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The Large Binocular Telescope (LBT) is now operating with the first of two permanently installed adaptive secondary
mirrors, and the first of two complementary near-IR instruments called LUCIFER is operational as well. The ARGOS
laser-guided ground-layer adaptive optics (GLAO) system, described elsewhere at this conference1, will build on this
foundation to deliver the highest resolution over the 4 arc min
wide-field imaging and multi-object spectroscopic modes
of LUCIFER. In this paper, we describe a planned upgrade to ARGOS which will supplement the Rayleigh-based GLAO
system with sodium laser guide stars (LGS) to fulfill the telescope's diffraction-limited potential. In its narrow-field
mode of 30 arc sec, LUCIFER will deliver imaging at the Nyquist limit of the individual 8.4 m apertures down to J band
and long-slit spectroscopy with resolution up to 40,000. In addition, the LBT Interferometer2 (LBTI) will cophase the
two apertures, offering imaging at the diffraction limit of the 22.8 m baseline at wavelengths from 1.2 to 20 μm. In the
first phase of the upgrade, a 10 W sodium LGS will be added to each half of the LBT, using the same launch telescopes
mounted behind the two secondary mirrors as the Rayleigh LGS. The upgrade will rely on other components of the
ARGOS infrastructure such as acquisition and guiding, and fast
tip-tilt cameras. New wavefront sensors will be added to
LUCIFER and LBTI. In the upgrade's second phase, the sodium and Rayleigh LGS will be used together in a hybrid
tomographic sensing system. This configuration will offer the advantage that a single tip-tilt star will continue to be
sufficient even for MCAO operation3, which is planned with LBT's LINC-NIRVANA instrument4,5.
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