宽带激光的联合幅度-相位优化将绝对双等离子体衰变阈值提升至相干时间预测之上
Joint Amplitude-Phase Optimization of Broadband Lasers Raises Absolute Two-Plasmon-Decay Thresholds Above Coherence-Time Predictions
- Ergodic LLC（Ergodic有限责任公司）
- Laboratory for Laser Energetics, University of Rochester（罗切斯特大学激光能量学实验室）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文通过可微包络波求解器优化宽带激光的幅度与相位，将双等离子体衰变阈值提升至相干时间预测之上，联合优化在低峰值比下优于变换受限方案。
AI中文摘要：
宽带激光抑制了预热惯性约束聚变靶的绝对双等离子体衰变不稳定性。通常的标度关系将该抑制与驱动源的相干时间联系起来，相干时间是功率谱统计量，对光谱相位不敏感。通过可微包络波求解器中的梯度下降，我们表明在固定功率谱下，相位优化将阈值从随机相位中位数 $2.8\\,I_\mathrm{mono}$ 提升至 $4.1\\,I_\mathrm{mono}$，但产生了变换受限（TL）脉冲序列，其峰值与平均值之比 $R=32$。联合幅度-相位优化在 $R=3.6$ 时达到 $5.6\\,I_\mathrm{mono}$，高于最佳测试的 TL 线计数结果（$R=16$ 时的 $4.5\\,I_\mathrm{mono}$）；放宽峰值约束将联合阈值提升至 $6.4\\,I_\mathrm{mono}$。在模拟内部评估的精确增长率预算将两种机制区分开来。TL 主要通过将泵浦场集中为短脉冲串来抑制耦合，从而在固定平均强度下降低其时间平均幅度。联合最优值保持该幅度度量的近随机值，同时抑制可用耦合以及通过泵浦-子波对齐实现的耦合比例。联合优化的优势在 $1\\%$ 至 $4\\%$ 带宽以及从 OMEGA 尺度到点火尺度条件下均持续存在。
英文摘要：
Broadband lasers suppress the absolute two-plasmon-decay instability that preheats inertial-fusion targets. The usual scaling relates this suppression to the drive's coherence time, a power-spectrum statistic insensitive to spectral phase. By gradient descent through a differentiable enveloped wave solver, we show that at fixed power spectrum phase optimization raises the threshold from the random-phase median of $2.8\,I_\mathrm{mono}$ to $4.1\,I_\mathrm{mono}$, but produces a transform-limited (TL) pulse train with peak-to-average ratio $R=32$. Joint amplitude--phase optimization reaches $5.6\,I_\mathrm{mono}$ at $R=3.6$, above the best tested TL line-count result of $4.5\,I_\mathrm{mono}$ at $R=16$; relaxing the peak constraint raises the joint threshold to $6.4\,I_\mathrm{mono}$. An exact growth-rate budget evaluated inside the simulation separates the two mechanisms. TL suppresses coupling mainly by concentrating the pump field into short bursts, thereby lowering its time-averaged magnitude at fixed average intensity. The joint optima retain near-random values of this amplitude measure while suppressing both the available coupling and the fraction realized through pump--daughter alignment. The advantage of joint optimization persists from $1\%$ to $4\%$ bandwidth and from OMEGA-scale to ignition-scale conditions.
