  Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad
gain bandwidth benefiting from the material stability of sapphire. These
favorable characteristics of Ti:sapphire have given rise to femtosecond lasers
and optical frequency combs. Shaping a single Ti:sapphire crystal into a
millimeter sized high quality whispering gallery mode resonator ($Q\sim10^8$)
reduces the lasing threshold to 14.2 mW and increases the laser slope
efficiency to 34%. The observed lasing can be both multi-mode and single-mode.
This is the first demonstration of a Ti:sapphire whispering-gallery laser.
Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near
infrared region is demonstrated by introducing a probe laser with a central
wavelength of 795 nm. This method results in decreasing linewidth of the modes
excited with the probe laser, consequently increasing their $Q$. These findings
open avenues for the usage of whispering gallery mode resonators as cavities
for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire can
also be utilized as an amplifier inside its gain bandwidth by implementing a
pump-probe configuration.
