Self-referenced ultra-broadband transient terahertz spectroscopy using air-photonics

Abstract

Terahertz (THz) air-photonics employs nonlinear interactions of ultrashort laser pulses in air to generate and detect THz pulses. As air is virtually non-dispersive, the optical-THz phase matching condition is automatically met, thus permitting the generation and detection of ultra-broadband THz pulses covering the entire THz spectral range without any gaps. Air-photonics naturally offers unique opportunities for ultra-broadband transient THz spectroscopy, yet many critical challenges inherent to this technique must first be resolved. Here, we present explicit guidelines for ultra-broadband transient THz spectroscopy with air-photonics, including a novel method for self-referenced signal acquisition minimizing the phase error, and the numerically-accurate approach to the transient reflectance data analysis.

Crystallization of CsPbBr3 single crystals in water for X-ray detection

“…The change of the THz reflectivity, i.e., photoconductivity, was recorded as a function of time after photoexcitation at fluence 37 μJ cm −2 . The charge-carrier sum mobility μ was extracted from the peak of the photoconductivity decay curve according to the following equation 44 :…”

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

“…Equation (3) can be solved analytically in the case of weak photoexcitation (ΔE ≪ E 0 ) both in transmission [71] and reflection [72] geometries or numerically in the general case. The spatial dependence Δσ(z) is defined by the Lambert-Beer absorption law of the pump pulse and by averaging the local properties.…”

Approximations used in the analysis of signals in pump-probe spectroscopy

“…All of these approximations are based on a number of assumptions and approximations in terms of the probe wavelength and the magnitude of the relative change in transmission/reflection due to photoexcitation. It is important to note that improper use of these simplified equations can give a significant deviation from the expected material parameters, which may in turn lead to incorrect conclusions regarding the underlying charge-carrier dynamics of the material [6,12,59,60]. However, assessing the appropriate approximation for a given sample is not always trivial, since there are no clear boundaries for validity.…”

“…However, assessing the appropriate approximation for a given sample is not always trivial, since there are no clear boundaries for validity. Despite this uncertainty, only a few groups have investigated the validity of these approximations in depth, and only for few specific cases in the reflection geometry [12,59]. Using a 0.33 mm undoped GaAs wafer as a case study, D'Angelo et al [59] demonstrated that the approximations of a step-like excitation and a thin film approximation are generally insufficient for extracting the transient optical properties of thin films in the reflection geometry, due to the strong phase-sensitivity of these measurements.…”

“…Despite this uncertainty, only a few groups have investigated the validity of these approximations in depth, and only for few specific cases in the reflection geometry [12,59]. Using a 0.33 mm undoped GaAs wafer as a case study, D'Angelo et al [59] demonstrated that the approximations of a step-like excitation and a thin film approximation are generally insufficient for extracting the transient optical properties of thin films in the reflection geometry, due to the strong phase-sensitivity of these measurements. Similarly, Hempel et al [12] investigated the effect of substrate refractive index and thickness on the sensitivity of thin film transient reflection measurements.…”