Abstract-Invisible Security Printing on Photoresist Polymer Readable by Terahertz Spectroscopy

Hee Jun Shin, Min-Cheol Lim, Kisang Park, Sae-Hyung Kim , Sung-Wook Choi,  Gyeongsik Ok

http://www.mdpi.com/1424-8220/17/12/2825

We experimentally modulate the refractive index and the absorption coefficient of an SU-8 dry film in the terahertz region by UV light (362 nm) exposure with time dependency. Consequently, the refractive index of SU-8 film is increased by approximately 6% after UV light exposure. Moreover, the absorption coefficient also changes significantly. Using the reflective terahertz imaging technique, in addition, we can read security information printed by UV treatment on an SU-8 film that is transparent in the visible spectrum. From these results, we successfully demonstrate security printing and reading by using photoresist materials and the terahertz technique. This investigation would provide a new insight into anti-counterfeiting applications in fields that need security.

Abstract-Thermally controllable filter at terahertz region

 Hee Jun Shin, Min-Cheol Lim, Sae-Hyung Kim, Kisang Park, Sung-Wook Choi, Gyeongsik Ok

https://www.sciencedirect.com/science/article/pii/S1350449517306722

We experimentally investigated terahertz (THz) filters fabricated using dodecanoic acid (DDA) particles and polyethylene (PE) by performing THz time-domain spectroscopy. Since the refractive indices of DDA and PE are the same in the THz range, no optical scattering occurred when they were mixed. However, heating caused air voids to replace the DDA particles, and the DDA melted into the spaces between the PE particles. Furthermore, as the DDA particle size, heating time, and DDA content increased, the THz band width became narrower. Based on the results, we propose a new, low-cost type of THz filter with a simple manufacturing method.