Frequency conversion in a high Q-factor sapphire whispering gallery mode resonator due to paramagnetic nonlinearity.
Nonlinear frequency conversion is a well known and widely exploited family of effects in optics, often arising from a Kerr nonlinearity in a crystal medium. Here, we report high stability frequency conversion in the microwave regime due to a χ(3) nonlinearity in sapphire introduced by a dilute concentration of paramagnetic spins. First, we produce a high stability comb from two microwave fields at 12.029 and 12.037 GHz corresponding to two high Q-factor whispering gallery (WG) modes within the electron spin resonance bandwidth of the Fe3+ ion. The resulting comb is generated by a cascaded four-wave mixing effect with a 7.7 MHz repetition rate. Then, by suppressing four-wave mixing by increasing the threshold power, third harmonic generation is achieved in a variety of WG modes coupled to various species of paramagnetic ion within the sapphire.
ARC Centre of Excellence for Engineered Quantum Systems, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Austsralia. daniel.creedon@uwa.edu.au
Daniel L
DL
Creedon
Karim
K
Benmessai
Michael E
ME
Tobar