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K: Fachverband Kurzzeit- und angewandte Laserphysik
K 3: Poster
K 3.2: Poster
Tuesday, March 21, 2023, 16:45–17:45, HSZ OG2
Spectroscopic Pump-Probe-Reflectometry of NIR Excited Silicon — •Philipp Lungwitz, Nick Börnert, Theo Pflug, and Alexander Horn — Laserinstitut Hochschule Mittweida, Technikumplatz 17, 09648 Mittweida
Ultrashort pulsed laser radiation with photon energies below the indirect bandgap of silicon enables the in-volume structuring of wafers due to multiphoton processes. Therefore, laser sources with wavelength in near infrared (NIR) spectral range are increasingly common for processing semiconductors. During laser mater interaction of ultrashort pulsed laser radiation (λpump=1950 nm, τH<50 fs) with silicon, the resulting nonlinear excitation of electrons by NIR radiation also affects to the optical properties in the visual spectral range. Imaging pump-probe reflectometry enables the measurement of the transient reflectivity for different probe wavelengths (420 nm ≤ λprobe ≤ 1000 nm, τH≈40 fs) and time delays up to Δ t=500 ps after irradiation. Assigning the spatial coordinates to local fluences allows a fluence dependent interpretation as well. Below the fluence for material modification Hth, a reduction of reflectivity was detected which become more and more significant with an increasing probe wavelength. For fluences above Hth, the reflectivity increases rapidly after irradiation and features a local minimum between Δ t=2 ps and Δ t=50 ps for all probe wavelengths.