Nikolai Tolstik | Searcharxiv

arXiv2024

Chirped pulse waveguide amplifier

We introduce a single-mode Cr:ZnS crystalline waveguide ultrafast amplifier that provides a high gain of 5.5 dB/cm and 2.35 W of average output power. The depressed-cladding buried waveguide is produced by an ultrafast laser writing procedure, which allows a high degree of flexibility in fabrication when the geometry, size, and even effective index can be modified along the waveguide. An analytical model that includes both, pump and pulse propagation, allows calculation and optimization of the waveguide design. In a CPA arrangement with a volume Bragg grating-based stretcher/compressor, we demonstrate a broadband 34-mm long amplifier in a polycrystalline Cr:ZnS with a single-pass gain factor of 75 (5.5 dB/cm) and a high average output power up to 2.35 W.

physics.optics↗

arXiv2020

Sub-surface modifications in silicon with ultrashort pulsed lasers above 2 microns

Nonlinear optical phenomena in silicon such as self-focusing and multi-photon absorption are strongly dependent on the wavelength, energy and duration of the exciting pulse. Thus, a pronounced wavelength dependence of the sub-surface modifications with ultra-short pulsed lasers exists, especially for wavelengths > 2 $μ$m. This wavelength dependence is investigated for wavelengths in the range of 1950-2400 nm, at a pulse duration between 0.5-10 ps and the pulse energy varying from 1 $μ$J to 1 mJ. Numerical and experimental analyses have been performed on both the surface and sub-surface of Si wafers processed with fibre-based lasers built in-house that operate in this wavelength range. The results have been compared to the literature data at 1550 nm. The analysis carried out has shown that due to a dip in the nonlinear absorption spectrum and a peak in the spectrum of the third-order non-linearity, the wavelengths between 2000 - 2200 nm are more favourable for creating sub-surface modifications in silicon. This is the case even though those wavelengths do not allow as tight a focusing as those at 1550 nm in the linear regime. This problem is compensated by an increased self-focusing due to the nonlinear Kerr-effect around 2100 nm at high light intensities, characteristic for ultra-short pulses.

physics.optics↗