A new mechanism for excitability in a class B laser

This paper examines a different mechanism for excitability and demonstrates it experimentally on a YAG laser. It occurs for all class B lasers characterized by different relaxation rates for the population inversion and the laser field. These lasers are dynamically stiff and may deliver large amplitude pulses if pumped from below to above threshold. When pumped by square wave pulses in the near threshold region, such lasers deliver single spike pulses that satisfy conditions like any excitable pulses. Double pulse experiments demonstrate the refractory effect of a first pulse. Although the first intensity spike starts slightly before the end of the first pump pulse, the second intensity spike appears long after the end of the second pulse. Moreover, the amplitude of the second spike depends on the time interval between the two square wave pulses. The second pulse exhibits the same amplitude as the first one only if the interpulse interval is sufficiently large.