  Presented here are observations that demonstrate how the deformation of
millimetric cavitation bubbles by a uniform pressure gradient quenches single
collapse luminescence. Our innovative measurement system captures a broad
luminescence spectrum (wavelength range 300-900 nm) from the individual
collapses of laser-induced bubbles in water. By varying the bubble size,
driving pressure and the perceived gravity level aboard parabolic flights, we
probed the limit from aspherical to highly spherical bubble collapses.
Luminescence was detected for bubbles of maximum radii within the previously
uncovered range $R_{0}$ =1.5-6 mm for laser-induced bubbles. The relative
luminescence energy was found to rapidly decrease as a function of bubble
asymmetry quantified by the anisotropy parameter $\zeta$, which is the
dimensionless equivalent of the Kelvin impulse. As established previously,
$\zeta$ also dictates the characteristic parameters of bubble-driven microjets.
The threshold of $\zeta$ beyond which no luminescence is observed in our
experiment closely coincides with the threshold where the microjets visibly
pierce the bubble and drive a vapor-jet during the rebound. The individual
fitted blackbody temperatures range between $T_{\rm lum}$=7000 and 11500 K but
do not show any clear trend as a function of $\zeta$. Time-resolved
measurements using a high-speed photodetector disclose multiple luminescence
events at each bubble collapse. The averaged full width at half maximum of the
pulse is found to scale with $R_{0}$ and to range between 10-20 ns.
