2.5-THz frequency difference measurements in the visible using metal-insulator-metal diodes

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Abstract
Using point-contact metal-insulator-metal diodes, we have demonstrated heterodyne detection of visible laser radiation at frequency differences up to 2.5 THz (generated by a 119-μm laser). The signal to noise on the observed rf beat falls off at 2.3 dB/octave of laser frequency difference and would seem to indicate that 30-THz difference beats will be obervable with improved laser stability or signal averaging. While the diode detector ‘‘bandwidth’’ per se has not been evaluated, these measurements demonstrate an increase in the frequency difference which can be measured in the visible by more than an order of magnitude over that previously reported.