high frequencies, frequency dependent squeezed light could be used to reduce the limiting noise over the whole frequency band. To create this frequency dependence, we use a so called filter cavity.

An ideal laser source has a Gaussian intensity distribution. However, optical defects and mode mismatches between the optical systems can transform the near ideal laser beam into some new spatial distribution. We usually describe the laser beam in terms of Hermite-Gauss or Laguerre-Gauss modes, where the ideal Gaussian beam is described by the fundamental mode or zeroth-order mode. For describing defect beams we add some Higher Order Modes (HOMs) as perturbations to the fundamental mode. However, these HOMs pick up phases different from the fundamental mode as they propagate through the optical system. My current main project is to investigate if this could transform squeezed light into anti-squeezed light, which would lead to extra noise. Furthermore, I am investigating if the sensitivity to optical defects and mode mismatches could be reduced by injecting squeezed HOMs, and if we could avoid the risk of the squeezed HOMs becoming anti-squeezed as they travel through the gravitational wave detector.

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