Distance calibration via Newton's rings in yttrium lithium fluoride whispering gallery mode resonators

TL;DR

This paper introduces a novel distance calibration method for whispering gallery mode resonators using Newton's rings in yttrium lithium fluoride, enhancing experimental control and coupling precision.

Contribution

The work presents the first YLF WGMR with high Q-factor and a new microscopic imaging technique for precise distance calibration using Newton's rings.

Findings

Achieved a high intrinsic Q-factor of ~10^9 in YLF WGMR.

Demonstrated the effectiveness of Newton's rings imaging for distance calibration.

Improved control over the coupling gap in WGMR experiments.

Abstract

In this work, we analyze the first whispering gallery mode resonator (WGMR) made from monocrystalline yttrium lithium fluoride (YLF). The disc-shaped resonator is fabricated using single-point diamond turning and exhibits a high intrinsic quality factor ($Q$) on the order of $10^9$. Moreover, we employ a novel method based on microscopic imaging of Newton's rings through the back of a trapezoidal prism. This method can be used to evanescently couple light in to a WGMR and monitor the separation between the cavity and the coupling prism. Accurately calibrating the distance between a coupling prism and a WGMR is desirable as it can be used to improve experimental control and conditions, i.e., accurate coupler gap calibration can aid in tuning into desired coupling regimes and can be used to avoid potential damage caused by collisions between the coupling prism and the WGMR. Here, we use two different trapezoidal prisms together with the high-$Q$ YLF WGMR to demonstrate and discuss this method.