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MO: Fachverband Molekülphysik

MO 3: Novel Spectroscopies

MO 3.4: Vortrag

Montag, 11. März 2024, 17:45–18:00, HS 1015

Next generation fs transient spectroscopy based on 1030 nm pump — •Ferdinand Bergmeier and Eberhard Riedle — Lehrstuhl f. BioMolekulare Optik, Fakultät f. Physik, LMU München

The measurement of transient electronic spectra, vital for unraveling complex photophysical, chemical, and biological processes, is achieved through fs excitation and broadband UV to NIR detection. We present an innovative transient absorption spectrometer based on a newly engineered kHz noncollinear optical parametric amplifier (NOPA) pumped by a modern Yb-based 250 fs industrial-grade pump laser. Coupled with a fully redesigned CaF₂-based ultrabroad probe pulse, this spectrometer retains the positive aspects of the earlier Ti:Sa-based system. This ensures compactness with minimal optics and adjustments, boasting a warm-up time of under ten minutes.

The probe continuum spans 320 to 950 nm with 1030 nm pumping and to below 280 nm with 515 nm pumping. The pump is tunable from 220 to 950 nm with a sub-20 fs pulse length and no spectral gaps. The instrumental response function is below 40 fs. Single-shot spectral referencing achieves a sensitivity of approximately 20 uOD for a half-hour measurement, near the shot noise limit. The continuum splitting onto the signal and reference arm is achromatic and dispersion-free. A perfectly round probe focus is achieved with a Schief-Spiegler.

With the extreme precision of the setup, we address surface-resolved coherent artifacts that are crucial for investigating processes on the 100 fs time scale. Detailed reference and precise chirp measurements of the probe continuum enable sub-10 fs time-zero correction.

Keywords: Transient electronic spectra; Femtosecond resolution; Ultrabroad probe pulse; coherent artifact; time zero determination