  This paper reexamines a 60 year old mystery of spiking behavior in ruby
lasers with a cw 532 nm pump, paying special attention to mode matching between
the pump and lasing beam within a ruby crystal placed in a semi-confocal laser
cavity. Periodic spiking oscillations were observed in a limited pump power
regime, where spikes obeying the generic asymmetric hyperbolic function
appeared at a repetition rate around 50 kHz and with a 130-150 ns width and
0.1-0.6 microjoule energy depending on the pump power. The physics of the
spiking behavior based on Kleinman's mechanical approach and a plausible
interpretation for the periodic spiking oscillation in terms of self-induced
mode matching between the pump and laser beams through the self-induced
Kerr-lens effect are addressed. The statistical nature inherent to spiking and
the associated self-organized critical behavior in quasi-periodic spiking
oscillations as well as chaotic states occurring outside the periodic spiking
regime are also explored from a nonlinear dynamics point of view.
