Wideband heterodyne detection in the far infrared with extrinsic Ge photoconductors

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Abstract
The heterodyne performance of Ge photoconductors doped with shallow impurities was investigated using optically pumped far infrared lasers. Two lasers operating on the 67-μm NH3 Raman line generated difference frequencies from 0–100 MHz. An additional frequency point at 1.155 GHz was produced with two methanol-isotope lasers at 118 μm. For three detectors with different doping levels IF bandwidths of 141, 63, and 8 MHz were measured using local oscillator powers of a few milliwatts. The detector gain and quantum efficiency were calculated from shot noise measurements. For impedance matched operation the calculated noise equivalent power (NEP) values are 2×10−18 W Hz−1 for the fastest detector and 6.5×10−19 W Hz−1 for the slowest detector.