theia is a 3D Gaussian optics simulation program and library, with support for various optical components, non-sequential tracing, and general astigmatism. It was developed by the Optics Group of the Virgo collaboration at EGO in Cascina, Italy.

theia is written in Python2.7, in order to offer full modularity, portability and the object-oriented programming style to users.

In its executable form, theia allows for readily written text-based input of the optical setup and clear output of the physical data on the propagation of Gaussian beams through the optical setup, also in text form. When used in its library form, theia exploits the scripting possibilities of Python and can be used as a powerful tool for tasks such as optical bench design and optimization, stray light hunting, component alignment, etc.

Building theia and its documentation requires a small number of Python and latex packages which are listed in the REQUIREMENTS file.

Once in the project root directory, issue the following to install theia locally (this will install the theia to ~/.local/bin and this directory must be in your PATH to use theia):

• installation and documentation compilation: make install;
• only installation in the local environment: make build-theia;
• only documentation: make build-doc.

You can then move the pdf documents found in doc/ and the tutorial files found in tutos/ to wherever you feel is best and get rid of the project directory if you like.

For a system-wide installation, issue the following with root privileges: python setup.py install (this will nonetheless not compile documentation).

To remove a local theia installation from your system, cd to the theia root repository wherever it is (or download a new one) and issue: make clear

To remove a system wide installation is generally a system-specific procedure but the Python2.7 libraries are generally kept in /usr/local/lib/python2.7/*-packages

In general: theia [options] FNAME

theia takes a .tia formatted input text file for the optical setup configuration and has a number of options concerning the output of information to the console and the writing of the output text file.

For the format of the input file, see theuserguide.pdf and quickref.pdf files in doc/ and for details on the command line options, you can also see the output of theia -h.

As usual, you can use the

from theia.running.simulation import Simulation

idiom from Python to use specific functions or modules from the theia library. Please refer to the apiguide.pdf file for more details on the API.

To learn on theia, you will find (after installation) in doc/:

• userguide.pdf as a global guide to the operation of theia on the command line and an introduction to the theia library;
• quickref.pdf for an at-a-glance reference on the .tia format;
• apiguide.pdf for a detailed guide to the theia library.

For an easy online documentation, surf to http://theia.hopto.org/docs/html/index.html.

Don't forget that once you've installed theia you can call pydoc [IMPORT PATH TO A THEIA MODULE OR PACKAGE] from the command line for a quick query.

In the effort of taking down walls in the way of physics and computation, theia is free software and is released under the GNU General Public License, version 3+. So please feel free (as in freedom) to copy, take home, modify, teach, learn, and redistribute theia.

See the LICENSE file it the project root directory for more details.

The Theia Project is also an open source project, so please feel inventive and contact raphael.duque@polytechnique.edu for suggestions, comments, access to the git repository and bug reporting.

This work owes a great deal to many people in and out of the gravitational interferometry community. We would like to thank G. Hemming, H. Yamamoto, and G. Duque among others.