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  • Laser Spots Unique Codes in Materials

Photonics Spectra
Oct 2005
Anne L. Fischer

As identity theft becomes more common, security companies are seeking advanced tools to help guard against fraud in such documents as passports, identification cards, credit cards and banknotes. Current methods all have drawbacks; for example, they may require the integration of a watermark, hologram or radio-frequency ID chip.

Laser Spots Unique Codes in Materials
As the laser scans across the surface of an item, the speckle pattern fluctuates in intensity, typically around 1 percent of the average reflectivity. Four of these measurements (taken from four parts of the speckle pattern) make up the fingerprint. Courtesy of Russell Cowburn, Imperial College London.

Russell P. Cowburn of Imperial College London and his colleagues there and at the Universities of Durham and Sheffield, also in the UK, have developed an alternativeanticounterfeiting method, which they call laser surface authentication. Almost all paper documents, plastic cards and packaging have unique microscopic irregularities that can be read like fingerprints, Cowburn explained. Surface imperfections of less than a few hundred nanometers scatter a laser beam, and this scattering, or “speckle,” forms the basis of an item’s signature.

The identification system works by scanning the surface of an item with 635-nm light from a 1-mW laser diode. The item is placed flat on the scanner and is pushed along guide rails that ensure that the same section is scanned each time. A bar code can be output and attached to the item, or the results of the scan can be stored in a database, against which they later can be compared for authentication. Each of these fingerprints takes up only 125 to 750 bytes of storage space, so a standard desktop PC can be used for validation and can check up to 10 million entries per second.

The method offers several advantages over other forms of authentication. The speckle pattern is naturally occurring, it is robust, and it cannot be reproduced. The scanning requires no changes in the manufacturing process.

Cowburn said that the new method, despite being optically based, is not directly comparable to holography because holograms can be seen by the eye and the laser scanning method is machine-readable only. It is most similar to packaging applications that integrate ID chips, which are expensive and which can be difficult to implement.

The greatest challenge in development was in the optical hardware setup and in producing software algorithms that would make the fingerprint immune to damage to the object. In testing, materials were subjected to extensive wear and tear, and the original fingerprints were still intact.

In 2003, the developers commercialized the scanning system and formed Ingenia Technology Ltd. of London to market it. Two types of scanners are available: a static device for scanning moving items on a production line or printing press, and a handheld, moving-head scanner for checking static items. The first installation is under way on a production line.

Besides checking the obvious proofs of identity, potential applications of the systems range from currency to pharmaceutical packaging to just about any type of valuable document that needs authentication.

An interference pattern that is recorded on a high-resolution plate, the two interfering beams formed by a coherent beam from a laser and light scattered by an object. If after processing, the plate is viewed correctly by monochromatic light, a three-dimensional image of the object is seen.  
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