Nonlinear absorption and optical limiting in Duran glass induced by 800 nm femtosecond laser pulses

Nonlinear absorption of Duran glass by irradiation of a focused 200 fs pulsed laser were investigated using the z-scan technique at 800 nm. Optical limiting behaviour in this glass has also been measured. The limiting threshold was measured to 33 μJ pulse energy (peak intensity of 2.4 x 1012 W cm-2) in this sample. The decrease in transmitted intensity is around 75% compared with the theoretical linear transmission for incident pulses pulse energies 320 μJ (peak intensity of 5 x 1012 W cm-2). A comparison of the theoretical analyses with the experimental results shows that three-photon absorption and three-photon generated free-carrier absorption within the glasses are the main mechanisms for the observed nonlinear response. The values of the three-photon absorption coefficient and the photo-generated free-carrier cross section are measured as γ = 2 x 10-24cm3 W-2 and σ = 1.2 x 10-18 cm2, respectively