Setup for coherent multidimensional electronic spectroscopy

• Subject Area: Condensed Matter Physics
• Term: Funded in 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521128316

We wish to build a coherent multidimensional spectrometer tunable over the visible spectral range to investigate the electronic structure and dynamics of nanoscale systems, such as quantum dots, nanotubes, 2D materials, J-aggregates or combination thereof in heterostructures. To realize such a setup, the aim is to produce phase-locked sequences of 10 femtosecond, spectrally broad (> 100 nm) pulses tunable in the 450-750 nm range. In a two-dimensional electronic spectroscopy (2DES) experiment, the sample’s nonlinear optical response is represented as a 2D spectrum, where electronic couplings directly show as cross-peaks and the homogeneous and inhomogeneous contributions to spectroscopic lineshapes can be separated. These unique features of 2DES will be exploited to provide quantitative information about the microscopic couplings between electronic excitations, phonons and spins in nanomaterials. These couplings give rise to a range of quasiparticles such as excitons, multi-excitons, polarons, and polaritons. We wish to reveal quantities like quasiparticle binding energies (e.g. biexciton, polaron binding energies), homogeneous linewidths, dephasing times and lifetimes. These quantities inform on the basic physics at the origin of functionality in devices, of direct relevance for applications. The following key items are needed to build such a setup: (i) broadband (> 100 nm) pulses tunable over the visible range with several microjoules energy (ii) components for the characterisation and guiding of pulses to the sample, (iii) components to generate controllable phase-locked sequences of pulses, and (iv) components for low-noise detection of the signals. The implementation of (i) requires an amplified Ti:Sapph laser system (pulse energy ~5 mJ, pulse duration 100 fs, repetition rate 1 kHz, central wavelength 800 nm), a visible optical parametric amplifier (OPA, wavelength range 475-750 nm), and a hollow-core fiber setup to spectrally broaden the OPA pulses. For the realization of (ii), one needs a home-built transient-grating frequency resolved optical gating (TG-FROG) setup, powermeters, a portable spectrometer, a small camera, and various optical components. Item (iii) can be realized thanks to programmable commercial pulse shaping technology. Finally, item (iv) requires a spectrograph and low-noise CCD/CMOS sensor capable of continuous acquisition at 1 kHz. The requested measuring station would form the starting infrastructure for the AG Seiler. Not only would it be essential to establish the independent scientific career of the applicant during her tenure-track period, but it would also be essential for the implementation of requested and planned third-party funded projects, such as CRCs. Since the responsible spokesperson has extensive experience with building a similar multidimensional spectroscopy instrument during her PhD work, we expect the setup to be built in an efficient manner.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Messplatz für kohärente mehrdimensionale elektronische Spektroskopie
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Freie Universität Berlin
• Leader: Professorin Dr. Hélène Seiler