Numerical phase correction method for terahertz time-domain reflection spectroscopy

Abstract

We propose a numerical method for the misplacement phase error correction in terahertz time-domain reflection spectroscopy (THz-TDRS). The developed algorithm is based on the maximum entropy principle and can be readily implemented into data processing, allowing one to reveal material parameters of the opaque materials from the THz reflection measurements. The method resolves the phase retrieval problem in the THz-TDRS and dramatically simplifies the experimental procedure.

Transmission and Reflection Terahertz Spectroscopy of Insensitive Melt-Cast High-Explosive Materials

“…The surface of all samples and the gold mirror were positioned exactly in the focus of the optical system with an error of about 10 μm, which was controlled by the micrometer screw (in the Z direction). This condition is crucial for appropriate determination of the reflection spectrum; however, a misplacement phase error correction was also developed [22]. In the transmission (reflection) set-up, we also determined beam diameters using the knife-edge method [23]; these are equal to about 1.9, 0.9 and 0.5 mm (1, 0.7 and 0.4 mm) at frequencies of 0.5, 1 and 2 THz, respectively.…”

Detection and correction of the misplacement error in terahertz spectroscopy by application of singly subtractive Kramers-Kronig relations

“…Various experimental techniques have been suggested to remove the misplacement error [2][3][4] but the problem has not been solved clearly by such experimental procedures. Recently, a numerical method based on maximum entropy model (MEM) has been successfully applied for the reduction of this misplacement error [5,6]. The main conceptual problem in this method is that MEM is not relying on any physical principle, but rather on information mathematics.…”

Testing the validity of terahertz reflection spectra by dispersion relations

“…Otherwise due to the sample misplacement the measured reflection spectrum is not correct but distorted because of a finite phase shift of the THz wave reflected from the sample with respect to that of a reference. Recently we have presented two methods to correct the phase of the THz-TDS signal [1,2]. The first one is based on maximum entropy method (MEM) [1], which relies purely on mathematical model in information theory, and it is to some extent complicated.…”

“…Recently we have presented two methods to correct the phase of the THz-TDS signal [1,2]. The first one is based on maximum entropy method (MEM) [1], which relies purely on mathematical model in information theory, and it is to some extent complicated. The second method is based directly on singly subtractive Kramers-Kronig relations (SSKK) [2].…”

“…It is shown that these algorithms can be used in particular for checking the success of correction of the spectra by the methods of Vartiainen et al [1] and Lucarini et al [2] to remove the negative misplacement error in the terahertz time-domain spectroscopy. …”