超连续谱干涉方法测量古依相移

利用两束超连续光干涉得到的信号,测量了透镜焦点附近飞秒激光脉冲的古依(Gouy)相移。根据得到的光谱干涉信号,利用傅里叶变换得到相对相位值。激光光束在聚焦透镜后的束腰半径可以由成像方法测得。根据测量得到的激光光束束腰半径,用非线性拟合的方法得到了古依相移曲线,拟合曲线与实验结果符合得非常好。给出了古依相位在焦点前后1 mm区域内的移动量。

二次光栅在波前测量中的应用

采用一种特殊的二次光栅用于激光波前测量, 它对非零级衍射光束具有不同的聚焦效应, 其光栅线为圆弧型而非直线。导出了在会聚光束情况下的两平面成像在单一像平面上的距离关系, 实验上实现了二次光栅用于会聚光束的波前测量, 测量得到会聚光束具有较大的散焦(-2.93λ)和球差(1.34λ), 与该透镜引起波前的离焦像差理论理想值(-2.695λ)基本符合。该技术可以实现波前的高空间分辨力和高精度实时测量, 大大减少光学元件数量, 降低装置成本。由于大功率激光束的不稳定性, 其波前变化非常快, 所以该方法的实时性非

频率分辨光学开关法测量飞秒脉冲

阐述了频率分辨光学开关法测量飞秒脉冲的原理，详细分析了模式尺寸效应和非线性效应对飞秒脉冲测量的影响。构建了一台用于飞秒脉冲测量的二次谐波-频率分辨光学开关装置，利用该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。得到了飞秒脉冲的时间宽度及光谱宽度、电场及其相位在时域和频域的详细信息。谐振腔直接输出脉冲的时间宽度为56 fs，光谱宽度为27 nm，时间带宽积为0.686，算法中的最小误差为0.001792。脉冲压缩后的测量结果为27 fs，光谱宽度为92 nm，时间带宽积为1.27，算法误差为0.00

掺钕材料激光终态能级寿命测量

介绍了目前测量掺钕材料激光终态能级寿命的三种方法，通过对三种测量方法比较，采用间接法测量激光终态能级寿命相对简单易行。

Spectral hole-burning of Eu3+: Y2SiO5 crystal at 579.62 mm

By using an Ar+ ion laser, a tunable Rh 6G dye laser(Linewidth : 0.5 cm(-1)) and a Coherent 899-21 dye laser as light sources and using a monochromator and a phase-locking amplifier, the optical properties of Eu3+ : Y2SiO5 crystal were detected. Persistent spectral hole burning (PSHB) were also observed in (5)Do-(7)Fo transition in the crystal at the temperature of 16 K. For 15 mW dye laser (Wavelength : 579.62 nm) burning the crystal for 0.1 s a spectral hole with about 80 MHz hole width were detected and the hole can been keep for longer than 10 h.

Influence of growth pressure of a GaN buffer layer on the properties of MOCVD GaN

The influence of growth pressure of GaN buffer layer on the properties of MOCVD GaN on alpha-Al2O3 has been investigated with the aid of a home-made in situ laser reflectometry measurement system. The results obtained with in situ measurements and scanning electron microscope show that with the increase in deposition pressure of buffer layer, the nuclei increase in size, which roughens the surface, and delays the coalescence of GaN nuclei. The optical and crystalline quality of GaN epilayer was improved when buffer layer was deposited at high pressure.

一种快速获取激光拼焊焊缝错配的新算法

本文讨论了基于视觉和结构光的焊缝形貌视觉检测系统的组成原理,针对拼板激光焊接工程中对焊缝检测的实时性要求高的特点,创新性地提出了一种快速获得焊缝错配缺陷的算法,主要步骤为:首先基于有关标准的检测指标阈值的设定,再次,针对在线提取到的图像进行预处理,主要是加窗和中值滤波;最后为Radon变换与错配检测。该算法能减少计算任务,从而快速获得错配检测指标。实验给出了不等厚板拼焊时的线性错配的数值和分布,同时验证了该算法的有效性。

Effect of polymeric properties on the operation of gel-type audio transducers.

A novel design of a moving-coil transducer coupled with a low-hardness elastomer called “the gel surround” is presented in this thesis. This device is termed a “gel-type audio transducer”. The gel-type audio transducer has been developed to overcome the problems that conventional loudspeakers have suffered - that is, the problem with size of the audio device against the quality of sound at low frequency range. Therefore the research work presented herein aims to develop the “gel-type audio transducer” as a next-generation audio transducer for miniaturized woofers. The gel-type audio transducer consists of the magnetic and coil-drive plate assembly, and these parts are coupled by the gel surround. The transducer is driven by the electromagnetic conversion mechanism (a moving-coil transducer) and its output driving force can be greatly enhanced by applying the novel mechanism of the gel surround especially at low frequency range, resulting in the enhanced acoustic efficiency. The transducer can be attached to a stiff and light panel with both the optimized impedance matching and minimised wave collisions. The performance of the gel-type audio transducer is greatly influenced by the mass of the magnetic assembly and compliance of the “gel surround”. But as the size of the magnet and its weight have to be kept minimal for a miniaturisation of the device, the focus of the research is on the effect of the of the gel surround. As a result, the effect of the gel surround, made of the RTV (room-temperature vulcanising) silicone elastomer, TPE (thermoplastic elastomer), and the silicone foam, on generation of the output driving force, the energy transfer from the transducer to a panel to which the transducer is attached, and sound radiation from the vibrating panel, was investigated. This effect was studied by COMSOL multiphysics (FE analysis) and thereby, the simulated results were verified by experiments such as the laser scanning measurement, DMA (dynamic mechanical analyzer), and the acoustic test. Successful development of prototypes of the gel-type audio transducers, with an enhanced acoustic efficiency at reduced size and weight, was achieved. Implementation of the transducers into consumer applications was also demonstrated with their commercial values.

Photoemission optogalvanic studies with copper as target electrode

Photoemission optogalvanaic (POG) effect has been observed by irradiating copper target electrode, in a nitrogen discharge cell using 1.06 μm and frequency doubled 532 nm Nd:YAG laser pulse. Measurement of the nature of the variation of POG signal strength with 532 nm laser fluence confirms the two photon induced photoelectric emission from copper. However, using 1.06 μm laser pulses thermally assisted photoemission is observed.

Ortsaufgelöster Nachweis von Elementspuren mittels Laserablation und Resonanzionisations-Massenspektrometrie und Untersuchungen zur Laserablations-Dynamik

Im Rahmen dieser Arbeit wurde eine neue Methode für einen empfindlichen und isotopenselektiven Elementnachweis entwickelt. Unter Einsatz von Laserablation geschieht der Probenaufschluß direkt und mit einer Ortsauflösung von unter 30 m. Hierzu wurde ein hochauflösendes MALDI-TOF-Massenspektrometer, welches üblicherweise für biochemische Fragestellungen eingesetzt wird, mit einem spektroskopischen Aufbau zur resonanten Ionisation von Elementgehalten modifiziert. Die Methode ist somit insbesondere für die Untersuchung von Elementspuren in Festkörperproben mit mikroskopischer Struktur konzipiert. Methodische Entwicklungsarbeiten wurden anhand des Elements Gadolinium durchgeführt. Durch die Verwendung gepulster Farbstofflaser stehen ausreichend hohe Laserfelder zur Verfügung, um unabhängig von Hyperfeinstruktur und Isotopieverschiebung Übergänge aller Isotope im Rahmen des Resonanzionisations-Verfahrens zu sättigen. Darauf konnte eine Isotopenverhältnisanalyse mit einer Genauigkeit im Prozentbereich verwirklicht werden. Verschiedene Anregungsleitern wurden untersucht, und mit elementspezifischen Resonanzüberhöhungen bis zu zwei Größenordnungen über dem nicht-resonant gebildeten Untergrund konnte eine Nachweiseffizienz von über 10-4 (entsprechend sub-fg/g-Niveau) erzielt werden. Dazu wurden Simulationsrechnungen zum atomaren Sättigungsverhalten in starken resonanten Laserfeldern durchgeführt. Erste Anwendungen des Laserablationsverfahrens waren Proben kosmologischer Herkunft. Der physikalische Prozeß der Laserablation bei Metallen wurde unter Hochvakuum-Bedingung systematisch in Abhängigkeit der Laserfluenz untersucht. In der ablatierten Plasmaphase erwies sich der Neutralanteil als besonders geeignet für geschwindigkeitsselektive Laserionisations-Messungen. Eine bimodale Struktur wurde beobachtet, bestehend aus einer thermischen und einer schockwellen-induzierten Komponente. Der ionische Anteil der ablatierten Dampfphase konnte über variable elektrische Feldpulse untersucht werden. Laserablation unter Atmosphärenbedingung wurde an einem beschichteten Messingtarget untersucht. Dabei wurde die Entstehung von permanenten Oberflächenstrukturen beobachtet, welche sich durch Nichtgleichgewichts-Prozesse in der Dampfphase erklären lassen.

Analytical BER performance in differential n-PSK coherent transmission system influenced by equalization enhanced phase noise

Long-haul high speed optical transmission systems are significantly distorted by the interplay between the electronic chromatic dispersion (CD) equalization and the local oscillator (LO) laser phase noise, which leads to an effect of equalization enhanced phase noise (EEPN). The EEPN degrades the performance of optical communication systems severely with the increment of fiber dispersion, LO laser linewidth, symbol rate, and modulation format. In this paper, we present an analytical model for evaluating the performance of bit-error-rate (BER) versus signal-to-noise ratio (SNR) in the n-level phase shift keying (n-PSK) coherent transmission system employing differential carrier phase estimation (CPE), where the influence of EEPN is considered. Theoretical results based on this model have been investigated for the differential quadrature phase shift keying (DQPSK), the differential 8-PSK (D8PSK), and the differential 16-PSK (D16PSK) coherent transmission systems. The influence of EEPN on the BER performance in term of the fiber dispersion, the LO phase noise, the symbol rate, and the modulation format are analyzed in detail. The BER behaviors based on this analytical model achieve a good agreement with previously reported BER floors influenced by EEPN. Further simulations have also been carried out in the differential CPE considering EEPN. The results indicate that this analytical model can give an accurate prediction for the DQPSK system, and a leading-order approximation for the D8PSK and the D16PSK systems.