  We investigate the efficient free-space excitation of high-Q resonance modes
in deformed microcavities via dynamical tunneling-assisted coupling. A quantum
scattering theory is employed to study the free-space transmission properties,
and it is found that the transmission includes the contribution from (1) the
off-resonance background and (2) the on-resonance modulation, corresponding to
the absence and presence of high-Q modes, respectively. The theory predicts
asymmetric Fano-like resonances around high-Q modes in background transmission
spectra, which are in good agreement with our recent experimental results.
Dynamical tunneling across Kolmogorov-Arnold-Moser tori is further studied,
which plays an essential role in the Fano-like resonance. This efficient
free-space coupling holds potential advantages in simplifying experimental
condition and exciting high-Q modes in higher-index-material microcavities.
