Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer

Ji Zhao; Liang-liang Zhang; Yi-man Luo; Tong Wu; Cunlin Zhang; Yue-jin Zhao

doi:10.1117/12.2036332

31 December 2013 Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer

Ji Zhao, Liang-liang Zhang, Yi-man Luo, Tong Wu, Cunlin Zhang, Yue-jin Zhao

Proceedings Volume 9042, 2013 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments; 904210 (2013) https://doi.org/10.1117/12.2036332
Event: International Conference on Optical Instruments and Technology (OIT2013), 2013, Beijing, China

Abstract

Terahertz wave which can provide innovative sensing and imaging techniques can obtain spectroscopic information unavailable at other wavelengths. The terahertz air-biased-coherent-detection (ABCD) method can achieve the third-order nonlinear susceptibility tensor to produce field-induced optical second harmonic photons. Therefore, the intense terahertz wave generated and detected by the laser-induced air plasma provides a promising ultra-broadband terahertz source and sensor for spectroscopy and imaging technique. Aiming at that purpose, an understanding of the frequency spectrum characterization of terahertz pulse is crucial. In this work, we investigated the variation of the THz pulse bandwidth measured through the third harmonic generation using the coherent detection scheme, by increasing the optical probe pulse power and biased electric field. A bandwidth broadening of the measured THz pulse is observed by increasing either the probe pulse power or the bias voltage strength. We speculate that a pulse shape change of the probe beam and a saturation effect during the second-harmonic generation might cause the bandwidth broaden with probe power. To further investigate the mechanism, we fixed the power of probe laser at 150mW and changed the bias voltage. The results show that the frequency spectrum width becomes wider gradually with the increasing of the bias voltage. A theoretical explaination shows that the bandwidth broadening with bias field might be introduced by a pulse shape change of the bias field induced second harmonic wave. This study reveals that we can control THz intensity and bandwidth by changing probe power and bias voltage in the ABCD system.

Citation Download Citation

Ji Zhao, Liang-liang Zhang, Yi-man Luo, Tong Wu, Cunlin Zhang, and Yue-jin Zhao "Terahertz frequency spectrum characterization of coherent heterodyne time-domain spectrometer", Proc. SPIE 9042, 2013 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments, 904210 (31 December 2013); https://doi.org/10.1117/12.2036332

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KEYWORDS

Terahertz radiation

Imaging spectroscopy

Plasma

Laser beam diagnostics

Spectroscopy

Pulsed laser operation

Heterodyning

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