Sub-terahertz sound excitation and detection by long Josephson junction

The paper reports on experimental observation of sub-terahertz sound wave generation and detection by a long Josephson junction. This effect was discovered at spectral measurements of sub-terahertz electromagnetic emission from a flux-flow oscillator (FFO) deposited on optically polished Si substrate. The back action of the acoustic waves generated by the FFO and reflected by the bottom surface of the Si substrate results in the appearance of resonant steps in the FFO IVCs with spacing as small as 29 nV for 0.3 mm substrate thickness; these steps manifest themselves in a pronounced resonant structure in the emission spectra with spacing of about 14 MHz precisely according to the Josephson relation. The mechanism of acoustic wave generation and detection by the FFO is discussed; a possibility for employing the discovered effect for FFO frequency stabilization has been demonstrated. A simple and reliable way to suppress the superfine resonant structure has been developed and proven; this invention allows for continuous frequency tuning and FFO phase locking at any desired frequency, all of which is vitally important for most applications.