Currently available projects can be found
here.
The following Yr4 projects have been offered within my group
in the past.
How to upgrade gravitational wave detectors
Supervisors: Andreas Freise
The LIGO project has recently announced the first detection of a gravitational wave. This achievement is the result of several decades of work, in particular in experimental physics. We are involved in the design, construction and operation of large scale detectors, such as LIGO and the Einstein Telescope. We want to improve these detectors further, to a sensitivity which allows regular detections of GW events, establishing the new era of gravitational wave astronomy. The laser interferometers in the detectors consist of many optical and electrooptical components and can only be analysed or understood as a whole. We have developed our own numerical modelling tools to analyse the performance of laser interferometers at the quantum limit. One of the current challenges is to understand and improve the optomechanical sensing and control systems.
The aim of this student project is to investigate the control systems
for the postion and orientation of the mirrors and laser beams
in the LIGO interferometers. The students will first be studying
the theory of laser interferometry and their description in
numerical models. Expertise in programming is required
as the students will develop Python scripts to perform modelling
tasks. Examples for our use of Python for laser interferometer
can be found at http://www.gwoptics.org/learn/.

Optimization of quantumlimited gravitationalwave detectors for compact binaries
Supervisors: Haixing Miao, Andreas Freise
Description: Current and nextgeneration advanced gravitationalwave (GW) detectors are extremely sensitive laser interferometers. One of the noise sources that limit their sensitivity for detecting GWs from astrophysical objects is the quantum noise that arises from quantum mechanical fluctuations of the optical field. It is closely tied to interferometer configuration, i.e., arrangement of optical components and their parameters, that determines how the quantum fluctuations propagate and mix with our GW signals at the output. This project will investigate several advanced configurations and study how we can optimize their parameters for detecting compact binaries: two black holes, one black hole with one neutron star, or two neutron stars. The research outcome will provide insights to the design of advanced GW detectors. The student is not required to have background knowledge in astrophysics, as the only astrophysical inputs for this project are standard GW waveforms.

Optimal control in GravitationalWave detectors
Supervisors: Conor MowLowry, Andreas Freise
Gravitationalwave observatories are the most sensitive instruments
ever made. Our work helps to improve the sensitivity and
robustness of these delicate instruments, increasing their
astrophysical reach and operating time. Seismic motion (and
other sources of vibration) shake the mirrors of the
observatories, and despite having the most sophisticated
vibration isolation systems in the world, they still limit
performance. We are looking to apply optimal control techniques,
such as those commonly found in drone stabilisation and
navigation systems, to improve the vibration isolation systems
of gravitationalwave observatories.
The aim of this student project is to implement optimal control, based on Kalman filtering, to reduce the motion of a mirror using an interferometer readout system. The students will develop Kalman filter algorithms that will be implemented in a digital controller and used to optimally suppress the motion of a mirror. Some practical experience with programming or electronics is required.

Spatial light modulation and laser mode analysis
Laserinterferometer gravitationalwave detectors have pushed the limits of what is technologically possible in precision measurement for 30 years  reaching and surpassing quantum limited performance. A crucial element in the operation of these detectors is matching the mode of the input laser beam  angle, position, size  with a set of suspended mirrors. Even tiny mismatches can cause crippling operational problems.
The project aim is to experimentally test a new method of measuring the mode composition of a laser beam by reflecting the beam off a 'spatial light modulator' such that each mode is separated and independently measurable. This will involve calculating the required modulation, simulating the expected results, and measuring the mode content of a laser.

Understanding the limits to the sensitivity of future gravitational wave detectors
Gravitationalwave detection is one of the greatest experimental challenges today. The LIGO detectors have been upgraded will soon start taking data again. They strive to make the first direct detection of gravitational waves. However, future generations of detectors are required to have enough sensitivity to provide a constant stream of astrophysical data. In order to achieve that, several research and development programs have been started. One important aspect of the design of future detectors is understand how to optimise the interferometers for different astrophysical goals, such as binary black hole, or supernovae signals.
The aim of this student project is to provide an easy to use numerical model for the fundamental noise sources limiting the sensitivity of future detectors in conjunction with simple models of gravitationalwave signals for different classes of sources in order to explore tradeoffs between instrument configurations and science return. Most of the time will be spend on developing analytical expressions for the fundamental noise sources for different interferometer configurations and the consequent observability range for the classes of sources. The next step will be to develop a Pythonbased interface for these equations.

Highperformance Computing for Laser Optics Simulations
Modern gravitational wave detectors represent a new class of optical systems which combine many classical concepts of laser interferometry with advanced techniques such as quantumnon demolition signal detection. Our group is responsible for the optical design for the Einstein Telescope detector and develops new laser technologies in the lab. We have developed a number of simulations tools in the past, which we provide to the community. During the last years, the use of Graphics processing units (GPUs) for scientific computing has become a focus of interest and several standard numerical problems can now be accelerated by dedicated GPU cards, or by the graphics processor in your own computer.
The aim of this student project is to develop and investigate multicore algorithms for sparse matrix solvers and numerical integration routines as used in our own simulations. A new dedicated GPU will be used as a testbed to benchmark different implementations. The students will first be getting familiar with numerical simulations of laser optics. Simple examples can be used to perform proof of principle demonstrations and eventually an implementation of accelerated routines in our simulations codes is envisaged. One student should focus on the implementation of a matrix solver for large sparse systems of equations. The second student will focus on performance testing and evaluation of the implemented solvers. Please note that good programming skills are essential for this project.
Reading:

Visualising the effects of mirror surface distortions
Gravitationalwave detection is one of the greatest experimental
challenges in physics today. Our group is leading the optical design of the
kmscale European detector `Advanced Virgo'. One of our tasks is to
coordinate the development and use of numerical models for the
core instrument, a 3km long laser interferometer. The simulation
tools as well as some of the underlying mathematical methods have been
developed by scientists working on gravitational wave detection.
The aim of this student project is to develop a optical simulation
of a two mirror cavity which can be used to demonstrate the effect
of mirror surface distortions. The tool should be mathematically
accurate and visually clear so that it can be used for teaching
purposes as well as research. The students will first be introduced
to the main principles of numerical methods for modelling of laser
interferometers. Most of the project time will then be devoted to
the software design and realisation of the optical simulation.
One student will focus on the development of the mathematical
framework in the form of a Java library whereas the second student
will develop a user interface and design a display method which
visualises the physical properties of the model of a light field
resonating in a two mirror cavity.

Optical Vortices for gravitational wave detectors
Certain ring shaped laser light modes (special LaguerreGauss modes)
are know as optical vortices because the light's phase resembles
a spiral and carries angular momentum. This fact has led to a number
of applications for these type of light in connection with
ultracold atoms. In addition, these light fields provide a more
homogeneous intensity pattern than basic laser modes. Which means
that a LaguerreGauss mode can carry a much larger total power if
the peak power density must remain below a given maximum.
This feature is crucial for applications of fibre optics in
telecommunication and also makes LaguerreGauss modes an interesting
option for future gravitational wave detectors.
he aim of this student project is to investigate how higherorder
LaguerreGauss modes can be created from a standard laser
beam with high efficiency and high purity. The students will first be
introduced to the main principles of modular description of laser
light fields as well as precision interferometry. Most of the
project time will then be devoted to the design and construction
Mode Converter. One student will focus on the design of the optical
system whereas the second student will setup a prototype of
a Mode Converter and a FabryPerot cavity which will be used to
analyses the prepared Laguerre modes.

Design of modern optical systems with numerical simulations
Modern gravitational wave detectors represent a new class
of optical systems which combine the classical concepts of laser
interferometry with advanced techniques such as quantumnon demolition
signal detection. The resulting laser interferometers consist
of many optical and electrooptical components and can only
be analysed or understood as a whole. A system design approach,
which, for example, is common in space projects, is required. Our
group is responsible for the optical system design for the
Advanced Virgo detector. We make use of a number of simulation
software to model the optical system of the new detector. Several of
the simulation tools are written and maintained by our group.
The aim of this student project is to investigate and implement
automatic systems with our numerical models in order to analyse and
optimise design candidates for the Advanced Virgo
interferometer in a standard test environment. Commercial
tools offer this type of automation but do not provide the
core functionality we require for the optical models.
The students will first be studying the theory of laser
interferometry and their description in numerical models.
Some expertise in programming is required and the
knowledge of a scripting language would be helpful.
One student should focus on the implementation of 'tolerancing',
a method to automatically identify critical design parameters
of a given model. The second student will set up a set of
scripts which can automatically tune the optical system
to their operating point. Optionally the automatic system would
be controlled via a graphical user interface.

Virtual Interferometry
Gravitationalwave detection is one of the greatest experimental challenges today. Current groundbased detectors (GEO, VIRGO, LIGO) are already taking data. They strive to make the first direct detection of gravitational waves. However, future generations of detectors are required to have enough sensitivity to provide a constant stream of astrophysical data. In order to achieve that, several research and development programs have been started. One important aspect of the design of future detectors is to optimise the interferometer topology. One idea is to adapt the concept of the space mission for detecting gravitational waves (LISA), which is based on three independent length measurements. The actual measurement is then performed by combining the three signals during the data analysis process, thus creating virtual Michelson and Sagnac interferometers.
The aim of this student project is to investigate how this concept can be adapted for groundbased projects. The students will first be introduced to the main principles of gravitationalwave detection as well as precision interferometry. Most of the project time will then be devoted to the design and construction of a virtual Michelson interferometer from two optical length measurements using FabryPerot cavities. One student will focus on the design of the optical layout and the processing of the signals whereas the second student will setup the FabryPerot cavities and perform the length measurements by means of electronic feedback systems.

High Finesse Cavities with RetroReflectors
Modern laser interferometers rely on high quality optical components, which are isolated from external disturbances. The longbaseline interferometers used for gravitationalwave detection have set new standards in the interferometer sensitivity as well as the quality of the optical subsystems. The performance of future gravitational wave detectors in their most sensitive frequency band is, for example, predicted to be limited not by optical properties but by mechanical properties responsible for thermal noise in the highreflective mirror coatings. In 2004 Braginsky suggested using corner reflectors as end mirrors in advanced gravitationalwave detectors. These use total internal reflection rather than special coatings to create the required high reflectivity. In addition, corner reflectors can possibly be set up such that the optical system becomes insensitive to misalignment of the optics.
The aim of this student project is to investigate the properties of optical systems using corner reflectors or similar retroreflectors. The aim is to find a cavity setup which provides a high finesse and low sensitivity to misalignment of the optics. The students will first be studying the theory of laser interferometry. Most time of the project will be spent on investigating different implementations of corner reflectors. One student should focus on the experimental realisation and verification of the chosen optical design while the second student will make use of optical modelling software and analytical computations to chose and optimise possible designs.

Numerical Simulation for a New Class of Laser Beams
A new class of laser beams has been recently proposed for
interferometric gravitationalwave detectors, the socalled
`flattop' beams. These beams have a more uniform intensity
distribution than standard Gaussian beams while, at the
same time, maintaining a similar diffraction angle.
Numeric simulations must be employed to test the feasibility of
this type of beam in largescale interferometric detectors. However,
the available simulations have been written and optimised with Gaussian
beams in mind.
The aim of this project is to extend one of the existing software
packages (or optionally write a new software package) with the tools
required for investigating the basic properties of flattop beams.
The students will first study the properties of flattop beams.
Most time of the project will then be spend on developing source code, using one
of the major programming languages, for example, C, C++ or Matlab.
One student will focus on the translation of the mathematical
framework of flattop beams into computer algorithms whereas the
second student will integrate the core algorithms into
a full simulation.

The Quantum Noise Limit of Interferometry
One of the practical limits in interferometric detection
of gravitational waves has its origin in the quantum
nature of light. A good understanding of the interferometer
and the quantum noise limit can be obtained by describing
the quantum noise via vacuum fluctuations that enter the
interferometer through open ports. Recently, this model
has been used to compute analytically the quantumnoise limited
sensitivity of a typical interferometer for gravitationalwave
detection.
Currently the computer simulation Finesse is being extended
to correctly calculate the coupling of vacuum
fluctuations into the output signals of a userdefined
interferometer. Once available this simulation allows to
characterise different optical interferometer configurations
quickly with respect to their quantum noise limit. The hunt is up
for new, lownoise topologies.
The aim of this student project is to investigate known and
new interferometer types for the quantum noise. The students
will first be studying the underlying model for describing
quantum noise in laser interferometry. Most time of the
project will be spend on designing and validating interferometer
topologies. The two students will be analysing different classes
of interferometers and the results should be compared at the end
of the project.

Shaping the photon noise for the Einstein Telescope
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.etgw.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
socalled 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 socalled `squeezed light' can reduce this noise.
For ET the squeezed light needs to be prefiltered
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 frequencydependent 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.

