We report the demonstration of a diode-pumped Tm:YLF laser operating at 1.88 µm that produces pulse energies up to 3.88 J in 20 ns. The compact system consists of a
Q
-switched cavity-dumped oscillator generating 18 mJ pulses, which are then amplified in a four-pass power amplifier. Energies up to 38.1 J were obtained with long-pulse amplifier operation. These results illustrate the high energy storage and extraction capabilities of diode-pumped Tm:YLF, opening the path to high peak and average power mid-infrared solid-state lasers.
We report on the generation of high energy, high power pulses in a tabletop diode-pumped Tm:YLF-based laser system, which delivers amplified pulse energies up to 108 J, as well as GW peak power performance when seeded with nanosecond duration pulses. Furthermore, the high power and efficiency capabilities of operating Tm:YLF in the multi-pulse extraction (MPE) regime were explored by seeding the experimental setup with a multi-kHz burst of pulses exhibiting a low individual pulse fluence, resulting in a 3.6 kW average power train of multi-joule-level pulses with an optical-to-optical efficiency of 19%.
High Power Lasers
In article number 1700211, Issa Tamer and co‐workers utilize Yb:CaF2 crystal and Yb:FP‐glass within the high power ultrashort POLARIS laser system to amplify near‐infrared laser pulses up to energies in the Joule regime. A comprehensive spatio‐temporal characterization of pump‐induced aberrations across the free aperture of the considered diode‐pumped active materials is presented. All relevant material constants are determined, allowing for accurate modeling of the aberrations. For the further development of next‐generation high power laser systems, extensive knowledge of the spatio‐temporal behavior of these aberrations is required.
A comprehensive spatio‐temporal characterization is presented describing the pump‐induced wavefront aberrations in Yb3 + ‐doped YAG, CaF2, and fluorophosphate glass. Time‐resolved interferometric measurements were performed to reveal the profiles of the total optical path differences (OPDs), which are described by the spatio‐temporal superposition of thermal as well as electronic contributions, across the free aperture of the considered diode‐pumped active materials. These contributions were individually determined by a COMSOL‐based thermal profile model along with a detailed characterization of the electronic changes by measuring the single‐pass gain and the spatial fluorescence profile. Due to the low quantum defect, the amplitude of the electronic component becomes comparable for all three materials and, in the case of Yb:CaF2, almost completely compensates the thermal component resulting from a pump pulse during the time frame of laser pulse amplification. Finally, all relevant material constants – such as the photoelastic constant Cr′ and the polarizability difference Δα – could be determined during this investigation, allowing the accurate modeling of the total pump‐induced wavefront aberrations and subsequent optimization for laser systems worldwide employing these Yb3 + ‐doped materials.
Thermal profile modification of an active material in a laser amplifier via optical pumping results in a change in the material’s refractive index, and causes thermal expansion and stress, eventually leading to spatial phase aberrations, or even permanent material damage. For this purpose, knowledge of the 3D spatio-temporal thermal profile, which can currently only be retrieved via numerical simulations, is critical for joule-class laser amplifiers to reveal potentially dangerous thermal features within the pumped active materials. In this investigation, a detailed, spatio-temporal numerical simulation was constructed and tested for accuracy against surface thermal measurements of various end-pumped
$\text{Yb}^{3+}$
-doped laser-active materials. The measurements and simulations show an excellent agreement and the model was successfully applied to a joule-class
$\text{Yb}^{3+}$
-based amplifier currently operating in the POLARIS laser system at the Friedrich-Schiller-University and Helmholtz-Institute Jena in Germany.
A compact, femtosecond-pumped noncollinear optical parametric amplifier (NOPA) is presented with a passive spectral shaping technique, employed to produce a flat-top-like ultrabroadband output spectrum. The NOPA is pumped by a dedicated 2 mJ, 120 fs Yb3+-based CPA system, which generates both the second harmonic pump pulse and white light supercontinuum as the signal pulse. A chirped mirror pair pre-compensates the material GVD within the optical path of the signal pulse to produce a near-FTL pulse duration at the OPA crystal output. By optimizing both the pump/signal cross angle and the pump/signal delay, the 40 cm × 40 cm footprint, single-pass, fs-pumped, direct NOPA (non-NOPCPA) system generates a record 20 µJ, 11 fs pulses at 820 nm central wavelength with a bandwidth of 230 nm FWHM, to be used as an ultrashort optical probe pulse for relativistic laser-plasma interactions at the petawatt-class POLARIS laser system.
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