refractive index computed for a given temperature

[mattemilio]

In case the thermal dispersion coefficients are available in the yml file the coefficients are read and used to compute refractive index of the material for a specific temperature
This is important for optical designs that do not work at ambient temperature (e.g. some optical systems in space missions)
I am not a programmer and this is the first time I contribute to a repository. Please forgive any potential mistake

[HarrisonKramer]

Hi @mattemilio,

Thanks for the contribution! Adding support for temperature- and pressure-dependent refractive index is a great improvement, and this will be very useful for many applications.

Since this is your first time contributing: welcome! Don’t worry about formatting or coding conventions. What matters most is that you’ve taken the time to improve the package, and that’s always appreciated.

Before merging, there are just a few things I’d like to clean up:

• The docstrings should follow Google style to stay consistent with the rest of the project. Tools like Gemini or GPT can help reformat them automatically if you like.
• There are a few small typos and minor issues in the comments and docstrings that need correction.
• Some of the constants used in _nair() would benefit from brief comments or references, just so it’s clear where they come from. We try to avoid using "magic numbers" without explanation.

I’m happy to make these changes myself, but if you’d prefer to continue working on the PR, that’s very welcome too. If you push new commits to this branch, they’ll appear automatically here. I can also push my own edits to your branch if you’re okay with that.

Let me know how you’d like to proceed, and thanks again for your contribution!

Best,
Kramer

[mattemilio]

Thanks @HarrisonKramer for the feedback.
I am happy to contribute.
I am just learning how to work on github and I am happy if you do the changes yourself.
Concerning the formulas I used the approach in https://support.zemax.com/hc/en-us/articles/1500005576002-How-OpticStudio-calculates-refractive-index-at-arbitrary-temperatures-and-pressures

Kind regards
Matteo

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
optiland/materials/material_file.py	97.50%	1 Missing ⚠️

@@           Coverage Diff           @@
##           master     #203   +/-   ##
=======================================
  Coverage   95.51%   95.51%           
=======================================
  Files         163      163           
  Lines        9133     9169   +36     
=======================================
+ Hits         8723     8758   +35     
- Misses        410      411    +1     

Files with missing lines	Coverage Δ
optiland/materials/material_file.py	97.94% <97.50%> (-0.17%)	⬇️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[HarrisonKramer]

Thanks again for writing this, @mattemilio!

I made some formatting changes, keeping the original mathematics from your code. We still need to add tests for the new functionality before we can merge. That could involve making comparisons against commercial code or just systematically going through the equations by hand for a few materials and comparing them to the values calculated in Optiland.

I will try to do these comparisons and add some tests in the coming days. You can also do this if you prefer - just let me know if so.

Regards,
Kramer

[mattemilio]

Thanks a lot @HarrisonKramer.
I can work on the comparison with commercial software.
Kind regards
Matteo

[mattemilio]

I obtain very similar refractive index values but not exactly the same.
For instance refractive index N-BK7 at -40 degrees and 0 atm is 1.51888076 with optiland and with Zemax I get 1.5188807836

I simulated an aspheric N-BK7 lens in Zemax optimised to have perfect geometrical spot on axis at a temperature of -40 degrees and P = 0 atm. I compare the spot size between optiland and Zemax
spots_zemax_optiland.pdf

[HarrisonKramer]

Hi @mattemilio,

Thanks for making the comparison. The results look very close, and the discrepancies seem minor enough to merge for now, especially given potential differences in coefficients or even numerical precision.

Before merging, I'd like to add unit tests to structurally test the model outputs against the underlying equations. I will do this over the coming days and will push my changes to this PR.

Regards,
Kramer

[HarrisonKramer]

Hi @mattemilio,

I just added a few more tests to improve coverage. Everything else remains as it was. I also added you to the authors page. If you prefer not to be listed, just let me know.

Thanks again for the solid addition. For a first contribution, it's excellent - and we'd be happy to see more ideas, suggestions or PRs from you in the future!

Best,
Kramer

[HarrisonKramer]

Hi @mattemilio,

We have a discord server for all contributors. We use it to discuss new features, get feedback on implementations, etc. Feel free to join if you like, even just as an observer.

Link to join:
https://discord.gg/ejNgkP9t

Regards,
Kramer