Completing the VLT/I in the LGS Era: The case for at least 4 lasers on each UT

The pressure factor on UT4 has been high ever since the commissioning of the highly successful MUSE instrument. Commissioning of MAVIS by 2030 will bring another internationally unique facility to UT4, further increasing pressure. However, neither of these instruments harness the full predictive adaptive optics power of a single telescope equipped with LGS, combining LGS with NGS for extreme adaptive optics. Gravity+ will bring in the era of LGS on all unit telescopes, but will be limited by only having the laser pointed at the science target and not the fringe tracking star. I will show how in addition to single telescope modes, 4 laser guide stars per telescope will enable more than double the effective sky coverage for interferometry in a quad star mode, in addition to astrometry significantly better than Gaia and enabling coherent integration for interferometric spectroscopy at shorter wavelengths. This staged facility upgrade would ensure VLT/I remains highly unique and competitive beyond 2040.