Coherent optical transition radiation (COTR)

[steveksmith]

Dear Developer,

Thanks for making such a nice work an open source. I have a query: can we use synchrad to calculate Coherent Optical Transition Radiation (COTR) ?

Best,
Steve

[steveksmith]

Hi @hightower8083 ,

Thanks for making such a nice work an open source. I have a query: can we use synchrad to calculate Coherent Optical Transition Radiation (COTR) ?

we want to see if synchrad can be used for experiments as given in the recently published paper: naturephtonics

Best,
Steve

[hightower8083]

Dear @steveksmith

Thank you for you interest in the code. Concerning the CTR, I don't have much experience with such modeling and I guess it depends of the process particularities (e.g. particle energies, bunch duration). The OTR radiation is coherent for the wavelengths of around of the bunch length and in the HZDR paper, it seems to corresponds to the visible range. I would assume that such field could be resolved more or less correctly even with the coherency level by the PIC solver itself. Maybe you can see if you find more recipes in this paper dedicated to the subject.

In synchrad we sum the fields generated by individual particles, which means that the coherent emission would only be correct when each macro-particle represents a single physical electron. For this reason, the coherent emission regime is not well suited to work with the PIC data where each macro-particle typically represents many real electrons. There was a discussion on this subject some time ago (see issue #23), and code was actually used for the coherent radiation case , but not in PIC and using a very large number of tracks.

So in principle, if you have particles tracks recorded during COTR process from a PIC simulation, you may see what radiation it would produce, but keep in mind, that quantitatively the amplitude of the coherent field wouldn't be correct (not sure absolute field amplitude is important for the beam reconstruction). But before doing that, I would suggest to analyze the e.m. fields you get in the PIC code and see if they make sense.

Hope this helps, and feel free to share the technical aspects of your finding and any problem you encounter.

[steveksmith]

Dear @hightower8083 ,

Thank you for the deep insight of the issues (that one should keep in mind before dwelling in such cases).

Your overall discussion is very very helpful (it reminds me of one of the most dedicated and excellent Prof. in our university, who share all his years learning with students).

I will check the cases carefully, however, it may take some time. I will keep discussing with you on this subject.

Best,
Steve