PhoSim Tutorial 8: How to turn on and off Physics Modules

PhoSim has many options to modify or override the default settings. The nominal settings are based on the most realistic physics. There are many cases where it is useful to study parts of the simulation to determine what aspect of the simulation may affect a particular measurement or property of the images. A series of commands can be placed in an physics override file for many different kinds of simulations. One example of this would be to place these commands in a file (called commandfile):

opticsonlymode 0

backgroundmode 0

pixelsize 0.1

This would then ignore aspects of the sensor and atmosphere simulation and simulate objects with very small pixel sizes (0.1 microns). Then a simulation with the following command

phosim examples/brightstar -i lsst -c commandfile

would produce an image like this:

PhoSim Optics Only PSF

which demonstrates the large amount of detail in the optical raytracing in PhoSim. This is just one example of the many uses of the command file. There are many ways to turn the physics of modules on and off as well as affect some of the internal parameters that are generated. This can be used to exaggerate the physics as well as determine the relative importance of various physics to a given type of measurement.

Another example of the functionality in this in great detail is the PSFs with various physics turned on and off on the front page and below. Here you can turn off individual physics and make three color images to show the chromatic dependence of various effects.

PhoSim On-Axis PSFs