Advanced VIRGO optical design
The 3km arm length Virgo detector located in Pisa, Italy, is the largest and most sensitive gravitational wave detector in Europe [1]. Around 2010 this instrument will undergo a major upgrade, called Advanced Virgo, aiming for a 10 times better sensitivity than initial Virgo detector [2].
![[Virgo Detector]](images/avod-virgo.jpg)
Building Advanced Virgo includes the following upgrades [3]:
- Increasing the laser input power from 20W to 200W
- Implementation of Signal-Recycling
- Changing from a RF-heterodyne detection scheme to DC-readout (homodyne detection)
- Replacing the core optics (larger and heavier mirrors of improved quality)
- Changing the beam geometry inside the arm cavities (beam waist in the centre of the arms instead of at the input mirrors)
Other potentially beneficial upgrades currently under investigation are:
- Using non-degenerate recycling cavities
- Implementation of wedges for several optics
- Changing to higher-order Laguerre-Gauss mode
![[AVOD graph]](images/avod-hilm.jpg)
The change from using only Power Recycling to more advanced optical topologies, such as the simultaneous use of Power and Signal Recycling or non-Gaussian beams, will increase the complexity of the system. Advanced VIRGO will thus face an increasingly difficult control problem and probably additional unwanted cross-coupling between ideally independent degrees of freedom. In addition, Advanced VIRGO will make use of higher circulating light power, which results in more stringent requirements for several interferometer parameters, including optical losses and the mirror positions. Therefore a detailed and thorough system design of Advanced Virgo will be required to reach a mature design.
Our group signs responsible for the optical design of Advanced Virgo, a key point within the project, connecting to all the other subsystems.
The next steps towards the Advanced Virgo optical design are:
- Evaluation and decision on mode-matching, beam sizes and beam geometry.
- Investigation of feasibility of higher-order Laguerre-Gauss modes.
- Compile a list of all optical parameters and constraints (including noise models).
- Provide an optimised parameter set.
References:
- [1] Acernese F et al: Class. Quantum Grav. 21 (2004) S385-94.
- [2] http://wwwcascina.virgo.infn.it/advirgo/
- [3] http://wwwcascina.virgo.infn.it/advirgo/docs/AdV_Design.pdf