Tuesday, 18 January 2011

Laboratorium Astrofisika

 “If we do not hope, we will not find what is beyond your hopes.”

"Orang-orang sukses di dunia ini, awal dari kesukesaannya dimulai dari bermimpi.
Dari mimpinya mereka berusaha untuk mewujudkannya, hingga mereka berhasil mencapai mimpinya.
 Semoga, Amin"

Astrophysics Laboratory


Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Cambridge, MA 02138

Superconducting Submillimeter Detectors
Instructors: Edward Tong and Abby Hedden

The heart of the best current millimeter- and sub-millimeter-wavelength radio receivers used for astronomy is a superconducting microelectronic device known as an SIS junction. This experiment is intended to demonstrate the unusual quantum mechanical properties of SIS junctions that permit them to be used as sensitive detectors of electromagnetic radiation.

The devices consist of a micron-scale sandwich of alternating layers of Superconductor/ Insulator/Superconductor (hence the acronym SIS), with the insulating barrier sufficiently thin (~100 A) to permit quantum-mechanical tunneling of charge carriers. Tunneling of single electrons leads to a highly nonlinear current-voltage characteristic that permits heterodyne detection (mixing). Tunneling of Cooper pairs leads to a DC current through the device with no voltage drop (the Josephson effect).

Specific experiments to be carried out in the Submillimeter Receiver Lab include: (1) observation of the quantum-mechanical current-voltage characteristic when SIS junctions are immersed in liquid helium; (2) suppression of the zero-voltage supercurrent via application of a magnetic field; (3) inducement of photon-assisted tunneling steps in the current-voltage characteristic when the SIS junction is exposed to high-frequency radio waves. In addition, the operation of a complete 230-Gigahertz heterodyne receiver will be demonstrated in the lab.

Making the measurements will expose students to laboratory practice in vacuum, cryogenic, electronic, microwave, and optical technology. Understanding the data gathered will involve exploration of some fascinating aspects of the macroscopic quantum state that is superconductivity, and of quantum-mechanical tunneling.

Laboratory Astrophysics
Science is successful because the physical laws we discover on Earth work everywhere and every when. We use laboratory experiments to expand our understanding of physical processes and then apply these results to the processes throughout the Universe. In some cases laboratory experiments can reproduce similar physics. For example, highly charged plasmas can be created in the laboratory to study the collisions between electrons and ions that occur in the hot solar corona. In other cases, such as in the extreme environments of black holes, we cannot reproduce the conditions. However, even in those cases, the pattern of observed spectral signatures allows us to identify the species and determine some of the physical conditions and processes. Spectral features observed in the solar corona are also observed from black hole sources.  

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