【作者】 陈思；

【导师】 张洁；

【作者基本信息】 华中科技大学 ， 精密测量物理， 2022， 硕士

【摘要】 光学频率梳如同一座桥梁,直接连接了电磁波的射频与光频波段,自其发明以来,极大地推动了光学频率标准、时间频率传递以及长度测量等研究领域的技术进步和发展。基于光参量振荡器（Optical Parametric Oscillator,OPO）的飞秒光学频率梳具有宽谱调谐和高能量输出等优势,因此,近些年在原子光谱分析和量子光学等众多领域获得了人们的重视和青睐。本文立足于利用紫外激光直接冷却铝离子光频标的研究背景,针对基波脉冲光源缺乏的难题,围绕高功率飞秒OPO光梳光源的实验研究展开工作,主要的研究内容包括:第一,设计了一套波长可灵活调谐并能够产生瓦量级功率的飞秒光学参量振荡器实验系统。基于三波耦合方程模型,通过仿真计算,指导选取腔内晶体参数;通过基于谐振腔理论,研究腔内光模匹配特性,并设计腔体布局结构。第二,实验上成功实现了一套基于多周期Mg O:PPLN晶体的单谐振OPO。测得输出的脉冲具有790～980 nm的宽谱覆盖范围,调谐带宽达到了190 nm;进一步优化系统结构与参数配置,成功获得了重复频率250 MHz、功率高达1.16 W的850 nm高功率飞秒脉冲,对应的泵浦光转换效率达到20.2%。第三,实现对OPO输出脉冲的重复频率和载波包络偏移频率的探测和锁定。采用“共模抑制”技术,成功探测了OPO光梳的载波包络偏移频率,信噪比高达30d B;进一步,通过采用经典的微波锁定方案,建立锁相环电子线路,初步实现了飞秒OPO光梳梳齿锁定至氢钟参考。在20 h的测量时间内,重复频率时域抖动标准差为70μHz,秒稳稳定度达到3×10^-13;锁定后的载波包络偏移频率抖动量由自由运转下的MHz量级降低至k Hz量级。这种功率瓦量级、波长可灵活调谐的高重复频率飞秒OPO光梳,为234 nm紫外光梳的制备提供了一个高脉冲能量、性能可靠的基频光源,不仅为直接激光冷却铝离子光频标的研究奠定了扎实基础,并有望应用于光谱学等更宽广的研究领域。更多还原

【Abstract】 The optical frequency comb acts like a bridge,providing a bidirectional coherent connection between the optical and radio frequency domains.Since its invention,it has greatly promoted the technological progress and development of optical frequency standards,time-frequency distribution,and length measurement.An femtosecond optical frequency comb based on an optical parametric oscillator（OPO）has advantages of broader spectral coverage and higher power capability,and has gained attention and favor in many fields such as atomic spectroscopy and quantum optics in recent years.Aiming on the application in a directly ultraviolet laser cooling aluminum ion optical frequency standard,and solving the problem of the shortage of the fundamental pulse laser source,this study focuses on the experimental research of a high-power femtosecond OPO optical frequency comb.The main researches are the following:Firstly,an experimental system of femtosecond OPO laser with flexible wavelength tuning and watt-level power level is designed and developed.Based on three wave coupling equation model,appropriate parameters of nonlinear crystals in the cavity are selected through a rigorous simulation;and by using the resonant cavity theory,mode-matching characteristics of the optical cavity are designed,as well as the cavity layout structure.Secondly,we successfully realize a resonant OPO based on the multi-grating Mg O:PPLN crystal in the experiments.The measured output of the pulse laser has a wide spectral coverage of 790～980 nm,and the tuning bandwidth covers 190 nm;Furthermore,after optimizing the OPO system structure and parameter configuration,we also successfully obtain a high-power femtosecond pulse with a repetition frequency of 250 MHz and an average power of up to 1.16 W at 850 nm,corresponding to a pump light conversion efficiency of 20.2%.Thirdly,we realize the detection and locking of the repetition rate and the carrier-envelope offset frequency of the OPO comb.Using the“common mode rejection”technique,and by optimizing the spatial overlap and time-domain synchronization of the heterodyne pulsed lasers,we successfully detect the carrier-envelope offset frequency of the OPO comb with a 30 d B signal-to-noise ratio.Furthermore,based on the classic microwave locking scheme,and the phase-locked loop electronic circuits,both the repetition rate and the carrier-envelope offset frequency of the OPO comb are stabilized to a hydrogen maser.Measurement results show that the standard deviation of repetition rate is 70μHz over 20hours,and the stability reaches 3×10^-13 at 1 s.Compared to the free-running condition,the counted jitter results of the carrier-envelope offset frequency are reduced from tens of MHz to a level of k Hz.We build a high-repetition-rate femtosecond OPO laser source with a watt-level power and flexible wavelength tunability.It can provide a high pulse energy fundamental light source for the preparation of the 234 nm ultraviolet light comb.It not only lays a solid foundation for the research of the direct laser cooling aluminum ion optical frequency standard,but also expected to be used in a broader application fields such as optical spectroscopy.更多还原