Research On Determining The Sequence Of Intersecting Lines By Optical Coherence Technology

In the field of questioned document examination,determining the sequence of intersecting lines is usually a key technique for assessing the authenticity and the relative production time of documents.Due to the impact of the equipment cost and the expertise of appraisal personnel,the test is difficult.Therefore,the determination of the sequence of intersecting lines still remains a challenge for forensic document examiners.Optical coherence tomography(OCT)is a high-resolution tomography technique,which has the advantages of in situ,lossless,rapid and high resolution.On the basis of a large pre-study,this paper firstly proposed the use of OCT to determine the sequence of intersecting lines,and carried out a large number of OCT-based determination of the sequence of intersecting lines,which proved that this technique perform non-destructive,tomographic imaging of the intersecting line samples,and the effect of the experiments was great,providing new technologies and new methods for the determination of the sequence of intersecting lines.This paper utilized a frequency domain OCT system consisted of a wideband SLD near infrared light source with lateral resolution of 4.0μm,longitudinal resolution of 3.0μm,a central wavelength of 900 nm,and made an experimental study on 220 intersecting line samples:(1)By employing the OCT system to perform OCT imaging on the intersecting line samples formed by different types of gel pen inks and different types of inkpad inks,We recorded the two dimensional(2D)and three-dimensional(3D)OCT images characteristics of the inkpad/stamp pad ink over gel pen ink and the gel pen ink over inkpad/stamp-pad ink,and found that there were a certain differences in the OCT image characteristics of the intersecting line samples formed by the gel pen inks and the inkpad/stamp-pad inks.Based on this,the OCT system can be used to determine the sequence of intersecting lines.(2)By employing the OCT system to perform OCT image on the intersecting line samples formed by different types of laser printing inks and different types of inkpad/stamp-pad inks,we recorded the characteristics of the 2D cross-sectional OCT images and 3D volumetric OCT images of different intersecting line samples,and found that there were a certain differences in the two-dimensional and threedimensional OCT images of the intersecting line samples formed by the laser printing inks and the inkpad/stamp-pad inks.The OCT system can be used to identify the sequence of laser printing inks and inkpad/stamp-pad inks.(3)By employing the OCT system to perform OCT image on the intersecting line samples formed by different types of inkjet printing inks and different types of inkpad/stamp-pad inks,We recorded the two-dimensional and threedimensional OCT images characteristics of intersecting lines created by inkjet printers and seals with different sequences and found that there were a certain differences in the OCT images of the intersecting line samples with different sequence formed by inkjet printing and seal printing,which can provide evidence for identifying the sequence of inkjet printing and seal printing.But the inspection effect was not as good as laser printing.(4)By employing the OCT system to record and analyze the two-dimensional and three-dimensional OCT images characteristics of the intersecting line samples of different types of ballpoint pen inks and different types of inkpad/stamp-pad inks,we found that the two-dimensional OCT image and three-dimensional OCT image characteristics of the intersecting line samples formed by ballpoint pen inks and printing inks were not obvious,and it was difficult to determine the sequence.The experimental results showed that(1)OCT technique had a strong ability to inspect the sequence of gel pen inks and inkpad/stamp-pad inks,laser printing inks and inkpad/stamp-pad inks,inkjet printing inks and inkpad/stamp-pad inks,and ballpoint pen inks and inkpad/stamppad inks.It could visualize the intersection area of crossing lines of different samples at the twodimensional and three-dimensional levels.The different characteristics of the image realized the optical non-destructive inspection of intersecting line samples.(2)Compared with traditional inspection techniques,OCT technique could obtain the depth characteristics and layering information of the samples.And the two-dimensional and three-dimensional OCT tomographic imaging made determination of the sequence of intersecting lines objective and reliable.(3)OCT could assist in the determination of the sequence of intersecting lines that was difficult to examine by other techniques.This paper introduced OCT technique into the verification and identification of sequence of intersecting lines problems in the field of forensic document examination for the first time.The results illustrate that the tomographic high-resolution imaging capability of OCT technique can provide a new technical means for determining the sequence of intersecting lines through experimental research,which may become a powerful supplement to the existing technique and may further enrich the conventional methods used in the examination of questioned documents.