A mode-locked ruby laser consists of a short rod inside a cavity of length 1.2 m. Given that the full width at half maximum of the 694.3 nm transition is 2 x 1011 Hz, and that the laser is producing the shortest possible pulses, estimate: (i) the duration of the pulses, (ii) the number of longitudinal cavity modes that are oscillating, and (iii) the coherence length of the light.

A mode-locked ruby laser consists of a short rod inside a cavity of length 1.2 m. Given that the full width at half maximum of the 694.3 nm transition is 2 x 1011 Hz, and that the laser is producing the shortest possible pulses, estimate: (i) the duration of the pulses, (ii) the number of longitudinal cavity modes that are oscillating, and (iii) the coherence length of the light.