scholarly journals Measuring Complex Refractive Indices of a Nanometer-Thick Superconducting Film Using Terahertz Time-Domain Spectroscopy with a 10 Femtoseconds Pulse Laser

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 651
Author(s):  
Hyoung-Taek Lee ◽  
Gang-Seon Ji ◽  
Jun-Yung Oh ◽  
Choong-Won Seo ◽  
Byeong-Won Kang ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Optical Properties ◽  
Pulse Laser ◽  
Optical Constant ◽  
Time Domain ◽  
Refractive Indices ◽  
Superconducting Thin Films ◽  
Terahertz Time Domain Spectroscopy ◽  
Time Domain Spectroscopy

Superconducting thin films are widely applied in various fields, including switching devices, because of their phase transition behaviors in relation to temperature changes. Therefore, it is important to quantitatively determine the optical constant of a superconducting material in the thin-film state. We performed a terahertz time-domain spectroscopy, based on a 10 femtoseconds pulse laser, to measure the optical constant of a superconducting GdBa2Cu3O7−x (GdBCO) thin film in the terahertz region. We then estimated the terahertz refractive indices of the 70 nm-thick GdBCO film using a numerical extraction process, even though the film thickness was approximately 1/10,000 times smaller than the terahertz wavelength range of 200 μm to 1 mm. The resulting refractive indices of the GdBCO thin film were consistent with the theoretical results using the two-fluid model. Our work will help to further understand the terahertz optical properties of superconducting thin films with thicknesses under 100 nm, as well as provide a standard platform for characterizing the optical properties of thin films without the need of Kramers–Kronig transformation at the terahertz frequencies.

Soot Optical Properties in the Terahertz Spectra Domain

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Fei Wang ◽  
Ting Xu ◽  
Zhishen Qiang ◽  
Qunxing Huang ◽  
Dong Liu ◽  
...  
Keyword(s):  
Optical Properties ◽  
Time Domain ◽  
Wavelength Region ◽  
Optical Methods ◽  
Optical Data ◽  
Refractive Indices ◽  
Spectroscopy Technique ◽  
Terahertz Time Domain Spectroscopy ◽  
Time Domain Spectroscopy ◽  
Combustion Diagnostics

For understanding and accurately modeling combustion, the important questions are what species are present in the flame, and the spatial distribution and temperature of these species. Traditional optical methods used only the electromagnetic waves in the wavelength region from the ultraviolet region up to the infrared. Terahertz time-domain spectroscopy technique can be used for the combustion research as a novel tool. However, for some sooty combustion environments, the strong absorption, spectral interference from soot scattering, and fluorescence from large molecules must be considered. The optical properties of soot in the terahertz domain are the main basic data for terahertz application. In this paper, the terahertz time-domain spectroscopy technique was used to study the optical properties of flame soot within 0.2–1.6 THz. The complex refractive indices of the soot were deduced by the fixed-point iteration method. In order to validate the results, the complex refractive indices of the soot from the four different fuel flames were deduced. It was found that the complex refractive indices in the terahertz domain of the soot from the different fuel flames are very close to each other. The comparisons of complex refractive indices between the visible–IR domain and the terahertz domain indicate that the value of absorption index in terahertz domain is smaller than in IR domain, which implies that the terahertz wave will penetrate the sooty flame with smaller absorption than the IR rays. The results can provide the basic optical data of flame soot for the application of terahertz time-domain spectroscopy technique in the optical combustion diagnostics and extend the optical combustion diagnostics application area.

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