The dissertation is devoted to the study of physical phenomena and processes induced by femtosecond laser pulses with the central wavelength of 1550 nm in semiconductor materials (c-Si, InP, As2S3) and in chalcohalide glass 65GeS2-25Ga2S3-10CsCl at a wavelength of 800 nm. For this research, an Er-Yb-doped fiber laser with a wavelength of 1.55 µm was developed. The femtosecond laser source delivers a maximal value of the pulse energy of 2 µJ at a pulse duration of 410 fs and repetition rate of 250 kHz.
Using a time-resolved pump-probe technique, non-destructively interact radiation with the crystals at wavelength 1550 nm was shown. The spectral changes of pulses during the interaction with c-Si, As2S3, InP were observed for the first time. Those are an asymmetric expansion of the spectrum of the output pulse from 25 nm to 100 nm with a shift to the short-wavelength region in c-Si, symmetrical expansion spectrum in As2S3 from 25 nm to 300 nm, and slight changes in the spectrum of InP, and also third-harmonic generation in c-Si and As2S3.
Non-linear spatial-temporal transformation of the fs pulse, which results in the transformation of the angular profile of the beam from Gaussian to Bessel in c-Si and multifilamentation in As2S3 and generation of green third harmonic, was observed. The dependence of the angular distribution of radiation at a wavelength of 1.55 µm and its third harmonic in c-Si was investigated. Also, an increase in the duration of fs of laser pulses has been registered in c-Si. The physical mechanisms of their formation have been proposed, namely: two-photon absorption processes, Kerr self-focusing, refraction, and solid-state plasma absorption. All these processes are the cause of complex pulse conversion.
The advent of ultrafast infrared lasers provides a unique opportunity for the direct fabrication of three-dimensional microdevices. However, strong nonlinearities prevent access to modification regimes in narrow gap materials with the shortest laser pulses. In our study, by a judicious choice of the writing parameters, including laser pulse energy, repetition rate, and inscription speed, the optical structures inside c-Si by the femtosecond laser at a wavelength of 1.55 um were recorded. In the study, it was found that there exists a threshold of the pulse energy to produce a high-quality groove, which is 0.65–2 µJ. It was shown that optimal writing velocity is in the range 0.01–0.07 mm/s at a repetition rate of 0.25–1 MHz.
Using femtosecond pulses at wavelength 1.55 um, the structures in As2S3, near-surface modifications in InP have been demonstrated. Focused laser pulses have induced the refractive index modification inside the 65GeS2-25Ga2S3-10CsCl glass at 800 nm wavelength. It was revealed that the main contributions that prevent modification with the shortest pulses are beam depletion by multiphoton absorption, Kerr-induced phase distortions, and defocusing of strong plasma in c-Si and InP.
