  We report on a GHz fundamental repetition rate Kerr-lens mode-locked Ho:CALGO
laser emitting at 2.1 um. The laser employs a ring-cavity to increase the
fundamental repetition rate to 1.179 GHz and can be made to oscillate in both
directions stably with nearly identical performance: for counterclockwise
oscillation, it generates 93-fs pulses at 1.68 W of average power, whereas 92
fs and 1.69 W were measured for clockwise operation. Our current results
represent the highest average power from a 2-um GHz oscillator and the first
sub-100-fs pulse duration from a Ho-based oscillator.
