Far-infrared imaging antenna arrays

A far-infrared monolithic imaging antenna array with diffraction-limited resolution has been demonstrated. The optical system is similar to an oil-immersion microscope, except that the position of the object and the image are interchanged. The array is a series of evaporated silver bow-tie antennas of 75 nm thick, spaced at 310 microns, on a fused-quartz substrate; the bow angle of 60 deg gives an impedance of 150 ohm to match to bismuth microbolometers. The measured responsivity of the array elements is 1-2 V/W at the relatively low bias of 1 mA. Previous measurements have shown that the bolometers are 1/f noise limited up to 100 kHz and that they have a frequency response of 5 MHz. The antenna array should be adequate for far-infrared plasma interferometer measurements.