TELIS-SIR channel

Technology STO2

The detector of STO2 is based on a superconducting hot electron bolometer (HEB) mixer, using nanotechnology developed at TU Delft. This detector is the most sensitive heterodyne detector now available in the terahertz domain. A heterodyne receiver can convert a high-frequency spectral line signal from space into a spectral line at a microwave frequency without losing any information. Similar to FM radio, this mixing of frequencies makes the reception clearer and the signal from space can be amplified better. It can deliver an unparalleled high spectral resolution.

A quantum cascade laser at 4.7 terahertz, actually a tiny semiconductor chip developed through a collaboration between TU Delft, SRON and MIT, will be used as a so-called local oscillator, providing a reference frequency for the incoming signals from space.

STO2: balloon observatory ride at the edge of space

Stars and planets are born in molecular clouds that form and finally get disrupted again in the interstellar medium, the matter that exists in the space between the star systems in a galaxy. Astronomers still don't fully understand how this life cycle works in our Milky Way. The Stratospheric Terahertz Observatory (STO2), a NASA balloon-borne mission, led by the University of Arizona, will travel to the edge of space above Antarctica in the end of 2015 to provide a missing piece of the puzzle.

At an altitude of 40 kilometers above Antarctica, the sky is crystal clear. There is hardly any water vapor which can block the far-infrared radiation (also called terahertz radiation) from space. The edge of space is therefore a perfect environment for doing astronomical observations in the terahertz range. NASA uses super pressure balloons to lift observatories to that altitude. STO2, which will fly over Antarctica at the end of December 2015, is one of them. STO2 plans to fly longer than 14 days.

STO2 will measure radiation with high frequencies between 1 - 5 terahertz, corresponding to a wavelength between 60 and 300 micrometers. As leading experts in the field of terahertz receivers, SRON and the Delft University of Technology( TU Delft) have been asked to deliver new receivers for three different channels (4.7, 1.9, and 1.4 terahertz).

Facts & figures
In 2012 the first Stratospheric Terahertz Observatory (STO) circled Antarctica in 14 days, using the stable polar wind. On board was a 0,8 m telescope. STO2 will re-fly STO, equipped with two new two-pixel receivers (at 1.4 terahertz and 1.9 terahertz), and a state of the art 4.7 terahertz single pixel receiver. All three receivers have performed extremely well in lab tests. The receivers at 1.4 and 1.9 terahertz showed a sensitivity (receiver noise temperature) of 640-670 K, while the 4.7 terahertz receiver demonstrated 800 K.

Jian-Rong Gao, Senior instrument scientist, SRON/TU Delft, This email address is being protected from spambots. You need JavaScript enabled to view it. / This email address is being protected from spambots. You need JavaScript enabled to view it.

Science STO2

Especially the 4.7 terahertz receiver is important because no one has ever flown such a receiver at this frequency, which means that this new channel on STO2 is a proof-of-concept. "Missions with such a terahertz receiver will provide missing pieces in the puzzle of the life cycle of stars and planets" says team leader Jian-Rong Gao. "The 4.7 terahertz receiver will for instance map neutral atomic oxygen, a longstanding dream of astronomers. That is why STO2 is an important stepping stone for future terahertz missions in space. The outcome of this study will enable us to make a Milky Way template which we can compare to other galaxies. "

The fine-structure line of electrically neutral atomic oxygen (OI) at 4.7 terahertz is the dominant cooling line of warm, dense, and neutral atomic gas. In strongly UV irradiated photodissociation regions (PDRs), the OI line flux is generally larger than that of the carbon CII line, making it an ideal diagnostic for probing the physical conditions in regions of massive star formation and galactic centers. The spectrally resolved OI line is necessary to untangle the complexities of the interstellar medium.

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