50-W average power Ho:YAG SESAM-modelocked thin-disk oscillator at 2.1 µm

Abstract

Ultrafast laser systems operating with high-average power in the wavelength range from 1.9 µm to 3 µm are of interest for a wide range of applications for example in spectroscopy, material processing and as drivers for secondary sources in the XUV spectral region. In this area, laser systems based on holmium-doped gain materials directly emitting at 2.1 µm have made significant progress over the past years, however so far only very few results were demonstrated in power-scalable high-power laser geometries. In particular, the thin-disk geometry is promising for directly modelocked oscillators with high average power levels that are comparable to amplifier systems at MHz repetition rate. In this paper, we demonstrate Semiconductor Saturable Absorber Mirror (SESAM) modelocked Ho:YAG thindisk lasers (TDLs) emitting at 2.1-µm wavelength with record-holding performance levels. In our highest average power configuration, we reach 50 W of average power, with 1.13-ps pulses, 2.11 µJ of pulse energy and ~1.9 MW of peak power. To the best of our knowledge, this represents the highest average power, as well as the highest output pulse energy so far demonstrated from a modelocked laser in the 2-µm wavelength region. This record performance level was enabled by the recent development of high-power GaSb-based SESAMs with low loss, adapted for high intracavity power and pulse energy. We also explore the limitations in terms of reaching shorter pulse durations at high power with this gain material in the disk geometry and using SESAM modelocking, and present first steps in this direction, with the demonstration of 30 W of output power, with 692-fs pulses in another laser configuration. In the near future, with the development of a next generation of SESAM samples for this wavelength region, we believe higher pulse energy approaching the 10-µJ regime, and sub-500-fs pulses should be straightforward to reach using SESAM modelocking.

Progressive pulse dynamics in a mode-locked fiber laser

“…As a vigorous method to achieve Q-switched or mode-locked operation, various low-dimensional SA materials are utilized as modulating devices to generate the laser pulses. Common materials are graphene [17,18], semiconductor saturable absorption mirrors (SESAMs) [19,20], carbon nanotubes (CNTs) [21,22], transition metal dichalcogenides (TMDs) [23,24], topological insulators (TIs) [25], black phosphorus (BP) [26], Mxenes [27], Xenes [28], phosphorene [29,30], ferromagnetic insulators (FIs) [31,32], silicene [33,34], and tellurene [35]. Mid-Infrared PQS and mode-locked fiber lasers at 2-3 μm wavelength range were demonstrated by incorporating CNT/SESAM/Selenide-nanoflowers SAs in the cavity [14,36,37].…”

Highly efficient nonlinear compression of mJ pulses at 2 μm wavelength to 20 fs in a gas-filled multi-pass cell

“…The latter case, where conversion efficiencies reach a maximum of 16%, distinctly illustrates the drawback in efficiency resulting from the pumping mechanism typically initiated from 1 µm wavelength. Besides OPCPA systems, a promising solution for achieving high average power ultra-short pulses around 2 µm is to use active gain media such as holmium-or thulium-doped materials in chirped-pulse amplification systems [11,12]. However, the bandwidth of these gain media does not support the desired pulse durations directly.…”

High efficiency in-band pumped Tm- and Ho-doped 2-μm solid-state lasers

“…Tm 3+ -or Ho 3+ -ions are the main doping ions for the laser crystals and ceramics at 2 µm [1][2][3][4]. Lasers based on Tm 3+ -or Ho 3+ -doped crystals and ceramics operated in CW, Q-switched or mode-locking modes have demonstrated both high average and peak power and high pulse energy [7][8][9][10].…”