Examination Of Automative Paint By Optical Coherence Tomography

In the field of forensic science,automotive paint chipping is one of the key material evidence in criminal cases and traffic accident cases.Based on the identification of its rich information about the involved vehicles,it could provide clues and the direction in which the involved vehicles can be found,which narrows the scope of investigation,so as to provide strong evidence for case detection.Optical Coherence Tomography(OCT)is a kind of optical inspection technology using the scattered light of biological tissue coherent imaging principle;It is similar to the Ultrasonic imaging technology and is a kind of measurement method based on low coherence interference,which has the characteristics of nondestructive,rapid,as well as high-resolution tomography.Due to different vehicle paint layer structures of different automobiles,by means of the optical tomography to detect body paint cross-sectional images nondestructively,the automobile body paint structure characteristics can be obtained,and the different paint can be distinguished,which provides a new method for automobile paint identification.The frequency domain OCT imaging system used in this paper consists of broadband SLD near infrared light sources with 5 micron depth resolution,5 micron lateral resolution and 832 nm center wavelength.We did the preliminary imaging studies for 153 automobile body paint with different colors,brands,models from 9 different provinces and areas.The results showed that the OCT technology can accurately distinguish the same kind of automotive paint with the same color;Furthermore,we also obtained its optical scattering characteristic parameters,such as the optical path of finish varnish layer,the optical path of finishing coat layer,scattering intensity ratio and so on,which could provide new features for the same or the same class paint material evidence.Compared to the traditional paint morphology examination technology,such as optical microscopy,scanning electron microscopy and spectral imaging technology,OCT technology can realize real-time tomography imaging detection for paint examination without any paint slice processing,only simple operation and intuitive analysis process.In addition,OCT technology can also combined with traditional composition testing methods for complementary advantages,which would greatly improve the timeliness and the accuracy of vehicle paint examination,and has important significance for the case detection.