Dome A Fourier Transform Spectrometer (FTS)

FTS inside view
Inside view of the interferometer

The Dome A FTS was first installed in PLATO at Dome A during January 2010. It is a site survey instrument to evaluate the atmospheric transmission from 0.75 THz to 15 THz. This broad spectral coverage is particularly important at Dome A, where the extremely cold temperatures lie well outside the tested range of water vapor continuum models. The FTS is a polarizing Martin-Puplett interferometer operated in rapid-scan mode. The two output ports of the interferometer are equipped with different detector/filter combinations, providing a high throughput, low frequency band covering 0.75 THz to 3.5 THz, and a lower throughput, high frequency band covering 0.75 THz to 15 THz. The resolution for both bands is 10 GHz.

At Dome A, cryogenic cooling of the detectors and calibration loads is not practical due to the large power requirements. Instead, the FTS is equipped with ambient-temperature DLATGS pyroelectric detectors. For calibration, one input port of the interferometer always views a passive reference load on the optics bench, while the second input port alternates between the sky and a second movable passive reference load at outdoor ambient temperature. A complete measurement cycle on load and sky takes 10 minutes.

FTS calibration subsystem
Schematic of the outdoor calibration subsystem

The interferometer subsystem and detectors were built to specification by Blue Sky Spectroscopy of Lethbridge, Canada, and QMC Instruments in the UK. The data acquisition system and outdoor calibration load assembly were produced at Purple Mountain Observatory in Nanjing. The first of two identical instruments was installed at Dome A in January 2010.

Dome A FTS team

Sheng-Cai Shi (PI), Q.J. Yao, X.X. Li, X.G. Zhang, Z.H. Lin, K.M. Zhou, Q.G. Huang, and J. Yang Purple Mountain Observatory.

Scott Paine, Q.Z. Zhang, Harvard-Smithsonian Center for Astrophysics.

H. Matsuo, National Astronomical Observatory of Japan.

Participating institutions in alphabetical order

CAS Chinese Academy of Sciences, China
CFA Harvard-Smithsonian Center for Astrophysics, USA
NAOJ National Astronomical Observatory of Japan
PMO Purple Mountain Observatory, China