An Experimental Study of Multiphoton Ionization in Fused Silica at IR and Visible Wavelengths

We present the results of an experimental study of multiphoton ionization in fused silica, using a linearly polarized femtosecond Satsuma fiber laser with an active medium based on Yb+3 ions, at 515 -nm and 1030 -nm wavelengths. The radiation transmission in the fused silica was measured as a function of the laser intensity and wavelength and the data were analyzed using a theoretical model based on the Keldysh theory. We determined the multiphoton absorption cross-sections in the fused silica in the case of four- and eight-photon ionization and analyzed the contribution of avalanche ionization. The obtained results provide insight into the fundamental processes involved in multiphoton ionization and have implications for its applications, such as laser micromachining and material processing.