Abstract
Terahertz-range dielectric properties of the common polymers low-density polyethylene (LDPE), cyclic olefin/ethylene copolymer (TOPAS®), polyamide-6 (PA6), and polytetrafluoroethylene (PTFE or Teflon®) are characterized in the ultra-broadband frequency window 2-15 THz, using a THz time-domain spectrometer employing air-photonics for the generation and detection of single-cycle sub-50 fs THz transients. The time domain measurements provide direct access to both the absorption and refractive index spectra. The polymers LDPE and TOPAS® demonstrate negligible absorption and spectrally-flat refractive index across the entire spectroscopy window, revealing the high potential of these polymers for applications in THz photonics such as ultra-broadband polymer-based dielectric mirrors, waveguides, and fibers. Resonant high-frequency polar vibrational modes are observed and assigned in polymers PA6 and PTFE, and their dielectric functions in the complete frequency window 2-15 THz are theoretically reproduced. Our results demonstrate the potential of ultra-broadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science.
Highlights
THz time-domain spectroscopy (THz TDS) is a commonly used, phase-sensitive method to measure the complex-valued dielectric function of materials in the THz spectral window
Our results demonstrate the potential of ultrabroadband air-photonics-based THz time domain spectroscopy as a valuable analytic tool for materials science
In this paper we demonstrate the application of the ultra-broadband air-photonics-based THz TDS in both technologically and fundamentally oriented polymer research
Summary
THz time-domain spectroscopy (THz TDS) is a commonly used, phase-sensitive method to measure the complex-valued dielectric function of materials in the THz spectral window This technique is traditionally based on the nonlinear-optical or photo-conductive conversion of femtosecond laser pulses into single-cycle THz transients. With the recent advent of THz air-photonics [13,14] the crystal-based limitations of THz TDS can be avoided, providing the opportunity for efficient conversion of the full bandwidth of the ultra-short laser pulse into the THz signal This allows for THz TDS in a significantly extended frequency range, up to 20 THz and beyond, providing indispensable direct information about the properties of the materials in this new frequency range. Despite the increasing availability of tabletop air-photonics-based THz TDS systems with an exceptionally broad spectral bandwidth, we note that only a very limited number of reports is available in the literature describing the response of different materials in this extended frequency window [15,16,17]
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