Traceable terahertz power measurement from 1 THz to 5 THz

Abstract

The metrology institute in Germany, the Physikalisch-Technische Bundesanstalt (PTB), calibrates the spectral responsivity of THz detectors at 2.52 THz traceable to International System of Units. The Terahertz detector calibration facility is equipped with a standard detector calibrated against a cryogenic radiometer at this frequency. In order to extend this service to a broader spectral range in the THz region a new standard detector was developed. This detector is based on a commercial thermopile detector. Its absorber was modified and characterized by spectroscopic methods with respect to its absorptance and reflectance from 1 THz to 5 THz and at the wavelength of a helium-neon laser in the visible spectral range. This offers the possibility of tracing back the THz power responsivity scale to the more accurate responsivity scale in the visible spectral range and thereby to reduce the uncertainty of detector calibrations in the THz range significantly.

Planar hyperblack absolute radiometer

“…The experimental setup for measuring FIR laser power consisted of a continuous wave (CW) laser source, focusing optics and a spatial filter, a reflective optical chopper, a monitor detector, and a THz camera. This facility is described in greater detail elsewhere [10]. The camera and the detectors were mounted upon a platform, the position of which was controlled remotely.…”

Novel broadband THz-detector

“…4). In combination with the large diameter of 30 mm it is well suited for power measurements of THz radiation as well as for calibration at PTB's worldwide unique THz detector calibration facility [4]. …”

Terahertz power calibration using absolute reference calorimeter

“…For a source-based approach, several techniques based on blackbody radiation have been reported [3][4][5][6]; however, these approaches suffer from the presence of unwanted radiation, such as infrared radiation. A second approach that utilizes a detector-based standard has the advantage of precisely measuring absolute power; therefore, several national metrology institutes around the world have focused on the development of the detector-based standard [7][8][9][10][11][12][13]. In this regard, pulse THz power measurements have also been demonstrated with the use of certain types of calibrated detectors [14,15].…”