基于光谱密度的差分吸收光谱法气体测量系统的校准研究

差分吸收光谱法(DOAS)是基于朗伯比尔定律的光谱法测量气体的重要方法,按此原理建立的测量系统是测量痕量气体的主要方法。用于测量痕量气体的DOAS系统的关键是其检出限的校准,传统的方法是使用标准气体进行校准。但是由于标准气体自身的量值确定问题,在ppb甚至ppt级的不确定度大于10%,而一般的ppt级的DOAS测量系统本身的不确定度也会高于标准气体,导致传统方法失效。提出一种基于光谱密度的DOAS系统校准方法,利用朗伯比尔定律将DOAS系统的检出限和光谱密度建立关系。由于光谱密度作为光学量值可以测量到10-6甚至更高,所以通过该方法可以实现DOAS系统在ppb乃至ppt级的校准。本方法需要根据待校准的测量系统光学结构的基本参数计算其总的标准光学密度值,然后把标准光学密度片放入测量系统光程中,测得其光学密度值,根据前后两次光学密度计算测量系统的测量偏差,进而分析计算测量系统的标准不确定度和标定的扩展不确定度,所得到的标定的扩展不确定度即为测量系统的检出限。该方法完全基于光学测量,不需引入标准气体评估,基于光学密度的精密测量和测量系统光学结构的装调误差,实现测量系统在较小不确定度水平上的标定,提高检出限标定的精度。本方法在开放光程式的DOAS系统上进行了实验验证。     

Effect of N5+ ion irradiation on l-ornithine monohydrochloride single crystals: an organic nonlinear optical material

In this work, the authors have grown good-quality single crystals of l-ornithine monohydrochloride (LOHCL), an organic nonlinear optical material, in the aqueous solution by the slow cooling technique. N⁵⁺ ion irradiation of three different doses (i.e. 1?×?10¹⁶, 5?×?10¹⁶ and 1?×?10¹⁷?ions/cm²) at room temperature was done on the cut and polished crystal specimen of appropriate size from the grown crystal. A detailed study of FT-Raman spectroscopic was carried out to see the effect of irradiation on structure and vibrational modes of the LOHCL crystal. The results revealed that there is no structural modification even at high doses except the variation in peak intensity, which indicates that the grown crystals of LOHCL have good stability and also confirms that the nitrogen ions do not substitute into the crystal lattice. The UV–Vis–near-infrared spectroscopic study was done on all the samples to see the effect of irradiation and various optical parameters such as transmittance (～50–70%), absorption coefficient, energy band gap (～4.75–4.96?eV), extinction coefficient, refractive index (～1.31–1.24), optical permittivity (～1.7–1.6) and susceptibility (～0.7–0.6). The calculated optical parameters were found to vary with change in doses.