Hi Niu,

Thank you for your post!

Regarding your first question, i think the answer is yes, you should be able to model the 'reabsoring' of the rays by this source volume. What you could do is to place a retangular volume to model the real volume. You can turn on the Inside of flag on the source to place the source inside of this rectangular volme. If you want the rays to ignore this volume when they first launch and only interact with this volume after rays are launched and come back through this volume, you can turn on the 'Rays Ignore Object: On launch' option, as shown below. 

Regarding your second question, currenlty OpticStudio supports modeling of Photoluminesence effect via the bulk scattering process. You can find this tool under Object Properties\Volume Physics. I think you might be able to use this to model spontaneous emission. But i don't think there is a way to model the gain or amplification process. By default the bulk absorption is modeled using material transmission data which shows light attenuation at different wavelengths.

Let us know if you have any other questions.

Best regards,

Hui