Combination of Kramers-Kronig transform and time-domain methods for the determination of optical constants in THz spectroscopy

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• 作者：Michael Herrmann^a ; ^{michael.herrmann@ipm.fraunhofer.de} ; Frank Platte^b ; Konstantinos Nalpantidis^b ; René ; Beigang^a ; H. Michael Heise^c
• 关键词：KKR/KKT ; Kramers&ndash ; Kronig relation/Kramers&ndash ; Kronig transform ; TDS ; time-domain spectroscopy ; THz ; terahertz ; PABA ; p-aminobenzoic acid ; 4-aminobenzoic acid ; PTFE ; polytetrafluoroethylene ; Teflon&trade
• 刊名：Vibrational Spectroscopy
• 出版年：2012
• 期刊代码：113_09242031
• 类别：ms
• 出版时间：May, 2012
• 卷：60
• 期：Complete
• 页码：107-112
• 文件大小：388 K

摘要

Absorption and reflection spectra have successfully been used for substance identification, which is also applicable to the THz spectral range. For optical spectroscopy, the Kramers-Kronig transformation (KKT) is a powerful tool to determine the complex refractive index (with k, n absorption and refractive indices, respectively) from either an absorption or reflection measurement. By terahertz time-domain spectroscopy (THz-TDS) materials are probed with short pulses of radiation. The detection is sensitive to the sample on both the amplitude and the phase of the electrical field. Thus, THz-TDS spectroscopy can provide more information than conventional Fourier-transform spectroscopy, by which a power spectrum is measured. In the case of transmission measurements, for instance, formulae exist by which the frequency-dependent complex refractive index is directly calculated from the time-dependent electrical field (waveform) without the necessity of a KKT. In the case of reflection experiments, a comparable computation is possible for the frequency-dependent phase angle; here a KKT can help to recover essential parameters. We present a combination of KKT and TDS methods for the calculation of optical constants in the THz regime.