Raman effect in HCF filled with no active Raman modes gases

[valentina-utriolanfaloni]

Hi, According to this paper (https://www.ias.ac.in/article/fulltext/pram/085/05/0993-1007) (section 4, page 998) the incident wave undergoes a downshift of the carrier frequency, due to the Raman effect by interacting with the fiber material. Is this effect included in Luna? How could we reproduce this effect? We tried to include it using Raman.molecular_raman_response function and run prop_capillary with Raman = true.

[jtravs]

Hi, yes we include Raman vibrational and rotational response for diatomic molecules. At the moment this is only included for H2, D2 and N2. To add this for other gases you need to find all of the required physical data. If you choose one of those gases, then Luna should default to including the Raman response.

[jtravs]

I think I missunderstood your question. I believe that paper is still referring to the Raman response of the core material (either solid glass core PCF, or liquid core, both of which have a Raman response). It is, however, also possible to get a Raman response from non-core glass making the fibre structure in a photonic bandgap PCF, but Luna doesn't have a model for bandgap PCF at all, let alone this effect. This only occurs in photonic bandgap PCF because the core mode light is evanescent in the photonic crystal cladding, so there is significant overlap with it. In the anti-resonant PCF or hollow capillary fibres we mostly model with Luna, there is negligible overlap between the core mode and the glass structure of the fibre, so no Raman effect will result.