Fast THz time-domain spectrometer

In this paper we present a concept of a THz time-domain spectrometer to be used in millisecond pulsed magnets with 24 mm clear bore. The design is based on fiber coupled semiconductor antennas, both for THz light emission and detection, gated with ultrafast femtosecond laser pulses. Both, THz emitter and detector are installed inside the magnet bore, close to the sample. The laser pulses gating the emitter and the detector are guided from outside by optical fibers (Fig.1). A fast acquisition rate is achieved due to implementing recently developed asynchronous optical sampling (ASOPS) technique that requires no mechanically moving parts. We employ two different Ti:sapphire oscillators with slightly different repetition rates (F and F+Δ) to gate the emitter and detector (fig. 1). As a result, the lasers produce two pulses with a time delay linearly ramped between zero and 1/F. The beat frequency Δ determines time delay scan rate.
We will present the design of the emitter/detector system, first results of THz spectra recorded with this system, and discuss the critical issues, such as the type of the fibers employed. In the future it will be possible to investigate the broadband-THz properties of semiconductors and other solids in pulsed high magnetic fields. In addition, the ASOPS laser system can of course be employed for pump-probe spectroscopy at the 750-850 nm laser wavelengths.