History

Finesse beginnings (1997 - 2010)

Finesse has been originally developed by Andreas Freise during his PhD at GEO 600 (Frequency domain interferometer simulation with higher-order spatial modes). The idea for Finesse was first raised in 1997, when I (Andreas) was visiting the Max-Planck-Institute for Quantum Optics in Garching, to assist Gerhard Heinzel with his work on Dual Recycling at the 30 m prototype interferometer [32]. We were using optical simulations which were rather slow and not very flexible. At the same time Gerhard Heinzel had developed a linear circuit simulation ‘LISO’ that used a numerical algorithm to solve the set of linear equations representing an electronic circuit. The similarities of the two computational tasks and the outstanding performance of LISO lead to the idea to use the same methods for an optical simulation. Gerhard Heinzel kindly allowed me to copy the LISO source code which saved me much time and trouble in the beginning.

In the following years Finesse was continually developed at the University in Hannover within the GEO project [33, 34]. Finesse has been frequently utilised during the commissioning of GEO 600 [35, 36, 37].

Finesse 1 and 2 (2011 - to date)

At the University of Birmingham Andreas started a new research group with a focus on optical technology and interferometer design. Over the years many members of the research group contributed to or used Finesse for their research. In particular, PhD student Daniel Brown became lead programmer and improved the code overall while adding several new features. With his efforts Finesse reached version 1.0 and was made available as open source. Charlotte Bond became a specialist in modelling higher-order optical modes and ensured mirror surface maps or strange beam shapes implemented correctly in Finesse. Keiko Kokeyama, Paul Fulda, Ludovico Carbone and Anna Green have helped making Finesse a useful tool for the Advanced LIGO commissioning team. Mengyao Wang and Rebecca Palmer and Jan Harms helped Daniel with implementing radiation pressure effects and a full quantum noise treatment in the two-photon formalism.

Pykat (2014 - to date)

Modelling the complex gravitational wave detectors often involves an iterative sequence of many tasks. From the beginning we have used scripting languages to prepare, run and post-process Finesse simulations, for example using Octave and Matlab (http://www.gwoptics.org/simtools/). In 2014 we could see that Python would become one of the most common and powerful scripting tools in gravitational wave research. We therefore started to port our existing Matlab tools and scripts related to optical modelling to Python. In addition, Daniel Brown wrote a new comprehensive Python wrapper for running Finesse. These tools have been merged and then published as the open source package Pykat (https://www.gwoptics.org/pykat/) with contributions Philip Jones, Samuel Rowlinson, Sean Leavey, Anna C.Green and Daniel Töyrä.

Acknowledgements

In the early days of the Finesse development, when the software was not much more than an idea, many people in the gravitational wave community have helped with feedback, bug reports and encouragement. Some of them are Seiji Kawamura, Guido Müller, Simon Chelkowski, Keita Kawabe, Osamu Miyakawa, Gabriele Vajente, Maddalena Mantovani, Alexander Bunkowski, Rainer Künnemeyer, Uta Weiland, Michaela Malec, Oliver Jennrich, James Mason, Julien Marque, Mirko Prijatelj, Jan Harms, Oliver Bock, Kentaro Somiya, Antonio Chiummo, Holger Wittel, Hartmut Grote, Bryan Barr, Sabina Huttner, Haixing Miao, Benjamin Jacobs, Stefan Ballmer, Nicolas Smith-Lefebvre, Daniel Shaddock and probably many more not mentioned here.

Gerhard Heinzel greatly supported the original development; he had the idea of using the LISO routines on interferometer problems and he provided his code for that purpose. Roland Schilling spent hours with Andreas on the phone discussing C and Fortran, or interferometers and optics. Ken Strain has been a constant source of help and support during the initial years of development. Jerome Degallaix has often helped with suggestions, examples and test results based on his code OSCAR to further develop and test Finesse. Paul Cochrane has made a big difference with his help on transforming the source code from its messy original form into a more professional package, including a test-suite, an API documentation and above all a readable source code.

Last but not least we would like to thank the GEO 600 group, especially Karsten Danzmann and Benno Willke, who allowed Andreas to work on Finesse in parallel to his experimental work on the GEO site. Finesse would not exist without their positive and open attitude towards science.