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Heterodyne Instrument for the Far Infrared (HIFI)

Preparing HIFI for the tests. (Photo : SRON)

HIFI will advance our understanding of interstellar chemistry with its high spectroscopic resolution and sensitivity. The instrument can detect and analyze emissions from a variety of molecules. It uses far-infrared and sub-millimetre wavebands to observe molecules in various chemical processes and astrophysical environments.

How it works

The instrument uses a local oscillator to generate the reference signal that is essential for the heterodyne system to work properly. The local oscillator acts like the tuning fork that is used to tune a musical instrument. This is mixed with the signal from the source object, captured by the telescope and transmitted to the HIFI, and the result is a signal frequency much lower than the original and much easier to process with electronic circuits

Canadian scientists developed the "tuner" (above) for Herschel's HIFI instrument, which will explore the chemistry of our galaxy. (Photo: Michel Fich)

Musicians will recognize the heterodyne principle, since it is what they use when they tune their instruments: they listen for the beat frequency. Similarly AM radio is broadcast at too high a frequency for a human ear to hear. AM radio frequencies are typically at 1000 kHz while humans can only hear at frequencies around 1 kHz. When one tunes their AM radio they are changing the frequency of the local oscillator in the radio, which is mixed with the AM signal. We hear the difference frequency between the radio's oscillator and the AM signal. For HIFI, the reference signal must be extremely stable and pure. This is where Canada is contributing by providing the local oscillator source unit. The unit being contributed by Canada has unprecedented precision, stability low-noise, and contains a number of back-up components to ensure a long life for this mission-critical system.

The Principal Investigator for HIFI in Canada is Professor Michel Fich of the University of Waterloo. For technical information on HIFI, visit the Herschel-HIFI Web site of the University of Waterloo.