Fabry–Perot cavity locking with phase-locked frequency-synthesized light

We propose to use frequency-synthesized light for Fabry–Perot cavity locking. The scheme allows arbitrary control of the amplitudes and phases of the modulation sidebands relative to the carrier. In comparison with phase-modulated light, use of frequency-synthesized light provides an artful way to suppress laser instability arising from intracavity relative intensity fluctuation and residual amplitude modulation (RAM) of light and, thereby, may considerably facilitate laser frequency stabilization at an unprecedented level. We experimentally demonstrate the scheme with RAM fluctuation between 0.3 and 100 mHz reduced by two orders of magnitude and being 10 dB below the RAM noise of a phase-modulated light, when a simple RAM servo is activated.