  Broken time-reversal symmetry in the absence of spin order indicates the
presence of unusual phases such as orbital magnetism and loop currents. The
recently discovered family of kagome superconductors AV$_3$Sb$_5$ (A = K, Rb,
or Cs), hosting an exotic charge-density wave (CDW) state, has emerged as a
strong candidate for this phase. While initial experiments suggested that the
CDW phase breaks time-reversal symmetry, this idea is being intensely debated
due to conflicting experimental data. In this work we use laser-coupled
scanning tunneling microscopy (STM) to study RbV$_3$Sb$_5$. STM data shows that
the Fourier intensities of all three CDW peaks are different, implying that the
CDW breaks rotational and mirror symmetries. By applying linearly polarized
light along high-symmetry directions, we show that the relative intensities of
the CDW peaks can be reversibly switched, implying a substantial
electro-striction response, indicative of strong non-linear electron-phonon
coupling. A similar CDW intensity switching is observed with perpendicular
magnetic fields, which implies an unusual piezo-magnetic response that, in
turn, requires time-reversal symmetry-breaking. We show that the simplest CDW
that satisfies these constraints and reconciles previous seemingly
contradictory experimental data is an out-of-phase combination of bond charge
order and loop currents that we dub congruent CDW flux phase. Our laser-STM
data opens the door to the possibility of dynamic optical control of complex
quantum phenomenon in correlated materials.
