Fig. 4: Microwave detection via difference-frequency generation.
From: Broadband microwave detection using electron spins in a hybrid diamond-magnet sensor chip
a Sketch of the spiraling precession of the magnetization M when driven by microwave frequencies fs and fp. The longitudinal component of the magnetization oscillates with amplitude δM at the difference frequency (\(|{\,f}_{{{\mbox{s}}}}-{f}_{{{\mbox{p}}}}|\)), which is detected when resonant with \({f}_{{{\mbox{NV}}}}\). b Field dependence of the FMR (solid blue line) and the NV ESR frequencies, with the solid (dashed) black line corresponding to the on-axis (off-axis) NV families. fNV of the on-axis family enters the MHz regime near BNV = 100 mT (red arrow). c Sketch of the frequency spectrum. Difference-frequency generation creates a detectable signal at fNV when the pump frequency is at \({f}_{{{\mbox{p}}}}={f}_{{{\mbox{s}}}}\pm {f}_{{{\mbox{NV}}}}\). d Photoluminescence versus fs and fp at BNV = 101.3 mT, such that fNV = 35 MHz [red box in (b)]. The parallel, diagonal lines [labeled + and – as in (c)] indicate the difference-frequency detection. Also visible are idler spin waves (indicated by the arrows) generated by four-wave mixing at the off-axis ESR frequency (dashed black lines). The data is normalized, leaving artefacts at the off-axis frequency (“Methods”). Inset: Line traces at fs = 4.5 GHz (dotted red line in main panel) for different BNV, showing the shift of the frequency difference resonant with fNV. Scalebar: 0.1% ESR contrast.
