基于中红外DFG光源的甲烷气体光谱检测方法研究

基于中红外光源的气体光谱检测是新的痕量气体监测与分析方法,在大气监测领域具有重要的应用。构建了一套基于中红外DFG光源的甲烷气体光谱检测系统。该系统以1 550 nm和1 060 nm波段可调谐半导体激光器作为基频光源,采用PPLN晶体作为差频非线性变频器件,实现了3.3 μm处的窄线宽可调谐中红外光源输出。实验结果表明,当PPLN晶体工作温度为99.5℃时,闲频光的输出功率为112 μW,差频转换效率达到1.246 mW/W2。晶体的温度接受带宽为4.3℃,泵浦光波长接受带宽为5.3 nm。在此基础上,分别利用直接吸收法和谐波检测法获得了3 028.751 cm-1处的甲烷气体吸收光谱和二次谐波检测信号。     

基于Gabor变换的TDLAS检测信号的降噪研究

可调谐二极管激光吸收光谱(TDLAS)技术结合波长调制光谱(WMS)技术是用于痕量气体检测的重要技术手段。通过锁相放大器进行谐波检测,对解调得到的二次谐波信号进行分析可获得气体吸收的信息。但由于二次谐波信号受到噪声的影响,降低了检测系统的精度和稳定性。为了提高TDLAS检测系统的信噪比(SNR),提出了一种基于Gabor变换对二次谐波信号进行数字滤波降噪的方法。以CH₄在1 653.72 nm处的吸收光谱为例,通过仿真和实验对该降噪方法的有效性进行了验证。仿真结果表明,通过Gabor变换对信噪比为0dB的二次谐波信号进行处理后,系统的信噪比可提高15.73 dB。实验结果表明,基于Gabor变换进行降噪处理后,CH₄浓度在0.001%～0.02%区间内与二次谐波峰值的线性相关系数r达到了0.996 59,且系统的检测精度和稳定性明显提高。     

基于可调谐激光吸收光谱的大气甲烷监测仪

可调谐二极管激光吸收光谱(TDLAS)技术利用二极管激光器波长调谐特性,获得被测气体的特征吸收光谱范围内的吸收光谱,从而对污染气体进行定性或者定量分析,这种方法不仅精度较高,选择性强而且响应速度快,已经被用于大气痕量气体监测以及工业控制。在对空气中的痕量气体进行检测中,由于气体浓度较低,需要和长吸收光程技术相结合。将可调谐二极管激光吸收光谱与经过108次反射后达到27 m光程的多次反射池相结合研制了用于地面环境空气中甲烷含量监测的便携式吸收光谱仪,并结合了用于微弱信号检测的二次谐波检测技术,从而达到了体积分数低于1×10-7的检测限,并利用不同体积分数的甲烷气体对系统进行了测试,得到了很好的测试结果。     

棱镜气室在光纤甲烷检测系统中的应用研究

棱镜气室相较于传统渐变折射率透镜(GRIN)气室在灵敏度调节性及抑制干涉噪声方面优势明显。基于比尔-朗伯(Beer-Lambert)定律在气体弱吸收时的近似表述,以大气环境为背景,利用背景扣除和谐波检测技术,实现了常压下甲烷不同体积分数水平(0~20%)的检测。依据实测的甲烷在不同体积分数时的直接吸收谱,结合现有分布反馈式激光二极管(DFB-LD)光源选择2ν3带的R5支(1648.212 nm)作为被测吸收峰。气体配置过程中的在线实验表明系统示值与体积分数变化间线性关系良好,而且系统的稳定性和动态响应特性理想。该系统可根据不同现场环境的甲烷体积分数水平,通过步进电机调节气室内有效吸收光程,动态调整系统灵敏度,可作为煤矿巷道或天然气管道沿线的瓦斯监测仪器。     

基于TDLAS-WMS的痕量甲烷气体检测仪

甲烷是一种无色、无味、易燃、易爆的气体,不仅造成煤矿作业的重大安全隐患,而且又是温室效应的重要气体之一,对于甲烷气体的监测具有极其重要的意义。采用混合可调谐二极管激光吸收光谱(TDLAS)与波长调制光谱(WMS)的检测技术,利用甲烷的2v3(第二泛频带)带R(3)支带吸收谱线,设计并研制出痕量甲烷气体检测仪。通过调谐系数-0.591 cm-1·K-1,采用改变DFB激光器工作温度的方式来获得甲烷在1.654 μm处的最佳吸收谱线。待DFB激光器激射中心谱线选择后,通过调节其注入电流幅值来获得合适的发光强度。同时,结合频率调制技术将待测信号频率移至高频区,减小1/f噪声。在光学结构方面,采用有效光程为76 m的herriott气室,确保对痕量甲烷气体进行检测。利用该痕量甲烷气体检测仪,在被测气体浓度为50～5 000 μmol·mol-1的范围内,对二次谐波信号进行了提取,并利用最小均方误差准则分别对气体浓度、信噪比的关系、谐波峰值信号与气体浓度的关系进行了线性拟合,最低检测限达到了1.4 μmol·mol-1。实验表明,谐波波形对称性良好,未观察到强度调制现象,消除强度调制等因素对谐波检测的影响。     

一种基于谐波检测技术的光纤甲烷气体传感器

甲烷是易燃易爆气体,是矿井瓦斯及天然气等多种气体燃料的主要成分.气体爆炸一直是困扰煤矿安全生产的重大难题,因此现场实时检测甲烷气体浓度对于工矿安全运行,人身安全有着至关重要的作用.基于甲烷气体近红外吸收的机理,研究了一种以DFB LD为光源的高灵敏度光谱吸收型光纤甲烷气体传感器.利用光源调制实现气体浓度的谐波检测,用二次谐波与一次谐波的比值来消除光路干扰.建立了谐波检测的数学模型,给出了甲烷气体的测量结果.利用光纤作为传光通道,使得探头可以与测量电?肥迪滞耆绺衾?增强了系统的安全性.     

一种差分吸收式光纤瓦斯传感系统

基于差分吸收法,研究了一种光纤瓦斯传感系统.采用双波长参考测量法,选取输出波长为1551nm的分布式反馈半导体激光器作为参考光源,输出波长为1 653nm的激光器作为甲烷气体的吸收峰处光源,通过改变甲烷气体吸收峰处激光器的输出波长,使其扫描到甲烷气体的吸收峰,通过比较吸收峰处和没有吸收峰处的光功率,测得甲烷气体浓度的分辨率达到0.038%.实验结果表明该系统的分辨率高、稳定性好、抗干扰能力强,可用于对煤矿瓦斯气体的检测.     

可调谐二极管吸收光谱痕量气体浓度算法的研究

基于可调谐二极管激光吸收光谱学的大气痕量气体在线监测分析仪具有高灵敏、快速响应和高选择性的特点。分析了可调谐二极管激光吸收光谱(TDLAS)二次谐波信号的特征,以高浓度谐波信号作为标准,采用线性最小二乘拟合的方法对谐波信号进行数值拟合,高精度的反演出了痕量气体浓度值。并对标准信号和检测信号之间的相关系数和浓度反演规律进行了研究。以甲烷气体的测量信号和浓度反演为例,验证了算法。     

基于多特征波长光谱分析的天然气泄漏遥测系统

为快速地、 大范围地对天然气管道进行泄漏监测,设计了基于静态傅里叶变换干涉系统的甲烷气体浓度遥测系统。 采用对准甲烷分子吸收峰的红外光源照射被测区域,再由聚光准直系统和干涉模块完成干涉条纹的获取。 最后,通过多特征波长光谱分析算法计算被测区域的浓度程长积,进而反演相应的甲烷浓度。 通过HITRAN光谱数据库选择了1.65 μm的主特征吸收峰,从而光源使用1.65 μm的DFB激光器。 为了在不增加系统硬件结构的基础上提高检测精度及稳定性,引入辅助波长求解吸光度比值,进而通过多特征波长比例运算的方法获得被测气体的浓度程长积。 实验针对泄漏速度恒定的标准甲烷液化气罐检测,采用PN1000型便携式甲烷检测仪的检测数据作为标准数据与本系统的测试数据进行对比,测试距离分别为100,200和500 m。 实验结果显示,甲烷浓度检测值在泄漏一段时间稳定后,系统检测值也基本保持稳定。 对100 m的检测距离而言,浓度程长积的检测误差小于1.0%。 随着测试距离的增大,检测误差也相应的增大,距离500 m的检测误差小于4.5%。 总之,在气体泄露稳定后系统检测误差均小于5.0%,满足野外天然气泄漏遥测要求,该方法采用差分思想,在求解吸光度比率的过程中将误差消除,降低了外界干扰造成的误差,从而提高系统的检测精度及稳定性。     

粒子群优化BP神经网络在甲烷检测中的应用

为了准确、快速地检测和预测甲烷气体的浓度,设计了基于红外差分吸收法的甲烷浓度检测系统.为了降低系统部件不稳定带来的影响,检测系统采用双气室结构,气室的输入和输出接口处通过渐变折射率透镜连接到传输光纤,以降低光强的损耗.系统对甲烷检测结果的平均误差为0.007 5.基于粒子群优化的误差反向传播神经网络算法构建了甲烷预测模型,以浓度在0.2%～2.0%范围内的甲烷气体为研究对象.在样本训练过程中,预测模型的精度达到10-4,实际输出值与期望值线性回归的相关系数为0.998 8,最大相对标准偏差为0.248%.实验结果表明,在甲烷浓度预测中,相对于误差反向传播神经网络预测模型,粒子群优化误差反向传播神经网络的预测性能更优.     

Five-hundred-milliwatts distributed-feedback diode laser emitting at 940 nm

A DFB laser emitting at a wavelength around 940 nm in a single longitudinal mode up to an output power of 500 mW with a side mode suppression ratio greater than 50 dB is presented. More than 4 nm tuning range was reached by varying the current between 100 and 800 mA. Up to a power of about 300 mW, the lateral far field revealed stable fundamental mode operation.     

Self-Frequency-Doubling Ytterbium Lasers

Ytterbium-doped self-frequency-doubling lasers offer high efficiency, tunable, visible and near-infrared, cw and pulsed operation from compact devices. We review the performance of ytterbium-doped yttrium aluminium borate (Yb:YAB) self-frequency-doubling lasers. Because of the detailed dynaMisc of the interaction of the nonlinear pulse shaping process for mode-locking or for Q-switching self-frequency-doubled lasers, we observe pulse lengthening in each process when frequency doubling is optimised, with high average output power. However, for continuous wave operation, the self-frequency doubling process may be optimised to give highly efficient, robust, widely-tunable output in the visible as well as fundamental output in the infrared.     

Lasing of a single crystal Nd fluoride fiber

We present laser action in a single crystal fluoride fiber obtained by the micro-pulling-down technique. The 700 μm diameter and 1 cm long Nd:LiYF₄ fiber was pumped by a beam shaped diode bar emitting at 806 nm. A peak power of 300 mW was achieved with a slope efficiency of 12%. When considering the pump power fraction absorbed by the laser mode, a slope efficiency of 37% was achieved. To the best of our knowledge, this is the first report of a Nd: LiYF₄ fiber laser.     

Suppression of Q-switching instabilities in broadened-waveguide monolithic mode-locked laser diodes

It is predicted theoretically that broadening the optical confinement layer in monolithic mode-locked semiconductor lasers may suppress Q-switching instability, by increasing the carrier transport time, and lead to emission of shorter, more stable optical pulses.     

GaInAsSb/AlGaAsSb lasers in the wavelength range between 2.73 μm and 2.93 μm

Compressively strained multiple quantum well lasers in the GaInAsSb/AlGaAsSb material system are reported. Indium concentrations between 40% and 47.5% were chosen for the GaInAsSb quantum wells. Compressive strains varied between 1.16% and 1.43%. The lasers worked continuous wave at room temperature up to a wavelength of 2.81 μm. For a laser with 2.93 μm wavelength continuous wave operation was found up to a temperature of −23°C. This laser worked in pulsed operation at 15°C.     

Optically pumped potassium laser

We present an optically pumped continuous wave potassium vapor laser operating in a single longitudinal and a single transverse mode at 770 nm. The measured value of the input power to the output power slope efficiency was 20%.     

A small scale, supersonic chemical oxygen-iodine laser

A supersonic chemical oxygen-iodine laser of 5 cm long active medium has been operated utilizing a simple sparger-type O₂(¹Δ) chemical generator and a medium size pumping system. A grid nozzle was used for iodine injection and supersonic expansion. 9 W of cw laser emission at 1315 nm were obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long periods make it a convenient tool for studying parameters important for high-power supersonic iodine lasers.     

Propagation parameters of the beam extracted from a diode pumped Nd:YAG ceramic slab laser with a hybrid stable–unstable resonator

We analyze the propagation properties of the beam extracted from a diode pumped ceramic Nd:YAG slab laser adopting a hybrid stable–unstable resonator. Such a resonator produces a beam characterized by an Hermite–Gauss mixture-like distribution in one transverse direction and a hard-edge diffracted distribution on the other transverse direction. The beam propagation parameters M_x² and M_y² are measured for different values of the diodes driving current. We obtain a beam parameter product smaller than 3 mm mrad in both transverse directions and in the whole range of powers, up to an extraction of 220 W in a QCW regime.     

Assignment of Fir Laser Lines of Fully Deuterated Dichloromethane

We have recently reported 16 new far-infrared laser emissions of CD₂Cl₂. While the overwhelming majority of the previously known FIR laser emissions of this molecule were polarized parallel to the polarization of the pump CO₂ line, 13 of our 16 new lines are polarized perpendicularly to the exciting CO₂ radiation. In principle, the presence of perpendicular/parallel emission pairs is extremely important for the assignment of laser transitions. In the present work we discuss the possible assignments of 16 far-infrared (FIR) laser emission pairs of CD₂Cl₂.     

Highly efficient optically pumped cesium vapor laser

We have demonstrated an optically pumped continuous wave Cs vapor laser with an input power to output power slope efficiency of 81%. The laser power was 0.35 W for an input power of 0.57 W, yielding an overall optical efficiency of 63%.