  We demonstrate a high average power terahertz time-domain (THZ-TDS)
spectrometer based on optical rectification in the tilted-pulse front geometry
in lithium niobate at room temperature, driven by a commercial, industrial
femtosecond-laser operating with flexible repetition rate between 40 kHz - 400
kHz. The driving laser provides a pulse energy of 41 uJ for all repetition
rates, at a pulse duration of 310 fs, allowing us to explore repetition rate
dependent effects in our TDS. At the maximum repetition rate of 400 kHz, up to
16.5 W of average power are available to drive our THz source, resulting in a
maximum of 24 mW of THz average power with a conversion efficiency of ~ 0.15 %
and electric field strength of several tens of kV/cm. At the other available
lower repetition rates, we show that the pulse strength and bandwidth of our
TDS is unchanged, showing that the THz generation is not affected by thermal
effects in this average power region of several tens of watts. The resulting
combination of high electric field strength with flexible and high repetition
rate is very attractive for spectroscopy, in particular since the system is
driven by an industrial, compact laser without the need for external
compressors or other specialized pulse manipulation.
