Frequency stabilization of a 399-nm laser by modulation transfer spectroscopy in an ytterbium hollow cathode lamp

The modulation transfer spectroscopy in an ytterbium hollow cathode lamp at 399 nm is measured. The error signal for frequency locking is optimized by measuring the dependences of its slope, linewidth and magnitude on various parameters. Under the optimum condition, the laser frequency at 399 nm can be stabilized. The long-term stability of laser frequency is measured by monitoring the fluorescence signal of the ytterbium atomic beam induced by the locked laser. The laser frequency is shown to be tightly locked, and the stabilized laser is successfully applied to the cooling of ytterbium atoms.

A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy

We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy(MTS)technology with good reproducibility.A frequency stability of 2.5×10^(-14)at 1 s averaging time is achieved,and the frequency reproducibility has a relative uncertainty of 3.5×10^(-13),demonstrating the great stability of our setup.The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated,especially the contribution of the residual amplitude modulation(RAM).The contribution of the RAM in MTS cannot be evaluated directly.To solve this problem,we theoretically deduce the MTS signal with RAM under large modulation depth,and prove that the non-symmetric shape of the MTS signal is directly related to the MTS effect.The non-symmetric shape factor can be calibrated with a frequency comb,and in real experiments,this value can be obtained by least-squares fitting of the MTS signal,from which we can infer the RAMinduced frequency shift.The full frequency uncertainty is evaluated to be 5.3 kHz(corresponding to a relative frequency uncertainty of 9.4×10^(-12)).The corrected transition frequency has a difference from the BIPM-recommended value of 2 kHz,which is within 1σ uncertainty,proving the validity of our evaluation.

Modulation transfer spectroscopy based on acousto-optic modulator with zero frequency shift

We present a modulation transfer spectroscopy（MTS） configuration based on an acousto-optic modulator by using a variant of the typical double pass structure. One beam is modulated by using an acousto-optic modulator in opposite diffraction order to cancel the carrier frequency shift and produce a modulated pump beam. The line shape performance is investigated theoretically and experimentally. Laser frequency stabilization of the proposed configuration is demonstrated for the133 Cs ｜62 S1/2, F = 4 → ｜62 P3/2, F = 5 transition. The Allan deviations, which are measured by using beat note signals and the three-cornered hat method, are 3.6×10-11 in an integration time of 100 s and approximately 4×10-11 in a longer integration time.

基于全球导航卫星系统应用的光频原子钟发展现状与可用性分析

随着光频原子钟技术迅速发展,光频原子钟不确定度已超越微波原子钟性能4~5个数量级,达到了10^(−19)数量级,在可靠性和小型化方面也不断提升,使得未来全球导航卫星系统(Global Navigation Satellite System,GNSS)搭载光频原子钟成为可能。介绍了几种GNSS光频原子钟的工作原理及国内外的研究进展,从稳定度、集成度及影响稳定度的因素等方面总结了几种光频原子钟的性能,并将四种光学时钟(离子光钟、光晶格钟、双光子跃迁光频原子钟、基于碘调制转移谱光频原子钟)与目前GNSS上搭载的四大导航系统进行比较,讨论了光频原子钟的应用潜力,并提出了各光频原子钟的发展建议。针对提升离子光钟和光晶格钟可靠性的需求,提出了通过提高激光器和超稳腔的稳定性、降低核心器件环境敏感性的建议。针对提升原子束光频原子钟稳定性的需求,提出了提高原子束利用率、进一步迭代实验等方案。针对提升双光子跃迁光频原子钟和调制转移谱光频原子钟的长期稳定性的需求,提出了结合真空技术及人工智能降低频率漂移率的解决方案。

调制转移光谱对激光频率起伏分辨率的影响因素分析及优化方法

采用电光位相调制器对泵浦光进行位相调制,得到射频调制转移光谱(MTS),并研究MTS光谱的类色散信号中心过零点斜率优化问题。通过改变泵浦光的调制频率,泵浦光与探测光的光斑大小,研究MTS光谱信号过零点斜率与二者之间的参数依赖关系,在泵浦光调制频率为~3.6 MHz(大约是自然线宽的0.69倍)时,得到最佳的MTS光谱信号。最后利用最优的MTS光谱将DL Pro@852 nm激光频率锁定到铯原子D2线(F=4)-(F=5’)循环跃迁,在60 min采样时间内激光频率起伏约为170 kHz,与自由运转时激光器~11 MHz的频率起伏相比,频率起伏得到了显著改善。

Frequency Stabilization and Linewidth Narrowing with Modulation Transfer Spectroscopy

We report laser frequency stabilization with modulation transfer spectroscopy（MTS） on 85 Rb atoms. With both PZT（piezo-electric transducer） slow-loop feedback and current fastloop feedback to the laser head, we get a linewidth narrowing less than 5 kHz simultaneously. Laser injection to a laser diode and frequency beating with another polarization spectroscopy based stabilization setup are also employed to check the narrow linewidth property. With the help of the technique, a linewidth around k Hz-level laser is obtained and pave the way for the locking of the lattice laser of ytterbium clock with transfer cavity technique. The setup can be used as a frequency reference for precise frequency control of atomic clock system.

强度调制光电流谱研究纳晶薄膜电极过程

用强度调制光电流谱研究半导体纳晶薄膜电极光生电荷的界面转移和输运动力学过程．从测量不同外加电压和不同硫化钠溶液浓度下ＣｄＳｅ纳晶薄膜电极的光电流响应得到了参数：归一化稳态光电流和表面态寿命，分析界面空穴的直接转移和通过表面态的间接转移过程．通过测量不同背景光强下ＴｉＯ２纳晶薄膜电极的电子扩散系数研究电子输运过程．应用ＨＣｌ化学处理方法明显增大了电子扩散系数，改善了电子在ＴｉＯ２纳晶薄膜电极中的输运性能．

基于399 nm激光调制转移谱的频率锁定及频移测量

为了获得高信噪比的激光检测光谱,激光光源的频率必须实现锁定,本研究仿真了不同调制频率下的调制转移谱信号,并在实验上利用空心阴极灯中的调制转移光谱技术实现了399 nm激光稳频,同时测量了镱原子同位素~1S_0-~1P_1跃迁频移。结果表明,调制频率的最佳选择值是0.8Γ;闭环锁定后,399 nm激光器的激光线宽小于±1.3 MHz,可以得到很好的谱线信噪比;利用调制转移谱还可以获得精确的~1S_0-~1P_1跃迁的同位素频移。

碘吸收激光稳频中调制信号的理论计算

激光频率标准是将激光频率锁定于原子或分子的超精细能级间的跃迁频率,从而获得高精密度的激光频率输出。在激光稳频研究工作中,通常将碘分子的吸收谱线采用导数谱、FM光谱和调制转移光谱MTS(ModulationTransferSpectroscopy)进行频率的精密控制。为更好地消除吸收谱线的本底噪声,目前最好的稳频方案是采用调制转移光谱法。它具有高灵敏度、高分辨率和无多普勒背景等特点。从物理学的原理出发,分析了激光对介质的极化机理,导出介质对激光的吸收和色散作用的数学模型,用信号处理的技术从理论上推导了MTS谱线线型,分析了光谱线型的特性,讨论了提高激光频率稳定度的各种情况。

光栅型光谱仪波长准确度校准方法

针对低压汞灯谱线能量弱且量值无法溯源的难题,本文以1 064 nm单块固体环形激光器作为基频光,经过两次倍频分别得到532 nm、266 nm激光,通过调制转移光谱技术将532 nm激光频率锁定在碘分子超精细谱线上,以此为基础对光栅型光谱仪的波长准确度进行校准。实验结果表明,稳频波长源输出的三波长具有严格的倍数关系,能够准确有效地对光栅型光谱仪波长准确度进行校准,具有很好的实际应用价值。

新型激光光源染料HA宽带调谐发光物理机制

为了研究和揭示竹红菌甲素(HA)的宽带调谐发光物理机制,采用强激光激发的方法,主要研究了HA的强激发辐射效应,从一个侧面证实了激发态质子转移(ESIPT)的存在,同时进行了理论分析和实验验证,并给出了HA分子能级模型。结果表明,对于HA分子需要双光子吸收才能实现ESIPT过程。这一结果对进一步认识HA的发光物理机制是有帮助的。

用调制转移光谱技术研制微型全固体稳频激光器

报道采用自行研制的半导体激光泵浦微片Ｎｄ∶ＹＶＯ４晶体,经驻波腔内ＫＴＰ晶体倍频获得５３２ｎｍ激光输出的全固体单频可调谐微型激光器．采用光外差调制转移光谱技术获得超高信噪比碘分子跃迁超精细结构光谱,并实现频率稳定度优于１０－１２(１秒积分时间)的激光频率高精度绝对锁定．

温度和吸收程对稳频精度的影响

调制转移光外差光谱信号的信噪比和中心斜率与碘池温度和吸收程等有关。通过搭建稳频系统,得到碘的调制转移光谱信号,然后把激光频率锁定在碘的调制转移光谱谱线上。研究了温度、吸收长度对稳频精度的影响。

用置于环形谐振腔内的碘吸收室进行高灵敏调制转移饱和吸收激光光谱学研究

本文研究中获得了迄今为止612nm 处腔外碘吸收最高信噪比(S/N)的饱和吸收信号.文中讨论分析了主要影响因素,给出了所测得的谱线信号及调频信号的频谱.研究结果表明,应用此系统可实现612nm 激光器10^(-14)级的高精度稳定.

基于调制转移光谱多参量相关的激光稳频特性研究

基于调制转移光谱技术实现了分布式反馈半导体激光器在87RbD2线F=2→F΄=3上的频率锁定,并理论和实验研究了调制频率、解调相位、泵浦光偏振和磁场等多参量对调制转移光谱信号幅值、过零点斜率的影响,为选择和优化调制转移光谱稳频技术提供依据。研究表明,当泵浦光调制频率位于9~15 MHz,调节信号相位改变量在π/5附近时,可获得最佳的锁频信号。实验中,当调制频率为12.5 MHz,泵浦光与探测光偏振角为90o,外加磁场为5 Gs时,通过优化解调信号相位和比例积分微分控制参数,使调制转移光谱信号幅值及过零点斜率达到最佳,实现了分布式反馈半导体激光器的高精度频率锁定。锁频后的激光线宽约为1.6 MHz,频率稳定度小于1.75×10-9,该锁频激光系统可用作冷原子干涉的光源。

基于^(85)Rb 5S_(1/2)→6P_(3/2)的小型超稳铷原子光频标

传统的铷原子钟主要是工作在微波频段,系统结构简单可靠,但受限于钟跃迁频率,其频率稳定度很难进入10^(-14)量级水平。利用^(85)Rb基态5S_(1/2)与第二激发态6P_(3/2)之间的跃迁作为钟跃迁,并结合高信噪比的调制转移谱稳频技术和高速环路锁定,直接将420nm激光输出频率稳定在铷原子的超精细跃迁谱线上,实现将传统的铷原子微波钟拓展到铷原子光钟。通过自评估的方法,得到该系统的秒级频率稳定度为1.6×10^(-14),接近微波钟的量子极限,与目前国际上最好的532nm碘分子光频标性能相当。

Studies on the interfacial charge transfer processes of nanocrystalline CdSe thin film electrodes by intensity modulated photocurrent spectroscopy

Interfacial charge transfer kinetics of the nanocrystalline CdSe thin film electrodes have been studied in sodium polysulfide solutions by intensity modulated photocurrent spectroscopy (IMPS). The interfacial direct and indirect charge transfer and recombination processes were analyzed in terms of the parameters: normalized steady state photocurrents and surface state lifetimes obtained by measuring the IMPS responses under different applied potentials and different solution concentrations. IMPS responses of polycrystalline CdSe thin film electrodes were also presented for comparison.

A novel method to measure the isotope shifts and hyperfine splittings of all ytterbium isotopes for a 399-nm transition

We report the experimental results on measuring the isotope shifts and hyperfine splittings of all ytterbium isotopes for a 399-nm transition by using a quite simple and novel method. It benefits from the advantages of the modulation transfer spectroscopy in an ytterbium hollow cathode lamp and the Doppler-free spectroscopy in a collimated ytterbium atomic beam. The key technique in this experiment is simultaneously measuring the frequency separations of the two spectra twice, and the separation difference between two measurements is solely determined by the well-defined frequency of an acousto-optics modulator. Compared with the most of previously reported experimental results, ours are more accurate and completed, which will provide the useful information for developing a more accurate theoretical model to describe the interaction inside an ytterbium atom.

基于LabVIEW的光纤激光器稳频系统设计

本文利用工控机、NI数据采集卡、外围光路搭建激光稳频硬件系统,以调制转移光谱技术为基础,使用LabVIEW FPGA开发了一套单频光纤激光器数字稳频控制软件。基于调制转移光谱产生的伺服控制信号,通过采集误差信号,经PI处理后控制压电陶瓷伸缩,将780nm的激光频率锁定在铷原子的超精细跃迁谱线上。Allan方差结果显示,短期稳定度为1.52×10^(-11)@10s;长期稳定度优于1.56×10^(-11)@100000s,可连续运行20天以上。该数字稳频软件利用图形化编程语言,大大节约开发周期,操作界面直观简洁,方便用户分析处理。已成功应用于铷87喷泉钟系统中,且该稳频系统具有通用性,可应用于原子干涉仪、激光陀螺仪等精密测量领域。

应用于积分球冷原子钟的窄线宽激光稳频系统

通过调制转移光谱稳频的方式,将外腔半导体激光器频率锁定于^(87)Rb原子D_(2)线超精细跃迁5^(2)S_(1/2),F=2→5^(2)P_(3/2),F=3,使激光器线宽由自由运转的382.18 kHz压窄至稳频后的37.94 kHz。稳频后的窄线宽激光用于积分球冷原子钟的探测光,可以将激光频率噪声对原子钟短期稳定度的影响降低至5.6×10^(-14)τ^(-1/2)。