Laser Surface Authentication
Laser Surface Authentication (LSA) is a method to verify the authenticity of an object by shooting a coherent laser beam onto a surface of the object and analyze its speckle pattern. A speckle pattern is a pattern of bright and dark spots which is formed by reflection of the laser by a rough surface (Fig. 1).
An example of speckle pattern recorded under microscope connected to a CCD camera is shown in Figure 2. The pattern is unique to a particular spot of the object and can be used for authentication of the same object in the future. In this project we focused on low-cost LSA application to authenticate various types of papers and its robustness against spatial and angle disturbance.
Advantages and disadvantages of LSA
To date, LSA offers the strongest authentication security compared to other methods because it utilizes naturally occurring randomness at microscopic level. It is virtually impossible to recreate an object’s surface at microscopic level with our current technology. Furthermore, LSA does not tamper the scrutinized object in any way while other artificial authentication methods (i.e watermarks, holograms, security threads, etc…) all tamper with the object in one way or another. However since LSA is a relatively new technique, there is no standardized LSA procedures yet, and further researches in figuring out the cheapest and most efficient method are still few and far between. Nonetheless, this can also be another advantage because if there is no standardized method then fraudsters can not access the details of LSA technique used (such as the wavelength of the laser, the location of the paper from which the speckle pattern was taken, incidence angle of the laser, magnification of microscope, and the algorithm for analyzing the speckle pattern) from publicly available sources.
Authentication Method
Figure 3 shows our experiment set-up for static LSA. A He-Ne laser is redirected with a mirror onto the paper. The resulting speckle pattern on the paper is captured by a microscope connected to CCD Camera and recorded on computer. We repeat this process for various incident angles, types of papers, and spatial and angular disturbances.
Results
1. Due to the uniqueness of speckle patterns, this method never yields false positive result. False negative results, however, may still happen.
2. We observed that smaller incidence angle yields higher success rate of authentication. This finding is consistent across multiple types of papers.
3. In order to maintain at least 95% authentication accuracy, our experiment set-up has estimated spatial and angular tolerances of 0.154 ± 0.008 mm and 3.59 ± 0.18 degrees respectively. This result was obtained with incidence angle of 46°.
Further information:
1. “Recognizing Document’s Originality by laser Surface Authentication” https://ieeexplore.ieee.org/document/5675850
2. “Static Laser Surface Authentication with Low-cost Microscope Tolerances on Spatial and Angular Disturbance” https://link.springer.com/article/10.1007/s12596-015-0250-0
