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.
Highlights
IntroductionTime-domain terahertz (THz) spectroscopy (TDS) is a well-established method for the determination of optical properties (such as complex permittivity, conductivity, or refractive index) of materials and systems of interest in the THz spectral range [1,2,3]
Time-domain terahertz (THz) spectroscopy (TDS) is a well-established method for the determination of optical properties of materials and systems of interest in the THz spectral range [1,2,3]
We have provided general guidelines for ultra-broadband transient THz spectroscopy with THz air-photonics
Summary
Time-domain terahertz (THz) spectroscopy (TDS) is a well-established method for the determination of optical properties (such as complex permittivity, conductivity, or refractive index) of materials and systems of interest in the THz spectral range [1,2,3]. In order to improve the phase stability in transient THz spectroscopy, and to suppress the effects of the long-term drift or jitter of the time-offset for optical pump-THz probe measurements (OPTP), Iwaszczuk et al [30] proposed a self-referenced data acquisition scheme based on the double-modulation of both the optical pump and the THz probe using a dual-blade optical chopper This experimental procedure ensures that both the reference (THz reflection from or transmission through the optically-unexcited sample) and the differential (optical pump-induced change in the THz reflectance or transmittance of the sample) signals are acquired simultaneously in one single scan, instead of comparing the two consecutive acquisitions separated by minutes or even hours of lab time. For the weak signal limit, we derive an analytical expression for conversion of the measured transient THz reflectance into the quantity of interest, the complex-valued THz conductivity spectrum of the sample
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