  We present an angle resolved photoemission study of the surface and bulk
electronic structure of the single layer ruthenate Sr$_2$RuO$_4$. As the early
studies of its electronic structure by photoemission and scanning tunneling
microscopy were confronted with a problem of surface reconstruction, surface
aging was previously proposed as a possible remedy to access the bulk states.
Here we suggest an alternative way by demonstrating that, in the case of
Sr$_2$RuO$_4$, circularly polarised light can be used to disentangle the
signals from the bulk and surface layers, thus opening the possibility of
investigating many-body interactions both in bulk and surface bands. The
proposed procedure results in improved momentum resolution, which enabled us to
detect an unexpected splitting of the surface $\beta$ band. We propose that
spin--orbit splitting might be responsible for this, and discuss possible
relations of the newly observed surface feature to topological matter.
