High-power Ytterbium femtosecond laser amplifier system

• Subject Area: Condensed Matter Physics
• Term: Funded in 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532577495

One of the research foci of my group is nonlinear THz spectroscopy of cavity quantum electrodynamical (c-QED) structures and novel materials. Our recently improved cavity designs have enabled extreme light-matter coupling strengths with light-matter hybridized states extending over as many as six optical octaves simultaneously, from < 0.1 THz to > 6 THz. As a next step, we seek to investigate the nonlinear polarization dynamics of these structures which is expected to include mixing of polariton modes beyond the normal-mode approximation, the generation of non-classical light, dynamical squeezing and entanglement of polariton modes as well as the generation of vacuum radiation. The large spectral range and multi-mode nature of extremely strong coupling requires a new approach to two-dimensional strong-field spectroscopy providing THz pulses which simultaneously feature several features that are difficult to unite: strong electric field amplitudes on the order of several 100 kV/cm, short durations close to the single-cycle limit and gap-free, ultrabroadband spectra. With the requested equipment, we will implement a new generation of 2D THz spectroscopy by combining several only recently established approaches for THz generation. The approach is based on an Yb femtosecond laser amplifier system delivering ultrashort pulses centred at a wavelength of 1030 nm, pulse energies of up to several mJ, and tuneable repetition rates ranging from 100 kHz to the MHz range. The light source features remarkably low noise levels approaching 10^-3 of relative pulse-to-pulse energy fluctuations, excellent pulse energy scalability, and high long-term reliability. The laser power will be split into three parts: a weak pulse which serves for electro-optic detection and two strong ones which are individually switched on a pulse-to-pulse basis by acousto-optic modulators at a rate of up to half the repetition rate. This unique design enables fast modulation on the order of 1 MHz, greatly exceeding the commonly employed kHz-rate modulation achieved by mechanical means, and correspondingly, provides exceptionally low noise levels. Further measures to optimize the signal-to-noise ratio of our system include custom-cut detection electronics based on FPGA technology developed in our group, as well as optical beam stabilization systems. In order to achieve the required THz bandwidth, the laser pulses will be compressed to < 50 fs by Heriott-cell based, multi-pass, multi-plate continuum generation and chirp compensation. Broadband THz strong-field generation will subsequently be performed using water-cooled, large-area spintronic emitter structures which provide single-cycle THz strong-field pulses with a gap-free spectrum extending from 0.1 THz up to > 10 THz – an unprecedentedly broad spectral range for two-dimensional strong-field spectroscopy which will open up new vistas for nonlinearities in the THz range.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Hochleistungs-Ytterbium-Femtosekundenverstärkerlasersystem
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Technische Universität Dortmund
• Leader: Professor Dr. Christoph Lange