The Einstein Telescope (ET) is a conceptual design for a large underground gravitational wave observatory in Europe. Despite the name, ET is not a typical telescope but uses sophisticated laser interferometers with a 10 km baseline. Our group has led the optical design work for the design study document presented at: http://www.et-gw.eu. The next phase of the project involves a closer look at the proposed new ideas and technologies.

The challenge of the ET project is the reduction of the so-called fundamental noise sources by a factor of ten compared to the state of the art. In a wide frequency band the sensitivity of the observatory is limited by the quantum noise of the laser light itself. We have recently shown at the GEO 600 detector that injection of so-called `squeezed light' can reduce this noise. For ET the squeezed light needs to be pre-filtered by reflecting it off one or two optical cavities. The parameters of these filter cavities are yet to be determined.

The aim of this student project is to investigate optical designs for the generation of frequency-dependent squeezed light for the Einstein Telescope. The students will first be studying the underlying model for describing quantum noise in laser interferometry. Most time of the project will be spent on designing and validating filter cavities for squeezed light. One student will concentrate on optimising the cavity parameters while the second student will study the feasibility of the practical implementation of such a system.