In this newsletter I would like to share my research work experience at Virgo detector located in Cascina near to Pisa, Italy. I joined the Squeezing group at Virgo for my thesis work, which is responsible for the development of a squeezed light source to reduce the quantum noise effect in interferometric measurements for Gravitational waves (GW) interferometers. I am about to finish the second year of my PhD course, and by the end of December 2018, I will finish the PhD program. Just to give an idea, what quantum noise is and how does it affect the interferometric measurement.

Quantum Noise (QN) arises due to the quantum nature of light itself, and it comprises of photon shot noise at high frequencies (photon counting error) and the photon radiation pressure noise at low frequencies, when light field is measured with a photodiode. The photons in a laser source follow Poisson statistics instead of being equally distributed. The photon shot noise can be sensed in measurement, where one can see fluctuations in the voltage signal monitored on a oscilloscope for instance, while the photon radiation pressure noise makes the test masses to displace around their equilibrium position. Since the very basic principle of GW measurement involves the test masses to be quieter than the signal you want to measure and also, no noise due to measurement itself to affect the detection, so QN needs to be addressed to improve the GW interferometer’s detection performance. These principles put tight limit on the noise sources to be eliminated out of the interferometer in order to detect the tiny ripples in the fabric of spacetime caused by the GW. Shot noise dominates above 100 Hz up to 10 KHz in the GW detection bandwidth and attenuating the shot noise increases the radiation pressure noise, which is present below 100 Hz. The future upgrades of GW detectors need the reduction of QN to improve the sensitivity in most of their detection band and thus to enhance the reach of detectors further deep into the universe.

In order to address the challenge of QN, Injecting squeezed vacuum states into the interferometer’s output port in a so-called squeezing experiment is a promising solution. The vacuum states allow the reduction in photon shot noise on the expense of increasing the photon radiation pressure noise or vice versa. The idea is to use a nonlinear optical phenomenon to generate squeezed vacuum states for example in degenerate parametric oscillation/amplification process (a 2nd order non linear optical effect). I worked on the development of couple of subsystems for the Virgo squeezing experiment, their installation and alignment on the optical bench. I spent most of my time at the squeezing experiment facility at Virgo site, where we are now implementing the coherent cntrol for the squeezer.

The development of squeezed light source at Virgo site gave me an amazing and challenging experience of work in a clean room. The Virgo site is quite silent and located in beautiful vicinity of Cascina town. This experience allowed me to further improve my experimental skills in optics and to work in collaboration with colleagues from other research groups. I had the opportunity to interact with researchers of other subsystems of the Virgo detector on site to understand this complex instrument and to widen my professional network. I attended the weekly meetings within the collaboration, also the Virgo weeks, which allow the researchers of different subsystems to discuss their research work with the collaboration researchers. Also, I am participating to the GEO600-Virgo collaboration for the development and installation of a new squeezer in Advanced Virgo (AdV) for the next scientific run, which is an exciting collaboration opportunity for Virgo and GEO600. It is an immense pleasure for me to be a member of Virgo collaboration and LIGO-Virgo scientific collaboration.

Apart from the squeezing activity at Virgo site, I spent three months as secondment at Max Planck Institute for Gravitational Physics, which was also a wonderful experience. I worked out an experimental activity on the generation of green light source for squeezing experiment in single pass configuration, which was an effort to optimize the second harmonic generation subsystem for the squeezing experiment. The institute is located in Hannover, Germany and I had the opportunity to explore Germany a bit, though didn’t travel too much. I experienced a different laboratory with helping colleagues and collaborative work environment. Living in Hannover was also a good experience, not a big city, more calm and less crowdy but the weather sometimes can make you a bit uncomfortable with its fluctuating nature.

At present, I am working in the optics group at European Gravitational Observatory (EGO) for the development of all fibered green laser sources for AdV auxiliary lasers. This activity involves the generation of green laser light source in second harmonic generation (SHG) process using single pass configuration. The main advantage of all fibered system is, it eliminates the need of employing additional auxiliary laser sources, the related phase locked loops (PLLs) implementations and ease of optical alignment. It only needs couple of millliwatts of infrared (IR) laser power from the Virgo Master laser, and through an optical amplifier, one can achieve the required amount of IR laser power to produce the desired green laser power, so a simple and economical solution.

I attended the GraWIToN school on laser, optics and simulation held between 12-16 September 2016 at Max Planck Institute for Gravitational Physics, Hannover, Germany and the GraWIToN school on Project Management (PM) held between 21-25 November 2016 at EGO, Cascina, Italy. The LIGO-Virgo collaboration (LVC) meeting in August 2017 at CERN was also an amazing experience. I got the opportunity to visit CERN located at Fraco-Swiss border, the place where some of the most sophisticated and complex instruments are used to understand the interaction of fundamental particles and also to search for new particles, which allows scientists to understand the laws of nature and the structure of the universe.

The GraWIToN project gave me a unique opportunity towards my personal and professional development by allowing me to experience thesis work at one of the leading GW detector in the world, visiting and collaborating with colleagues around the globe and the opportunity to know about diverse culture, traditions and social lives. I would like to thank Marie Skłodowska-Curie actions (MSCA) for providing excellent platform to young researchers to work at the frontiers of science and to contribute to the ongoing human developments in science and technology.



Additional information