Speaker
Description
The $10\,\mathrm{m}$-Prototype Interferometer of the Albert-Einstein-Institute Hannover will test new techniques to surpass the Standard Quantum Limit. The required displacement sensitivity of the Fabry-Perot Michelson interferometer is below $10^{-19}\,\mathrm{m / \sqrt{Hz}}$ at $200\,\mathrm{Hz}$. The $100\,\mathrm{g}$ test mass mirrors are designed as triple suspensions, where the last pendulum stage is quasi-monolithic. Four $20\,\mathrm{\mu m}$ thin glass fibers are laser welded to each of the mirrors. This welding procedure needs to be done with micrometer precision to ensure the suspended mirrors to be straight within a differential pitch angle of $10\,\mathrm{mrad}$. In cooperation with the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena, a semi-automated fiber welding machine was designed. The setup is equipped with a $120\,\mathrm{W}$ $\text{CO}_2$ laser to cleave and weld the glass fibers with micrometer precision. A piezo-driven fiber gripper with 12 degrees of freedom is used to hold and align the fiber. With an autocollimator telescope, we measure the differential pitch angle, which can be corrected through repeated welding steps. In the future, this technique will also be applicable to other mirror suspensions of similar dimensions.
