飞秒光学频率梳在精密测量中的应用

飞秒光学频率梳通过锁定飞秒锁模激光的重复频率和偏置频率至微波频率基准,在时域上得到重复频率稳定的飞秒脉冲激光,在频域上得到频率间隔稳定的激光频率梳。飞秒光学频率梳作为微波频率与光学频率的桥梁,可以实现对激光频率的直接精密计量,同时作为一种有别于传统连续波稳频激光的特殊激光光源,在激光频率标尺、绝对距离测量和精密光谱测量等光学精密测量领域都有着重要应用。综述了飞秒光学频率梳在若干光学精密测量应用中的研究进展、关键技术和研究动向,分析了其在未来光学测量中的重要作用。     

高功率高重复频率飞秒掺镱光纤激光频率梳的研究(特邀)

飞秒光学频率梳在精密计量学和光谱学中扮演着革命性的推动角色,成为近二十年超短脉冲激光技术及应用研究领域最活跃的前沿方向之一。文中基于250 MHz重复频率（frep）的掺镱（Yb）光纤激光器,研究了不同腔内色散以及锁模机制对飞秒脉冲序列载波包络相位偏移频率（fCEO）噪声的影响。通过对飞秒光梳细节的优化,得到了49 dB信噪比的fCEO拍频信号并获得了秒稳3.210-10的锁定结果,同时frep的锁定结果也达到了到了秒稳3.410-13的精度。此外文中还研究了不同啁啾状态的种子光飞秒脉冲对基于大模场面积双包层Yb光子晶体光纤放大器输出光脉冲宽度的影响。以携带-3.8104 fs2预啁啾量的光脉冲作为种子光,在60 W 976 nm半导体激光泵浦下,获得了250 MHz重复频率、23 W平均功率和66 fs压缩后脉冲宽度的激光输出。     

掺铒光纤飞秒光梳频率锁定研究

飞秒光梳可以直接实现光频到微波频率转换,广泛应用于时频和计量领域,掺铒光纤飞秒光梳因其良好的频率稳定性、鲁棒性和可搬运性而倍受科学家青睐.本文报道了对掺铒光纤飞秒光梳载波包络相移频率和梳齿频率的锁定,通过控制腔内色散方法,利用反馈泵浦驱动电流方法实现载波包络相移频率的锁定;利用控制光学腔长度的方法,通过反馈电光调制晶体...     

新型全固态超快激光及光学频率梳

目前基于掺钛蓝宝石晶体的飞秒激光在强场物理、超快过程、精密计量、先进制造等领域已成为不可或缺的重要工具,但由于该激光不能采用二极管激光直接抽运,因此在光电转化     

集成电光频率梳研究进展（特邀）

光学频率梳是由一系列离散且等间隔分布的频率成分所组成的光谱结构,作为光谱分析的天然刻度尺,其已广泛应用于光谱学、精密测量、光通信、传感等多个领域。光学频率梳根据其产生技术可分为基于锁模激光器的光学频率梳、克尔微腔光学频率梳、电光频率梳。电光频率梳由于其频率间隔可调、梳齿功率较高、可实现微波到光波的转换等优势,得到了充分发展。但传统电光频率梳的产生器件存在体积大、功耗高的缺点,限制了其进一步应用。随着微纳加工技术的不断发展,越来越多的材料应用于片上集成光学器件,包括硅、氮化硅、氮化铝、磷化铟、铌酸锂、砷化铝镓等。集成电光频率梳器件具有体积小、功耗低等优势,是构建光电集成芯片的重要器件。文中旨在对集成电光频率梳的研究现状进行综述,首先介绍光学频率梳的类型,并详细论述电光频率梳的产生机制;其次介绍产生集成电光频率梳的材料平台、相应的光梳性能指标及其应用;最后基于目前集成电光频率梳领域存在的问题,对未来的研究趋势做出展望。     

光纤飞秒光梳频率精密控制的研究

新一代光纤飞秒光梳在精密测量和基础物理研究领域中有着广阔的前景,一种通过数字电荷泵锁相环和温控电路相结合的方法可以精密控制光纤飞秒光梳。在实验中,我们成功搭建了光纤飞秒光梳系统。光梳的重复频率为129MHz,初始频率大约为33MHz。我们通过自主研发的温控和数字电荷泵锁相环成功地把光纤飞秒光梳成功地锁定在了由Agilent PSG Analog Singal Generator提供的标准微波信号上,锁定时间至少长达1天。锁定后的重复频率的抖动标准差为0.78mHz,与基准源同一个数量级且很接近,锁定后的初始频率的抖动标准差可达8.98Hz。     

飞秒激光脉冲的腔外压缩

为了获得更高的时间分辨率,更短的飞秒脉冲,采用双棱镜和一个平面镜结构对飞秒激光脉冲进行腔外压缩,构建了一台二次谐波频率分辨光学开关装置,对谐振腔输出的飞秒脉冲及压缩后的脉冲进行了测量,取得了脉冲压缩前和压缩后的实验数据,压缩前脉冲的宽度为89fs,脉冲的时间带宽积为0.9096,误差为2.4‰,输入脉冲的平均功率约为480mW;脉冲压缩后的测量结果为22fs,光谱宽度为43nm,时间带宽积为0.44203,误差为1.1‰,压缩脉冲的平均功率约为250mW.压缩比为4:1,高于有关文献的报道.结果表明,该装置实现了飞秒脉冲腔外压缩,对获得更短的飞秒脉冲是有帮助的.     

飞秒激光技术与相关学科

本文阐述了超快激光发展的四个阶段及其内容、特点。对当前超快激光的研究特点、发展方向进行了综述。对与飞秒激光技术相关的几个新兴学科, 如飞秒激光物理学、飞秒激光化学、飞秒光孤子通讯和飞秒电子学给予概括评述。     

飞秒激光作用下透明介质材料的反射率演化

利用800 nm抽运和400 nm探针技术,测量了CaF2和MgO的时间分辨反射率,研究了材料的电子激发和弛豫超快动力学过程。采用耦合动力学模型,探讨了飞秒激光对透明介质材料的激发,以及材料的激发对抽运激光在材料中的传输、分布和反射特性的影响。根据这个理论模型计算了时间分辨反射率的演化,计算结果和实验结果相吻合。研究表明,多光子电离(MPI)和碰撞电离(II)在介质材料的导带电子激发中起着重要的作用。     

飞秒光频梳基于鉴相信号处理实现速度测量

以激光测速为基础,引入飞秒光频梳,通过鉴相信号处理,研究出了一种高精度的测速方法,理论测量下限低至m/s量级。文中详细分析了飞秒光频梳经运动目标反射后梳齿相位发生变化的原理,建立了较为全面的数学模型并使用MATLAB软件进行了仿真。采用快速傅里叶变换方法对仿真测量信号相位信息进行提取并处理,分别对m/s、mm/s和m/s量级速度值进行了测量,理想情况下测量误差在1 m/s以下。同时,还对做任意运动的目标进行了测量仿真实验,结果表明文中方法还可以还原目标的运动状态。最后搭建了实验装置对mm/s量级的速度进行测量,测量相对误差均在4%以内,验证了此方法的可行性。     

Wide-span optical frequency comb generator for accurate opticalfrequency difference measurement

An optical frequency comb (OFC) generator was realized for accurate optical frequency difference measurement of 1.5 μm wavelength semiconductor lasers by using a high frequency LiNbO₃ electrooptic phase modulator which was installed in a Fabry-Perot cavity. It was confirmed that the span of the OFC was wider than 4 THz. By using semiconductor lasers whose spectrum linewidths were narrowed to 1 kHz and a sensitive optical balanced-mixer-receiver for measuring beat signal between the sideband of the comb and the laser, we demonstrated a frequency difference measurement up to 0.5 THz with a signal-to-noise ratio higher than 61 dB, and a heterodyne optical phase locking with a heterodyne frequency of 0.5 THz in which the residual phase error variance was less than 0.01 rad². The maximum measurable frequency difference, which was defined as the sideband frequency with the signal-to-noise ratio of 0 dB, was estimated to be 4 THz     

Novel optical frequency comb synthesis using optical feedback

An optical frequency synthesiser configured as a loop comprising a frequency translator and an amplifier, is proposed and demonstrated for the first time. Generated comb spectra show that the number of teeth observed increases dramatically as the loop losses approach zero.<>     

Theory of the frequency comb output from a femtosecond fiber laser

The output of a femtosecond fiber laser will form a frequency comb that can be phase-locked through feedback to the cavity length and pump power. A perturbative theory is developed to describe this frequency comb output, in particular for a solitonic fiber laser. The effects of resonant dispersion, saturation of the self-amplitude modulation, cavity loss, third-order dispersion, Raman scattering, self-phase modulation, and self-steepening on the spacing and offset of the fiber-laser frequency comb are given. The mechanisms by which the pump power, cavity length and cavity loss control the frequency comb spacing and offset are identified. Transfer functions are derived for the comb response to change in cavity length, pump power or cavity loss. This theory can potentially be applied to other frequency comb sources as well.     

Phase locking of a continuous-wave optical parametric oscillator to an optical frequency comb for optical frequency synthesis

A continuous-wave optical parametric oscillator (OPO) was phase locked to an optical frequency comb in the 830-nm region. The optical frequency of the OPO was controlled by changing the cavity length of the pump laser. The residual phase noise under phase locking was 220 mradrms and the energy concentration to the carrier was 95%. Furthermore, the optical frequency fluctuations of a free-running OPO were measured by using an optical frequency comb that was phase locked to an atomic clock. The measured fluctuations were around 10 MHz in an hour.     

Low-noise synthesis of microwave and millimetre-wave signals with optical frequency comb generator

The phase noise of a 20 GHz picosecond optical pulse train generated by a modulator-based optical frequency comb generator is analysed. The residual timing jitter is ⩾10 fs for Fourier frequencies from 10 Hz to 10 MHz. Photodetection of the optical pulse train provides millimetre-wave signals with similarly low residual jitter at 40, 60, and 80 GHz with applicable powers of 27.5, 210.5, and 213 dBm, respectively.     

Optical clockworks and the measurement of laser frequencies with amode-locked frequency comb

Femtosecond laser-frequency comb techniques are vastly simplifying the measurement and synthesis of optical frequencies. A single mode-locked femtosecond laser, with its spectrum broadened by self-phase modulation in a microstructured or tapered nonlinear fiber, can produce millions of sharp laser lines in a precise evenly spaced grid spanning much of the visible and near-infrared spectrum. The absolute frequency of each line is determined by two observable radio-frequency signals. The pulse repetition rate gives the spacing of the comb lines and the rate at which the phase of the lightwave slips, relative to the intensity envelope from pulse to pulse determines the offset frequency by which each line is displaced from a precise integral multiple of the repetition frequency. This offset frequency can be measured most easily if the comb spans more than an optical octave so that one can observe a radio frequency beat note between the second harmonic of the infrared comb lines with the corresponding comb lines at the blue end. Such an optical-frequency synthesizer makes optical oscillations readily countable and provides the long-awaited compact optical clockwork for an all-optical clock     

30-THz span optical frequency comb generation by self-phasemodulation in an optical fiber

The width of an optical frequency comb (OFC) was increased to 30 THz by using self-phase modulation (SPM) in an optical fiber. This value is 2.7 times larger than the maximum OFC span obtained by the OFC generator alone. We compare the resulting spectrum to numerical simulations to confirm that the SPM and the higher order dispersion of the fiber contribute to broaden the spectral profile