Spiking ruby revisited: self-induced periodic spiking oscillations leading to chaotic state in a Cr:Al₂O₃ laser with cw 532-nm pumping

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.