aquilesC / PyAstroPol

Instrumental Polarization Analysis of Astronomical Optics

PyAstroPol

Instrumental Polarization Analysis of Astronomical Optics

Overview

The package has one simple goal : compute 4x4 Mueller matrix for the given optical system, and it is developed keeping astronomical optics in view. It uses geomatric optics approach i.e., all the analysis uses strictly ray treatment. Users should keep in mind that this is NOT for optical design i.e., it is presumed that the user already knows the optical system that is to be analyzed.

The package imports following libraries, all of which are ubiquitous. They accompany any decent Python distribution hence this package should function with virtually no dependency issues however it should be noted that it is developed with Python3.6.

os
numpy
copy
random
matplotlib
mpl_toolkits
datetime

Getting Started

Installation

The package need not be installed as the installation scheme is not final yet. Follow these steps to start using the package.

1. Download the package and extract it to a directory of liking - <User directory>/PyAstroPol.
2. Add <User directory>/PyAstroPol to the PYTHONPATH.

Examples

PyAstroPol/Examples/ contains several examples files to demonstrate the applications of the package. They are provided in the form of IPython notebook and it is a good way to quick-start using the package. They also function as the test cases.

Analysis on own

As previously mentioned, this is not a design software. Hence, one needs to know the optical system they wish to analyze. As per the framework of the optical system, there are thee types of objects :

1. Source
2. Components
3. Detector

Following steps illustrate how to devise a simple optical system.

1. import the required package.

from PyAstroPol import * 

2. Create a source, and optionally create a source for display. For analysis one can define a source with a lot of rays (say 10000), and for display one can define a source with fewer rays (say 10).

S_analysis = Source(10000, Clear=20)   # Source for analysis, with 10k rays and 20 mm size
S_display = Source(10, Clear=20)       # Source for disply, with 10 rays and 20 mm size

3. Create a component such as surface, lens etc., and position it.

L = UncoatedLens(50, Thick=10, R1=200, R2=-200)   # Simple bi-convex lens of 50 mm size
L.translateOrigin(z=100.0)                        # Move the lens from default position (origin)

4. Create a detector and position it.

D = Detector(50)                # Detector of size 50 mm
D.translateOrigin(z=200.0)      # Move the detector from default position (origin)

5. Put them together to create the optical system.

O_system = System(S_analysis, [L], D, dRays = S_display)
O_system.propagateRays()                                        # Propagate rays in the optical system

6. Display the optical system using matplotlib 3d axis.

Fig = plt.figure()
Ax = Fig.add_subplot(111, projection='3d')
O_system.draw(Ax)
plt.show()

7. Compute Mueller matrix and print it.

MM, T = O_system.getSystemMuellerMatrix()           # Compute Mueller matrix for the system
print(MM)

Directories

PyAstroPol/PyAstroPol/
It is the main directory containing all the source files. For more information on the classes check the documentation at PyAstroPol/Docs/_build/html/PyAstroPol.html.

PyAstroPol/Materials/
It has the refractive index data for different materials in a formatted manner. These files are loaded by the code to look-up the refractive index information of the given material. Users can easily create such files using following steps.

1. Download wavelength vs refractive index file as .csv from popular refractive index database RefractiveIndexInfo.
2. Rename the file to an appropriate material name e.g., for Aluminium the file name is Al.csv.
3. Copy the .csv file into PyAstroPol/Materials/ directory.
4. Format the material file using provided function i.e., formatMaterialFile(MaterialName) (without file extensions).
5. The material is ready to be used by the code e.g., M1 = Surface(50, n2='Al', Mirror=True).
6. An example is also provided.

PyAstroPol/Docs/
It contains documentation related codes and files.

Conventions used in this package

The most important aspect to remember while using the package is the convention, which is described below.

For astronomy :

Positive X-axis : West
Positive Y-axis : Zenith
Positive Z-axis : North
Positive Latitude : North
Positive Hour Angle : West
Positive Declination : North

For optics :

Complex refractive index is n-ik where n and k are positive real numbers.
Jones vectors corresponding to positive Stokes-V are and .

Contributing

Any mode of contribution is highly encouraged.

1. Bug reporting : Open an issue in github with the following details.
   • Description of the bug
   • Python, numpy and matplotlib versions
   • Operating system details
   • Snippet of code causing the issue
2. Feature request : Open an issue in github with the following details.
   • Description of the feature
   • Description of the application
   • If possible, an example
3. Example request : Open an issue in github with following details.
   • Description of the application
   • Expected output from the example
4. Bug fixes : Open a pull request in github with following details.
   • Description of the bug corresponding to the fix
5. Feature addition : Open a pull request in github with following details.
   • Description of the feature
   • Description of the application
   • At least one Example using the particular feature
6. Other : Open an issue on github with a description.

TODO

1. Add polarizing elements such as birefringent elements, waveplates and polarizers.
2. Add feature to create and save coatings as files.
3. Add rectandular and elliptical apertures.