Calorimetric measurement of absolute terahertz power at the sub-microwatt level

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Amemiya

et al. 2014

Self Cite

We have developed a calorimeter for a metrology standard for measuring the power of terahertz (THz) waves. Since the THz calorimeter is based on the thermal balance between heat produced by THz waves and direct current (DC), it requires an equivalent factor for converting from THz to DC power. The DC equivalent factor, which is defined as the ratio between the thermal efficiency of THz and DC powers, was calculated with a thermal simulator based on the finite element method. This factor was estimated to be approximately 1 with a maximum error of 0.7 %, which implies a good equivalence between DC and THz powers, enabling accurate measurement of the absolute power of THz waves.

Section: Introductionmentioning

confidence: 99%

Numerical simulation of DC equivalent factor of THz calorimeter

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Amemiya

et al. 2014

Self Cite

“…Therefore, a calibration technique at the sub-microwatt level is necessary for such applications. Given this background, we have developed a highly sensitive technique to measure such a small absolute THz power [4]. The technique is based on calorimetry by the isothermal temperature-control type calorimeter [4], [5].…”

Section: Introductionmentioning

confidence: 99%

“…Given this background, we have developed a highly sensitive technique to measure such a small absolute THz power [4]. The technique is based on calorimetry by the isothermal temperature-control type calorimeter [4], [5]. In this paper, we report the repeatability of the absolute THz power measurement at room temperature as a part of evaluation of uncertainties.…”

Section: Introductionmentioning

confidence: 99%

Repeatability of absolute terahertz power measurement using a sensitive calorimeter

2014 39th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Amemiya

et al. 2014

Self Cite

In this paper, we report the repeatability of calorimetric measurement of absolute terahertz (THz) power at room temperature. Highly sensitive measurement at a sub-microwatt level was performed by using a calorimeter based on an isothermal temperature-control technique. The experiment was demonstrated at 1 THz using a photomixer as a THz source. Type A uncertainty in repeatability was evaluated to be 2.4% for five repetitions at an incident power of 0.81 μW. A very small drift of 30 pW/s was evaluated as well.

“…However, metrology standards, which are essential for the public utilization of THz technologies, are yet to be established. The frequency standards as well as linearity and power standards are important for the THz-TDS [1]- [4]. For example, security and medical analyses require the frequency standards to share fingerprint spectra measured by different devices and operators.…”

mentioning

confidence: 99%

“…While the offset frequency was equal to zero under the assumption that and , its uncertainty was estimated using (4) In addition, the uncertainty of as a result of the phase shift is written as…”

mentioning

confidence: 99%

Frequency Calibration of Terahertz Time-Domain Spectrometer Using Air-Gap Etalon

IEEE Trans. THz Sci. Technol.

Shimada

2014

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Although various terahertz (THz) technologies have been rapidly developed in recent years, their metrology standards are yet to be established. We have developed a simple calibration method for the frequency of a THz time-domain spectrometer (TDS) using an optically transparent THz air-gap etalon (OT-TAGE). The OT-TAGE can be used in both the near-infrared (NIR) and THz regions. Therefore, a frequency measurement using THz waves can be directly compared with one using NIR light via the OT-TAGE. In this study, the frequency of a commercial THz-TDS was calibrated by referring to the NIR wavelength was demonstrated. The obtained frequency errors were within 3 GHz, with relative uncertainties within 1%.Index Terms-Time-domain analysis, frequency, air gaps, interferometers, calibration. I N CONSTRAST to radio waves and optics, which have seen widespread applications over the years, applications of terahertz (THz) waves, such as imaging, communications, and spectroscopy, have been developed only recently. In particular, the THz time-domain spectrometer (THz-TDS) is commonly used for analytic applications. However, metrology standards, which are essential for the public utilization of THz technologies, are yet to be established. The frequency standards as well as linearity and power standards are important for the THz-TDS [1]- [4]. For example, security and medical analyses require the frequency standards to share fingerprint spectra measured by different devices and operators. Although the THz frequency comb is promising as a frequency standard [5], it is only available in the few laboratories equipped with an optical frequency comb. While the absorption lines of standard gases contained in databases are used for practical calibration, establishing metrological traceability is challenging. Etalon-based calibration, which is expected to be superior to the H O-gasbased method, has been also suggested [6], [7]. The etalon is a simple resonator and consists of two reflection planes. It is practical and compact, which means that it can be used as a simple tool for obtaining a frequency reference. Its transmittance has equally spaced peaks due to interference from the multiple reflections between the two planes. The interval between each peak, namely, the free spectral range (FSR), can be written as (1) Manuscript where, is the speed of light, and and are, respectively, the refractive index and length of the resonant cavity of the etalon. In the case of a solid etalon, accurate measurement of or estimation of its uncertainty is required [6], [7]. However, it has proven difficult to verify the absolute value of and to evaluate its uncertainty. In contrast, the value of of an air-gap etalon, which has an air-filled cavity, can be approximated to 1 [8]. According to (1), the FSR of an air-gap etalon depends only on . Therefore, if can be precisely measured, air-gap etalons can potentially be used as simple tools for frequency calibration and verification in various THz applications. An optical method is typically used for measu...