  We present a new scheme for performing optical spectroscopy on single
molecules. A glass capillary with a diameter of 600 nm filled with an organic
crystal tightly guides the excitation light and provides a maximum spontaneous
emission coupling factor ($\beta$) of 18% for the dye molecules doped in the
organic crystal. Combination of extinction, fluorescence excitation and
resonance fluorescence spectroscopy with microscopy provides high-resolution
spatio-spectral access to a very large number of single molecules in a linear
geometry. We discuss strategies for exploring a range of quantum optical
phenomena, including coherent cooperative interactions in a mesoscopic ensemble
of molecules mediated by a single mode of propagating photons.
