发表机构
P.N. Lebedev Physical Institute of the Russian Academy of Sciences; Moscow Institute of Physics and Technology; Russian Quantum Center（俄罗斯科学院列别杰夫物理研究所; 莫斯科物理技术学院; 俄罗斯量子中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文分析连续波激光与飞秒光梳产生谐波的效率及相位噪声影响，发现飞秒谐波中心模功率在K>2时更高，且载波功率随谐波次数按高斯衰减。
AI 中文摘要
紫外和真空紫外波段的精密光谱学，包括钍-229核跃迁（148.4 nm）的光谱研究，需要通过对稳定激光进行倍频来获得窄带光源。在谐波产生过程中，辐射强度下降且相位噪声增加。本工作针对两类初级源分析了这两个因素：连续波单频激光器和飞秒光学频率梳。研究表明，在弱转换条件下，当平均输入功率相等时，飞秒辐射第K次谐波频谱中心模的功率在K=2时与连续波辐射的谐波功率相当，而在K>2时显著超过后者。在一阶色散近似内，群速度失配降低了总转换效率，但不影响精确相位匹配的中心模功率。超稳定激光相位噪声在谐波产生过程中的变换导致两个依赖于K的效应：谐波线宽线性增长，而载波中的功率分数以高斯函数形式下降，并由稳定环路的高频噪声（伺服凸起）决定。对锁定到法布里-珀罗腔的激光相位噪声谱的测量表明，对于典型的均方根相位偏移约100毫弧度，载波在第八次谐波时已损失约一半功率，而对于非最优稳定环路增益，载波在第二至第三次谐波时即发生崩溃。
英文摘要
Precision spectroscopy in the UV and VUV ranges, including spectroscopy of the thorium-229 nuclear transition (148.4 nm), requires narrow-band sources obtained by frequency multiplication of stabilized lasers. Upon harmonic generation, the radiation intensity drops and the phase noise grows. In this work, both factors are analyzed for two types of primary sources: a continuous-wave single-frequency laser and a femtosecond optical frequency comb. It is shown that in the weak-conversion regime for equal average input powers, the power of the central mode in the spectrum of the Kth harmonic of femtosecond radiation matches the harmonic power of continuous-wave radiation for K=2 and noticeably exceeds it for K>2. Within the first-order dispersion approximation, group-velocity mismatch reduces the total conversion efficiency without affecting the power of the exactly phase-matched central mode. The transformation of the phase noise of an ultrastable laser upon harmonic generation leads to two effects that depend on K: the harmonic linewidth grows linearly, whereas the power fraction in the carrier decreases as a Gaussian function and is determined by the high-frequency noise of the stabilization loop (the servo bumps). Measurements of the phase-noise spectra of a laser stabilized to a Fabry-Perot cavity show that for a typical rms phase excursion of ~100 mrad the carrier loses about half of its power already at the eighth harmonic, while for a non-optimal stabilization-loop gain carrier collapse occurs at the second-third harmonic.
Comments15 pages, 6 figures
