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Optics Letters , 2013, Volume 38 , Issue 18 , Page 3687.
Takuya Akiba, Naoya Kaneko, Koji Suizu, Katsuhiko Miyamoto, and Takashige Omatsu.
Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba 275-0016, Japan &
Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan.
Abstract
We report a novel sensing technique that uses an evanescent terahertz (THz) wave, without detecting the THz wave directly. When a THz wave generated by Cherenkov phase matching via difference frequency generation undergoes total internal reflection, the evanescent THz wave is subject to a phase change and an amplitude decrease. The reflected THz wave, under the influence of the sample, interferes with the propagating THz wave and the changing electric field of the THz wave interacts with the electric field of the pump waves. We demonstrate a sensing technique for detecting changes in the electric field of near-infrared light, transcribed from changes in the electric field of a THz wave.
© 2013 Optical Society of America
Additional Information
A terahertz (THz) wave is a form of electromagnetic radiation in the range of approximately 0.1 to 10 THz, corresponding to frequencies in the range between high-frequency microwaves and near-infrared light. The THz-frequency range is attractive for sensing in applications including biological imaging, long-distance detection of hazardous materials, and nondestructive testing. Thus, sensing in the THz-frequency range has developed rapidly in recent years. Monochromatic THz-wave sources for these applications have been developed using nonlinear optical crystals. These are attractive for these applications, due to their simplicity and compact size. However, special low-temperature and highly sensitive equipment is required for THz-wave detection. Hence, there has been considerable interest in simple sensing techniques that offer high-sensitivity detection of THz wave at room temperature.
In this study, we demonstrate a real-time sensing method that uses evanescent THz wave generated by Cherenkov phase matching, and interference between the reflected THz wave and the propagating THz-wave generated at different time. The interaction between the pump waves and THz-wave is recorded by an optical balanced detector with high sensitivity at room temperature. Hence, the method described provides the means to perform sensing in the THz-frequency range at room temperature. In this method, the moment when sample is contacted, the output was changed. As a result, it may be possible to measure the change of the sample in real-time. Moreover, THz-wave does not penetrate the sample, because the evanescent wave is a near-field wave with an intensity that exhibits exponential decay without absorption as a function of the distance from the boundary at which the wave was formed. Therefore, this new THz-sensing technique can be used to investigate liquid or powder samples without absorption or scattering effects. We believe this method has immense potential for applications that require real-time tracking changes.
