Domain pattern in ferroelectric triglycine sulphate using pyroelectric effect

A method to study domain structure in ferroelectrics, using pyroelectric effect is described. Variation of pyroelectric signal from the surface of a triglycine sulphate crystal plate has been studied by scanning the surface of the crystal with a low wattage He-Ne laser beam. The integrated pyroelectric signal is due to two components, namely, (1) the primary component arising out of the change in spontaneous polarization with temperature and (2) the delayed component arising out of the possible polarization reversal. The component of an electric field along the ferroelectric axis due to thermal hemisphere within the crystal plate formed by the laser beam has been calculated and shown to exceed coercive field, making polarization reversal possible. The delayed pyroelectric signal is a measure of polarization reversal within the patch illuminated and its observed variation over the surface yields information of the domain structure.     

Role of nanosecond processes in the formation of domains in ferroelectric crystals

The contribution from pyroelectric and photovoltaic effects to the formation of light-induced domains in crystals of oxide ferroelectrics of lithium niobate type upon irradiation by nanosecond focused laser beams is considered. It is established that inverted domains are formed in irradiated regions under the combined effect of generated pyroelectric and photovoltaic fields with a sharp increase in temperature. It is shown that the most stable domains are formed in lithium niobate samples containing Fe²⁺ and Fe³⁺ impurity ions.     

Optimized configuration of the pyroelectric sensor metal electrodes in the photopyroelectric technique

This article deals with the photopyroelectric (PPE) technique, a useful tool for optical spectroscopy and for measurement of thermal properties of condensed mater samples, in particular in the liquid state. It has been demonstrated here that, for constant laser power, the pyroelectric (PE) sensor response does not depend on the spatial distribution of the laser beam intensity. As a consequence of this, it follows that in the case of measurements in voltage mode, the signal amplitude is inversely proportional to the active area of the sensor. Then, if the active area is diminished, leaving the total area of the sensor constant, it is possible to increase the pyroelectric signal. On the basis of this result, a method is proposed to enhance the PPE signal measured in voltage mode by means of the optimization in the configuration of the sensor metal electrodes. It was experimentally demonstrated that using this improved technique, it is possible to increase up to ten times the amplitude of the signal without electrical noise rise.     

基于热释电探测器的重频脉冲激光诊断

摘以热释电探测器的工作原理为基础,研究了热释电探测器对重频脉冲激光的瞬态响应特性,建立了热释电探测器对单脉冲激光辐照响应的工作模型,分析了影响探测器频率特性的主要因素。根据材料和结构参数模拟计算了实际应用中的响应模型。设计了信号检测电路并对其进行计算仿事。完成了探测器的频率响应、脉宽响应等实验测量,验证了热释电探测器用于高重频、窄脉冲激光能量测量的可行性。     

基于热释电探测器的重频脉冲激光诊断(英文)

以热释电探测器的工作原理为基础,研究了热释电探测器对重频脉冲激光的瞬态响应特性,建立了热释电探测器对单脉冲激光辐照响应的工作模型,分析了影响探测器频率特性的主要因素。根据材料和结构参数模拟计算了实际应用中的响应模型。设计了信号检测电路并对其进行计算仿真。完成了探测器的频率响应、脉宽响应等实验测量,验证了热释电探测器用于高重频、窄脉冲激光能量测量的可行性。     

Submillimeter imaging with a pyroelectric TV camera

The use of a TV camera with a standard pyroelectric tube for imaging continuous submillimeter (submm) waves is described. The spectral sensitivity of such pyroelectric vidicon has been measured. The results of experiments on diffraction and interference using submm laser radiation are presented. For the first time, submm images of different objects have been obtained with the aid of a pyroelectric vidicon. It has been shown that a pyroelectric TV camera can be effectively employed in various laser studies as well as in submm imagery technique.     

The improved pyroelectric detectors for far-infrared laser interferometer measuring

In this paper, the application of the pyroelectric detectors for Far-Infrared laser diagnostics on TOKAMAK plasma is described. We discovered experimentally that the Fabry-Perot interference could affect the performance of the pyroelectric detectors (PED). The improved pyroelectric detector (IPD) was developed for FIR laser coheront measuring. Some designing considerations about the pyroelectric detectors used in high temperature plasma conditions are mentioned.     

双激光光源光吸收法甲烷浓度光纤监测仪

基于Lamber Beer定律,利用波长为1.33μm的脉冲InP/InGaAsP半导体激光器作为测量光源,用低损耗的光纤进行光信号的传输,并以钽酸锂热释电探测器作为光电转换器件,实现了一种可远距离监测甲烷浓度的仪器。该仪器主要由光纤传感系统、信号放大与处理系统和显示系统三部分组成。介绍了该仪器的基本结构与工作原理,讨论了其中的技术难点及其相应的解决方法。     

The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of a polymer-pyroelectric ceramic composite

The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of composites based on poly(vinylidene fluoride), vinylidene fluoride-tetrafluoroethylene copolymer (F-42), and pyroelectric ceramics of the lead zirconate titanate family with different structures is investigated. It is revealed that the pyroelectric coefficient of the composite is determined by the reorientation polarization and the mobility of domains in the pyroelectric ceramic phase, which depend on the homogeneous parameter of the spontaneous strain of the perovskite cell.     

Development of a small X-ray source using an ultraviolet laser and pyroelectric crystal

We investigate a miniaturized X-ray source using an ultraviolet (UV) laser and a pyroelectric crystal and discuss potential applications in medicine. The UV laser is the fourth harmonic of a Nd:YAG laser with a wavelength of 266 nm, repetition rate of 10 Hz, and pulse energy of 40 mJ. The pyroelectric crystal is a LiNbO₃ cylinder of diameter 10 mm and length 6 mm. The prototype X-ray source we fabricated is an aluminum parallelepiped of dimensions 3 × 3 × 5 cm. The X-ray count rate of the X-ray source is maximized at approximately 1,400 cps for UV laser irradiation of approximately 5 min. After 30 min of irradiation by the UV laser, the temperature of the pyroelectric crystal rose from 295 K to 312 K. The principles of X-ray generation ensure that X-ray sources using UV lasers and pyroelectric crystals offer ample opportunity for miniaturization. We believe the X-ray source developed in this work is suitable for medical applications, although further study is needed to address points such as increasing the X-ray count rate and adjusting the temperature of the pyroelectric crystal.     

Pyroelectric properties of an antiferroelectric liquid crystal

The effects of temperature and applied voltage on the pyroelectric properties of an antiferroelectric liquid crystal are given. It has been found that the pyroelectric signal depends strongly on the bias voltage across the sample. The pyroelectric signal behaviour is interpreted with the aid of spontaneous polarization data and good agreement is found between the results from the pyroelectric and polarization techniques. The spontaneous polarization of the sample exhibits the temperature- and field-induced `Devil's staircase' behaviour, as predicted by the Ising model.     

一种漫反射式激光谷物水份检测系统

基于Kubelka Munk理论,利用波长为2.0μm的InGaAs/I连续波半导体激光器(功率:300～500mW)作测量光源,以LiTaO3热释电探测器作光电转换器件,以8031单片机作信号处理中心,设计了一种漫反射式谷物水份检测系统。该系统由光学接收与发射系统、信号放大与处理系统及显示系统三部分组成。介绍了系统的基本结构与工作原理,讨论了其中的技术难点及其相应的解决办法,给出了部分实验结果。     

High sensitivity HCN laser interferometer for plasma electron density measurements

This paper describes a high sensitivity 337 μm HCN laser interferometer for plasma electron density measurements. The plasma phase shift is transferred to a low frequency signal obtained by slightly shifting the frequency of the 337 μm radiation in the reference beam of the interferometer. The frequency shift is produced by diffracting the radiation of a cylindrical rotating blazed grating. A phase shift is deduced from the time variation of the zero crossings of the low frequency signal, giving a result which is independent of amplitude fluctuations. Using pyroelectric detectors, the interferometer has a time resolution of 100 μsec and a sensitivity of 10^-2 fringe.     

Transverse second-harmonic generation from disordered nonlinear crystals

We investigate the transverse second-harmonic generation in as grown strontium barium niobate (SBN) crystals with a random structure of anti-parallel ferroelectric domains. We consider both, single and counter-propagating pulse geometries. We investigate polarization properties of the second harmonic signal and discuss applications of this process for short pulses characterization. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

热释电红外探测器在安全防护系统中的应用研究

利用人体发出的红外线,通过热释电红外传感器的接收和放大,形成具有一定电压幅度的控制信号,用这一控制信号去触发语音录放电路工作,就可制成具有自动控制功能的热释电红外探测语音录放系统。电路采用最新热释电红外探测模块与语音录放模块设计,当有人出现在热释电红外探测模块的探测范围时,热释电红外传感器首先将接收到的红外辐射能转换成电能信号,再经内部电路放大、比较处理后输出控制信号,触发语音录放模块工作,播放事先录制好的语音内容,提醒人们注意。该系统电路简洁、成本低、抗干扰能力强、耐低温、免调试、工作稳定和使用方便。适宜于安装在变电所、高压开关柜和电力变压器等危及人身安全的处所使用。     

Comparison of ferroelectric domain delineation in triglycine sulphate by the etching technique and the pyroelectric laser technique. Application to the study of polarization reversal

It is shown that the well-known etch technique and the newly developed pyroelectric laser technique can reveal similar domains. However the latter technique is so fast that it appears as the best one to study problems such as nucleation and domain wall motion.

In the case of an alanine doped TGS crystal it is shown that domain wall motions started at a given nucleation field E₁ stop at some characteristic boundary lines in the crystal. To carry on the polarization reversal, we have to increase the electric field up to some higher value E₂ which is the minimum value of the nucleation field in the next area. Then a new domain is growing very rapidly by wall motions until the characteristic boundary lines of this area are reached. These lines are probably dislocation lines. It is shown that a direct side observation of domains is possible. Conical and cylindrical domains are clearly visible.     

The detection mechanism of LiTaO3 type II pyroelectric detectors.: III. The total pyroelectric effects

The contributions of the primary and secondary pyroelectric effects and that of the tertiary pyroelectric effect are both considered in the discussion of the detection mechanism of type II pyroelectric detectors, and the total signal voltage and the voltage responsivity are given and analysed.     

Pyroelectric effect induced by the built-in field of the p-n junction in the quantum paraelectric PbTe: experimental study

We report here the first observation of a pyroelectric effect in a nonpolar semiconductor. This effect originates in the temperature-dependent electric dipole of the PbTe p-n junction. The junction was illuminated by a chopped CO(2) laser beam, and periodic and single-pulse pyroelectric signals were observed and measured as a function of temperature, reverse bias voltage, and chopper frequency. The measured pyroelectric coefficient is approximately 10(-3) microC/cm(2) K in the region of 40-80 K. The theoretical model describes quantitatively all experimental features. The time evolution of the temperature inside the junction region was reconstructed.     

多通道热释电IRFPA图像拼接采集系统

为了实现分辨率高的大规模热释电IRFPA探测器,设计了多路通道并行输出的读出电路。针对多路输出的热释电IRFPA探测器,依据热释电探测的时序要求,设计了图像拼接采集系统。利用外部驱动信号控制采集卡的触发及采样时钟,由斩波器同步信号判断热释电探测器的亮场及暗场信号。构造PC-DAQ虚拟仪器系统对多通道输出的热释电型IRFPA进行多路并行图像采集,并对每路图像信号进行亮、暗场判断后进行差分处理,通过软件拼接处理成一副完整的图像,最终在软件平台上显示。对实验室研制的160列120行双通道读出及320列120行四通道读出的热释电读出电路进行了图像采集实验,对于同样阵列大小的单通道读出探测器,双通道结构读出速度提高了1倍,四通道结构读出速度提高了3倍。通过采集成像实验验证了系统的可行性。     

Process control systems in laser materials processing

To obtain on-line information about the cutting and welding processes, optical sensors are integrated into the working head of a high-power CO₂ laser machining system. In order to detect the dynamic light or plasma intensity fluctuation during cutting and welding, these sensors provide the real-time signal of the metal vapour and plasma flame intensity in the wavelength range 200–1100nm. Simultaneously, the real-time intensity of the laser power is measured with a pyroelectric sensor. The aim is to analyse the transfer function of each process. With the knowledge of the transformation characteristics of the specific process, a closed-loop control is set up. Distinguishing between CW and pulsed processes, different control algorithms have been developed and tested. A control system based on microcontroller hardware and its theoretical background for failure detection are described.