The effect of light-induced plasma on propagation of intense fs laser radiation in c-Si

Spatio-temporal dynamics of femtosecond laser pulses at 1550 nm wavelength in crystal silicon

“…3b). As will be shown below, and according to [2,3], at sufficient pulse energy and increased thickness of the c-Si sample, actual shape of the pump beam becomes distorted by TPA and plasma refraction. Indeed, we found, that in 8-mm-thick c-Si sample, where the shape of the pump beam, focused on the exit face of the sample, is surely not Gaussian, the profile of TH emission acquires a ring component (Fig.…”

“…TH was also generated in photonic crystal waveguides as a result of spatial pulse compression involving the slow light phenomenon [12,13]. However, as far as we know, reports on THG in bulk c-Si at λ p = 1550 nm, visible by naked eye, are missing, despite the fact that THG in this material is an allowed process, in which third-order nonlinear polarization P (3) (3ω) at the tripled frequency is given by [7]: P (3)…”

“…Partially this issue has already been considered in the literature. In [3] refraction on the TPA-generated plasma was supposed to be the main factor changing the spatial shape of the fs laser pulses at 1.2 µm in c-Si. The authors of [2] introduced three parameters-diffraction-, TPA-and Kerr length, interplay of which defines the fs pulse transformation in c-Si.…”

“…Propagation of the fs laser pulses at 1.55 µm wavelength in c-Si was studied in [2] the regime of strong TPA. Interaction of fs laser pulses at 1200 nm wavelength with c-Si was reported in [3,4]. However, much more sophisticated equipment is required for generation of the fs laser pulses at 1200 nm, than at 1550nm, and therefore, 1550-nm fs lasers are more valuable for technological applications.…”

“…4 and 5b. One possible explanation of such behavior is that TPA, together with other factors, such as Kerr self-focusing, plasma refraction and absorption, lead to a complex transformation of the pulse, which is manifested as formation of conical Bessel waves [2,3]. The Bessel waves restore the original on-axis pulse time-width, because they form the energy flux directed on the axis from the surrounding lower-intensity areas, which have not undergone the temporal changes.…”