Engineering topics

Erlandson, A. C.

Publications and source records attributed to Erlandson, A. C..

4 records

DOE OSTI2024

Efficient general method for numerically modeling laser pulse propagation, overlap, and lifetime effects in amplifiers

An efficient numerical time-dependent general method is developed to address incoherent pulse overlap and lifetime effects in laser amplifiers. The alternating propagation-population laser energetics method (APPLE) has been validated against a semi-discrete coupled rate equation numerical method (SDRE) and analytic formalisms in bounding cases. APPLE is based on decoupled rates applied to a time-dependent framework where both space-time-dependent populations and pulse energetics are consistently updated in each time step. A significant advantage of APPLE lies in its conceptual simplicity, ease of implementation, and relatively small computational cost. SDRE tracks the populations through coupled rates and uses the method of lines to discretize the hyperbolic partial differential transport equations allowing for use of ordinary differential equation solvers. With reasonably sized mesh, we report both energetic and power pulse shape relative differences on the order of one percent between the models over a large range of initial conditions.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

Two-photon absorption measurements of deep UV transmissible materials at 213 nm

We report on two photon absorption measurements at 213nm of deep UV transmissible media including LiF, MgF 2 , CaF 2 , BaF 2 , Sapphire (Al 2 O 3 ) and high purity grades of fused-silica (SiO 2 ). A high stability 24ps Nd:YAG laser operating at the 5th harmonic (213nm) was used to generate a high intensity, long Rayleigh length Gaussian focus inside the samples. The measurements of the Fluoride crystals and Sapphire indicate two photon absorption coefficients between 0.004 and 0.82 cm/GW. We find that different grades of fused silica performed near identically for two photon absorption, however, there are differences in linear losses associated with purity. A low two photon absorption cross section is measured for MgF 2 making it an ideal material for the propagation of high intensity deep UV lasers.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Description of the NIF Laser

The possibility of imploding small capsules to produce mini-fusion explosions was explored soon after the first thermonuclear explosions in the early 1950s. Various technologies have been pursued to achieve the focused power and energy required for laboratory-scale fusion. Each technology has its own challenges. For example, electron and ion beams can deliver the large amounts of energy but must contend with Coulomb repulsion forces that make focusing these beams a daunting challenge. The demonstration of the first laser in 1960 provided a new option. Energy from laser beams can be focused and deposited within a small volume; the challenge became whether a practical laser system can be constructed that delivers the power and energy required while meeting all other demands for achieving a high-density, symmetric implosion. The National Ignition Facility (NIF) is the laser designed and built to meet the challenges for study of high-energy-density physics and inertial confinement fusion (ICF) implosions. This study describes the architecture, systems, and subsystems of NIF. Finally, it describes how they partner with each other to meet these new, complex demands and describes how laser science and technology were woven together to bring NIF into reality.

42 ENGINEERING↗

DOE OSTI2012

Compact, Efficient, Low-cost Lasers (CELL) Project (Final Report)

Development of clean, sustainable and affordable energy sources is a national and international challenge. Inertial Fusion Energy (IFE) may provide a transformational solution that is scalable, proliferation-resistant, and that generates negligible nuclear waste. To produce energy economically competitive with alternative power plants, the IFE laser drive must operate at a high repetition rate (≥10 Hz) with high efficiency (>10%), while maintaining beam quality suitable for focusing to a small spot suitable for compressing the fusion target. The NIF laser system meets the beam quality requirements using a solid-state gain medium pumped by flashlamps. Scaling from NIF to IFE requires increases of ~10 5 in rep rate and ~20X in efficiency, which adds significant challenges to the laser design. The increased repetition rate results in much more waste heat generated in the system, and the prevention of thermal beam quality degradation (through phenomena such as thermally-induced birefringence) becomes a critical issue. While thermal issues are mitigated by increasing the system volume, a major size increase renders the system less economical and less easy to site. LIFE laser efficiency targets can be achieved at high rep rate without reliability degradation by using diode lasers as pumps. An IFE plant requires ~10 8 diode laser bars. At current costs the diodes dominate the overall laser cost and render IFE less cost-effective. Thus, designing a compact and cost-effective laser system with the repetition rate, efficiency, and beam quality required for IFE presents a significant technical challenge. The goal of the CELL strategic initiative was to develop new laser architectures to address these challenges by leveraging recent advances in optical technology. New laser design options have become potentially feasible due to improvements in laser gain media, diode pumps, large aperture nonlinear optics, and damage-resistant optics that have occurred since NIF’s conception. The project investigated designs that take advantage of these advances, combining them with advanced and novel subsystem concepts to achieve laser designs with significantly improved performance, size, and cost.

42 ENGINEERING↗