High Performance THz Integrating Sphere
Chun-Lun Wang1*, Chuang-Pin Chiu1, Ming-Jye Wang1
1Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan
* Presenter:Chun-Lun Wang, email:clwang@asiaa.sinica.edu.tw
The SAFARI/SPICA, a proposed IR space telescope, requires a radiation source for calibrating the transition-edge sensor regularly. In order to offer a spatially uniform light source covering the full dynamic wavelength range (30-250 μm), integrating sphere working at terahertz (THz) is essential. We have developed high performance integrating spheres operating at 1~10 THz. Early report from SRON group, Netherlands, revealed strong absorption of integrating sphere with sandblasted and gold plated aluminum surface [1]. The performance of integrating sphere is significantly improved by introducing a aluminum wet-etch process. In this presentation, we show the fabrication details of our integrating sphere working at 1-10 THz. The 3D topography of the surface demonstrates that the complex substructure, causing the strong surface absorption, were removed by the wet-etch process. The FFT (fast Fourier transform) analysis of line profile confirms the significant reduction of FFT amplitude in the FFT wavelength of 7-100 μm. The surface reflectance of the surfaces with wet-etch process is 0.91 which is close to the reflectance of flat gold surface of 0.96 and much larger than that without wet-etch (0.67). The output uniformity of the integrating sphere with wet-etch process was measured by a scanning system. The detected spatial distribution is consistent with the simulation result based on spatially uniform radiation power at the output port, indicating that the scattering on the inner surface is Lambertian-like.

[1] Laauwen, W. M., de Jonge, C., Ferrari, L. & Dieleman, P. (2014, May 12-13). A Calibration Source for SAFARI on-ground Calibration - Design and design supporting tests - [Poster presentation]. Mission Concepts and Measurement Requirements for a Future Far-Infrared Space Mission, Goddard Space Flight Center, NASA, Greenbelt, Maryland, U.S. (https://asd.gsfc.nasa.gov/conferences/FIR/posters/Roelfsema_SAFARI-Calibration.pdf)

Keywords: SPICA, Integrating sphere, Terahertz, Surface reflectance