Suppression of residual amplitude modulation effects in Pound–Drever–Hall locking

Residual amplitude modulation (RAM) effects in Pound–Drever–Hall (PDH) locking are analyzed in this paper. The suppression of the RAM effect in PDH locking has been investigated by many groups, but the effect of cavity response has not been fully considered. Frequency shifts caused by RAM in PDH locking are found to be both related to the amplitude of the RAM and to the cavity’s mode matching and impedance matching. We measure the RAM-to-frequency conversion coefficients at different coupling efficiencies. The result agrees well with our theoretical model. According to our analysis, the RAM effect in principle can be fully suppressed by choosing proper impedance-matching parameters and mode coupling efficiency, and we give several examples to demonstrate the potential of full suppression of the RAM effect through proper design of cavities.