1．5μm波段连续单频光纤激光器的研究进展

连续单频光纤激光器在光纤通信、光纤传感、引力波探测、激光雷达、非线性频率转换、光谱学等领域有着广泛的应用前景,发展十分迅速．近20年来,1．5μm波段连续单频光纤激光性能不断提高,如激光线宽从兆赫兹到千赫兹、功率从毫瓦到近百瓦量级,但激光器的噪声抑制、放大线宽展宽、输出功率等仍有待进一步研究．本文回顾了获得1．5μm波段连续单频激光输出的关键技术,总结了本课题组基于磷酸盐玻璃光纤短腔Bragg反射（DBR）结构实现1．5μm波段连续单频光纤激光性能,以及单频激光功率放大的研究进展．     

Natural gas pipeline leak detector based on NIR diode laser absorption spectroscopy

The paper reports on the development of an integrated natural gas pipeline leak detector based on diode laser absorption spectroscopy. The detector transmits a 1.653 microm DFB diode laser with 10 mW and detects a fraction of the backscatter reflected from the topographic targets. To eliminate the effect of topographic scatter targets, a ratio detection technique was used. Wavelength modulation and harmonic detection were used to improve the detection sensitivity. The experimental detection limit is 50 ppmm, remote detection for a distance up to 20 m away topographic scatter target is demonstrated. Using a known simulative leak pipe, minimum detectable pipe leak flux is less than 10 ml/min.     

钙离子体系的振动双共振控制

研究了钙离子振荡体系在高、低两种不同频率信号作用下所产生的振动双共振(VBR)及其控制方法.结果表明:系统对低频信号响应的幅值随高频信号振幅的变化产生了振动双共振现象,并且低频信号的频率越低,振幅越大,系统通过振动双共振对微弱低频信号的放大倍数越大.体系离霍普夫(Hopf)分岔点的距离越近(控制参数域值越小),体系发生振动双共振所需要的最大高频信号幅值越往大的方向漂移,同时体系振动双共振的强度越小.细胞内钙波形成过程中的反馈机制对体系振动双共振的增强和减弱起着重要的作用,即正反馈机制对体系振动双共振强度起增强的作用,而负反馈机制却起减弱的作用.另外,体系中引入噪音所产生的随机共振不仅削弱振动双共振的强度而且还影响振动峰的个数,也发现存在极限噪音强度使体系产生不同的振荡行为,极限噪音强度之下,体系产生VBR现象,而极限噪音强度之上,体系则发生单峰振荡共振现象.     

Analysis of wave packet motion in frequency and time domain: oxazine 1

Wave packet motion in the laser dye oxazine 1 in methanol is investigated by spectrally resolved transient absorption spectroscopy. The spectral range of 600-690 nm was accessible by amplified broadband probe pulses covering the overlap region of ground-state bleach and stimulated emission signal. The influence of vibrational wave packets on the optical signal is analyzed in the frequency domain and the time domain. For the analysis in the frequency domain an algorithm is presented that accounts for interference effects of neighbored vibrational modes. By this method amplitude, phase and decay time of vibrational modes are retrieved as a function of probe wavelength and distortions due to neighbored modes are reduced. The analysis of the data in the time domain yields complementary information on the intensity, central wavelength, and spectral width of the optical bleach spectrum due to wave packet motion.     

Signal transduction in a coupled hormone system: selective explicit internal signal stochastic resonance and its control

Cooperative interactions of signal transduction and environmental noise are investigated with a coupled hormone system, in which selective explicit internal signal stochastic resonance (EISSR) is observed. More specifically, the large peak of a period-2 oscillation (i.e., a strong signal) is greatly amplified by the environmental noise while the small peak (i.e., a weak signal) does not exhibit cooperative interactions with noise. The EISSR phenomenon could be controlled by adjusting the frequency or amplitude of an external signal and a critical amplitude for external signal is found. Significantly, the maximal signal-to-noise ratio increases almost linearly with the increment of control parameter, despite that the magnitude of the large peak is decreased. In addition, the noise does not alter the fundamental frequencies of the strong signal and the weak signal, which implicates that the system can keep its intrinsic oscillatory state and resist the effect of environmental fluctuations.     

一种有效提取弱信号的新方法

随机共振 ( Stochastic Resonance,简称 SR)最初由 Benzi[1] 于 1 981年提出 ,并在气象学领域中得到了成功的应用 .根据随机共振理论 ,通过加噪声可在某一“共振”点处大幅度提高信号的信噪比 .这种方法也已成功地应用于方波脉冲信号的恢复 [2 ] ,但在化学信号中的应用尚属空白 .我们首次将这种方法用于化学弱信号的检测 ,并在简单喇曼谱图的解析中获得成功 [3 ] .但是 ,加噪声的方法作为一种有效的信号分析手段还显得很不成熟 .具体表现为处理过程较繁 ,分析信号的峰位偏移明显 ,而且结果在一定程度上要依赖人为判断来决定 [3 ] .　　在…     

一种有效提取微弱信号的新方法

根据小波变换能进行时频局部化分析的特性,本文提出一种用小波分段分析处理信号的方法。对任意长度的信号数据,在不增减信号点的情况下,提高分析信号的信噪比,有效地从信号中提取有用信息。将它应用于微弱信号检测,效果满意。     

Microgravimetric lectin biosensor based on signal amplification using carbohydrate-stabilized gold nanoparticles

A highly sensitive microgravimetric lectin biosensor has been developed using carbohydrate-stabilized Au nanoparticles as a signal amplifier; mannose-stabilized Au nanoparticles formed a sandwich-type complex with the target Con A specifically bound to a mannose-modified Au QCM electrode to give an amplified frequency response.     

Raman amplification spectroscopy using pulsed dye lasers

A picosecond laser system consisting of a mode-locked argon-ion laser synchronously pumping two dye lasers is used for studies of Raman amplification spectra. The two dye laser beams, one kept constant in frequency while the other is tunable, coincide in the Raman sample. Recording the gain or the loss in intensity of one of the lasers as a function of frequency difference produces the Raman spectrum. Good signal to noise ratios have been obtained for a variety of liquids and solids. Fluorescing samples can be studied in the Inverse Raman method where the loss on the higher frequency laser is monitored.     

Application of the stochastic resonance algorithm to the simultaneous quantitative determination of multiple weak peaks of ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry

The stochastic resonance algorithm (SRA) has been developed as a potential tool for amplifying and determining weak chromatographic peaks in recent years. However, the conventional SRA cannot be applied directly to ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC/TOFMS). The obstacle lies in the fact that the narrow peaks generated by UPLC contain high-frequency components which fall beyond the restrictions of the theory of stochastic resonance. Although there already exists an algorithm that allows a high-frequency weak signal to be detected, the sampling frequency of TOFMS is not fast enough to meet the requirement of the algorithm. Another problem is the depression of the weak peak of the compound with low concentration or weak detection response, which prevents the simultaneous determination of multi-component UPLC/TOFMS peaks. In order to lower the frequencies of the peaks, an interpolation and re-scaling frequency stochastic resonance (IRSR) is proposed, which re-scales the peak frequencies via linear interpolating sample points numerically. The re-scaled UPLC/TOFMS peaks could then be amplified significantly. By introducing an external energy field upon the UPLC/TOFMS signals, the method of energy gain was developed to simultaneously amplify and determine weak peaks from multi-components. Subsequently, a multi-component stochastic resonance algorithm was constructed for the simultaneous quantitative determination of multiple weak UPLC/TOFMS peaks based on the two methods. The optimization of parameters was discussed in detail with simulated data sets, and the applicability of the algorithm was evaluated by quantitative analysis of three alkaloids in human plasma using UPLC/TOFMS. The new algorithm behaved well in the improvement of signal-to-noise (S/N) compared to several normally used peak enhancement methods, including the Savitzky-Golay filter, Whittaker-Eilers smoother and matched filtration.     

The Morse oscillator under time-dependent external fields

A method to solve the equations for the Morse oscillator under intense time-dependent external fields is presented. Exact analytical formulas for the dipole matrix elements are calculated by the use of the hypergeometric algebra. The continuum is described by an expansion using Laguerre functions. The full algorithm for the calculation of wave functions can be controlled by the convergence of series and by the errors of a first order integration method. We apply our technique to the selective preparation of high overtones by femtosecond laser pulses. The population of the target state is optimized as a function of the intensity and frequency. Introducing a second simultaneous laser, we study the effects of relative frequency and phase over the target state population and dissociation channels. The calculations exhibit a rich interference pattern showing the enhancement and the suppression of the target population by varying the laser parameters.     

Stochastic resonance algorithm applied to quantitative analysis for weak liquid chromatographic signal of pyrene in water samples

The phenomenon of stochastic resonance (SR), which was discovered in recent years, rendered an entirely new way for the detection of weak signals, and it has been widely studied in many different science fields. This phenomenon is manifest in nonlinear systems whereby a weak signal can be amplified when the noise, signal and nonlinear system attain the proper cooperation. The introduced algorithm was employed to detect pyrene in drinking water samples with solid-phase extraction–liquid chromatography. The weak chromatographic peak of the analyte was amplified significantly, and the profiles of the peaks were also satisfactory. The limit of detection and the limit of quantification were improved from 0.022?ng?mL^?1 and 0.08?ng?mL^?1 to 0.004?ng?mL^?1 and 0.01?ng?mL^?1, respectively. The results showed an excellent quantitative relationship between concentrations and chromatographic responses. It is expected that the SR will be an effective tool to detect weak chromatographic peaks quantitatively in trace analysis.     

A Simple and Highly Sensitive Electrochemical Biosensor for microRNA Detection Using Target‐Assisted Isothermal Exponential Amplification Reaction

A simple and highly sensitive electrochemical biosensor for microRNA (miRNA) detection was successfully developed by integrating a target‐assisted isothermal exponential amplification reaction (EXPAR) with enzyme‐amplified electrochemical readout. The binding of target miRNA with the immobilized linear DNA template generated a part duplex and triggered primer extension reaction to form a double‐stranded DNA. Then one of the DNA strands was cleaved by nicking endonuclease and extended again. The short fragments with the same sequence as the target miRNA except for the replacement of uridines and ribonucleotides with thymines and deoxyribonucleotides could be displaced and released. Hybridization of these released DNA fragments with other amplification templates and their extension on the templates led to target exponential amplification. Integrating with enzyme‐amplified electrochemical readout, the electrochemical signal decreases with the increasing target microRNA concentration. The method could detect miRNA down to 98.9 fM with a linear range from 100 fM to 10 nM. The fabrication and binding processes were characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The specificity of the method allowed single‐nucleotide difference between miRNA family members to be discriminated. The established biosensor displayed excellent analytical performance toward miRNA detection and might present a powerful and convenient tool for biomedical research and clinic diagnostic application.     

自适应随机共振算法用于微弱信号检测

我们[1] 曾将随机共振方法应用于化学弱信号的检测 ,并提出了一种只利用测量信号本身所包含噪声的协作效应来检测化学弱信号的新方法 [2 ] ,即通过连续变化系统自身的稳态参数来实现共振 .在以往工作中 ,对输出结果的表征也只是将输出与已知结果进行比较 ,通过对输出的随时监控来判断是否得到最优结果 ,因而不能实现微弱信号的自适应检测 .这无疑也限制了此方法的实际应用 .本文在以上工作的基础上 ,研究了双稳系统的输出特性 ,提出了一种自适应随机共振算法 ,即基于双稳系统的系统输出可以通过调节系统自身的稳态参数达到共振 ,从而在连续…     

Phase control over decaying molecular states in intense laser pulses

A time-dependent approach to study phase control over molecular photoabsorption, provided by intense laser pulses, is elaborate. The method allows for the decay linewidth of molecular states and frequency bandwidth of the controlling laser field, and can be applied in weak and strong laser fields where the perturbation theory is invalid. It is shown that a frequency mismatch between the fundamental laser wave and its third harmonic can destroy control. For the example of the one-photon versus three-photon control a simple picture of interference from two monochromatic absorption pathways is not enough to explain phase control and one needs to consider a nonlinear temporal interference of multiquantum transitions. In the perturbation-theory limit an elegant generalization of the famous Shapiro-Hepburn-Brumer equation for the one-photon versus three-photon control is derived. Various numerical calculations illustrate the dependence of phase control on molecular linewidth, fundamental laser wavelength, pulse duration, and peak intensity. It is obtained, that the one-photon versus three-photon control is productive if the molecular state populations, individually produced by each laser wave, have beats of approximately the same frequency. The calculations demonstrate that an enough intense optical pulse can suppress molecular decay and may be used in order to keep stable the state population of a decaying molecule for a long time. The available experimental results for the one-photon versus three-photon control over simple and large polyatomic molecules are analyzed and recommendations for the experimental improvement of control are formulated.     

MALDI-MS imaging of features smaller than the size of the laser beam

The feasibility of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging of features smaller than the laser beam size has been demonstrated. The method involves the complete ablation of the MALDI matrix coating the sample at each sample position and moving the sample target a distance less than the diameter of the laser beam before repeating the process. In the limit of complete sample ablation, acquiring signal from adjacent positions spaced by distances smaller than the sample probe enhances image resolution as the measured analyte signal only arises from the overlap of the laser beam size and the non-ablated sample surface. Image acquisition of features smaller than the laser beam size has been demonstrated with peptide standards deposited on electron microscopy calibration grids and with neuropeptides originating from single cells. The presented MS imaging technique enables approximately 25 microm imaging spatial resolution using commercial MALDI mass spectrometers having irregular laser beam sizes of several hundred micron diameters. With appropriate sampling, the size of the laser beam is not a strict barrier to the attainable MALDI-MS imaging resolution.     

Efficient method for the calculation of time- and frequency-resolved four-wave mixing signals and its application to photon-echo spectroscopy

An efficient method has been developed for the calculation of third-order time- and frequency-resolved optical signals. To obtain the general four-wave mixing signal, seven auxiliary density matrices have to be propagated in time. For the special cases of two-pulse photon-echo and transient-grating signals, two or three density matrices, respectively, are required. The method is limited to weak laser fields (it is thus valid within the third-order perturbation theory) but allows for any pulse durations and automatically accounts for pulse-overlap effects. To illustrate the method, we present the explicit derivation of the three-pulse photon-echo signal. Any other third-order optical signal can be calculated in the same manner. As an example, two- and three-pulse photon-echo and transient-grating signals for a weakly damped displaced harmonic oscillator have been calculated.     

Mass spectrometry signal amplification for ultrasensitive glycoprotein detection using gold nanoparticle as mass tag combined with boronic acid based isolation strategy

We describe a novel method for rapid and ultrasensitive detection of intact glycoproteins without enzymatic pretreatment which was commonly used in proteomic research. This method is based on using gold nanoparticle (AuNP) as signal tag in laser desorption/ionization mass spectrometry (LDI-MS) analysis combined with boronic acid assisted isolation strategy. Briefly speaking, target glycoproteins were firstly isolated from sample solution with boronic acid functionalized magnetic microparticles, and then the surface modified gold nanoparticles were added to covalently bind to the glycoproteins. After that, these AuNP tagged glycoproteins were eluted from magnetic microparticles and applied to LDI-MS analysis. The mass signal of AuNP rather than that of glycoprotein was detected and recorded in this strategy. Through data processing of different standard glycoproteins, we have demonstrated that the signal of AuNP could be used to quantitatively represent glycoprotein. This method allows femtomolar detection of intact glycoproteins. We believe that the successful validation of this method on three different kinds of glycoproteins suggests the potential use for tracking trace amount of target glycoproteins in real biological samples in the near future.     

Amplified electrochemiluminescence detection of nucleic acids by hairpin probe-based isothermal amplification

Here, we present a straightforward method for isothermal amplified detection of nucleic acids. In this proof-of-concept study, a specific DNA sequence is amplified through hairpin probe-based isothermal strand-displacement polymerization reaction and then detected via a sensitive and commercially available ECL detection platform. Results show that the DNA sequence derived from the Listeria monocytogenes hly gene can be detected down to 10 pM in solution, together with correlation of the detected signal with the initial concentration of target DNA. Moreover, the designed stem-loop structured hairpin probe shows single-base variation differentiating ability. Considering the superior sensitivity and specificity, as well as the simple-to-implement features, the developed assay demonstrates a great potential of becoming a first-line tool for quantitative analysis of nucleic acids for biomedical research.     

A ligation-triggered DNAzyme cascade for amplified fluorescence detection of biological small molecules with zero-background signal

Many types of fluorescent sensing systems have been reported for biological small molecules. Particularly, several methods have been developed for the recognition of ATP or NAD(+), but they only show moderate sensitivity, and they cannot discriminate either ATP or NAD(+) from their respective analogues. We have addressed these limitations and report here a dual strategy which combines split DNAzyme-based background reduction with catalytic and molecular beacon (CAMB)-based amplified detection to develop a ligation-triggered DNAzyme cascade, resulting in ultrahigh sensitivity. First, the 8-17 DNAzyme is split into two separate oligonucleotide fragments as the building blocks for the DNA ligation reaction, thereby providing a zero-background signal to improve overall sensitivity. Next, a CAMB strategy is further employed for amplified signal detection achieved through cycling and regenerating the DNAzyme to realize the true enzymatic multiple turnover (one enzyme catalyzes the cleavage of several substrates) of catalytic beacons. This combination of zero-background signal and signal amplification significantly improves the sensitivity of the sensing systems, resulting in detection limits of 100 and 50 pM for ATP and NAD(+), respectively, much lower than those of previously reported biosensors. Moreover, by taking advantage of the highly specific biomolecule-dependence of the DNA ligation reaction, the developed DNAzyme cascades show significantly high selectivity toward the target cofactor (ATP or NAD(+)), and the target biological small molecule can be distinguished from its analogues. Therefore, as a new and universal platform for the design of DNA ligation reaction-based sensing systems, this novel ligation-triggered DNAzyme cascade method may find a broad spectrum of applications in both environmental and biomedical fields.