Local Oscillators from 1.4 to 1.9 THz

Local oscillators have been produced for band 6 of the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory and for the Harvard-Smithsonian Center for Astrophysics Receiver Lab Telescope (RLT) in northern Chile. These local oscillators pump hot-electron bolometer (HEB) mixer front-ends to perform high resolution spectroscopy of the interstellar medium. Local oscillator assemblies amplify 1 mW input signals in the 86 to 107 GHz band before multiplying the frequency by 16 or 18 with cascaded chains of Schottky diode frequency doublers and triplers, ultimately covering nearly the entire 1.4 to 1.9 THz band with 3 μW or more at the nominal operating temperature of 120 K. Peak output power at the nominal operating temperature is typically 30 μW or higher. Room temperature performance is sufficient to pump HEB mixers with moderately reduced bandwidth compared to cryogenic operation, with room temperature output power typically in the 1 to 10 μW range. The chain outputs are Gaussian beams produced by diagonal horns integrated into the final stage multiplier blocks. Beam pattern measurements at 1.8 THz confirm the predicted performance of the horns.

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