Calibration of laser frequency scan with an electro-optic modulator

An electro-optically modulated laser beam was used to excite the Yb1S0 (6s ) 2?3P1 (6 s 6 p ) transition. Fluorescence was recorded as the laser frequency was scanned across the transition. Each isotope generated multiple peaks in the spectrum separated by the modulation frequency that permitted the frequency scan to be calibrated. The resulting isotope shifts agree well with existing data obtained with an interferometer to monitor the change in laser frequency. Electro-optic modulators have the advantages of being relatively inexpensive and simpler to operate than interferometers whose length must typically be stabilized with a laser whose wavelength is locked to an atomic transition.     

Injection laser with a functionally integrated frequency modulator based on spatially shifted quantum wells

A method for designing injection lasers with functionally integrated optical-radiation frequency modulators based on spatially shifted quantum wells in conduction and valence bands is proposed. The structure and variants of band diagrams of functionally integrated laser modulators are considered. It is shown that, in the proposed nanoheterostructures, maximum modulation frequencies are determined by the time of controlled relocation of charge-carrier density maxima in quantum domains and correspond to the terahertz range.     

A fiber optic phase modulator with an optical frequency shift of up to 20 GHz

A fiber optic phase modulator is described in which the phase of a light wave traveling in an optical fiber is modulated by a composite electromechanical resonator with Q≌1000. The instantaneous frequency of the wave at the modulator output varies according to a harmonic law. The interval of tuning of the instantaneous light wave frequency achieved in the experiment is 20 GHz, which corresponds to a modulation index of ≌10⁶. It is demonstrated that a maximum value of the frequency tuning range is determined by the elastic limit of the resonator material.     

一种高频热驱动脉冲管制冷机不稳定现象的研究

报道了一种高频驻波热声发动机驱动脉冲管制冷机的热声不稳定现象.通过实验对此种热声不稳定现象的产生原因进行了探讨,发现增加加热功率或缩短声压放大器可以抑制此种不稳定现象;理论方面主要通过快速傅立叶变换对不稳定的压力波形进行分析,对其产生原因进行了初步分析.     

Development of a high spectral resolution lidar based on confocal Fabry-Perot spectral filters

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5?GHz and a finesse of 50.7 (312) at 532?nm (1064?nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.     

Design and analysis of a phase modulator based on a metal-polymer-silicon hybrid plasmonic waveguide

A plasmonic-hybrid-waveguide-based optical phase modulator is proposed and analyzed. The field enhancement in the low-index high-nonlinear polymer layer provides nanoscale optical confinement and a fast optical modulation speed. At 2.5 V drive voltage, a π phase shift can be obtained for a 13-μm-long plasmonic waveguide. Because of its small capacitance and parasitic resistance, the modulation bandwidth can reach up to 100 GHz with a low power consumption of ～9 fJ/bit. The plasmonic waveguide is connected to a silicon wire waveguide via an adiabatic taper with a coupling efficiency of ～91%. The phase modulator can find potential applications in optical telecommunication and interconnects.     

Automated compensation of misalignment in phase retrieval based on a spatial light modulator

In this paper, the issue of misalignment in phase retrieval by means of optical linear filtering is discussed. The filtering setup is based on a 4f configuration with a spatial light modulator (SLM) as an active element, located in the Fourier domain. From the analysis, crucial parameters for the alignment procedure of the setup's optical axes and the center of the SLM are identified. Furthermore, a method to automatically as well as electronically compensate such effects by modifying the phase pattern displayed on the SLM is introduced. Experimental results are presented that validate the compensation approach.     

Demonstration of a DFB laser with an integrated electro-absorption modulator produced using a novel quantum-well intermixing technique

Bandgap engineering is used extensively in the telecommunications field. Quantum well intermixing (QWI) is a post-growth method of bandgap engineering that has been studied for the integration of photonic devices (Marsh et al., J. Vac. Sci. Technol. A16 (1998) 810). A novel method of QWI has been discovered that uses layers of indium phosphide grown by helium-plasma-assisted gas source molecular beam epitaxy, subsequently referred to as He*-InP, in combination with thermally induced QWI. The He*-InP has been shown to contain large numbers of defects that can act as fast non-radiative recombination centres. These can be used with the thermally induced QWI to produce regions with a larger bandgap and containing the fast, non-radiative defect centres. This novel intermixing process has been used to fabricate integrated distributed feedback lasers and electro-absorption modulators.     

Polarization states and output powers of a CO(2) laser with an electro-optic phase retarder

We study the power output and polarization state of a CO(2) laser that contains both passive polarization-sensitive elements (Brewster plates) and an active phase-retarding electro-optic modulator (CdTe crystal). The theoretical threshold condition (i.e., the retardation required to extinguish the laser) is obtained from a cavity round-trip Jones matrix. We show that adding extra Brewster plates may be counterproductive in that the required retardation voltage increases. We calculated the output power, which depends on the saturated gain properties of the active media, by iterative modeling, with the elliptically polarized light propagated repeatedly around the cavity. We compare the theory with results from a folded rf-excited waveguide CO(2) laser (Laser Ecosse Model CM3500). Theory and experiment are in fair agreement for low powers. As expected, at high powers there are extra difficulties in modeling the cavity behavior, probably because of distortions induced in and by the crystal.     

The dynamics of the response of an electro-optic cell based on a nematic layer with controlled surface anchoring

We investigate the electrooptical characteristics of a cell based on a nematic liquid crystal layer controlled with the use of modification of the surface anchoring by an ionic surfactant. The inverse mode of the effect is used with the nematic oriented homeotropically in the initial state and transferring to the hybrid homeoplanar structure in an applied dc electric field. We consider the applied voltage dependences of the dynamic parameters of the optical response.     

Photonic full-range phase shifter with simultaneous tunable frequency multiplying capability based on a DMZM

In this paper, a novel microwave photonic full-range phase shifter with simultaneous frequency-multiplying capability is proposed. The main device is a dual-drive Mach–Zehnder modulator (DMZM) embedded in a Sagnac loop. Under the assistance of two electrical phase shifters (EPS) and a following polarizer (Pol), the optical carrier is eliminated with desired phase tunable carrier-suppressed double-sideband (CS-DSB) signal reserved. So after photoelectric conversion, the frequency-multiplied phase tunable signals are generated. The frequency multiplication factor (FMF) switching and phase tuning operation of multiplied signals can be achieved easily by adjusting the corresponding EPS. The simulation results show that the proposed structure driven by a 10?GHz RF signal can generate a frequency-doubled signal (20?GHz) or frequency-quadrupled signal (40?GHz) that features full-phase tunable range and flat power response. What is more, the proposed phase shifter has a relatively good robustness to the non-ideal factors, large frequency operation range and good frequency tunable capability.     

Capillary electrophoresis with an integrated on-capillary tubular detector based on a carbon sol-gel-derived platform

An integrated on-capillary tubular electrochemical detector for capillary electrophoresis systems has been fabricated based on sol-gel technique. It consists of a sol-gel carbon composite tubular electrode attached permanently onto the outlet of the separation capillary. The device greatly eases the setting up of capillary electrophoresis with electrochemical detection (CEEC) as it makes possible electrode/capillary alignment without the aid of a micromanipulator since this integrated unit can be simply immersed in the CE separation buffer in an ordinary three-electrode stationary cell. To improve analytical performance of the integrated unit, the external wall of the exit capillary was etched with HF after the polyimide coating of the capillary had been removed. Influences of the working electrode length and the wall thickness at the outlet of capillary on the separation efficiency and amperometric sensitivity were assessed and optimized. The practical applicability of this configuration is demonstrated with the detection of both catecholamines and carbohydrates. The advantages, namely, versatility, convenience, ease of operation, and low-cost, of the new design combined with an excellent performance lead to high stability and low detection limits.     

38-GHz relativistic backward-wave tube based on a modulator with an inductive energy accumulator and a semiconductor current interrupter

The results of an investigation of a 38-GHz relativistic backward-wave tube with an output power up to 40 MW are presented. An electron-beam injector based on a 5-ns high-current pulsed periodic modulator with an inductive energy accumulator and a semiconductor current interrupter is used for the first time in experiments. Pis’ma Zh. Tekh. Fiz. 25, 89–95 (May 12, 1999)     

基于生物发光的高灵敏度ATP自动测试系统研究

针对高灵敏度、宽响应范围及自动检测三磷酸腺苷(ATP)的需求,设计了一种基于生物发光原理的ATP检测系统.系统采用自动加样技术,在发光反应的同时开始记录光强,使仪表检测自动化,且提高检测灵敏度;在优化光电检测单元设计和减小杂散光及电磁干扰的同时,提高荧光检测效率;通过电路和数据处理算法优化提高仪表检测范围.以浓度为10-15～10-6 M范围内的标准ATP溶液进行了实验,结果表明仪表测量光强与ATP实际浓度相关系数为0.974,检测范围达9个数量级.与市场相关仪器相比,该系统具有自动化测试,性能和灵敏度高、响应范围宽的特点,在ATP测量以及相关领域如细菌测量、毒性测试及卫生状况检测等方面具有广泛的应用前景.     

A note on a study of an integrated inventory with controllable lead time

Pan and Yang (Pan, C.H. and Yang, J.S., 2002. A study of an integrated inventory with controllable lead time. International Journal of Production Research, 40 (5), 1263–1273.) proposed the paper about integrated inventory with controllable lead time. The vendor produces the item in the quantity of mQ, and the purchaser would receive it in m lots, with which each having a quantity of Q. In practice, the vendor manufactures the product in the quantity of mQ with a finite production rate P at one set-up. Based on the practical fact, a modified model is proposed in this note. The proposed model takes the crashing set-up time into account. Numerical examples are presented to illustrate the procedures and results of the proposed algorithm. The modified model is shown to provide lower total costs and shorter lead time compared with those of Pan and Yang.     

Radiograph X-ray source based on interaction of femtosecond laser pulse with solid-state targets in an air medium

We study the charcteristics of X-ray radiation of a laser plasma generated in the interaction of a femtosecond pulse with solid targets in an air medium and conside the possibility of using it for radiography. We show that the mechanism for generating X-ray radiation in the interaction of short, powerful laser pulses with solid targets in a gas atmosphere is related to the generation of fast electrons in the gas breakdown region. We prove experimentally that under such conditions, even under relatively low laser radiation densities <10¹⁵ W/cm², a copper target quite effectively emits photons with energies of up to 10 keV. We measure the spectrum of such an X-ray source containing the expressed Cu K_α and Cu K_β lines and moderate bremsstrahlung. We demonstrate that the source can be used to obtain micron-resolution absorption images of low-contrast objects in an air medium, and in the same way, open possibilities for studies of medical-biological objects in vivo.     

Numerical fatigue life analysis of a high frequency mechanical impact treated industrial component based on damage mechanics models

After post weld treatment with high frequency mechanical impact (HFMI) treatment of welds, a significant increase of fatigue life (up to a factor of 10) can be achieved. During the last years numerous experimental tests of welded joints with simple geometry under constant amplitude loading have been performed to quantify the positive effect of high frequency mechanical impact treatment. Due to the lack of methods for the prediction of the high frequency mechanical impact benefits, a widespread use of this process is not the case yet. Furthermore, it is still not clear if the results of these fatigue tests can be transferred to complex geometries and complex loading conditions such as in industrial applications. Therefore, an approach to assess the fatigue life of complex welded structures under variable amplitude loading was developed. For this purpose, high frequency mechanical impact treatment and fatigue load of simple welded specimen made of S690QL steel were simulated with finite element analysis (FEA) firstly. Then, the needed damage parameters for the fatigue life correlation were evaluated from the finite element post‐processing. The calculated life time to crack initiation was in good agreement with the experimental fatigue test results. In the next step, this procedure was implemented on a welded arm of an evacuator of type EW180B of the company Volvo Construction Equipment made of S700MC. The variable amplitude load measured under real service condition was transferred to single constant amplitude load cycles using a rainflow‐counting algorithm. By simulation and damage mechanics evaluation of each load cycle the total damage sum could be calculated and compared with the experimental results from Volvo Construction Equipment.     

Complications to optical measurements using a laser with an unstable resonator: a case study on laser-induced incandescence of soot

Temporal behavior of pulses from a Q-switched Nd:YAG laser with an unstable resonator can vary significantly with radial position in the beam. Our laser provides pulses with position-dependent durations spanning 8-11.5 ns at 1064 nm and 7-10 ns at 532 nm. Pulses emerge first and have the longest duration at the center of the beam; they are shorter (by up to 4 ns) and increasingly delayed (by up to 10 ns) with increasing radial distance from the center. This behavior can have a dramatic effect on time-sensitive experiments, such as laser-induced incandescence of soot, if not taken into account.     

The influence of the absolute phase of a short light pulse on the third harmonic generation in an optically thin nonlinear layer

The third harmonic generation dynamics and the response spectrum of an optically thin layer of a medium possessing cubic nonlinearity depend on the absolute phase of a short light pulse with a small (～2%) detuning of the carrier frequency from that of the linear oscillator in the medium. The results of computer simulation show that a relatively small change in the absolute phase can result in a two-fold increase in the amplitude of the response pulse generated at the triple frequency.     

SAW filters with high stopband rejection based on a cascadeconnection of selective elements

To achieve a high stopband rejection in surface acoustic wave (SAW) filters a construction that includes a cascade of some elements (interdigital transducers (IDT) and multistrip couplers (MSC)) is used. In this case each element has to maintain a comparatively low frequency selectivity, and this permits a simple model and a high-speed calculation process to be employed for its design. The proposed constructions have an apodized transducer with a metal coating instead of a passive electrode region as the input IDT and broadband withdrawal weighted unapodized transducer as the output IDT. One or two group-type multistrip couplers (MSC) provide an additional frequency selectivity. The original synthesis algorithms have been developed for design of IDT and MSC structure