Measurement of the collision time of dense electronic plasma induced by a femtosecond laser in fused silica

Electronic plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in fused silica was investigated by use of pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging were combined to determine electronic collision time τ in the conduction band, and τ was measured to be 1.7 fs at an electron density near 5 × 10¹⁹ cm ^-3. The lifetime of the electronic plasma is also measured to be ∼170 fs by use of the time-resolved shadow imaging technique.