We demonstrate THz generation using the tilted pulse front method in Lithium Niobate, driven at unprecedented high average power of more than 100 W and at 13.3 MHz repetition rate, provided by a compact amplifier-free modelocked thin-disk oscillator. The conversion efficiency was optimized with respect to pump spot size and pump pulse duration, enabling us to generate a maximum THz average power of 66 mW, which is the highest reported to date from a laser-driven, few-cycle THz source. Furthermore, we identify beam walk-off as the main obstacle that currently limits the conversion efficiency in this excitation regime (with moderate pulse energies and small spot sizes). Further upscaling to the watt level and beyond is within reach, paving the way for linear and nonlinear high-average power THz spectroscopy experiments with exceptional signal-to-noise ratio at MHz repetition rates.Terahertz time domain spectroscopy (THz-TDS) has been one of the cornerstones of THz science for several decades, leading to a vast number of advances in science and technology. One example in scientific research where THz-TDS continues to enable major breakthroughs is in condensed matter physics, where timeresolved spectroscopic techniques (pump-probe, multidimensional spectroscopy) in the THz region have become ubiquitous [1]. However, in this and many other fields, new challenges keep arising, as THz-TDS is performed to study increasingly difficult samples, such as water with large THz absorption or at long distances, such as in imaging applications and/or sensing. These and other applications would benefit from greater signal-to-noise ratios and shorter measurement times, enabled by high repetition rates, while maintaining sufficient THz pulse energy -i.e. from sources with high average power. Experiments requiring high average powers are thus typically exclusively performed in accelerator facilities, at the expense of extremely high cost, very restrictive accessibility and difficulties in achieving phase stability required for TDS [2]. Meanwhile, labbased few-cycle THz sources for TDS have immensely progressed in terms of pulse energy [3,4], bandwidth [5] and tunability [6] in recent years, but this progress is typically made at the expense of the repetition rate of the source (<1 kHz), therefore average power levels remain very low, typically in the few to hundreds of µW range. This is mostly due to the limited average power of commonly used energetic Ti:Sapphire amplifiers as drivers, which are typically limited to <10 W of average power.One promising yet widely unexplored path to increase the average power of current THz sources is therefore to adopt novel ultrafast solid-state lasers based on Yb-doped gain media as driving sources, which nowadays reach kilowatt average powers [7][8][9], possibly in combination with efficient THz generation schemes. Among these novel ultrafast technologies, we focus our attention on modelocked thin-disk lasers (TDLs), which are capable of providing femtosecond pulses with tens of microjoules of pu...

We report on an in-band pumped SESAM mode-locked Ho:CALGO bulk laser with a record-high average power of 8.7 W and an optical-to-optical efficiency of 38.2% at a central wavelength of 2.1 µm. At this power level, the bulk laser generates pulses with a duration of 369 fs at an 84.4-MHz repetition rate, corresponding to a pulse energy of 103 nJ and a peak power of 246 kW. To the best of our knowledge, this is the highest average power and pulse energy directly generated from a mode-locked bulk laser in the 2-3 µm wavelength region. Our current results indicate that Ho:CALGO is a competitive candidate for average power scaling of 2-µm femtosecond lasers.

We demonstrate pulse compression of 310-fs, 150-MW peak power pulses at 400-kHz repetition rate down to 27 fs, 1.05 GW of peak power using a single, dispersion-optimized Herriott-type multipass cell compressor with 92 % overall efficiency.

We demonstrate a THz source using the tilted pulse front technique in Lithium Niobate, reaching a record-high average power of 66mW at 13.3MHz repetition rate, driven by a high-power Yb-based modelocked thin-disk laser.

No abstract