  We demonstrate intracavity plasmonic laser spectroscopy using a plasmonic
laser created from a periodically-perforated silver film with a liquid gain
medium. An active zone of the laser is formed by a highly elongated spot of
pumping. This results in an 80x decrease in the threshold pumping level; in a
significantly more efficient diffusive mixing of dye molecules, which
substantially suppresses the effect of their bleaching; and in the ability to
reduce the volume of the gain medium to as little as 400 nL. We use this design
for a stable plasmonic laser in multiple measurements and demonstrate that it
is highly effective as a spaser spectroscopy sensor for intracavity detection
of an absorptive dye at 70 ppb. This work provides an opportunity to develop
applications of intracavity plasmonic laser spectroscopy in biological label
detection and other fields.
