Hannover 2020 – scientific programme

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K: Fachverband Kurzzeit- und angewandte Laserphysik

K 7: Laser Beam Interaction and Laser Diagnostics

K 7.1: Talk

Wednesday, March 11, 2020, 14:00–14:15, f428

Broadband mid-infrared phase reconstruction in the focal plane of a microscope — •Niklas Müller, Florian Nicolai, and Tiago Buckup — Physikalisch-Chemisches Institut, Universität Heidelberg, Deutschland

The temporal shape of ultrashort laser pulses has high impact on nonlinear and time-resolved spectroscopy. However, its exact shape is often not known due to challenges in phase reconstruction in all spectral regions, especially far beyond the visible region. The successful phase reconstruction over 1000 cm⁻¹ of a mid-infrared (MIR) laser pulse ranging from 1750 cm⁻¹ up to 3200 cm⁻¹ is presented. After reconstructing the complex near-infrared (NIR) electric field by a dispersion scan based on a spatial light modulator, the phase retrieval in the MIR is performed on the sum-frequency signals generated by the NIR-MIR interaction. Two different approaches are implemented: (i) In a time scan method, the NIR laser beam is delayed by inserting a specific amount of glass. Thus, the detected sum-frequency light depends on the temporal overlap of the NIR and MIR laser pulses and allows a phase reconstruction. (ii) In the second method, the dispersion of both laser pulses is scanned via glass insertion in the collinear MIR and NIR beam path and phase reconstruction is provided by the dispersion scan method. Although not restricted to it, the nonlinear feedback signals are generated inside the focal plane of a nonlinear microscope and the phase reconstruction provides knowledge about the temporal shape of the driving laser pulses in the point of interest.