Optical frequency standard based on a single 40Ca+

Research on the development of the optical frequency standard based on trapped and cold 40 Ca+ with the 4s2S1/2-3d2D5/2 clock transition at 729nm is reported. A single calcium ion was trapped and laser cooled in the Paul trap and stay in trap for more than 15 days. The linewidth of a 729nm laser was reduced to less than 10Hz by locking to a cavity for longer than 50 hours uninterruptedly. The overall systematic uncertainty of the clock transition has been characterized to be better than 6.5×10 16 . The absolute frequency of the clock transition was measured at 10 15 level using an optical frequency comb referenced to a Hydrogen maser, which was calibrated to the SI second through the global positioning system (GPS). The frequency value was 411042129776393.0(1.6)Hz after the correction of the systematic shifts.     

Active optical clock based on four-level quantum system

Active optical clock,a new conception of atomic clock,has been proposed recently.In this work,we propose a scheme of active optical clock based on four-level quantum system.The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam.To three-level quantum system,they are mainly limited by light shift of pumping laser field.These limitations can be avoided effectively by applying the scheme proposed here.Rubidium atom four-level quantum system,as a typical example,is discussed.The population inversion between 6S 1/2 and 5P 3/2 states can be built up at a time scale of 10-6 s.With the mechanism of active optical clock,in which the cavity mode linewidth is much wider than that of the laser gain profile,it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory.An experimental configuration is designed to realize this active optical clock.     

Frequency Calibration and Stabilization of the Cooling Laser of Ytterbium Lattice Clock with Molecular Iodine Spectroscopy

In order to apply the frequency comparison among the different optical clocks, transportable optical clocks(TOCs) is suggested as a valuable tool. For transportable clocks, the key technique is how to lock the lasers involved in the whole system. In this paper, we carry out a new way to calibrate and lock the second stage cooling laser of the ytterbium lattice clock with molecular iodine spectroscopy. The locking spectral width of 556 nm laser can be narrowed to 195 kHz, which can be used for frequency control and the stabilization of the second stage cooling. So the new method will make the transportable optical clocks more compact and robust in the future.     

基于OOK体制的激光统一测控系统设计与实现

激光统一测控系统采用激光链路同时实现高速通信、高精度测距和时钟同步.为了实现激光统一测控系统,根据异步应答测距方法,设计研制了基于OOK体制的激光统一测控系统原理样机,样机包含两套激光模拟终端,分别向对方发送包含测量数据帧的激光调制信号,并记录发送测量数据帧和接收测量数据帧的本地钟时间,据此计算得到距离、钟差、相对频差的测量结果.样机有线对接试验表明,在码率为2.5 Gbit/s的双向激光通信条件下,测距随机误差为6.2 mm,测距系统误差为1.3 mm,钟差测量随机误差为27 ps,相对频差测量随机误差为2.7×10-13.该样机为激光统一测控设备的研制和应用提供了技术支撑.      

一种低噪声窄线宽光纤激光器

提出一种低噪声窄线宽结构的光纤激光器,经参数优化,光纤激光器线宽可以窄至0.8kHz以下;通过采用PID光电负反馈电路使弛豫振荡降低25dB,光源强度噪声平均降低5-10dB,对于不同的输入电流,光纤激光器在低频段的相对强度噪声保持稳定。     

窄线宽可调谐半导体激光器

研究了一种利用光栅弱耦合外腔改善可见光半导体激光器性能的方法,并对６５０ｎｍ半导体激光器进行了实验,外腔镜由一个闪耀光栅构成,通过转动光栅角度,获得了窄线宽单模激光输出,谱线宽度０．１ｐｍ,线宽压窄比达９８００,边模抑制比＞２０,并且在约２０ｎｍ的荧光谱宽基础上得到约５ｎｍ波长的连续调谐范围     

单频外腔半导体激光器的主动稳频

采用鉴频反馈电路控制外腔长，对长外腔单纵模半导体激光器进行主动稳频，获得线宽小于２００ｋＨｚ的稳定单频输出，在２ｈ内频率漂移小于２ＭＨｚ     

Frequency stabilization of Nd: YVO4 mini-laser using the third-harmonic detection

Via saturated absorption spectroscopy and the third-harmonic detection technique, the hyperfine spectra of ¹²⁷I₂ near 532 nm have been observed within the tuning range of a mini Nd︰YVO₄-KTP laser. The laser is frequency stabilized against one hyperfine structure (hfs) component of ¹²⁷I₂. The analysis of error signal shows that it is possible to realize a frequency stability of 3.0×10^-13 at 1 s average time.     

Rayleigh backscattering: a method to highly compress laser linewidth

Ultra-narrow linewidth laser with several hun- dred hertz at room temperature has attracted a great deal of attention in recent years and played a critical role in both optical sensing and communication fields. In this paper, a new method based on Rayleigh backscattering to highly compress the laser linewidth was proposed and demon- strated theoretically and experimentally. By theoretical analysis and simulation, Rayleigh backscattering can be collected in any waveguide structure and all wave bands, which could have a revolutionary impact on the field of laser. A single-longitudinal mode fiber ring laser with 130-Hz linewidth was achieved with self-injection feed- back structure at normal atmospheric temperature. The linewidth compression based on Rayleigh backscattering lies in the fact that laser linewidth after scattering is narrower than that of incident light in high Rayleigh scattering structure. The self-rejection feedback method expanding free spectra range of laser cavity simultaneously was used to further suppress the mode-hopping and stabilizing output. Experimental results showed that the laser linewidth can be easily narrowed to hundreds of hertz with side-mode suppression up to 75 dB. This agrees with the theoretical analysis and simulation results qualitatively.     

Active optical clock

This article presents the principles and techniques of active optical clock, a special laser combining the laser physics of one-atom laser, bad-cavity gas laser, super-cavity stabilized laser and optical atomic clock together. As a simple example, an active optical clock based on thermal strontium atomic beam shows a quantum-limited linewidth of 0.51 Hz, which is insensitive to laser cavity-length noise, and may surpass the recorded narrowest 6.7 Hz of Hg ion optical clock and 1.5 Hz of very recent optical lattice clock. The estimated 0.1 Hz one-second instability and 0.27 Hz uncertainty are limited only by the relativistic Doppler effect, and can be improved by cold atoms. Supported by the National Basic Research Program of China (Grant No. 2005CB724500) and National Natural Science Foundation of China (Grant No. 10874009     

用于光纤传感网的窄线宽多波长光纤光源研究

窄线宽多波长光纤光源是光纤传感系统中的重要光源,可同时为多路复用技术中的传感器阵列提供所需的多个工作波长．为此对多波长光纤光源的稳态输出进行了数值模拟,理论分析了未泵浦掺铒光纤长度对输出线宽的窄化作用．同时实验构建了一种带有单程反馈和线宽窄化机制的多波长光纤光源,测量分析了这2种机制以及激光腔输出耦合比对多波长输出结果的影响．实验实现功率谱不平坦度〈土3dB时,多波长个数可达27个,3dB线宽约0．06nm,波长在50GHz范围内整体连续可调．     

A novel differential velocity modulation laser spectroscopy

Experimental investigation of a novel differential velocity modulation laser spectroscopy is reported and demonstrated with the spectra of N⁺₂A²Π_m-X₁Σ⁺E Meinel system. The S/N ratio excesses 500︰1, about 60 times higher than that with the traditional non-differential technique. With this technique, we obtained the high-resolution electronic absorption spectra of A2Π-X²Σ⁺(1, 0) vibration-al band of CS⁺ for the first time. It is confirmed that this technique will be a powerful method and receive wide application in studies of new molecular ions.     

The v-v energy transfer of highly vibrationally excited states (II)

The vibrational energy transfer from highly vibrationally excited CO to H₂O molecules is studied by time-resolved Fourier transform infrared emission spectroscopy (TR FTIR). Following the 193 nm laser photolysis of CHBr₃ and O₂ the secondary reactions generate CO(v). The infrared emission of CO(v → v−1) is detected by TR FTIR. The excitation of H₂O molecules is not observed. By the method of the spectral simulation and the differential technique, 8 rate constants for CO(v)/H₂O system are obtained: (1.7 ±0.1), (3.4 ±0.2), (6.2 ±0.4), (8.0 ±1.0), (9.0 ±2.0), (12 ±3), (16 ±4) and (18 ±7) (10¹³cm³ · molecule^-1· s^-1). At least two reasons lead to the efficient energy transfer. One is the contributions of the rotational energy to the vibational energy defect and the other is the result of the complex collision. With the SSH andab initio calculations, the quenching mechanism of CO(v) by H₂O is suggested.     

面向媒体的粗粒度可重构架构层次化存储设计

为了优化粗粒度可重构架构REMUS-II(Reconfigurable Multimedia System 2)的数据流通路,使其能够完成高性能媒体解码,针对媒体算法的数据访问特征,对REMUS-II的片上存储与片外存储访问模块进行优化.片上存储通过二维数据传输和转置等访问模式进行优化,片上数据传输效率分别平均提高了69.6%和15.1%.片外存储通过块缓存设计优化参考帧访问,平均减少37%的外存访问时间.经过层次化存储设计,REMUS-II数据流可满足计算需求,在200MHz主频下实现H.264算法和MPEG2算法高级档次的1 920像素×1 080像素高清分辨率实时解码.     

基于延时零拍法的DFB光纤激光器线宽测量

DFB单频光纤激光器输出的超窄线宽作为光学系统中的一个重要参数需要进行准确的测定,因此,采用延时零拍法重点对1053 nm波长的DFB掺Yb3 光纤激光器的超窄线宽进行了测量,并且研究了差拍光电流谱线的输出特性.针对超窄线宽DFB光纤激光器输出的特点设计了相应的光电转换放大电路,测得1053 nm的DFB光纤激光器的线宽为31 kHz.该测量结果对于窄线宽DFB光纤激光器应用于光纤传感、光纤通信领域具有一定的指导意义.     

Stabilization of mini-Nd: YVO4 laser using I2 hyperfine transition

By using a diode-pumped Nd:YVO₄ / KTP intracavity frequency-doubling mini-laser and frequency modulation optical heterodyne spectroscopy, we have obtained spectrum of¹²⁷I₂ hyperfine structure near 532 nm. The laser frequency is locked to hyperfine transitions of I₂. The analysis of error servo signal demonstrates that the laser frequency stability can reach 10⁻¹² at 1 second average time.     

级联三能级系统超快调制光谱学频谱分辨率的研究

对级联三能级系统超快调制光谱学的光谱分辨率进行了研究，发现其对能级差的测量决定于光学跃迁的均匀增宽，在符合拍频条件时，能级差可超出激光线宽，其测量精度可达到与激光线宽同一数量级。     

全光纤激光器中光栅作为腔镜的特点研究

选用介质膜作谐振腔镜,光纤激光器就缺乏有效的选频机制,使得输出激光线宽较宽,纵模频率和输出功率不够稳定;而光纤光栅作为激光器的谐振腔镜,可以得到稳定的窄线宽激光输出.通过对光纤光栅的形成机理和布拉格光栅选频原理分析,得到双布拉格光纤光栅线型谐振腔的理论.光纤光栅谐振腔的长度与光纤光栅中心波长满足S=(2m-1)λmax...     

Measurement of aerosol optical extinction using diode laser cavity ringdown spectroscopy

Accurate measurement of optical extinction of atmospheric aerosols is important for quantifying the direct climate effects of aerosols. A portable cavity ringdown spectrometer utilizing a modulated multimode blue diode laser (linewidth ～0.2 nm) is developed to measure the aerosol optical extinction. Laboratory generated ammonia sulfate particles (<1 μm in diameter) are characterized, with good agreements between the experimental measurements and Mie theory calculations. An optical extinction detection sensitivity of 0.24 Mm-1 (1σ) is achieved. Measurements of ambient aerosols are also carried out. This study demonstrates the feasibility of a compact, multimode diode laser cavity ringdown spectrometer for sensitive measurements of the optical extinction of atmospheric aerosols.     

高分辨率双频激光回馈的位移测量方法

在分析双频激光回馈测量原理的基础上,提出了一种基于双频激光回馈原理的高精度位移测量方法,研究了双频激光回馈的基本现象并给出了理论依据,进一步在回馈光学系统基础上,对两路正交的光回馈条纹,利用电路进行细分处理:即5细分和4倍频电路相结合,细分产生的计数脉冲最后送入单片机进行计算及显示.采用可编程逻辑器件FPGA和单片机设计信号处理电路,利用FPGA实现4倍频细分,利用电阻链细分实现5细分.全部电路通过逻辑、时序仿真,验证了本方法的可行性.目前此系统可满足高精度位移测量的要求.