研究目的
To measure the complex refractive index of α-quartz (SiO2) at various temperatures between 0.5 THz and 5.5 THz using terahertz time-domain spectroscopy (TDS) and to understand the temperature-dependence of the phonon mode and its effect on TDS and optical pump terahertz probe spectroscopy (OPTPS) measurements.
研究成果
Quartz is an ideal substrate for optical spectroscopy measurements at terahertz frequencies, except for a narrow band around 3.9 THz due to a phonon absorption feature. The study provides detailed measurements of the complex refractive index of α-quartz across a range of temperatures, contributing to the accurate optical characterisation of samples on quartz substrates in the terahertz region.
研究不足
The study is limited to the frequency range of 0.5 to 5.5 THz and temperatures between 10 and 300 K. The spectral feature at 3.9 ± 0.1 THz due to the lowest energy optical phonon modes affects the transmission properties of quartz in this region.
1：Experimental Design and Method Selection:
The study used terahertz time-domain spectroscopy (TDS) to measure the complex refractive index of α-quartz at temperatures between 10 and 300 K. The method involved measuring the amplitude and phase of the transmission through α-quartz of a broadband terahertz pulse in the time-domain.
2：Sample Selection and Data Sources:
Single-crystal α-quartz wafers were used, which were z-cut to an accuracy of ±15°, had a specified thickness of 2 ± 0.05 mm and diameter of approximately 13 mm.
3：05 mm and diameter of approximately 13 mm. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: A terahertz time-domain spectrometer built at Oxford was used, along with a cold-finger cryostat (Oxford Instruments) for temperature-dependent measurements. Terahertz pulses were generated using a spintronic emitter and detected by electro-optic sampling using a 0.2 mm thick GaP(110) crystal.
4：2 mm thick GaP(110) crystal. Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The terahertz transmission in the frequency-domain was obtained by measuring the signal response of quartz and vacuum in the time-domain and dividing the Fourier transformed signal of the quartz by that of vacuum.
5：Data Analysis Methods:
The complex refractive index was extracted from the terahertz transmission function using a numerical method to overcome convergence issues, with an alternate error function used in the fitting algorithm.
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Bruker Vertex 80v Fourier transform infrared (FTIR) spectrometer
Vertex 80v
Bruker
Used to measure reflection and transmission spectra from 100 to 350 cm?1.
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terahertz time-domain spectrometer
Oxford
Used to measure the complex refractive index of α-quartz at various temperatures.
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cold-finger cryostat
Oxford Instruments
Used for temperature-dependent TDS measurements of quartz.
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spintronic emitter
Used to generate terahertz pulses.
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GaP(110) crystal
0.2 mm thick
Used for electro-optic sampling to detect terahertz pulses.
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Wollaston prism
Used in the detection setup for terahertz pulses.
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balanced photodiodes
Used in the detection setup for terahertz pulses.
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liquid helium cooled silicon bolometer
Infrared Laboratories Inc.
Used for FTIR measurements.
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Mylar beamsplitter
Used for FTIR measurements.
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