We study the near-field probing of the slow Bloch laser mode of a photonic crystal by a bowtie nano-aperture (BNA) positioned at the end of a metal-coated fiber probe. We show that the BNA acts as a polarizing nanoprobe allowing us to extract information about the polarization of the near-field of the slow-light mode, without causing any significant perturbation of the lasing process. Near-field experiments reveal a spatial resolution better than λ /20 and a polarization ratio as strong as 110. We also demonstrate that the collection efficiency is two orders of magnitude larger for the BNA than for a 200 nm large circular aperture opened at the apex of the same metal-coated fiber tip. The BNA allows for overcoming one of the main limitations of SNOM linked to the well-known trade off between resolution and signal-to-noise ratio.