News

Numerical modelling for the design or commissioning of laser interferometer often involves a series of related tasks. At some point it becomes more efficient to write scripts to automate the sequence of tasks. This has also the advantage of documenting the full activity from preparing the models to the post-processing of the result. So far we have used a set of Matlab tools (Simtools) to automate modelling with Finesse. Now are moving to Python using PyKat!

The move away from Matlab to Python has been on out ToDo list for a while. A big part of automating Finesse simulations consists of parsing and writing text files, for which Matlab is not ideal. More importantly Matlab licences can be very expensive so that many people cannot use our Matlab tools. Python, especially the interactive IPython, combines easy string handling with an intuitive interactive shell and the possibility to write reasonably elegant and readable script files.

PyKat has been written by Daniel Brown and is available as an open source Python package. It has already been used for serious work, the examples included in the package provide the results presented in the document: `Comparing Finesse simulations, analytical solutions and OSCAR simulations of Fabry-Perot alignment signals' (available for download: http://arxiv.org/abs/1401.5727). Try it out! Contributions and suggestions to the Python code are very welcome too!

One of my favourite activities is to use numerical simulations to model real laser interferometers. The three links below show you some examples on what we have been working on during the last months.

• Investigation of beam clipping in the Power Recycling Cavity of Advanced LIGO using FINESSE, a LIGO technical note by Charlotte Bond, Paul Fulda et al.
• Revisiting Sidebands of Sidebands in Finesse, a LIGO technical note by Jordan Clarke, Haoyu Wang et al.
• Modelling mirror surface distortion effects in low-loss, near-unstable Fabry-Perot cavities, a poster by Daniel Brown et al., see also the screenshot below.

Are you interested in advanced laser optics? Do you want to set up your own experiment, or would you like to contribute to one of the largest interferometer projects world-wide? Are you excited by porting numerical algorithms to GPUs and would you like to compare numerical models directly with experiments? We have PhD positions available now (start date October 2014, apply by 15. December 2013). For more information see our groups's PhD admission page and the project descriptions on my research page.

A new version of Finesse is available for download. (You can also compile it directly from the source code.) The coupling of multiple frequency components has been completely rewritten. Now all laser fields and modulator sidebands are computed simultaneously (rather than sequentially as before). This change is a necessary preparation for the implementation of radiation pressure and quantum noise effect. It has the bonus feature of allowing the correct modelling of `sidebdands of sidebands' (such as created by two modulator components in series).

This is mostly a bug fixing release: We have changed a lot of the underlaying code, in preparation for the implementation of radiation pressure effects. This release marks the point in which all our tests produce the same results as before. For a full list of changes since version 1.0 see the file CHANGES.

Today a new paper has been published on the arxiv.org server: Sensitivity of intra-cavity filtering schemes for detecting gravitational waves by Mengyao Wang et al.

Also, I realised that I never added a news item about our video paper! Already published in August, this is still worth a look: We demonstrate our recipe for creating pure, high-power ring-shaped laser beams:

Recently some new files have been submitted by Finesse users Emil Schreiber and Will Vousden, so that Syntax Highlighting modes for Finesse are now available for Emacs, Vim, SublimeText (and TextMate, Textastic), Notepad++ and Ultraedit. You can download the necessary files from the GEO Simulation Group Wiki and of course Finesse from this page.

The third issue of the LIGO Magazine is out now! In this issue we bring you stories about the squeezing of light, a relatively recent concept from quantum optics, which might sound 'strange'. Hopefully the stories in the magazine will help to make squeezed light a little bit less strange. If you want to know more about gravitational waves and about what is going on in our community download the magazine now!

Our plotting library gwoptics for the Processing programming environment has been updated to version 0.5 and is now fully compatible with Processing 2.0. Give it a go, it also works on Android!

The library provides basic plotting functions for making 2D or 3D graphs with Processing. The examples included in the package show you how to plot data streams, data from lists or files or the output of equations.

In February 2013 I was invited by the Institute of Physics to give a lecture in the famous lecture theatre of the Royal Institution of Great Britain as part of their Physics in Perspective series. I was to expect about 400 students and teachers from schools across the country. The IOP has now published a recording of my presentation on youtube.

The main work behind the scenes of the release of Finesse 1.0 has been the testing, debugging and checking of the source code and of the simulation results. We are planning to collect this material and publish it as notes on the arxiv server. Today the first of these has arrived: Interferometer responses to gravitational waves: Comparing FINESSE simulations and analytical solutions by Charlotte Bond et al. It shows not only example Finesse results but also analytic solutions for simple interferometer responses - something we felt was lacking in the online literature.

After more than 13 years of work and 25 releases we are proud to announce version 1.0 of the interferometer simulation tool Finesse!

Finesse is a fast and relatively easy to use software to simulate laser interferometers. It can be used for detector commissioning, interferometer design, or simply for learning more about laser optics. It is freely available for many platforms and fully open source. We also provide simple examples and an extensive manual.

Of course, we will continue to extend and improve Finesse. This version 1.0 completes the open source release of Finesse after a period of extensive testing and optimising the modeling of higher-order modes for beam shape changes and mirror surface distortions. The future of Finesse lies in the implementation of radiation pressure effects and quantum noise calculations; in fact, we have already started work on this.

We have been quite busy recently and have submitted four new papers to the arxiv.org pre-print server. These papers provide a good glimpse into the work we do in our group, from investigating optical effects in detail to the design of future gravitational wave detectors. The pre-print server is open access, so have a look:

I am pleased to present the second issue of the LIGO Magazine! This issue of the magazine of the LIGO Scientific Collaboration (LSC) features articles about black holes, and the astrophysics and data analysis that LIGO can do to find out more about these elusive objects. We also include a mix of conference reports, news items and stories from the detector sites. If you want to know more about gravitational waves and about what is going on in our community download the magazine now!

Our Korean colleagues have organized their first gravitational wave conference Gravitational Waves: New Frontier. The talks cover a wide range of existing and planned projects. The slides are available for download, have a look!

Today and on Saturday this week, we are taking part in a BBC Stargazing Live event on the University Birmingham campus. We are showing our exhibition Looking for Black Holes with lasers with a new addition: the Mirror Suspension model with the full Advanced LIGO BOSEMs and control electronics.

It's been a lot of fun so far with a great audience, see the queue in front of the Physics building.

Thanks to Reinier Jonker at NIKHEF we can now also provide a Dutch version of Space Time Quest. We have also posted a new Processing sketch Reflection which demonstrated how electromagnetic waves behave at an optical surface.

At the moment all our interactive applets are based on Java applets, but because Java is disappearing from browsers more and more we plan to re-post all the interactive sketches as HTML5+Javascript, making use of Processing's Javascript mode.

A new version of Space Time Quest has been released. If you want to know how we design gravitational wave detectors such as Advanced LIGO or the Einstein Telescope, download the game and try for yourself!

The LIGO Scientific Collaboration (LSC) today has published the first issue of a new magazine: The LIGO Magazine has been designed for the scientific collaboration itself as the main audience. However, it is published as a free download (pdf file) and I believe that this magazine is an interesting read also for people outside that community. It contains a lot of articles, stories and fascinating photos, have a look!

It is now 15 years since we had the idea to create the interferometer simulation Finesse. The software has been used for more than 10 years to design and improve optical systems and it is time to have a look at the impact it had. I have started collecting references to scientific reports and papers that reference Finesse and so far I have found 56 such documents. Have a look at that list and read about the History and Impact of Finesse! Please let me know if you know of other documents that should be listed here.

During the last weeks I had a look at the gwoptics.org user statistics. Here is quick summary in case you are interested (or you can have a look at some plots): The data extracted from the webserver logfiles show a steady and fast increase in visitors to gwoptics.org since its launch, with currently an average of 140 unique visitors per day and more than 100,000 page impressions per month.

Our interferometer simulation Finesse has become open source! Not only can you download the source code, but we have also setup a professional Redmine project page for Finesse with a bug tracker, a Wiki, user forums and an easy way to view the code online. Have a look around and get involved! We are happy to help by answering questions in the forums and welcome any kind of contribution to the development of Finesse.