Cold avalanche ionisation

We show experimental evidence for cold avalanche and demonstrate how it can be distinguished from the traditional avalanche process. We analyse the nonlinear absorption of 800 nm, ultrashort pulses focused inside fused silica glass to study the ionization mechanisms. The light is focused tightly inside the glass using a microscope objective so as to avoid surface damage and self phase modulation. The transmission is monitored as a function of pulse energy and pulse length. The transmission drops at the onset of nonlinear absorption. Fitting the transmission curves allows us to distinguish the various ionisation mechanisms involved.