First international comparison of terahertz laser power measurements

Fig. 1:Happy faces after the work is done in the THz lab of PTB: John Lehman, Andreas Steiger, Qing Sun, and Yuqiang Deng (from the left to the right)

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Measurements of terahertz (THz) power are important for a variety of applications for climate research, security and communication technology, medicine, and manufacturing. The first international comparison of THz laser power measurements took recently place at PTB in Berlin. Andreas Steiger hosted the comparison with the visiting scientists Yuqiang Deng and Qing Sun from the National Institute of Metrology (NIM) of China and John Lehman of the National Institute of Standards and Technology (NIST) who is presently visiting PTB as a Research Fellow of the Alexander von Humboldt Foundation of Germany. Measurements were carried out at two frequencies, 2.52 THz and 0.762 THz and at a power level of approximately 3 mW. The measurement results from each participant agreed very well with the reference value and to each other within the stated uncertainties.

The pilot comparison was undertaken in a relatively short period from May 4 to 8, 2015. Typically, such key comparisons may last years. Organized in a new manner, the participants met in Berlin to compare their standards at one place at one time. The measurement infrastructure such as the laser source and other instrumentation provided by PTB were critical to meeting the proposed schedule.

The comparison was performed via the spectral responsivity of the three different national THz standard detectors used according to the guidelines provided by the Consultative Committee on Photometry and Radiometry (CCPR). The results have still to be approved by the CCPR and will then be published for a larger community. The work represents the first key comparison ever undertaken in the far-infrared spectral region. It represents a milestone which will greatly benefit commercial development of instrumentation and sensors for remote sensing, THz imaging, high-speed telecommunications and time-domain spectroscopy.

Contact:

A. Steiger, 7.34, e-mail: Andreas.Steiger(at)ptb.de

Abstract-Broadband high-absorbance coating for terahertz radiometry

Yuqiang Deng, Qing Sun, Jing Yu, Yandong Lin, and Jinghui Wang »View Author Affiliations
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-21-5-5737&id=249626

We report a simple, broadband and high-absorbance coating for terahertz radiometry. The spectral properties of this coating in THz region were characterized with a home-made terahertz time-domain spectrometer. The measured spectral reflectance is less than 0.3% ranging from 0.2 THz to 0.5 THz and less than 0.1% ranging from 0.5 THz to 2.0 THz. We assembled a terahertz radiometer with this coating as absorber, and discussed its heat transfer in comparison with that of a carbon nanotube array radiometer. This coating is highly absorptive both in terahertz region and in visible light; therefore, the responsivity of this radiometer is easily traceable to National Laser Power Standards. This coating is easily fabricated. It is useful in traceability of terahertz sources and detectors to the SI units.