A new type of laser-terahertz emission system for noncontact investigations of chemical solutions has been developed. The system monitors terahertz emission from a sensing plate, which consists of silicon oxide and silicon thin film layers on a sapphire substrate. Sensing of chemical solutions with pH values between 1.68 and 10.01 was demonstrated. The amplitude of the terahertz emission from the sensing plate increased with increasing pH value. This change in the amplitude was caused by a change in the depletion layers of the silicon thin film when protons were adsorbed on the surface of the sensing plate. This study demonstrates that full noncontact monitoring of chemical solutions is possible using the laser-terahertz emission system.
© 2008 Optical Society of America
Instrumentation, Measurement, and Metrology
Original Manuscript: June 19, 2007
Revised Manuscript: May 20, 2008
Manuscript Accepted: May 27, 2008
Published: June 13, 2008
Toshihiko Kiwa, Junichi Kondo, Shohei Oka, Iwao Kawayama, Hironobu Yamada, Masayoshi Tonouchi, and Keiji Tsukada, "Chemical sensing plate with a laser-terahertz monitoring system," Appl. Opt. 47, 3324-3327 (2008)