Dear members,
I am coupling He-Ne light into channel waveguides fabricated in a glass by Fs laser. The waveguides lie deep in the sample and sometime it is difficult to excite the propagation modes by end-fire coupling (i.e. the He-Ne laser focused through a microscope objective on the sample facet) because I cannot really see whether am actually at focus on the facet plane and at which point of the facet surface. Is there a way to image the spot that is focused onto the sample facet? I tried to put a beam splitter (a piece of glass a 45deg) just before the objective, but it seems the back image comes from the reflection on on the objective rather than the sample and does not give information on what's going on at the sample facet.
Any clue??
Thanks
M.A.