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Proceedings Paper

Terahertz wave reference-free transmission spectroscopy of aminophenol
Author(s): Chao Deng; Hua Zhong; Liangliang Zhang; Cunlin Zhang
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Paper Abstract

We present a reference-free transmission spectroscopy of two kinds of aminophenol (Tyrosine and Phenylalanine) using terahertz time domain spectroscopy (THz-TDS). The THz band, which refers to the spectral region between 0.1 to 10 THz, offers a plethora of fingerprints of many chemical and biological materials. Within the past few years, efforts have been focused on exploiting the broadband nature of the THz time domain spectroscopy (THz-TDS) system for material identification and characterization. The conventional spectroscopic sensing method involves measuring both the terahertz signal carrying the sample information and a reference terahertz signal. In transmission geometry measurement, the absorption peaks of the sample material are found by taking the logarithm of the power spectrum of the transmitted signal beam divided by a reference power spectrum. In this work, we propose a reference-free approach to extract the absorption feature in THz transmission spectroscopy. The samples are identified by their absorption peaks extracted from the negative first-order derivative of the sample signal phase divided by the frequency. Unlike in conventional transmission spectroscopy measurement, in this method, the amplitude spectrum of the terahertz signal is not considered at all. Instead, the absorption features are extracted exclusively from the phase information by taking advantage of the almost-linear phase spectrum of terahertz pulses and the correlation between dispersion and absorption. It is also noted that the spectral phase of the terahertz pulse can be determined with far greater accuracy than the amplitude, which makes this method even more favorable. We measured two kinds of aminophenol (Tyrosine and Phenylalanine), and calculated the absorbance spectrum of each by both methods: taking the ratio between the power spectra of the sample signal and the reference signal and the reference-free phase spectrum of each material. The agreement between the positions of the absorption lines calculated from both methods indicates that the reference-free method is valid.

Paper Details

Date Published: 9 February 2009
PDF: 7 pages
Proc. SPIE 7158, 2008 International Conference on Optical Instruments and Technology: Microelectronic and Optoelectronic Devices and Integration, 71580U (9 February 2009);
Show Author Affiliations
Chao Deng, Capital Normal Univ. (China)
Hua Zhong, Capital Normal Univ. (China)
Liangliang Zhang, Capital Normal Univ. (China)
Cunlin Zhang, Capital Normal Univ. (China)

Published in SPIE Proceedings Vol. 7158:
2008 International Conference on Optical Instruments and Technology: Microelectronic and Optoelectronic Devices and Integration
Xuping Zhang; Wojtek J. Bock; Xiaoyi Bao; Ping Shum, Editor(s)

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