Laser system for time-resolved THz spectroscopy

• Subject Area: Chemical Solid State and Surface Research
• Term: Funded in 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553761309

THz spectroscopy is a powerful tool to investigate a variety of different physical phenomena at low photon energy, e.g. free charge carrier dynamics, plasmons, or cyclotron motion. A big breakthrough for THz spectroscopy was the development of ultrafast laser systems about four decades ago: when the laser pulse with a duration of less then 100 fs impinges on a semiconductor, charge carriers are excited from the valence to the conduction band. When these carriers are accelerated by an applied bias voltage, a THz pulse is generated. The inverse technique can be exploited to measure such THz pulses, the spectral content can be calculated by Fourier transformation. Within our working group, we had such a Ti:Sapphire based amplified laser system for time resolved THz spectroscopy, though it had to be shut down due to a failing pump laser. The main part of the laser is about 20 years old, repair of the system would not be an economic option. Hence, we apply for a new amplified laser system that provides a pulse energy of above 1 mJ and a pulse duration below 50 fs, which would be sufficient for the generation of intense THz pulses, required for time-resolved spectroscopy. As the pulse duration is directly linked to the achievable THz bandwidth, short pulse duration is a requirement for broadband spectroscopic measurements. In order to enable experiments with a high signal-to-noise ratio, we aim for a repetition rate of above 10 kHz. The wavelength of the system has to be in the near-infrared range for efficient THz generation and detection, here we would like to acquire an Yb-based femtosecond laser at a wavelength of 1030 nm as those offer turn-key operation at the lowest cost. Due to the rather narrow band gain medium, the pulse duration is usually on the order of 200 fs or longer, though nonlinear compressor units can be exploited to decrease the pulse duration significantly below 50 fs. As this laser is aimed to replace a laser system, a setup for exploiting the laser system for time-resolved spectroscopy is already available, only minor adjustments, like new non-linear crystals and mirrors, are required. With this laser system we intend to continue our successful efforts to investigate charge carrier dynamics in a variety of different samples, e.g. in Bi2Te3, thin Bi films, graphene plasmons and many more.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Lasersystem für zeitaufgelöste THz Spektroskopie
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Universität Duisburg-Essen
• Leader: Professor Dr. Martin Mittendorff