The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a 192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to 351nm light or 3w. It was built to access the extreme high energy density conditions needed to support the nation’s nuclear stockpile in the absence of further underground nuclear tests, including studying Inertial Confinement Fusion (ICF) and ignition in the laboratory.
Over the last year, important results have been obtained demonstrated a fusion yield of 1.35MJ with 1.9MJ of laser energy (and 440 TW power) injected in the target, bringing the NIF to the threshold of ignition [2-3]. As the yield curve near ignition is steep, the laser performance team has focused on providing improved power accuracy and precision (better shot-to-shot reproducibility) with a high-fidelity pulse shaping system (HiFiPS), and also on extending the NIF operating power and energy space by 15% to 2.2MJ and 500TW.
Stimulated rotational Raman scattering in air is a powerful parasitic process that degrades high intensity pulses propagated over significant distances. Through this inelastic scattering process, laser photons are converted to higher (Anti-Stokes) or lower (Stokes) energies, according to rotational mode transitions in the nitrogen and oxygen molecules. The full wave-mixing problem involves numerous frequencies including both Stokes and Anti- Stokes processes, multiple rotational line transitions, and multi-harmonic generation, with each generated field acting as a seed for subsequent scattering processes. Multiple numerical models of these processes were integrated into Lawrence Livermore National Laboratory’s in-house nonlinear optical chain propagation software, Virtual Beamline++. The complex spatio-temporal dynamics of single, and multi-frequency stimulated rotational Raman scattering are highlighted and discussed. General limitations of steady-state, dynamic two-level, multi-harmonic, and multi-rotational models are demonstrated and compared.
Mode-locked vertical external-cavity surface emitting lasers are promising compact sources for high-power, ultrafast pulses with excellent beam quality and the flexibility offered by an external cavity. Typical models of these lasers use macroscopic or quasistatic approaches based on rate or delay differential equations. Although these approaches have shown widespread success, they often require numerous experimentally tuned parameters and cannot capture the ultrafast nonequilibrium dynamics present as the field interacts with the quantum well. The Maxwell Semiconductor Bloch Equations has reduced parametrization and captures the carrier dynamics by coupling together a numerical wave propagator to a first principles of quantum mechanical description of the induced microscopic polarization within the active semiconductor quantum well. We expand on this model utilizing a reference frame transform to model modelocking within VECSEL cavities with non-normally incident semiconductor heterostructures. Specifically, we demonstrate the effect of increased pumping on the fundamental and harmonic modelocking behaviors of V-cavity VECSELs as well as transverse kinetic hole burning during colliding pulse operation as seen in modelocked ring cavities.
Mode-locked vertical external-cavity surface emitting lasers are promising compact sources for high-power, ultrafast pulses with excellent beam quality and the flexibility offered by an external cavity. Classical models of these lasers use either phenomenological approaches, which rely heavily on experimentally observed macroscopic parameters, or are based on quasi-equilibrium conditions. Although these models enjoy widespread success, they cannot capture the underlying charge carrier dynamics, shown to be critical components of pulse formation and propagation. The Maxwell Semiconductor Bloch Equations capture these dynamics through a coupling of pulse propagation to the field induced polarization within an active semiconductor quantum well. We utilize a transverse implementation of this model to microscopically investigate fundamental Gaussian pulse formation as well as destabilizing effects of pump parameters. These behaviors are directly linked to the underlying charge carrier dynamics. Excess carriers around the pulse's spatial or spectral centers destabilizes the pulse and are shown to lead to the formation of higher order transverse modes and secondary pulses within the cavity.
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