Gravitational physics

Virgo

The first generation of interferometric detectors has a real chance of detecting gravitational waves. Neverthless, the rate of detected events expected on the basis of the astrophysical population models will be low: in the most optimistic scenario a few events/year of compact-star binary coalescences are expected. Thus, in order to start GW astronomy, 
Virgo has planned a two-step upgrade path towards a second generation detector:

Virgo+

The first upgrade has started in May 08. The changes were based on a well established R&D program and required a limited commissioning time. A system for thermal compensation has been implemented and the laser power will be increased. The electronics was upgraded. New payloads (with dielectric reference mass, fused silica fibers, new mirrors allowing to achieve an higher cavity finess) will be installed in 2010. The optical configuration of the interferometer has not been changed.

Nikhef designed and constructed the front-end system and demodulation electronics for the linear alignment (link to page). Nikhef also designed and installed, in collaboration with scientists from Roma 1 University, the end mirror system for the input mode cleaner (link to page).

Advanced Virgo

This is a major upgrade, with the goal of increasing the sensitivity by about one order of magnitude with respect to Virgo in the whole detection band. It is the detector that, with Advanced LIGO, is expected to see many events every year. The Virgo and LIGO interferometers operate as a network and should provide the start of the era of gravitational wave astronomy. 

Nikhef contributed to Advanced Virgo by providing cryogenic vacuum links in the interferometer arms (link to page). Also Nikhef will upgrade the linear alignment system (link to page) to accommodate higher modulation frequencies. Nikhef will improve the external benches (link to page) for the injection and detection optical tables, as well as for the optical tables at the end of the interferometer arms. In addition, Nikhef has responsibility for the internal injection and detection bench, and for the end-mirror of the input mode cleaner (link to page). Finally, Nikhef contributes to the development and commissioning of a new phase camera (link to page).

Einstein Telescope

Einstein Telescope is the long-term future project of ground-based gravitational wave astronomy. It will record thousands of high-frequency (1 Hz–10 kHz) events per year and will have unprecedented sensitivity to the stochastic gravitational wave background from the Big Bang due to its excellent performance at intermediate frequencies. In May 2008, Einstein Telescope received 3 M€ from the European Commission within the FP7 program to start a preliminary design study. This design study will define the specifications for the required site and infrastructure, the necessary technologies and the total budget needed, and can be considered an important step towards the third generation of gravitational wave observatories. Nikhef leads the work package on site selection and infrastructure (link to page). Here, the minimization of gravity-gradient noise is of utmost importance in order to guarantee excellent low-frequency performance. These activities are carried out in an international context and in close collaboration with geoscientists and industry.