Optimizing LIGO with LISA forewarnings to improve black-hole spectroscopy

As LIGO prepares for its third observing run, the expectation of further gravitational wave events provide the promise of further tests of general relativity. One type of test is to observe higher-order modes, beyond the dominant 22-mode, of a gravitational waveform during the ringdown stage of two merged black holes. Detection of these modes will enable black-hole spectroscopy: experimental checks that astrophysical black holes indeed have no hair and are faithfully described by the Kerr metric. The early inspiral of massive enough stellar mass black-hole binaries merging in the high frequency band will be detectable at low frequencies (10-100 mHz) by the upcoming space mission LISA. Thus, LISA will predict, with years of forewarning, the exact time and frequency with which a merged black hole will ring. This talk will discuss active interferometric techniques to target the central frequencies of subdominant modes and methods to optimize advanced (LIGO and Virgo) and third generation (e.g., Cosmic Explorer and Einstein Telescope) detectors to enhance black-hole spectroscopy.