  We demonstrate, what is to our knowledge, the shortest pulses directly
generated to date from a solid-state laser, mode locked with a graphene
saturable absorber (GSA). In the experiments, a low-threshold diode-pumped
Cr3+:LiSAF laser was used near 850 nm. At a pump power of 275 mW provided by
two pump diodes, the Cr3+:LiSAF laser produced nearly transform-limited, 19-fs
pulses with an average output power of 8.5 mW. The repetition rate was around
107 MHz, corresponding to a pulse energy and peak power of 79 pJ and 4.2 kW,
respectively. Once mode locking was initiated with the GSA, stable,
uninterrupted femtosecond pulse generation could be obtained. In addition, the
femtosecond output of the laser could be tuned from 836 nm to 897 nm with pulse
durations in the range of 80-190 fs. We further performed detailed mode locking
initiation tests across the full cavity stability range of the laser to verify
that pulse generation was indeed started by the GSA and not by Kerr lens mode
locking.
