On the application of cw external cavity quantum cascade infrared lasers for plasma diagnostics
On the application of cw external cavity quantum cascade infrared lasers for plasma diagnostics
复制标题
连续外腔量子级联红外激光器在等离子体诊断中的应用
DOI：
10.1088/0957-0233/23/11/115501
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发表时间：
2012
影响因子：
2.4
通讯作者：
J. Röpcke
中科院分区：
文献类型：
--
作者：
D. Lopatik;N. Lang;U. Macherius;H. Zimmermann;J. Röpcke
用三台连续波外腔量子级联激光器(EC-QCL)作为吸收光谱仪的辐射源，用于分析分子等离子体中的物理和化学现象。该激光器工作在−1 1305cm22660cm1(4.427.66um)之间。基于EC-QCL的宽光谱可调谐特性，多组分检测已经成为可能，并在以甲烷为碳氢前体的低压Ar/N_2微波等离子体的研究中得到了验证。在平面微波等离子体反应器中，用直接吸收技术测量了在p=0.5mbar、f=2.45 GHz的放电条件下，CH4、C2H2、HCN和H2O的浓度随放电条件的变化。浓度范围为10~11-10~14个分子cm−~3。此外，根据对选定吸收谱线的谱线轮廓的分析，计算了气体温度Tg与放电功率的关系。此外，在纯He/Ar微波等离子体中，波长调制光谱技术已被应用于对吸收系数低至10−5的瞬变等离子体物种的灵敏探测。所研究的EC-QCL的典型谱线宽度在24~38 MHz范围内(I)取决于所使用的斩波技术和(Ii)单一或平均测量方法。此外，还测试了用于激光辐射的调制和调谐的不同方法。将EC-QCL的功率值在0.1mW至154mW之间变化，用于低压条件下的直接吸收测量，在所用的实验条件下，即对于谱线强度在10−19至10−22 cm分子−1之间的谱线，在测定甲烷、乙炔和一氧化碳浓度时没有饱和效应。
Three continuous wave external cavity quantum cascade lasers (EC-QCLs) operating between 1305 and 2260 cm−1 (4.42–7.66 µm) have been tested as radiation sources for an absorption spectrometer focused on the analysis of physical and chemical phenomena in molecular plasmas. Based on the wide spectral tunability of EC-QCLs, multiple species detection has become feasible and is demonstrated in a study of low-pressure Ar/N2 microwave plasmas containing methane as a hydrocarbon precursor. Using the direct absorption technique, the evolution of the concentrations of CH4, C2H2, HCN and H2O has been monitored depending on the discharge conditions at a pressure of p = 0.5 mbar and at a frequency of f = 2.45 GHz in a planar microwave plasma reactor. The concentrations were found to be in the range of 1011–1014 molecules cm−3. In addition, based on the analysis of the line profile of selected absorption lines, the gas temperature Tg has been calculated in dependence on the discharge power. Tg increased with the power values and was in the range between 400 and 700 K. Further, in a pure He/Ar microwave plasma, the wavelength modulation spectroscopy technique has been applied for the sensitive detection of transient plasma species with absorbencies down to 10−5. The typical spectral line width of an EC-QCL under the study was found to be in the range 24 to 38 MHz depending (i) on the chopping technique used and (ii) on a single or averaged measurement approach. Further, different methods for the modulation and tuning of the laser radiation have been tested. Varying the power values of an EC-QCL between 0.1 and 154 mW for direct absorption measurements under low pressure conditions, no saturation effects in determining the concentrations of methane, acetylene and carbon monoxide could be found under the experimental conditions used, i.e. for lines with line strengths between 10−19 and 10−22 cm molecule−1.