Enabling high repetition rate nonlinear THz science with a kilowatt-class sub-100 fs laser source

Abstract

Manipulating the atomic and electronic structure of matter with strong terahertz (THz) fields while probing the response with ultrafast pulses at x-ray free electron lasers (FELs) has offered unique insights into a multitude of physical phenomena in solid state and atomic physics. Recent upgrades of x-ray FEL facilities are pushing to much higher repetition rates, enabling unprecedented signal-to-noise ratio for pump probe experiments. This requires the development of suitable THz pump sources that are able to deliver intense pulses at compatible repetition rates. Here we present a high-power laser-driven THz source based on optical rectification in LiNbO3 using tilted pulse front pumping. Our source is driven by a kilowatt-level Yb:YAG amplifier system operating at 100 kHz repetition rate and employing nonlinear spectral broadening and recompression to achieve sub-100 fs pulses with pulse energies up to 7 mJ that are necessary for high THz conversion efficiency and peak field strength. We demonstrate a maximum of 144 mW average THz power (1.44 μJ pulse energy), consisting of single-cycle pulses centered at 0.6 THz with a peak electric field strength exceeding 150 kV/cm. These high field pulses open up a range of possibilities for nonlinear time-resolved THz experiments at unprecedented rates.

Hybrid pulse propagation model and quasi-phase-matched four-wave mixing in multipass cells

“…The time and space parts are coupled through the evolution of peak intensity and beam size. The model presented here is particularly well suited to describe propagation in nonlinear regenerative amplifiers [6], or MultiPass Cells (MPCs) [7][8][9][10], where it was shown that an injected Gaussian beam essentially retains its character upon propagation and that space-time couplings are only observed at extreme levels of nonlinearity [11,12]. Compared to the model presented in [11], that is purely (t,z) without a description of spatial effects, the model presented here allows to take into account Kerr lensing that can have non negligible impact on the beam caustic, as will be discussed hereunder.…”

1 kW, 10 mJ, 120 fs coherently combined fiber CPA laser system

“…For the generation of those parameters, especially three laser architectures based on ytterbium-doped active media come into question. While thin-disk and slab lasers especially shine in terms of high pulse energies [4,5], ultrafast fiber lasers prevail in terms of average power [6] and pulse duration, owing to their broad gain bandwidth. However, largely exploiting it requires well thought out spectral shaping to counteract gain narrowing.…”

Kilowatt-average-power compression of millijoule pulses in a gas-filled multi-pass cell

“…In contrast, ultrafast Yb-based amplifiers are power-scalable into the kW regime [7][8][9], however, their output pulse duration is typically not shorter than 200 fs. Furthermore, highly efficient pulse compression in noble gasfilled compact multi-pass cells (MPC) has recently been utilized to compress the pulse duration of laser pulses in a broad energy range [2,[10][11][12][13][14][15][16]. Similar to gas-filled hollow-core-fiber (HCF) post-compression setups [17,18] the footprint of MPC setups scales with pulse energy leading to meter-scale assemblies in the multi-mJ range [2,11,12,15,16].…”

“…At all points during the spectral broadening the residual propagation path in the chamber L prop is much smaller than the dispersion length L d [25] √ e = 8.1 under the assumption of a Gaussian pulse shape [26]. The chirp after the MPC is removed with a chirped-mirror compressor comprising six bounces off chirped mirrors each having a group delay dispersion (GDD) of -350 fs 2 . The total GDD is -1923 fs 2 after fine-tuning the compression with inserted glass plates.…”

“…To the best of our knowledge, the MPC output represents the highest average power of sub-100 fs pulses ever demonstrated. Recently, it was shown that an even higher nonlinear phase shift per focus does not deteriorate the MPC performance [2,27]. Hence, further reduction of MPC round-trips seems feasible, which could in turn enable an even higher transmission.…”