Optical Signatures of Disordered Materials for Authentication Applications Hergen Eilers, Benjamin R. Anderson, and Ray Gunawidjaja Applied Sciences Laboratory, Institute for Shock Physics, Washington State University, Spokane, WA 99210-1495, USA eilers@wsu.edu Abstract: Authentication is critical in applications such as provenance verification and tamper- indication. Optical signatures of disordered materials can provide unique information suitable for authentication. Several approaches such as transmission, reflection, fluorescence, and random lasing are reviewed. OCIS codes: (260.6120), (300.6480), (300.6280), (290.4210), (270.1670), (160.4236), (030.1670) 1. Introduction Authentication has become a critical requirement in many applications. For example, the verification of international treaties regarding the storage of nuclear weapons requires seals that indicate any attempted tampering. Seals have been used for thousands of years with more or less success to indicate unauthorized access. However, no seal is completely foolproof. According to Johnston, the weakest point is the secure storage of information indicating that trespassing has occurred until the seal can be inspected [1]. One approach to address this problem is to store information in the seal or on the seal indicating that unauthorized access has not yet occurred. When tampering does occur, that information is erased. The absence of this information indicates that tampering has occurred [1]. Another example for the need for authentication is the semiconductor supply chain which typically involves companies and individuals from all over the world [2]. As a consequence, this supply chain offers many opportunities for intended and unintended tampering, including the insertion of counterfeit parts. Counterfeit parts may be parts that did not pass inspection or have been designed or manipulated in such a manner as to cause intentional damage. The potential of unintended or intended damage and manipulation is a great concern for many users, including defense, homeland security, health, utilities, transportation, etc. To address these challenges, it is desired to have artifacts or design elements – physical unclonable functions (PUFs) – that can be verified whenever and wherever needed [3]. We are currently evaluating various types of optical PUFs, including phase-adjusted transmission, reflection, fluorescence, and random lasing in nanocomposites for such authentication applications. 2. Experiments Various types of nanocomposites are evaluated for different optical approaches. A spatial light modulator (SLM) is used to adjust the phase of a laser beam in order to optimize a desired interaction. Fig. 1 shows schematics of the experimental setups for transmission, reflection, fluorescence, and random lasing measurements. Fig. 1. Schematics of experimental setups for transmission (top left), reflection (top right), fluorescence (bottom left), and random lasing (bottom right) measurements.