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Photon Simulator (PhoSim) – Official Site

Most Recent News: (4/13/22): PhoSim v5.6.11 is available-- See the detailed announcements.


Welcome to the official Photon Simulator (PhoSim) site! PhoSim is a set of extremely fast photon Monte Carlo codes that calculate the ab initio physics of the atmosphere and a telescope & camera in order to simulate realistic optical/UV/IR/X-ray astronomical images. It does this using modern numerical techniques applied to the physical response of photons (and electrons) to comprehensive physical descriptions of the atmosphere, telescope, and camera. After these detailed physics calculations, PhoSim simply generates images by collecting electrons into pixels. This photon simulation [left] shows the photon Monte Carlo method where photons and electrons are physically propagated through the system. The photon/electron interaction physics includes the appropriate application of novel advanced raytracing, diffraction, and quantum mechanical interactions. The physics of the site/telescope/camera includes: hydrodynamic-based descriptions [middle left] of the atmosphere, elasticity theory calculations [middle right] of optics deformations, and electrostatic simulations [right] of sensors. Since PhoSim is a physics-based code, it is written independent of the telescope/camera/site system, so there are a number of present, past, and future observatories implemented as different input configuration files.

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Despite the physics detail, PhoSim is quite fast due to both novel numerical techniques and efficient multithreading. Individual astrophysical objects can be simulated in milliseconds, and large fields of objects in minutes to hours depending on the size and depth. PhoSim is easy to install and has a tiered set of commands designed for both simple or complex applications. PhoSim has both a graphical user interface and a standard command line/file input interface. PhoSim can run on either your desktop or laptop as well as high performance computing systems (HPC).

There are a variety of uses of PhoSim. Some of the more common applications include: 1) detailed simulation of a telescope while it is being designed, constructed, or commissioned in order to understand scientific performance and unexpected behavior, 2) planning of future observations with straight-forward realistic image simulations, and 3) simulation of realistic training sets with perfect input knowledge for a variety of machine learning/AI and any advanced image processing algorithms.

PhoSim is currently being improved by: 1) asymptotically improving the ab initio physics implementation, 2) pursuing a number of validation studies, 3) enhancing computational performance, and 4) refining interfaces based on user feedback. Many additional large telescopes are currently being implemented. Besides large professional astronomical telescopes, PhoSim potentially has applications in remote sensing/earth-facing satellites, photography & cameras, and various optical instruments (amateur telescopes/binoculars/microscopes).

The links below describe how to use PhoSim, document detailed technical information about PhoSim, and show several example images.

PhoSim User Information:

PhoSim Detailed Technical Documentation:

PhoSim Examples:

  • A visualization of the photons through the optical designs for various telescopes that have been implemented is shown below.


  • An uncalibrated uiy 13'x6' PhoSim image is below. An explanation for what you are looking at is here.


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  • On-axis (left) and off-axis (right) examples of chromatic point-spread-functions with various physics:

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  • Large star and galaxy fields with real stars-- Orion (left) and the Big Dipper (right):

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  • PhoSim does not only have to be used to simulate astronomical objects through astronomical telescopes. It can also be used to simulate any optical instrument, camera, or even biological optical systems with any kind of input. Below is a simulation of the Mona Lisa painting (left) through the human eye (right).

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  • The sky rotation near the celestial pole through the human eye for a one hour exposure (left) and the Moon with synthetic clouds and scattering (right)

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PhoSim Contact Information: