基于紫外光诱导荧光的渗透性纸张上微量物证检测技术研究

Research on trace evidence detection on the porous paper based on ultraviolet laser-induced fluorescence technology

为解决刑事案件中附着于渗透性纸张上的无色微量物证探测难的问题,分析常用纸张的紫外荧光特性,为滤除纸张上的强背景荧光提供依据,研制基于紫外光诱导荧光的渗透性纸张上微量物证检测装置。检测装置中,为有效激发各种微量物质荧光,采用光子能量高的深紫外激光作为激发光源;为获得更准确的痕迹信息,装置接收多光谱荧光并进行结果比对;同时,提出以背景灰度标准差来衡量纸张荧光的均匀性,以图像痕迹对比度评价痕迹的检测效果。使用本装置对常用纸张上的指印、明矾等5种无色痕迹开展实验验证,结果表明,所提方法能清晰显现纸张上的潜指印,且获得的指印条纹对比度与纸张背景灰度标准差成反比;同时,学生作业纸上的10%明矾溶液痕迹信息、复印纸上的2.5%谷氨酸钠溶液痕迹信息、便利贴上的2.5%磺酸钠溶液痕迹信息、便利贴上的0.004%硫酸铜溶液痕迹信息均能清晰显现。所提方法具有检测灵敏度高、非接触性、非破坏性、多光谱等优点,能快速获得高荧光纸张上多种微弱痕迹的清晰图像,为刑事侦查提供有力的帮助。

To effectively detect the latent trace evidence on porous paper, the ultraviolet fluorescence characteristics of commonly used paper are analyzed, which provides the basis for filtering the strong background fluorescence from paper. A detection device based on ultraviolet laser-induced fluorescence is developed. To effectively stimulate the fluorescence of various trace substances, a deep ultraviolet laser is used as the excitation light source. To obtain more accurate trace information, the device receives multispectral fluorescence and compares the results. Meanwhile, the standard deviation of background gray value is utilized to measure the uniformity of paper fluorescence. The trace contrast of image is used to evaluate the trace detection effect. Five kinds of latent trace on the common paper are detected. Experimental results show that the proposed method can clearly display latent fingerprints on paper, and the contrast of fingerprint ridges is inversely proportional to the standard deviation of paper background gray. At the same time, the trace information of 10% alum solution on students work paper, 2.5% sodium glutamate solution on copy paper, 2.5% sodium sulfonate solution on sticky note and 0.004% copper sulfate solution on sticky note can be clearly displayed. The proposed method has the advantages of sensibility, non-destructiveness, non-contact and multispectral. By utilizing this method, clear images of various kinds of latent trace on paper can be obtained quickly, which can provide powerful help for criminal investigation.