  We present a close companion search around sixteen known early-L dwarfs using
aperture masking interferometry with Palomar laser guide star adaptive optics.
The use of aperture masking allows the detection of close binaries,
corresponding to projected physical separations of 0.6-10.0 AU for the targets
of our survey. This survey achieved median contrast limits of Delta_K ~ 2.3 for
separations between 1.2 - 4 lambda/D, and Delta_K ~ 1.4 at (2/3)lambda/D.
  We present four candidate binaries detected with moderate to high confidence
(90-98%). Two have projected physical separations less than 1.5 AU. This may
indicate that tight-separation binaries contribute more significantly to the
binary fraction than currently assumed, consistent with spectroscopic and
photometric overluminosity studies.
  Ten targets of this survey have previously been observed with the Hubble
Space Telescope as part of companion searches. We use the increased resolution
of aperture masking to search for close or dim companions that would be
obscured by full aperture imaging, finding two candidate binaries.
  This survey is the first application of aperture masking with laser guide
star adaptive optics at Palomar. Several new techniques for the analysis of
aperture masking data in the low signal to noise regime are explored.
