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1、利用可调激光二极管进行光谱调节年级：2011专业：光学工程学号：G111201008姓名：宦君工作单位：理波光电科技（无锡）有限公司摘要：Frequency-modulation spectroscopy is a powerful tool that can achieve high sensitivities with a relatively simple experimental setup. Tunable diode lasers, in particular, can make the setup even simpler because they provide a narro
2、w, tunable output that can be easily modulated. As new diode laser wavelengths become available the field of TDLAS (tunable diode laser absorption spectroscopy) will continue to grow rapidly, particularly when combined with nonlinear optical techniques that allow conversion of available wavelengths
3、to the blue,20 UV,21, 22 or far infrared.8调频光谱是一种强大的工具,可以用一个相对简单的实验装置获得高敏感性。可调谐二极管激光、特别是,可以使它的步骤更为简单,因为它们可以提供一个狭小的、可调的输出,并且可以很容易地调制。随着新型二极管激光波长变得可用 TDLAS 的领域(可调谐二极管激光吸收光谱)将继续快速增长,尤其是当结合非线性光学技术,允许转换可用的波长蓝、20、21、22 紫外线或远红外线 8引言Tunable diode lasers are ideal for optical spectroscopy because of their na
4、rrow linewidths, large tuning ranges and stable outputs. Because they are more compact and rugged than traditional spectroscopic optical sources, 可调谐激光二极管是理想的用于光谱学的一种器件，因为他们有着较窄的线宽，较大的调节范围和比较稳定的输出。因为相比较传统的光谱光源有着更小的体积并且更坚固。like Ti:Sapphire lasers, dye lasers, color-center lasers, hollow-cathode lamps
5、, and nonlinear systems (e.g. optical parametric oscillators), they have enabled spectroscopic methods to be used not only in laboratory environments but also in the real world. Applications of diode-laser spectroscopy include remote sensing, LIDAR, laser cooling and trapping of atoms,1 frequency st
6、andards,2 length standards,3 trace gas detection,4 and process monitoring.5像钛宝石激光器,染料激光器、激光、空心阴极灯色中心,和非线性系统(如光学参量振荡器),他们使光谱方法用于不仅在实验室环境的同时也在现实世界。应用程序的二极管激光光谱学包括遥感、激光雷达、激光冷却和俘获原子频率标准,1,2,3长度标准微量气体检测、4和过程监控5They can be used to monitor environmentally important species, such as methane, carbon dioxide,
7、 and water. In semiconductor manufacturing, they can be used for closed-loop control of deposition processes, including electron-beam, sputtering, molecular-beam epitaxy (MBE), and thermal evaporation, resulting in a significant increase in the yield of existing devices and making possible new and i
8、mproved ones. Indeed the field has grown so large that a review of the research journals reveals that it has developed its own acronym, TDLAS, which stands for Tunable Diode Laser Absorption Spectroscopy. 它们可以用来监控环境重要的物种,如甲烷、二氧化碳和水。在半导体制造,它们可以用于闭环控制沉积过程,包括电子束、溅射、分子束外延(MBE)和热蒸发,导致产量显著增加现有的设备和制造新的和改进的
9、可能。事实上应用领域变得如此巨大,回顾研究期刊,这表明它已经开发了自己的首字母缩略词,TDLAS,代表可调谐二极管激光吸收光谱。There is a wide variety of laser-spectroscopic techniques available to researchers.6 In this application note, we will focus on one particular technique, frequency-modulation spectroscopy, or FMS. FMS is a powerful technique that can ac
10、hieve a high signal-to-noise ratio with a relatively simple experimental setup. In a typical FMS experiment, the wavelength of a continuous-wave laser is modulated at a particular frequency. As the center wavelength is scanned across the atomic transition, the wavelength modulation is converted into
11、 amplitude modulation, giving rise to a modulation in the optical absorption of a sample at the same frequency. (See Figure 1 for a typical absorption line.) 研究人员有各种各样的激光光谱技术可用来研究。6在本文中,我们将关注一个特定的技术,调频光谱学,或FMS。FMS是一个功能强大的技术,可以实现高信噪比与一个相对简单的实验装置。在一个典型的FMS实验,连续波激光的波长调制在特定频率。为中心波长扫描整个原子跃迁,波长调制转换成调幅,逐步形
12、成一个调制的光学吸收的一个示例相同的频率。(请参见图1,一个典型的吸收线。)Figure 1: A typical absorption line for rubidium, showing transmitted intensity (IT) as a function of the laser frequency (v).图1:一个典型的吸收线对铷,显示射线强度(它)是一个函数的激光频率(v)。Narrow-band demodulation techniques, such as phase-sensitive detection using a lock-in amplifier, t
13、hen allow the absorption information to be realized at DC. Because the signal has been moved to a high frequency via modulation, FMS avoids the typical limitations of absorption measurements such as laser-intensity fluctuations, which peak at DC and fall off roughly as 1/f, hence the name 1/f noise.
14、 Using this technique, absorption sensitivities can reach the part per million (ppm) level. For example, H2S has been detected at the ppm level in air,7 absorption of yttrium has been measured at the ppm level,5 and methane has been detected with a precision of 1ppb.8窄带解调技术,如相敏检波使用锁定放大器,然后允许吸收信息意识到在
15、直流。因为信号已经搬到一个高频率通过调制、FMS避免了典型的局限性吸收测量如激光强度的波动,它最高直流和脱落大约为1 / f,因此得名1 / f噪声。使用这种技术,吸收敏感性达到百分率(ppm)水平。例如,H2S已经测到ppm水平在空气中,7吸收钇一直按ppm水平,5和甲烷已经被检测出一个精密的1 ppb 8As we will discuss later in this application note, further enhancements of the signal can be achieved by taking advantage of experimental geometr
16、ies that cancel particular noise sources or undesirable aspects of the signal. Finally, if a reasonable level of attention is given to the optics and electronics, systematic errors can be suppressed and high accuracy can be achieved with FMS.9 This is important, for instance, when trying to determine the exact center of an absorption line. For many applications the center must be found to better than 0.1% of the linewidth. 正如我们将在本文后面讨论到,进一步增强的信号可以通过利用实验几何图形,取消特定的噪声来源或不良方面的信号。最后,如果一个合理水
