Crossed optical cavities with large mode diameters

TL;DR

This paper presents a compact, stable optical assembly with large mode diameters for creating homogeneous optical lattices in ultracold atom experiments, featuring precise mirror positioning and enhanced power handling.

Contribution

It introduces a mechanically and thermally stable octagon-shaped cavity assembly with large, nearly plane-parallel mirrors and a novel procedure for precise mirror positioning, enabling large-scale optical lattices.

Findings

Achieved deviation from coplanarity of 1(5) μm.

Enhanced power at relevant wavelengths by up to three orders of magnitude.

Demonstrated stable, ultrahigh-vacuum compatible optical assembly.

Abstract

We report on a compact, ultrahigh-vacuum compatible optical assembly to create large-scale, two-dimensional optical lattices for use in experiments with ultracold atoms. The assembly consists of an octagon-shaped spacer made from ultra-low-expansion glass, to which we optically contact four fused-silica cavity mirrors, making it highly mechanically and thermally stable. The mirror surfaces are nearly plane-parallel which allows us to create two perpendicular cavity modes with diameters $\sim$1 mm. Such large mode diameters are desirable to increase the optical lattice homogeneity, but lead to strong angular sensitivities of the coplanarity between the two cavity modes. We demonstrate a procedure to precisely position each mirror substrate that achieves a deviation from coplanarity of $d = 1(5)$ $\mu$m. Creating large optical lattices at arbitrary visible and near infrared wavelengths requires significant power enhancements to overcome limitations in the available laser power. The cavity mirrors have a customized low-loss mirror coating that enhances the power at a set of relevant wavelengths from the visible to the near infrared by up to three orders of magnitude.