Optical transition radiation

Dear Geant4 users,

I have a problem with including optical transition radiation in my model. I need to get this radiation from the metal plate target. As I understand, I can include this radiation with G4VTransitionRadiation. For this, I set a refractive index for the world region and the metal plate target. Also, I set "SetRegion " as “World” and I don’t understand what I need to set in “SetModel”. Tell me if I’m doing the right thing.

Any help would be very appreciated! Thanks in advance!
Best regards.