Laser frequency instability of 6×10^-16 using 10-cm-long cavities on a cubic spacer

We demonstrate two ultra-stable laser systems at 1064 nm by independently stabilizing two 10-cm-long Fabry-Pérot cavities. The reference cavities are on a cubic spacer, which is rigidly mounted for both low sensitivity to environmental vibration and ability for transportation. By comparing against an independent ultra-stable laser at 578 nm via an optical frequency comb, the 1064 nm lasers are measured to have frequency instabilities of 6 × 10^-16 at 1 s averaging time.