A new software package for modeling laser interferometers such as Virgo and LIGO has been launched at an Einstein Telescope conference in Aachen. Nikhef is the driving force behind this Finesse3 package.
The software package is the successor to Finesse2, which is already widely used worldwide to model how laser light behaves within the system of mirrors and lenses in gravitational wave detectors. This software is used both to design systems and to optimize them in practice.
VU professor and Nikhef staff member Andreas Freise developed the first version of the program in the late 1990s and subsequently worked with a team to launch and further develop it into version 2. Finesse2 has been widely used in the measuring instruments for gravitational wave research. Teams from LIGO, Virgo and KAGRA have used the package.
A few years ago, Freise together with dr. Daniel Brown decided to build an entirely new software package using more modern computer techniques and offering greater coherence and flexibility. Finesse2 was written in the previously more common C language; the new version uses Python, the current standard in scientific programming.
The package models laser interference in a user-configurable system of lasers, mirrors, and other optical elements. In the laser interferometers of LIGO and Virgo, a beam is split and sent to two arms containing mirrors. The returning light waves cancel each other out or reinforce each other, depending on the distances traveled.
The interferometer measures changes in distances with extreme precision. In gravitational wave detectors, this is used to reveal minute changes in the distances to the mirrors caused by passing gravitational waves. To measure and interpret the signals, researchers must have a detailed optical understanding of their measurement equipment. Modeling with a package such as Finesse has proven crucial for this.
According to Freise, the reason for redeveloping the widely used software into version 3 is the need for further professionalization of instrument modeling tools, with fewer ad-hoc solutions and including careful documentation. The new package is open source and available via GitLab. “It is also a powerful tool for researchers and engineers working on other optical problems,” says Freise.
“It’s significantly faster than version 2 too – meaning it can be used to address the increasingly complex and subtle optical effects that emerge to challenge gravitational wave detector performance as we continue to upgrade our facilities” says Anna Green, UM assistant professor, Nikhef staff member, and scientific co-lead of the project.
The release is being led from Nikhef, where the team of senior scientists is supported by dedicated software engineers and a number of PhD students and postdocs. “Dedicated support has really made the difference for delivering a stable product that works for our diverse userbase. Thanks to the whole team, we put a special effort on providing documentation and training that is accessible for beginners,” says Green.
The new version is allowing contributors worldwide to extend and enhance the code. This is important to include new features, to make the software suitable for innovations such as crystalline mirrors, and very high laser power, as proposed for the Einstein Telescope.
Following the release, Freise and his colleagues plan a series of workshops to promote the use of Finesse3. “We’re going on a world tour with it!” he says.
