PAOS (Physical Optics Simulator) performs physical optics propagation simulations using Fourier optics and the Fresnel approximation to model the behavior of optical fields through complex optical systems. It combines paraxial ray tracing with wavefront propagation methods to analyze diffraction, wavefront aberrations, and imaging effects in user-defined optical configurations. The package accepts configurable input systems via files or interfaces, supports modeling of apertures, optical elements, and aberrations, and outputs propagated fields and related diagnostic data. PAOS includes command-line and library interfaces along with interactive notebooks for exploration and visualization of simulation results. Its modular design allows users to apply different propagation and aberration models, generate surface error fields, and retrieve metrics such as wavefront properties and optical system responses.

ExoSim 2 (Exoplanet Observation Simulator 2) makes spectro-photometric observations of transiting exoplanets from space, ground, and sub-orbital platforms. It is a complete rewrite of ExoSim (ascl:2002.008); it is implemented in Python 3 and uses object-oriented design principles. The package follows a three-step workflow: the creation of focal planes, the production of Sub-Exposure blocks, and the generation of non-destructive reads (NDRs). ExoSim 2 has demonstrated consistency in estimating photon conversion efficiency, saturation time, and signal generation. The simulator has also been validated independently for instantaneous read-out and jitter simulation, and for astronomical signal representation.

ExoRad 2.0, a generic point source radiometric model, interfaces with any instrument to provide an estimate of several Payload performance metrics. For each target and for each photometric and spectroscopic channel, the code provides estimates of signals in pixels, saturation times, and read, photon, and dark current noise. ExoRad also provides estimates for the zodiacal background, inner sanctum, and sky foreground.

ExoSim models host star and planet transit events, simulating the temporal change in stellar flux due to the light curve. It is wavelength-dependent, using an input planet spectrum to determine the light curve depth for any given wavelength and can capture temporal effects, such as correlated noise. ExoSim's star spot simulator produces simulated observations that include spot and facula contamination. The code is flexible and can be generically applied to different instruments that simulate specific time-dependent processes.

An updated re-implementation of ExoSim, ExoSim 2 (ascl:2503.031) is available.