Suppression of residual amplitude modulation effect in the Pound-Drever-Hall locking

TL;DR

This paper analyzes the residual amplitude modulation (RAM) effect in Pound-Drever-Hall locking systems, showing that proper cavity impedance matching and mode coupling can fully suppress RAM-induced frequency shifts.

Contribution

It provides a detailed analysis of how cavity response influences RAM effects and demonstrates that proper impedance and mode matching can completely suppress RAM in PDH systems.

Findings

RAM effect depends on amplitude and cavity matching

Proper impedance matching suppresses RAM

Experimental results confirm theoretical predictions

Abstract

Residual amplitude modulation (RAM) effect in a Pound-Drever-Hall (PDH) technique locked cavity system is analysed in this paper. Frequency shift caused by RAM in PDH is found to be both related to the amplitude of the RAM and to the cavity's mode matching and impedance matching. The cavity reflection contrast depends on the mode matching of the incident laser light and impedance matching of the cavity. The suppression of the amplitude of the RAM has been investigated by many groups, while the effect of the cavity response has not received full attention. According to our analysis, RAM effect can be fully suppressed by proper impedance matching and magic mode coupling. We have measured the RAM to frequency conversion coefficients at different coupling efficiencies. The result agrees well with the calculation, demonstrating the potential of full suppression of the RAM effect through proper design of cavities.