Ultrahigh continuous-wave intensities in high-NA optical cavities through suppression of the parametric oscillatory instability

TL;DR

This paper demonstrates achieving ultrahigh continuous-wave intensities in high-NA optical cavities by suppressing parametric oscillatory instability, enabling advanced applications in microscopy and molecular trapping.

Contribution

It identifies the mechanical modes causing instability and shows that using low-Q mirrors suppresses PI, allowing higher intensities in open cavities.

Findings

PI is caused by MHz-frequency bulk acoustic modes.

Low-Q mirrors reduce the Q factor of mechanical modes.

Achieved >500 GW/cm^2 intensities in an open cavity.

Abstract

Ultrahigh continuous-wave intensities (>300 GW/cm$^2$) in high-NA optical cavities enable applications from phase-contrast electron microscopy to ultradeep dipole traps for molecules. However, the intensity can be limited by the parametric oscillatory instability (PI), where mirror vibrations scatter light from one cavity mode into another. We observe PI in a table-top Fabry-P\'erot cavity, show that the mechanical modes are MHz-frequency bulk acoustic modes inside the mirrors, and measure their $Q$ factor. By using low-$Q$ mirrors, we achieve >500 GW/cm$^2$ intensities in an open, free-space cavity.